Signal Generator on Steroids

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I've got a project coming up where I need a signal generator on steroids to help in the development. I need to generate a signal which can go up to 30v or more in voltage mode and up to 5A in current mode. Frequency somewhere between 0.1Hz and 400Hz. Typical waveforms ie sine/square/ramp. If it did bipolar then so much the better. I need to run in either controlled voltage mode or controlled current mode.

 

Generating the initial (voltage) waveform isn't a problem. I've got a DDS function generator and two PC based AWGs within an arms length. My problem is beefing those up.

 

I could make something but, for me, time is money. By the time I've built something, built the power supply for it and put it in a box it'll not be cheap. So a voltage amplifier/voltage to current converter.

 

I could take some sort of commercial audio amplifier, bypass any output capacitor and figure a way to run it CC as well as CV. But again, it'll take time and might not work.

 

I have seen programmable DC power supplies out there for not too much money. Some have an RS232 port on the back so I guess I could knock up some simple code to control them. Other can be programmed from the front panel but they all seem to suffer from slow changes in output. It seems quite common that each step of the output waveform has a minimum time of 1s.

 

In my head I'm looking for a DC bench power supply with two input sockets: one which controls the output voltage, the other which controls the current limiter.

 

Anyone got any thoughts?

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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Programmable bi-polar power supplies. Older analog and digital versions can be found on Ebay. I have seen them on craigslist. Often called system power supplies.

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LT3080 might be a start.

It is basically a high power buffer with a 1A output capability.

You can put a bunch of them parallel.

http://www.linear.com/product/LT...

 

This thing takes care of it's own loop stability and can easily be tied to the ouptut of an opamp to make it do all kind of crazy stuff.

For current control you can add a shunt in the input with an in-amp, or differential amplifier or current mirror.

There are plenty of chips for "high side current measurement".

 

The design effort needed mostly depends on the accuracy needed.

Edit: Addition.

Oops. It seems that the LT3080 can only dissipate 12Watts. (Current limit graph in the middle of page 6).

2x Oops: Note 9: Current limit may decrrease to zero at Input-to-Output differential voltages greater than 26V...

 

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Had a peek at a Rigol programmable power supply. DP832

https://www.batronix.com/shop/po...

It has a "Voltage Programming Control Speed" with rise and fall times of 40ms to 50ms. Nowhere near your requirements.

 

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With this BK power supply I could not find setpoint speed settings in the manual / datasheet. Price Indication: EUR800

http://www.bkprecision.com/produ...

 

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Rohde & Schwartz HMP series has an "EasyArb-Function" with a time resolution of 10ms. Price indication: EUR 1500

https://www.batronix.com/shop/ro...

 

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Was thinking about a Keithley SMU (Source measurement Unit) But these things are bloody expensive.

 

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Audio ampilfier does not seem a too bad option.

Only cheap low power amplifiers have an output capacitor.

Almost all Audio amplifiers have an (relativily small) capacitor on the input. (Which can easily be bypassed).

Main reason for that capacitor is that loudspeakers do not like DC.

Audio amplifiers often have a DC- protection circuit which turns the amp of if DC on the output is detected.

Paul van der Hoeven.
Bunch of old projects with AVR's:
http://www.hoevendesign.com

Last Edited: Fri. Jan 26, 2018 - 10:07 PM
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Take a search for KEPCO BOP   ..these are 4 quadrant bipolar "op amp mode" supplies.  It's like having a 200, 500, or 1000 watt opamp.  These supplies not only output volts & amps, they can sink (absorb them)...so if you drive a motor and suddenly reduce the input signal, these guys will brake (slow) the motor, absorbing the inertia.

 

https://www.ebay.com/itm/Kepco-BOP36-5M-Bipolar-Operational-power-supply/272938686243?hash=item3f8c69d723:g:TGMAAOSwVA5aA754

 

I have a similar unit, the Electronic Measurements brand  "the boss"  supply    +/-50V +/-8A ....(Bipolar Oprational Source/Sink...BOSS)  ...got for about $200

 

I decided to take a look at my BOSS operators manual---I didn't realize it has a "dozen"  functions and 10-20KHz response

http://www.us.tdk-lambda.com/hp/product_html/legacy_data_sheets/BOS-S%20DATA%20SHEET%2003100006%20REV%20A.PDF

 

 

 

some photos of a 20v/20amp Boss  (scroll down to see remote connection photos):   https://www.ebay.com/itm/Electronic-Measurements-BOS-S-20-20-2-Bipolar-Operational-Source-Sink-00469001-/132427217060?hash=item1ed546f8a4%3Ag%3AascAAOSwbtNaKgjn&nma=true&si=nwpGs%252F6h%252BH2jXW8u7Ud197T1S5s%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

When in the dark remember-the future looks brighter than ever.

Last Edited: Sat. Jan 27, 2018 - 03:14 AM
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How about a function generator and an audio power amp? I have a CROWN macrotech 1000w unit that should be able to deliver he punch. You have an audio amp laying about you could use?

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?  - Lee "theusch"

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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avrcandies wrote:

 it has a "dozen"  functions and 10-20KHz response

 

Brian Fairchild wrote:

 Frequency somewhere between 0.1Hz and 400Hz.

 

So the question is:  How important is that 0.1Hz spec?

 

 

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 Frequency somewhere between 0.1Hz and 400Hz.

 

So the question is:  How important is that 0.1Hz spec?

 

Unlike (most) audio amps , it's a power supply, so it goes down to DC...the upper freq  is about 10KHz -20KHz , depending on specifics

 

When in the dark remember-the future looks brighter than ever.

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RickB wrote:

Programmable bi-polar power supplies. Older analog and digital versions can be found on Ebay. I have seen them on craigslist. Often called system power supplies.

 

Thanks, I'll add that to my eBay search terms.

 

 

Paulvdh wrote:

LT3080 might be a start....

 

Thanks for the ideas. I was hoping to avoid the DIY route but it's looking ore difficult to do that.

 

 

avrcandies wrote:

Take a search for KEPCO BOP   ..these are 4 quadrant bipolar "op amp mode" supplies. 

 

Thanks, I'd not come across Kepco before. Mind you, over this side of the pond they seem as rare as hen's teeth. Not much sign of them on eBay. There's a few in the US but shipping this direction will cost an arm and a leg. Anyways, that's a few more search terms for my eBay saved searches.

 

 

jgmdesign wrote:

How about a function generator and an audio power amp?

 

I suppose the ultimate would be an old DC300A.

 

 

Chuck99 wrote:

So the question is:  How important is that 0.1Hz spec?

 

It was, if I'm honest, plucked out of thin air as a number that is quite low in frequency but not quite DC. Any lower and I could just turn the knob on one of my lab power supplies.

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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How important is that "30V" spec?  I'd suggest a Nat Semi LM12 power op-amp, in a TO-3 (4-pin) can.  They're good to +/-25V  on +/- 30V rails to 10A.

 

And it's an op-amp, so wiring it up is trivial.  Frequency response is flat to 60kHz. It is a TO-3 can, with extra pins, so the heatsink mounting gets interesting, to say the least.

 

I'm not sure they make them anymore. Digikey lists them as ‘obsolete’.  I've got a few, if you want one.  S.

 

Attached spec:  LM12CL.pdf

 

 

Attachment(s): 

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Lost my post in the site update...

About the audio amp route:

Paralleling a few TDA7293 boards used as "power opamp" mith be a nice compromise.

Minimum reverse engineering and quick to build on their PCB's, and the go upto 50V power supply.

Note: These chips are made to be used in parallel, Check the power dissipation numbers fow how many you need.

 

https://www.aliexpress.com/whole...

 

Boards with a bridge recitfier & beefy elco's are also pretty cheap.

Add in a transformer and a chunck of aluminimum and you're almost there.

And for those prices you almost have no excuse not to try it.

 

Had a peek at the Crown DC-300A on the 'net. It goes down to DC, but I doubt it delivers 300A.

Paul van der Hoeven.
Bunch of old projects with AVR's:
http://www.hoevendesign.com

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Ditto on the venerable Crown DC300 (that's 300 *watts*, not amps). These are supposed to be DC coupled from input to output, and can be used as motor drivers, etc. Data should be available at crownaudio.com

Tom Pappano
Tulsa, Oklahoma

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Paulvdh wrote:

Paralleling a few TDA7293 boards used as "power opamp" mith be a nice compromise....These chips are made to be used in parallel...

 

 

I found some boards on eBay with 3 of these connected in parallel and have bought a couple to try. I think I'm going to end up building something with my plan being to gut a bench power supply to use the case, transformer and heatsink.

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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I looked a bit closer at the datasheet.

Figure 11 on page 14 shows an example circuit of putting 2 in parallel.

You'll have to short C1 and C2 for DC operation.

The bootstrap capacitor also needs special attention for DC operation.

Normally this is used to lift the internal power supply voltage above the power rails during the peaks.

You can probably connect the bootstrap input to the positive power rails.

Output voltage will then be limited to a few volts below the power rail voltage.

 

Audio amp stability can be an issue if you add things such as a shunt for current measuring or extra feedback.

Loop stability can become a serious problem.

- Boucherot network may help.

- Low inductance shunt resistor may help.

 

It might be an idea to put all TDA chips in slave mode and use an external opamp to feed into pin 11.

Paul van der Hoeven.
Bunch of old projects with AVR's:
http://www.hoevendesign.com

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I've been circling around the Crown DC-300 for some time, wanting one even though I had no particular use for it 8)  I already have four vintage Crown amps that shake the various walls of my shop, home living room, home office and garage (CT-400, CT-410, CT-210 and D75).  All this power supply/function generator talk forced me to buy the DC-300's little brother, the D150A, also DC coupled but 1/2 the power and less expensive.  This should make a nice dual +/- 35V 4A power supply/signal generator to replace my *ancient* Heathkit IP-20 bench supply that finally went TU (at least that's how I rationalized the purchase)

 

Tom Pappano
Tulsa, Oklahoma

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The D150A arrived but needed a little tlc.  Had to replace a small cap in a bootstrap charge pump and replace a 'wrong' op amp (that was causing instability on fast-rise signals) with the original specified ua739.  This thing rocks, either channel sources over 7 amps from -40 to +40 volts (or 3.5 amps if both channels equally driven and loaded).  Not bad for a 40 year old amp 8)

 

Tom Pappano
Tulsa, Oklahoma