Why do I keep frying MOSFET drivers in this motor circuit?

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Hi, Hoping someone can point out why this circuit seems to keep frying the 4427 driver chips. I thought I was killing the MOSFET, but after a closer look they seem to be okay, but the 4427 gets hot and stops working. the circuit seems to work if I measure the voltage at the motor connectors (motor disconnected) with an analog meter - reads 0 to 12 VDC as PWM duty cycle goes up. But if I attach the motor the 4427 burns up. Any help would be greatly appreciated -Tim

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Last Edited: Fri. Apr 10, 2015 - 03:08 PM
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Never used that chip so....is it supposed to run from 12V? Do you need some small resistance in series with the Gate?

edit: so I have a Micrel data book for the chip :roll: and it works up to 18V. One thing it says is to ground the unused driver, the input only I presume.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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This is a complete guess, based upon the posting by js, but on page 9 of the Data Sheet found at http://ww1.microchip.com/downloads/en/DeviceDoc/21422D.pdf it says:

Quote:
3.4 Supply Input (VDD)
The VDD input is the bias supply for the MOSFET driver
and is rated for 4.5V to 18V with respect to the ground
pin. The VDD input should be bypassed with local
ceramic capacitors. The value of these capacitors
should be chosen based on the capacitive load that is
being driven.
A value of 1.0 μF is suggested.

(Highlights mine own)

Regards,
Steve
(I really am clueless and guessing...)

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By the way where did you get the IRF5303? I have a IRF book but can't find it there. It seems to be the P type from google however have you wired it the right way aroud?

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Thanks for the help!

I got the MOSFET from digikey, but I just checked my order summary and it says IRF5305 (note last digit is 5). Sorry for the confusion. I read the number from the part when I made the schematic above. I assume I read it wrong, but I'll check when I get home and double check the wiring. I believe the same ciruit except for the diode has worked fine on a breadboard with smaller motors. This motor's "datasheet" is here The IRF5305 datasheet is here It's P type, 31A, 55V

RE resistance at the gate: I got the basic (not exact) idea for this circuit from a robotics book that used gate resistors with MOSFETS in parallel and I think when driving the gate with a transistor, but not with the 4427. If you think it's worth a try (or can't hurt) I'll try it.

RE capacitors bypasing VDD: Yes, those were included in the circuit I based this on, but the explaination made it sound like they were optimizations, so out of laziness, I left them out. Think that could be the problem? I'll kick myself if it is!

I'll also ground the unused driver (input) to cover my bases.

I bought 4 of the 4427's, and I'm down to my last one. I'll order more ASAP. But in the meantime, does any of this seem very likely to solve the problem? I hesistate to burn the last one quickly with the wrong test.

Thanks again!

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BTW, how many amps can one usually run through a solderless breadboard? This motor draws 2-20 Amps. It's under fairly light load (spinning a flywheel), so except for startup, it's probably on the lower end of that range. I've been afraid to build the circuit on a solderless breadboard, but soldering these experimental circuits together has been slow and painful.

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Maybe you need to run the driver chip from 5V and use a pullup on the gate to 12V?? Does it need 12V on the in to turn it on?? (AVR wont give it 12V!)

Imagecraft compiler user

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What frequency is the PWM running at? You really need to look with a scope at the various signals to see whats going on. Parasitic capacitances are injecting charges back into the gate, together with the stray inductances of the board spikes might be generated that kill the driver (there are two parasitic capacitances from the drain to the gate and from the source to the gate; when the FET turns on charge is injected back to the gate, delaying the turn on).

The gate of a MOSFET is high-impedance but that's only when the voltage applied is steady. A large MOSFET has significant capacitance, so large currents are needed to swing the gate around quickly. At high frequencies this can consume quite some power. If not enough current is available the gate voltage will not rise/fall quickly enough and the FET spends too much time in its linear region, dissipating power.

I would try a resistor of 10 to 100 ohms in series with the gate.

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Without a really beefy capacitance on the 12V, there is all kinds of junk as a result of the motor.

In addition to 1uF to assure proper operation of the driver, I would add at least 100uF (and maybe even 1500uF since this is a 20A motor) on the 12V, to protect this circuit as well as anything else on the same 12V.

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Thanks for the additional help!

Bob, sorry if I misunderstood, but the MOSFET does need 12V (at least more than 5V) at the gate to turn off. I experimented with applying 5V at the gate, and it did not turn off much if at all. That's why I'm using the driver chip, to deliver the higher voltage to the MOSFET gate. Sorry if I'm stating the obvious - this is all new to me.

JayJay: It's an 8bit phase correct PWM signal on a chip running at 1MHz. So if my math is correct, the frequency is 1,000,000 / 512 = 1,953Hz. Your explaination makes me think I need to add the capacitor as Steve also suggested above. My limited knowledge doesn't make it obvious why a resistor in series with the gate would help, but I'll try that too. Do you think these things would burn up the 4427 driver chip or just make it more efficient? I ask because if it's a likely fix, I'll try it on my last 4427 chip (before more arrive), but I'd hate to burn that one up if there is something else I should try first or at the same time. Unfortunately, I don't have a scope.

PS: I just saw mneary's comment added as I was Previewing this post. Another vote for adding capacitors. Okay, I'll cross my fingers and try it out. (may not have time tonight :( )

Thanks again!!

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You need high-side driver or N-chanel Mosfet.
Alexander.

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Thanks Alexander, but can you give me a few more words to explain? What's a "high-side driver"? I do have N-channel MOSFETs, so I could set up the analygous circuit, but shouldn't this work with P-channel?

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The circuit is basically correct IF the gate and drain (pins 1 and 2) are wired up correctly. If they are reversed then the motor will turn the mosfet fully on, putting a full 12V onto the drain which would be connected to the driver chip which in turn would try to pulse it low and..................... :( :(

edit: try it out without the motor to start off with, put say a 100R, 5W, in place of it and perhaps a led in parallel (with suitable resistor in series) so you can see the thing working.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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The p channel fets are like pnp transistors... you pull the gate up to vcc to turn it off, you pull it low to turn it on. The part that confuses me is the avr is giving 0-5v to the driver chip input which is running from 12v... does the output look like its switching full 12v ok?

Imagecraft compiler user

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Bob that's what the driver does, it converts 5v from the input to whatever the chip is running at (up to 18V). That particular chip has also the advantage of being able to deliver 1.5A peak to the load.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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I checked (and double/triple/etc. checked) the circuit. It is an IRF5305, and it looks to be wired correctly. So far suggestions are a few capacitors, grounding the unused input to the 4427 and a resistor in series with the gate. Just to make sure I have it correct, I've placed the capacitors in the revised schematic below - look correct? The rest is straight forward enough. I still don't understand the series resistor on the gate, but unless anyone thinks it's a bad idea, I'll try it too.

Any other suggestions?

Thanks,
Tim

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Last Edited: Sat. Aug 18, 2007 - 07:35 PM
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If you put 100R in series with the gate then the current will be limited to about 120mA which should keep your driver safe. I always start with a current limited power supply when I do something like that.

Quote:
It is an IRF5305, and it looks to be wired correctly
So your output to the motor is wired up to pin 2 (centre pin or the tab), the driver chip's output is going to the gate (pin 1 or l/h side) and 12V goes to pin 3 (r/h side this is looking at the front, plastic part of the fet)

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Rehashing comments by jayjay1974 and js.

The 4427 driver current paths are:

(1) Between Vcc and GND of the driver - transition dissipation.

(2) Between OUTA and alternating Vcc/GND - MOSFET gate capacitance charging and discharging.

Adding a resistor between driver output and MOSFET gate will move some of the power dissipation from the driver to the resistor when charging and discharging the MOSFET gate capacitance of 1200pF. The downside is increased power dissipation at the MOSFET, it's designed for that.

The PWM rate or frequency is directly related to how often the MOSFET gate capacitance is charged and discharged by the driver. If 1 kHz works, don't use 100 kHz.

Stan

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If I may...

I wonder whether the OP realises the fact that with the combination of driver and FET as specified the PWM output needs to be INVERTED since a m inimum outptu on the PWM will cause a MAXIMUM MOTOR CURRENT and vice versa...

Unless the driver chip incorporates an inverter stage ( have not checked the data sheet.. not in the spirit of giving advice...)

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Don't forget grounding the unused input.

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Quote:
Unless the driver chip incorporates an inverter stage
The 4427 is NOT inverting but the 4426 IS inverting.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Here some other tips that might be helpfull:

I think the driver is fried due to routing of the power-lines.
Tim, you're working with very high currents. Keep those away from the driver and the Mega16

In the sketch a suggestion. I forgot to draw the schottky (but scanned my artwork already :wink: ): place that directly across the motor-connections.

A few other things:
- Breadboards are not made for high currents. And defenitely not the currents that can flow in this circuit.
- A series-resistor between driver and fet: IMO not necessary; the driver is made for this purpose
- The powersupply for the motor: use adequate filtering, the Cm is the minimal filter
- Check the datasheet for C1 and C2
- Although AVR's are quite forgiving when abused .... I would suggest a 470ohms series resistor between AVR-output and driver4427; it will have hardly any influence on the signal, but it protects the AVR in case something goes wrong.

A picture of your set-up would help to determine the frying-cause.
What is the motor-power-supply? Batteries ?
And how gets the AVR its power?

Plons

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Thanks, thanks, and thanks!

Quote:
So your output to the motor is wired up to pin 2 (centre pin or the tab), the driver chip's output is going to the gate (pin 1 or l/h side) and 12V goes to pin 3 (r/h side this is looking at the front, plastic part of the fet)

Yes, if I'm remembering correctly from checking last night. I'll check once more tonight when I get home.

Quote:
I wonder whether the OP realizes the fact that with the combination of driver and FET as specified the PWM output needs to be INVERTED since a minimum output on the PWM will cause a MAXIMUM MOTOR CURRENT and vice versa...

Thanks for pointing it out. I did discover that, but it was a surprise. As a result I've compensated in SW by using a high duty cycle for slow and low duty cycle for fast. Let me know if there's something wrong with that approach.

Plons:
Thanks for the effort with the drawing! It has taken me awhile to do mine in PowerPoint. I need to learn to use a real schematic drawing application, but perhaps I should have done it by hand for now.

Does Cm = 1000uF?

What's the part at the top above the motor (looks like a resistor) labled "R or L"

Yes, the power for everything starts with a 12v battery. The AVR get's it's power through a 5v voltage regulator, which does have a couple capacitors per the data sheet.

Is part of what you are teaching me that routing is important? I have to take a closer look over lunch (have to get to work now), but at first glance, I suspect your circuit and mine have similar connections if you ignore relative placement, what's near/far to what, etc.

I'd be embarassed to show a picture of this point-to-point soldering mess, and it would be hard to interpret as the wires and components are on opposite sides. But I could doctor up a picture of the component side to show where the wires run, or I just might draw it to show placement and routing.

Thanks again,
Tim

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Tim, no need for embarassement ... you are amongst fellow-"artists" ... 8) a picture is IMO essential. And yes, routing of the wires is crucial.
Pitty that the datasheet does not tell the DC-resistance of the motor ... maybe you can tell us.

Quote:
Does Cm = 1000uF?
At least, it's a start. Add some ceramics of 100nF as well. I hope other members can do a more precise recommendation.
Quote:
What's the part at the top above the motor (looks like a resistor) labled "R or L"
It's an attempt to draw a european resistor ... :wink: A 1 Ohm resistor is OK, if you add the 1uF and 0.1uF as pointed out in the datasheet. But if you have a 100uH inductor, that is even better. The "R or L" create in combination with C1 and C2 a filter.
Quote:
....I suspect your circuit and mine have similar connections if you ignore relative placement
Indeed. My goal was to show the routing.

I adapted the sketch a bit to the now-known facts. And replaced the euro-resistors ...

Main things are:
1. Keep motor, fet, driver and associated filter {R1 C1 C2} close together. Cm as well, if possible.
2. Starpoint == motor-minus
3. Fat wires in the sketch should be fat wires in the real world. I am not so familiar with AWG, but 2.5 mm2 for the fat ones.

How do you like my kinda circular fet ? Neat huh ?

R2: I put in 1 ohm as default, but I don't know what the load is on the 5Volts, An inductor, if available, would be better.

Quite a motor, btw. At full load 20+ amps ... wouldn't it be better to use two fets, and both drivercircuits in the package?
And how about EMI/EMC ? Anyone tips ?
And I wonder if a low-side drive (using N-ch fet) and the 4427 on 5 V power would be preferable?

Plons

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Some other things that popped up: John (Samperi) already suggested to use a current-limited supply in test-phase: good advice, strongly recommended :!:

Add a fuse in Battery + when using battery

Use a small motor in test-phase, not the monster :wink: and before putting in your last driver: take a 100R resistor and a multimeter on 200 mA range; ground the gate of the fet with the 100R and MM in series, and see if the gate-current = zero, and the small testmotor is running @ full speed. Next, take the ground-side of 100R / MM to the +12V, and the motor should stop.

One more suggestion: do a search on this forum for Robotics or so .... There are a few guys that are more familiar with this than I am.

Plons

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Thanks again for all the advice. I can post a picture, since I perhaps owe it to all those who took the time to help. That might confirm suspicions. But, it looks like I should start over with a new circuit

I'm wondering what I can use for a current limited supply. Would a battery plus a fuse qualify? I have some salvaged computer power supplies with 12VDC outputs, but I'm not sure if they are limited or will just overheat.

I do have a few small 12 volt motors, which I used when developing a similar circuit on a solderless breadboard, but I'll start testing with them again on these.

I like the multimeter/resistor test of the fet gate idea!

This circuit was meant to be a quick one I could use for testing and experimenting with the motor. The real circuit for my application (ball throwing machine) was also meant to have a break mode (with another fet that would result in both motor leads connected to ground - essentially a half-bridge I believe). Now I'm wondering if I shouldn't build that circuit if I need to start over anyway. On the other hand there's the walk before you run strategy. Perhaps I can design the whole circuit, but only build the existing part first and get it working before adding the components for breaking.

Thanks again!!!!!

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forgot to respond:

Quote:
Pitty that the datasheet does not tell the DC-resistance of the motor ... maybe you can tell us

I guess that's the resistance of the motor when standing still. I tried measuring that, but couldn't seem to get a reading. Then I reasoned that it has to be less than 1 ohm if the motor can draw 20 amps when stalled at 12 VDC. (which is about what I think the datasheet shows)

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Quote:
.... some salvaged computer power supplies with 12VDC outputs, but I'm not sure if they are limited or will just overheat.

They can be used, but there is something involved: they don't like to operate without a decent load on 5V and 3.3V output. And current-limiting isn't their best property.

Quote:
Would a battery plus a fuse qualify?
Well, ... yes, if you have enough spare fuses ... :D

Do you have a LM317T ? Put that in series with battery and your circuit; connect the control-pin to the output-pin. Now it will act as a current-limiter of appr. 1.5Amp. And I think that I speak for all LM317's when I say: a heatsink would be appreciated :wink:

The resistance of the motor will be even less than 1 ohm. The 20A are when it's running under load ... umpff, I would go for at least 2 fets. But maybe I am too cautious ...

Plons

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Well, I just added a few LM317T's to my order along with some more mosfet drivers. Seems I have my plans laid out. Now just need to get to it! I'll update with progress, but this might take several days. Thanks again.

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I built a regulated supply (hmmm that would be about 20+ years ago...how time flies :) ) that allows me to adjust the voltage up to 80V and the current from a few mA to 3A, you should be able to buy something similar off the shelf pretty cheaply, I do see some supplies that would go up to 30V and have both voltage and current ajustment. This is something that ALL workshops need next to a multimeter :)
hmmm don't know why I'm no longer getting any notification from any threads...is it the forum or is it my ISP AGAIN?!!!

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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I'll have to check into a regulated supply. This hobby already seems expensive. All the odds and ends I added to yesterday's digikey order was over $100.

Plons thought pictures of the original set up would be helpful, so I'll suppress my embarassment at sloppy soldering and show you what I had put together. Seems like you'll find the routing suspect. In particular I wonder if sharing the ground between the motor and the driver chip before the schottky was a bad idea. The solder to the fet is especially messy (but no shorts I promise) because I twice removed one and soldered in a new one before I discovered that it is the driver chip that's going bad. There are 3 pictures below. The first is the front, the second is the back flipped side to side so it can be overlayed with the front, and the third is the back with the components from the front overlayed so you can see the whole thing.

EDIT: This site is giving me an error when I try to upload a picture, so I'll have to try again later.

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timwhunt wrote:
I'm wondering what I can use for a current limited supply.

Tim,

Check out the Texas Instruments LM317 adjustable voltage regulator datasheet.

Page 8, figure 4 shows an adjustable current source and, page 10, figure 9 shows a fixed current source.

The equation is ~1.2/R

There is also a 5 ampere version of the LM317 but, the number escapes me at the moment.

At least this will keep the current flowing throough the FETs to an ampere or less.

Note: I tryed to attach the datasheet but, for some reason, the system would not allow me to.

Hope this helps.

Edit:

Tim,

Here is the link to the TI LM317 datasheet, in PDF format.

http://focus.ti.com/docs/prod/fo...

You can avoid reality, for a while.  But you can't avoid the consequences of reality! - C.W. Livingston

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Thanks Carl! That LM317 sure looks useful. I think I should have ordered more of them!

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In a world of electronics where the life of most stuff is a year or two, a bench power supply and a meter and a scope should all last 20 years. Durable goods. Better than a car.

Imagecraft compiler user

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Well the forum seems to have gone to the dogs again!! I haven't received any topic reply notification on any thread for about 2 days now :( and no more pics either :(

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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For what it's worth, I'm getting topic reply notifications, but the pics issue is unfortunate.

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js wrote:
Well the forum seems to have gone to the dogs again!! I haven't received any topic reply notification on any thread for about 2 days now :( and no more pics either :(

I did notice last night that the forum was down for several hours. Since then, I've recieved no noticifications and I can't download pictures. In addition, I tried to attach the LM317 datasheet for Tim but, the system would not let me - no matter how many times I tried.

You can avoid reality, for a while.  But you can't avoid the consequences of reality! - C.W. Livingston

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Quote:
Since then, I've recieved no noticifications

hmmm Tim is getting notifications and we are not....are they discriminating against old geisers? :lol:

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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js wrote:
Quote:
Since then, I've recieved no noticifications

hmmm Tim is getting notifications and we are not....are they discriminating against old geisers? :lol:

Might be. But I don't think international law covers that.

You can avoid reality, for a while.  But you can't avoid the consequences of reality! - C.W. Livingston

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As far as the current source is concerned.. you dont need an active one.. ( no silicone.. it gives up too easily).

Use a light globe ..apropriately dimensioned.. it will act as a self limiting current source ( temp coefficient of the filament resistance is strongly positive )

PS... old geisers never die.. they just stop spouting

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Good idea, Igno ...

Car's light-bulbs are ideal for that purpose: a whole range to choose from. With Tim's 12 battery: perfect match.

Plons

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Some time ago I used Harris CPA 7667 as MOSFET drivers
and found them a little susceptible to LATCHUP.
This usually happened in a quite erratic way. Usually without load no problems, but with load sometimes even touching the gate of the MOSFET with a probe the
running system crashed and the driver was destroyed.

I never really found the cause. Perhaps something similar happens in your circuit. A resistor
between driver and gate may help.

If your PWM operates at a few kHz a simple Logic-level
translator 5V ->12 Volt may be sufficent as MOSFET driver.

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Thanks for the suggestions Igno and ossi!

I got tired of waiting for the forum to accept pics again, so I'll temporarily link to them on another site. I had intended to add them to a previous post, but since that's gotten a bit old, I'll put them here. Here's the text from the earlier post that was meant to go with them:

Plons thought pictures of the original set up would be helpful, so I'll suppress my embarassment at sloppy soldering and show you what I had put together. Seems like you'll find the routing suspect. The solder to the fet is especially messy (but no shorts I promise) because I twice removed one and soldered in a new one before I discovered that it is the driver chip that's going bad. There are 3 pictures below. The first is the front, the second is the back flipped side to side so it can be overlayed with the front, and the third is the back with the components from the front overlayed so you can see the whole thing.

Revised post to put pictures here.

Attachment(s): 

Last Edited: Sat. Aug 18, 2007 - 07:40 PM
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Ossi mentioned latchup, which can be a real problem.
Another very serious situation is when you have
a special function ic intended to handle higher
voltages and/or currents. A *rapid* application
of supply voltage can cause a sort of latchup
condition that can cause *spectacular* failures.
One needs a filter cap on the supply bus to limit
how *fast* the voltage can rise when the power is
switched on. I notice your board does not have
one. I believe the problem is that when power
instantaneously appears, the various internal
transistors etc. cannot respond quickly enough to
set up properly, so BOOM! Been there, done it, got
the t-shirt.

Tom Pappano
Tulsa, Oklahoma

Tom Pappano
Tulsa, Oklahoma

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The PWM return isn't shown, therefore it probably has a common current path with Motor-.

From the PWM, try running (PWM-) directly from the microcontroller to the driver chip.

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Tom, thanks for the analysis and suggestion. Sounds like it could be very important. I'm sorry to have to ask, but can you tell me more specifically where I need to connect the cap, and about what size you'd recommend?

Thanks mneary. I'll try that too. (I believe that would be running the ground from the uC to the ground for the driver chip instead of sharing the motor ground with the driver chip as I've currently done)

I sure seem to have done a lot of things wrong with such a seemingly simple circuit!

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timwhunt wrote:
I sure seem to have done a lot of things wrong with such a seemingly simple circuit!

Tim,

Believe me, most of us have had many failures while in route to our successes. You are learning from those failures! Nothing comes easy - for me, at least...

Hang in there!!!

You can avoid reality, for a while.  But you can't avoid the consequences of reality! - C.W. Livingston

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You would have had great success with something like an opamp filter or something that doesnt deal with hi current and hi speed square waves. You just skipped the easy stuff and went right for the problems. Keep on debugging!

Imagecraft compiler user

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Quote:
...can you tell me more specifically where I need to connect the cap, and about what size you'd recommend?

I would place maybe a 500 to 1000 uf cap right on
your board where +batt and -batt are connected.
That should help, if indeed it was a dv/dt problem,
and I just think it is a good idea to include one in
any case.

Tom Pappano
Tulsa, Oklahoma

Tom Pappano
Tulsa, Oklahoma

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Quote:
I sure seem to have done a lot of things wrong with such a seemingly simple circuit!

Not true. The high amp motor controllers go for big bucks. So it must not be so easy.

FYI there is a short article on Mosfets in the May issue of Nuts and Volts. There is a rebuttal on this article in the reader comments in the July issue, along with a heatsink article, which will be useful at sometime.

Interested in your outcome with the mosfet driver chip. Tried doing this with an analog input, and ended up smoking inverter outputs and fets both. So probably was not getting a full on voltage to the mosfets, they can get REALLY HOT!

Keep up the good work.

EDIT: Meant to say that I tried a mosfet h-bridge, but without the mosfet driver chip. The con-figuration was solar cell to op-amp to logic gate(s) to opto-isolator to inverter to diode logic to mosfets. No wonder this project has been shelved.

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As several others have suggested, the problem with your circuit is the lack of filtering capacitors.

When a high inductance load such as a motor is switched, the voltage at the output (in this case, the MOSFET drain) very easily over- and undershoots. This would cause severe spikes if it weren't for the free-wheeling diodes in the circuit - the Schottky and the anti-parallel diode integrated in the 5305. These diodes will clamp the output to the DC line levels, but without filtering capacitors the DC line will also over-/ undershoot due to circuit inductance and battery ESR.

I'd add an electrolyte of maybe 1 mF to the battery poles, a ceramic of 220 nF between the Schottky's anode and the MOSFET source, and a 470 nF between VDD and GND on the 4427.

Another thing: Do you have a heatsink for the MOSFET? With an on resistance of 0.06 ohm (from the datasheet) and a current of 20 A, the dissipation will be 24 W even if switching losses are ignored. Without a heatsink the MOSFET won't survive even 3 W.

/ Grimmy

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guys, this is a high side driver. i bet if a scope was hooked up, one would see that the mosfet is not turning on 'hard'

iv been there, done that :oops:

if one is switching 12v, you need about 18 volts or so to properly switch the mosfet (i was using a irf9540 i think)

switch to a low side driver, and your problem might go away

from irf5305 datasheet

Quote:

VGS(th) Gate Threshold Voltage -2.0 ––– -4.0 V VDS = VGS, ID = -250μA

so you would need to provide atleast 16v to your driver chip power pins

not a rookie anymore, still learning tho

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No, the 4427 is a low side driver, but here it's used in a high side configuration. It doesn't matter as long as the switched voltage is well below the maximum allowable gate voltage (and above the threshold voltage, and in the range of the driver chip, +6 to +20 V).

The 5305 is an enhancement mode P-channel MOSFET, so with +12 V at the source the gate voltage needs to be +8 V or lower to ensure that it's on. Increasing the voltage to the driver chip may cause the MOSFET to turn off a bit faster, lowering switching losses, but this should not be necessary.

/ Grimmy

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Now you all know why I'd perfer to use an application specific IC, such as the National Semiconductor LMD18201 H-Bridge 3 amp driver IC.

I got 5 free samples from National and it worked on first application of system voltage.

Also, you should take a look at the datasheet for the LMD18201 and take note of the Bootstrap circuit. You might see why you are blowing MOSFETs.

While the datasheet diesn't usually show every detail of the internal circutry, it will give you some insite on the circutry needed to control the un-tamed creatures lurking in the jungle.

You can avoid reality, for a while.  But you can't avoid the consequences of reality! - C.W. Livingston

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A bootstrap circuit isn't needed unless you want to switch voltages above 20 V or use an NMOS as the high side switching device. But NMOS devices usually have a lower on resistance than PMOS, so it may be a good idea to replace the 5305 with e.g. an IRF3708 anyway.

The LMD18201 looks useful but it seems a bit expensive and has a leg pitch that isn't breadboard friendly. It won't eliminate the need for capacitors.

/ Grimmy

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Thanks again for all the encouragement and help!

I've drawn out a new version where I've tried to incorporate all of the advice to the best of my ability.

You can see it below. Comments?

Again, thanks for the help, I hope I'm getting there! I hope I get to wire this up soon (new parts are here!)

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Tim,

If I'm not mistaken, you need a GND reference from the 4227 IC to the battery, as well as the uC. Else, your FET will be on or off all of the time, depending on wheter it's a 'P' channel or 'N' channel.

You can avoid reality, for a while.  But you can't avoid the consequences of reality! - C.W. Livingston

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Thanks Carl. What I haven't shown (but alluded to in the note) is that the uC also gets it's power and ground from the battery. So essentially the GND to the 4427 is from the battery. Does that make sense? I thought this was what someone suggested, I assume because it might be less noisy.

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It looks good Tim, have you tried it yet? The 4427 is now protected by the 100R resistror so it should not blow. As others sugested you may want to put a 12 V car lamp (20W??) in series with the 12 V from the battery as it will give you some current limiting. As I suggested before you may want to try and get it all working by using a 100R, 5W resistor instead of the motor and see what happens. Once you know that the voltage to the motor's output does what you want the start using the motor, still with the lamp in place to start, then remove it BUT put a fuse in it's place so that if you have a bad short the battery doesn't explode in your face :(

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Add a ceramic capacitor of 220 nF in parallel with the 1000 uF cap. Electrolytic capacitors have a relatively high ESR and are therefore not well suited for dealing with the high frequency transients.

Lose the gate resistor, or at least lower its value considerably. A high gate resistance will cause the switching times to increase, thereby increasing the time the MOSFET spends in the linear region, and this will increase the switching losses. The rise and fall times of the MOSFET that are specified in the datasheet are for Rg = 6.8 ohm, and the output impedance of the 4427 is 7 ohm, so it should work well as it is. The gate resistor will not likely protect the 4427 anyway, since it's overvoltage at Vcc (or undervoltage at GND) that causes it to fry. The input impedance of the gate is high enough to prevent any destructive currents to pass through that way.

I really don't think the 1 ohm resistor is needed. The main reason to have a decoupling capacitor at the 4427 is not that the IC needs a stable voltage, but that it needs to be able to charge/discharge the MOSFET gate capacitance without disturbing Vcc too much. For the FET you're using, a single ceramic capacitor of 1 uF should be enough.

/ Grimmy

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I appreciate the continued help! I was too busy to try it this weekend :( , but I guess the upside is I might get some more pointers before I solder it. I hope to get to it tomorrow night.

Quote:
BUT put a fuse in it's place so that if you have a bad short the battery doesn't explode in your face

Yikes! I didn't know that was a risk. I'll be more careful and get a fuse in there asap. Thanks for suggesting it.

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Quote:
Lose the gate resistor, or at least lower its value considerably
I guess it can go as low as about 12 Ohms to keep the max current under the 1.5A that the 4427 can handle.
Quote:
The gate resistor will not likely protect the 4427 anyway
I would be interested in your reasoning for this, my post above shows that I thought there may be a pin reversal (gate/drain) if that were the case then the resistor would limit the current to a safe 120mA into the 4427.
Quote:
it's it's overvoltage at Vcc (or undervoltage at GND) that causes it to fry
What is your suggestion to remove these overvoltages/undervoltages? Isn't the SR506 schottky + the internal zener inside the fet suppose to do this?

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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I really recommend a gate resisitor for protection
during transients. In the switching-moment the
miller-capacitance (drain-gate) may lead to
a high gate current that may cause latchup via the
drivers output even if the driver is latchup-immune
up to 500mA.

If everything works out fine, the gate resistor may be decreased.

I recommend a capacitor 0.1uF directly accross the
gnd-Vcc connections of the driver.

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Sorry John, I hadn't noticed that post. I guess I should have reviewed the whole thread before posting that. :oops: If possible pin swapping is the reason to use a gate resistor, then it should better be 100 Ohm. The 1.5 A mentioned in the datasheet of the 4427 is the peak current it can provide, not what it can handle continuously.

Can anyone say what the pinout of the 5305 really is? I can't find it in the datasheet - have I missed something? The web site of my supplier states that the pinout is G D S (http://www.elfa.se/en/, search for irf5305), but the spice model found at IRF's web site seems to indicate that it's D G S. Tim, do you have a multimeter with a diode tester? If so, you should be able to figure out which pin is which by looking for the anti-parallel diode going from D to S.

js wrote:
What is your suggestion to remove these overvoltages/undervoltages? Isn't the SR506 schottky + the internal zener inside the fet suppose to do this?

Yes, they will, once the capacitors we've been talking about have been added. Without those the over-/undervoltage at the drain has just been propagated to the FET source or Schottky anode where it can destroy the driver instead of the MOSFET. A ceramic capacitor (for its low ESR/ESL) is highly recommended for this protection - do a web search for "MOSFET snubber capacitor" if you want to know more. There should be a higher value (electrolytic) capacitor as well, but the ceramic should be placed closest to the MOSFET source and Schottky anode.

/ Grimmy

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Alrighty,

Here is a slightly revised drawing and some comments. Again, the help has been great!
(See Below)

Quote:
I recommend a capacitor 0.1uF directly across the gnd-Vcc connections of the driver.

Although it doesn’t appear that way in my circuit, the GND from the uC is connected to the battery NEG as the uC gets it’s power from the battery too (via a voltage regulator). So I believe that the 4.7uF and 0.1uF Caps shown would address this need. But please advise if those caps need to be connected closer to the ground pin of the driver. I found those values used as an application note in the datasheet.

Quote:
Can anyone say what the pinout of the 5305 really is?

Here’s an image from the datasheet, which can be found here. Note in my drawing above I have the middle pin bent out towards the back (heatsink) side

BTW, I've used these same MOSFETS hooked up the same way to drive small 12V motors, so I doubt I've got the pins wrong.

Additional advice noted (and appreciated):
1) 1R may not be needed
2) The gate resistor may not be needed, but would provide some protection if MOSFET pins are mixed up or may protect the gate during transients

Attachment(s): 

Last Edited: Sat. Aug 18, 2007 - 07:42 PM
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My recommendation to place a 0.1uF cap directly
between the drivers supply connections is here really
to be taken literally.

I try to explain:
If currents change very fast, its important
to take into account, that all conductors (wires etc.) have some inductance. Accross this inductance
a voltage builts up if currents change. So to say that "something is connected" gets more or less meaningless at higher frequencies.

Example:
Assume you switch 20Amps linearly within 10ns (Experts today do this). The current slope is
dI/d=20A/10ns. Assume you place a normal piece
of wire in this current path (for example the drain line of your MOSFET) that is 1 cm long (not quite
long), this has (roughly by rule of thumb) an
inductance of 10nH. The induced voltage accross this short connection is somewhere in the order of

U=L * dI/dt = 10nH * 20A /10ns = 20V (!!!)

Conclusion:
If you use a fast gate-drive without
gate-resistor, the MOSFET switches really fast.
If current rises fast, this may give nasty voltages
in all conductors.

Therefor its often necessary to avoid any additional wiring (stray) inductance. A direct placement of capacitors accross the driver-chip helps here to really keep the voltage for the chip constant during switching.

(The world in your case will not be that bad, because the wiring inductance of all your wires will limit the current slope, but nevertheless, fast rising currents can be dangerous.)

I believe in your case switching losses are not so important. Assume you switch 10000 times per
second. And the switching lasts for 1 us (quite slow)
and during switching you have 20A*20V=400W losses, mean switching loss is 400W*1us*10000 *(1/s)=4W,
which can be handled by a small heatsink,
and the loss-power will be much less than the 400 W !

Thats why I would suggest a slower gate-driver
with gate-resistor, perhaps constructed by some discrete transistors.

(Its the same as in digital: Never switch faster than necessary !)

Therefore in the test-phase I always prefer to switch
a little slowly.

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Thanks for explaining all that ossi!

So then would this be better:
EDIT: added replacement picture, as previous was broken. This is an old thread, but it was a hugh help to me, so I wanted to updated incase it helped others.

Attachment(s): 

Last Edited: Fri. Feb 2, 2007 - 02:44 PM
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I think its better, but I would also like to hear,
what others think. Making errors is quite common to me.

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Quote:
Here’s an image from the datasheet

I wonder how I managed to miss the lead assignments there. :shock: :oops: Thanks for pointing it out for me, now I'll know where to look the next time I check an IRF datasheet!

It's looking pretty good now, but I have one more (very minor) suggestion: Switch positions for the 4.7uF and 0.1uF capacitors. It probably won't make much of a difference in this application, but in general it's better to locate the smaller caps (lower ESR/higher frequency) closest to the IC.

/ Grimmy

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The folks flying ducted fan model jets have electronic speed controls the size of a postage stamp PWMing 40 amps on brushless motors, so SOMEONE knows how to make this technology work correctly.....

Imagecraft compiler user

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A stupid question on the mosfet driver chip rating. I see these chips rated from 1.5A up to 12A or so. One manufacturer states that somehow the switch rating is related to the mosfet max ampere rating. The microchip data sheet seems to implicate the mosfet gate capicitance as the determining factor.

The OP will be switching a 20A mosfet with a 1.5A switch part. Can someone explain how this works?

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qbob:
Sure they know:
Small loops avoiding inductance. Rugged drivers.
Proper decoupling. Efficient protection. And be sure: They are not beginners.

In many application-notes of power-electronics
devices you find good hints with recommended
layouts of PCBs, but often they tell not all
details why their layout is so good. And without
thinking about it, you miss some detail and have
the crash !

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Okay ossi, thanks.

Quote:
It's looking pretty good now...

I should tell you, reading that got me pretty excited. :D I hope I can wire this up tonight!

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Quote:
A stupid question on the mosfet driver chip rating. I see these chips rated from 1.5A up to 12A or so. One manufacturer states that somehow the switch rating is related to the mosfet max ampere rating.

For what it's worth: I just looked and this driver's datasheet says the typical "peak output current" is 1.5A, which suggests to me the 1.5A rating is NOT determined by the mosfet max ampere rating.

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Ok, some thoughts to "driver current rating"
(@ nickelflipper)

Many want to switch (turn-on resp. turn-off)
a MOSFET fast. This requires charging or
discharging the gate. The more current
(flowing in or out) the faster you are.
The larger the gate-capacitance the slower you are.
MOSFETS for larger currents often have a larger gate-capacitance than MOSFETS for smaller currents
(at the same voltage rating). Therefore at the same speed a "larger" MOSFET requires a larger driver.

Next complication:
Gate-capacitace is dependent on voltage ! So the
picture above is only qualitatively right.
Its not so easy to get it down to precise numbers.
But:
Gate capacitance of MOSFETS is often specified at the
same voltage level. Therfore some river-manufacturers
not only specify maximum output current, but also
say: "will switch 1000pF within 25ns".

Next complication:
Dependent on the voltages and currents at the
switching instance the gate-driver will have
to deliver additional current due to the Miller-effect (see Miller-capacitance).

Next complication:
The driver gets the current from its supply.
If your supply (due to stray-inductance ) is not
able to deliver it: Game-over
(This is, where a good capacitor near the chip helps)

Next complication:
The wiring-loop: driver, MOSFET-gate, return-path
must be of low inductance, otherwise the driver will not deliver the current: Game over
(Good layout of current loops helps)

Next complication:
If the main-current-loop and the gate-current loop share some impedance (usually in the DRAIN-wiring), voltage accross this impedance reduces effictive-gate voltage, if this is too much: Game over
(Good layout of current loops helps)

The faster you want to switch, the more important is all that. But its possible also without a PCB but
with breadboard-techniques !

Well, I told you:
I am slow and lazy, so I always switch as slow as possible.

Lazy means: I switch as seldom as possible,
so at low frequency !

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Thanks ossi.

Quote:
Well, I told you:
I am slow and lazy, so I always switch as slow as possible

If it's possible to add a prescaller to slow down the PWM frequency, should I? I assume it's possible, but should wait to get home to check the datasheet (forgive me for not checking now). Currently I'm using phase correct 8bit PWMs on a 1MHz ATMega16, which translates to about 2KHz PWM frequency.

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Some golf cart controllers switch in the audio range because the L of the motor wont let them switch faster. So you get to listen to the controller sing/whine. Power supplies try to switch faster than 20KHz so normal carbon based units wont be irritated by the sound. Does your meter have an L and C setting? Whats the L of your motor??

Imagecraft compiler user

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2 kHz is low enough, when not too low, because
you can hear it.

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Ossi, thanks for the explanation. So, it sounds like the higher amp mosfet drivers, are for big fets, driven at very high speeds. And since the speed here will only be in the very low khz range, no problem. Will someday pretend to understand those datasheets.

EDIT: Usual late post,sorry

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A few notes:

1. Looking at the spec-sheet of the motor, and using a ruler to extend the lines in the graph: max. current will be ~ 50 Amp. Tim is using a flywheel, and drives the motor with pwm. When it starts @ 0 rpm, and a pwm-signal is applied, the current will be in the range of pre-mentioned 50 A. Not 1 or 2 or 20 A, but 50 !
Two components will get a hard time: the fet, and the schottky. I think that (at least) two of both would be a good idea.
2. It was pointed out earlier (by Mneary IIRC): the battery-voltage under pwm-load from such a motor will be anything but DC: the spikes on the battery-voltage will be high, and contain quite some energy. Now let's look at Tim's first question: the driver got fried. IMO not because of the current it had to supply to the gate of the fet, but due to overvoltage. So I strongly recommend to put that 1 ohm resistor in the Vcc line to the driver, and yes, also a 1 ohm resistor in the 12v-line to the voltageregulator. As pointed out earlier: an inductor would be even better, but if that's not available, a 1 ohm resistor (250 or 400 mW suffies) will do.
3. The voltage regulator (with the cap's around it) : 12v direct from the battery, and ground from the star-point on motor-minus.

There is one other thing that worries me: is the diode in the fet fast enough to handle the spikes ? It's not a schottky .....

Plons

Edit: Ossi showed the power-losses in the transients. Then there is still the Rds-on .... also earlier mentioned; if you do some math, you'll see that a heatsink will be necessary.

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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The 'hidden' advantage of parallel FETS is that each will carry approximately 1/4 of the poweer (static) as one, since you're cutting the resistance in half and sharing the resulting (half) power between two devices. A third FET gets you to 1/9. The only downside is that the gates will take longer to charge. You don't need to worry about balancing the drain currents; if the RdsON are different, the circuit self-balances (unlike the bjt).

In this circuit the diode in the FET isn't supposed to conduct, so its speed isn't critical. However, be sure that the Schottky can handle 50A spikes.

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Plons has been nudging me towards more than one fet and he might be right.

As for the Schottky, here's a few specs from it's data sheet:
Max recurrent peak reverse voltage: 60V
Max RMS voltage 42V
Max ave forward rectified current (@TL=90 deg C): 5A
Peak forward surge current 8.3ms half sine-wave...: 150A

I'm not sure, but I'm hoping the last one is what I need to worry about for those 50A spikes. Look okay?

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Oh to have more time! I've placed the components, but didn't have time to add wires and solder. Watching part of what might have been Andre Agassi's last match (US Open Tennis) was part of the problem. Plons did persuade me to put two mosfets in parallel. If I add a second mosfet in parallel, do I have to change anything else (e.g., capacitors, driver)?

Any suggestions on needing a second Schottky based on the specs above?

Also, Bob asked a while ago if my meter had C and L settings, and what's the L (inductance?). Unfortunately meter doesn't seem to have those.

I did try to get a better reading of the coil resistance after Plons reread of the datasheet suggested 50A at startup. Reading it directly was too low for my meter, which is not surprising as discussed previously. So I made a simple voltage divider using a AA battery, a one ohm resistor, and two of these motors in series:

A---
1 ohm resistor
B---
motor 1
motor 2
C---

I found the A-B voltage was about equal to the B-C voltage, which suggests each motor is about 1/2 and ohm. I didn't expect this to be very accurate, and indeed A-B voltage + B-C voltage didn't match A-C voltage that well. But I thought it would put me in the ball park. The actual voltage readings were A-C = 1.41, A-B = 0.71, and B-C = 0.83. So if we believe it's 1/2 ohm, I believe that would mean about 24A at start up or stalled. Does that make sense, or is this too inaccurate to consider?

I think Plons has extrapolated a graph of amps vs. RPM (under different loads) down to zero (past point of stalling). Is that a better way to get the 0 RPM current? The site where I bought it (http://www.robotmarketplace.com/marketplace_motors_ame.html) lists the stall current at 22A

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Ossi (and others), are there any of these RC motor controller circuits I can find on line? I did a quick search, but haven't found anything showing a circuit that seems to fit my application.

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Quote:
I think Plons has extrapolated a graph of amps vs. RPM
Indeed I did .... it was a way to get an idea of the DC-resistance of the motor.
Quote:
So I made a simple voltage divider using a AA battery, a one ohm resistor, and two of these motors in series:
Okay Tim !! That's the spirit ! Maybe not accurate, but a smart way to measure a parameter that your DMM cannot give you as it is.
Suggestion: use 1 motor, and see if the reading varies when you turn the rotor slowly by hand.

Plons

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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timwhunt wrote:
If I add a second mosfet in parallel, do I have to change anything else (e.g., capacitors, driver)?

Possibly one more of those 220nF capacitors, unless you can put the mosfets very close to each other. (And the heatsinks may be in the way for that.) Since you will be driving twice the gate capacitance, you may want to have more capacitance at the 4427's Vcc too, but I think the combination of a 4.7u and a 0.1u will be sufficient as it is. If you decide to increase it, use a bigger ceram rather than increasing the ellyte's size.

The Schottky is more than sufficient, no need to add another one.

As for heatsinks, they will have to be able to dissipate around 10 W each if you go with two mosfets (assuming I = 25 A, Rds = 60 mOhm, and switching losses around 1 W), or just below 40 W if you use just one mosfet. The Wakefield 637-20ABP looks suitable in the former case, and 647-25ABP in the latter. They're a bit bulky, but you'll probably need a fan if you want smaller heatsinks. Mouser carries the first of them, Farnell has both.

/ Grimmy

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It works!!!! :D It even sings! :wink:

Thanks or all the help! I built the circuit as described in the last drawing I posted, except I put two MOSFETs in parallel. Seems to be running just fine and not even getting warm. Sorry for the delay, but it took me awhile to get it built, and then the freaks site was out yesterday.

One thing that surprised me is that when I unhook the battery that powers the motors and the microcontroller, the spinning motor (with flywheel) seems to generate enough power to keep the LCD on the circuit (and I assume the microcontroller) running for a few seconds before it fades out. Is that anything I should worry about? Just had another thought: Could it be the mF capacitor running down?

Another question: Can a circuit like this be built on a PCB? I assume it can, but how wide do the traces need to be? Would it be better with 2 oz copper?

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Carl said:

Quote:
Now you all know why I'd perfer to use an application specific IC, such as the National Semiconductor LMD18201 H-Bridge 3 amp driver IC.

Yes, Carl, I have to agree that sounds much easier. I haven't been sure that any H-Bridge IC's I've found would handle the current of this application, otherwise I'd be happy to avoid this complexity. For me the jury is still out (my fault for not testing) on the current requirements. The max amps (22 I believe), have been highlighted, but I don't believe it draws that for more than the first moment. But I'll have to see if the datasheets make it clear enough if max current includes brief periods(e.g., start up) or if you can exceed max current briefly on start up.

My plans for this project do include a few more smaller motors, and for those I have ordered some 5Amp H-bridges. There are the ones described in
This Thread. They were only about $4, but I orderd four from Arrow and paid about $8 in shipping.

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Congratulations !

Do you have an oscilloscope at hand ?
If so, Its now time to make some measurements.
This will show you how waveforms look like.
Measure maveforms under various loads and operating conditions.

This will help to get an impression
how waveforms look alike if the things are ok.
Than you have compare-values if something goes
wrong !

It is a well known fact, that spinning motors may supply circuits.

I have heard, that hard-disks use the energy of the main-spindle to power the head-arm to get it driven to the "home position" in an sudden power-off condition.

Energy people use this energy-recovery when braking.

And if not properly designed, this energy may blow
up your circuit.

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Unfortunately I do not have an oscilloscope, but wish I did to do some testing. I'll take some current readings on my DMM, but it doesn't update quickly enough to get much of a sense of what's happening at startup. I'm assuming the readings while it's running is something like the average across the PWM cycles.

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The next 'feature' would be to add a comparator across a .01 ohm resistor with a trimpot ref so you can adjust the overcurrent limit. And a status led on the output of the comparator... Green if OK, red if in current limit

Imagecraft compiler user

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Thanks for the interesting suggestion Bob. Took me a bit of Googling and reading to understand, but I think I get it. Also got me thinking about rigging up an ADC from an AVR to try to measure current (via a shunt) as a poor man's (low frequency) oscilloscope. Judging from the numberous related postings, ideas like that seem tempting to many. However, now that this is working, I'm too anxious to start doing things with these motors to fine tune this any more.