Tiny13 motor control circuit

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Hi :)

I need to spin a tiny dc motor using a tiny13.
I built what I think is an H-bridge suitable for
this by freeform wiring together 6 transistors.
I'm using an H-bridge since I will want to change
direction of this motor as well as it's speed.

Please look over this circuit (sorry for the crudity
of my drawing) and see if it looks OK to you.
The transistors are shown dead-bug style and
the top two are pn2907 and the bottom 4 are
pn2222a.

I'm thinking this should work...but it does not :(
I wrote a small program that is setting pin 5 high
for a second..then pause .25 sec then pin 6 high
for a second then pause .25 and repeat. I know the pins
are changing correctly by using a simple LED probe.
But the output polarity of the bridge is not changing.
I'm thinking maybe a transistor is bad but I thought
I'd post this here before I build another one as it takes
a while to solder that tiny mess together :)

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Hi Gwen,

Your circuit seems to suffer from a lack of 6 resistors.

Try adding 1k from base to emitter on each of the upper two and each of the lower two transistors.
Very important: also add about 1k between the bases of the upper transistors and the
collectors of the middle transistors. The lack of resistance here may have caused
some, or all six to blow right off the bat 8-(

Reduce your 100k resistors to maybe 10k for better turnon and turnoff performance. Additional refinements may be the addition of four transient
surpression diodes, from each motor lead to -12v, and each motor lead to
+12v, "arrows" all pointing toward the top. These should protect the transistors from damaging voltage transients as the motor is switched
on and off.

Tom Pappano
Tulsa, Oklahoma

Tom Pappano
Tulsa, Oklahoma

Last Edited: Sun. Feb 26, 2006 - 09:50 AM
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good

JChristoff
Illinois

Last Edited: Wed. Jan 12, 2011 - 02:24 AM
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Quote:
Do you have to have 6 ransistors? I though H-bridges used only 4 transistors.

She needs two transistors for voltage translation in order to drive the two high side switches.

Tom Pappano
Tulsa, Oklahoma

Tom Pappano
Tulsa, Oklahoma

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I built this bridge from info here
http://faq.solarbotics.net/BiomechMotorBridges.html
Here is a pic of the circuit...I don't see the extra 4 resistors?
Are you sure 4 more are needed?

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I've never seen an H-bridge like that before but it seems quite logical, though I don't think I would build it that way...
applying 5V to an input opens the middle transistor (assuming it's an NPN) which opens the upper transistor (assuming PNP) in the same side and the lower transistor in the opposite side an voila, current flows through the motor.
Normally you would have the 4 driver transistors driven from some control logic (transistors and resistors) which is basically what this does too but I don't really like the "floating" transistor in the middle but I can't come up with any good reason why except that I don't think it's good practice to have a transistor "floating" like that.

/claus

/claus

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Also, as Tom already hinted at, the base current for the upper and lower transistors without current limiting base resistors is solely determined by the 'middle' 3904 beta (=current amplification factor). This may or may not blow those parts -I haven't looked up the specs.

Andreas

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when both control-inputs are high , both sides of the H-bridge short the 12V power-supply .... :evil:

the only current-limiting factor : the 100k in the control-lines. so lowering them to 10k will defenitely blow out the bridge.
it COULD work if the 12V power is current-limited to the max. collector-current of the bridge-transistors. for 2n3904/06 that's 100mA (byheart ...) and for 2n2907 etc about 500 mA (by heart as well :wink: )

i DO like simple designs for simple tasks, but this one is buggy

nard

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tricia, and Ulyana. 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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I first came across that particular circuit inside a furby (left). As Plons states, set both outputs and you're fried. The one in the Furby was more production-reliable, but still had this problem.

The 'non-smoking Furby Circuit' (right) doesn't have this problem, and works with both bipolar transistors and fets.
When using bipolar transistors, remember to add reverse polarity diodes, otherwise the inductive kickback may lead to disaster. With the FETs they are free.

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Good suggestion, nice schematic, btw

For small H-bridge: BA6209 or BA6418. Often used in cassette-players, VCR's etc. For hobby-purposes I strip old equipment. Printers and scanners are a good source for motors and controller-chips
....
I checked an old VCR (Grundig) and found L272 and L293 as motor-drivers

that's how I solve problems with parts-availability

regards

Nard

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tricia, and Ulyana. 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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How about this one ?

It will not short the 12V power, simple to drive, no protection-diodes necessary (transistors take care of that)

Drawback: dissipation of transistors in the bridge when motor is active (there is about 1V over the transistor in action), and as there is no thermal protection for the transistors

BTW what a horrible sketch compared to the neat schematic of KPP ....

Comments are welcome

I did not test it btw

nard

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A GIF is worth a thousend words   They are called Rosa, Sylvia, Tricia, and Ulyana. 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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I got up this morning and decided to solder together another one
of these little bridges and test it using 2 power supplies. It seems
to work.

One supply has 4.5v and the other 12.14v

I hooked ground from both supplies together and used the pos lead
from the 4.5v supply to connect to the two 100k resistors in order to
switch the bridge on.

The 12.14v goes to the neg and pos connections on the bridge.

I connect my meter where the motor would go.
When I touch the leftmost resistors lead my meter reads +12.12v
when I touch the other one it reads -12.12

So I'm losing .2v ... I expected a bigger loss?

So I guess the bridge works and the one I soldered into my
tiny13 circuit must be faulty...so I will have to replace it and
try again...if this bridge works on the test bench I don't see why
a tiny13 cannot switch it just as I did by hand with the +4.5v lead
do you???

BTW.. I'm building this circuit because I am making some more
AVR shadow boxes...these are going to have little windmills inside
that turn at different speeds and directions at random..along with
a few other little touches. I am making the windmills with some
really small 12v brushless motors and constructing the windmill
towers by soldering together bare wire...I discovered that I can
solder 2 pieces of bare wire right onto the motor shafts to serve
as the blades :)

Here is a 3d pic of what the bridge is supposed to look like...

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Last Edited: Mon. Feb 27, 2006 - 12:42 AM
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Gwen: You get this low drop (0.1V per transistor) because you're driving the transistors into the saturation region (they are operating at a current amplification that's below ten).
With 3V or so over the base resistors you get around 30uA first-stage base current, resulting in 3-20mA second-stage base current, so the output stage will be in saturation up to, depending on the transistors, 50x that. So unless the motor current exceeds 100mA or somewhere in that ballpark, the voltate drop over the transistors will be 'unexpectedly low'.

Beware if you wish to pulse width modulate the bridge. It's going to be mightly slow at turning off, and the inductive kickback will kill it unless you add those reverse diodes.

And you just passed your dead-bug prototyping exam. Looks neat.

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How come it will be so slow turning off????

By slow do you mean slower than say 200ns ?
I though a bridge had a slower rise time than fall time?
Is the inductance of the motor causing slower fall time?

Would a different design have a faster fall time?

Last Edited: Mon. Feb 27, 2006 - 01:06 AM
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Whoa!

I smoked the test bridge :(
Was handling it while testing it with a 250ma load..
It was running cool and smooth but when I fiddled with the
bridge I accidently turned on both polarities by just touching the other
switch lead...I think..

This thing switches with an awfully tiny amount of current!
Holding the pos lead and then touching the 100k resistor lead
turns the current on fully.

what a stink :)

Maybe I could make a bridge with just four pn2222a transistors
and that would work just as well or better....

BTW... I tested the bridge at .5amp and it stood that current
through the bridge for 20 mins without getting hot.
I went up to .75amp and the 2 transistors began to get warm.
So..if I can keep from turning all 4 transistors on at once
the power handling is more than enough.

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Gwen: Here is an example of a bridge that does not have that problem.

http://www3.telus.net/chemelec/Projects/H-Bridge/H-Bridge-1.png

Rick

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Gwen wrote:
.....what a stink :)....

JChristoff
Illinois

Last Edited: Thu. Jan 6, 2011 - 06:36 AM
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Gwen: The turn-off time of the transistors, if they are anything like BC547 or 2N2222, going to be way over 200 ns.
I have measured this as 2.4 microseconds for 1mA base, 5mA collector current, and since your bridge doesn't have any base-emitter resistors to pull the other way, I'd say _at least_ 3 microseconds. Probably 10.

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I'm with jgrunt on this one. Plus, you can request free samples from TI here:
http://focus.ti.com/docs/prod/fo...

TI is very good about sending samples. I usually get what I have asked for in 2 days.

-Zoom

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Quote:
since your bridge doesn't have any base-emitter resistors to pull the other way

So if I add a resistor between the base and emitter of the 2222s that would speed up
the turn-off time?

What sort of value resistors might work?
Would the 2907s need them as well?

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Hi Gwen! If you don't already have the book "The Art of Electronics" you should get it asap. I'm sure you would wear out your first copy in 6 months.

-Zoom