Using uController + Amplifier to Create Multi-Channel Multi-Mode Lab PSU - Page 1
Forum section: electronics / projects

author: Negative Energy
author_rank: Newbie
timestamp: September 30, 2012, 07:10:20 pm
content: Hello World! First post alert!So I have an idea to create a very versatile multimode lab power supply:Use a class AB power amplifier design of suitable output power and able to pass DC to output, fed by a "programmed" input signal from a microcontroller (employing either a DAC or PWM and filter) to create the desired waveform. With this concept, you should be able to create an extremely versatile PSU supporting:DC Mode: Voltage Control both + and -, Current LimitingAC Sine Mode: Voltage Control (specified as any of rms, pk, or p-p), Frequency Selection, DC OffsetPulsed DC Mode: (rectified AC)Square Wave: Voltage Control, Pulse Rate, Pulse Width (or specified as duty cycle)and pretty much any other waveform you would want to add. It is similar to a signal or pattern generator except that you can supply larger currents and set constraints on combinations of voltage, current, etc. Programs including modulation and superposition of AC on DC and vice versa could be added to enhance testing of various devices like opamp CMRR and PSRR specs, etc.With multiple channels created by replicating the power sections but retaining control by a single ucontroller, you could even set up multi-phase AC and square wave power, and have programmable / variable phase relationship from a front panel. Floating grounds/returns on each channel with selectable interchanne; connections allow for more possibilities.In the interest of full disclosure: I am not a college educated engineer, so I apologize for any misuse of jargon. I am an avid electronics experimenter, and am looking to enhance my own amateur lab by creating novel instrumentation.I would love to hear comments and discussion from others on the board. I have not breadboarded anything for this design yet.

author: Psi
author_rank: Super Contributor
timestamp: September 30, 2012, 09:31:55 pm
content: If you want to make it simple you could use high current opamps eg OPA549They aren't cheap but come with- adjustable current limiting- thermal protection+/- 30V or 0-60V- Are able to supply 8A continuous and 10A peak.- Up to around 60khz without distortion (depending on your application this may not be enough)Couple that with a switching pre-regulator and microcontroller and you would have a pretty awesome powersupply.I've been wanting to do this for ages with some OPA549's i have laying around.

author: DaveW
author_rank: Frequent Contributor
timestamp: October 01, 2012, 10:58:25 am
content: Have a look at Class G/H amplifiers, which can be a class AB amp fed by switchable taps or an SMPS as a tracking pre-regulator. This will help with the heat dissipation resulting from a high Vin-Vout at a reasonably high current.You also might findhttp://wattcircuit.com/2012/01/28/100/interesting, it's a very similar idea with an off the shelf waveform generator and a common collector amplifier. That coupled with a DDS generator and that'll be most of your circuit. The high bandwidth current limiting will be interesting, should be easily possible with a shunt resistor though, could even feed the signal back into the pre-regulator stage and keep the feedback loop analog

author: ptricks
author_rank: Frequent Contributor
timestamp: October 01, 2012, 11:52:46 am
content: It sounds like you are combining two lab instruments into one box, power supply and function generator. Not sure the complication of the circuit would be worth it as a function generator can already do everything you described as reasons for using PWM in the lab PSU. If you have a function generator you can attach a pass transistor to the output and you have what you described. I am not a big fan of smps lab supplies simply because of the noise and the way you have to implement current limiting. I prefer to use the microcontroller to set a voltage and let specialized hardware like voltage regulators worry about the voltage and current rather than having a controller constantly monitoring voltage, adjusting output, etc.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 01, 2012, 12:47:35 pm
content: Quote from: Negative Energy on September 30, 2012, 07:10:20 pmhow much signal bandwidth and wattage are you talking about? and how do you think you will do the current limit feature without expecting say a sine wave power signal to get distorted (clipped) due to current limiting circuit activation?

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: October 01, 2012, 01:24:03 pm
content: Quotewouldnt you just use active gain control to turn down the amp until it is at its rms limit?

author: robrenz
author_rank: Super Contributor
timestamp: October 01, 2012, 01:34:18 pm
content: @ Mechatrommer,Did you ever finish your amplifier? I would like to build one to use with my DG1022.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 01, 2012, 02:15:21 pm
content: Quote from: robrenz on October 01, 2012, 01:34:18 pmjust a push pull mosfets or bjts up to the required bandwidth and slewrate and an opamp quick enough to stabilize the output from feedback... it was a very quick setup while working on something last time. pretty much by the book null engineered circuit, i dont know anything simpler. i believe i can start expanding from this if i want to get serious, but unfortunately i dont have the balls or need to do that yet(as i'm still in the process building my diff probe, and then only i can analyze at smps and probably will get back to this, quite a merry go round historic event) but i believe you are aware that for rigol AWG/FG there is separate power unit available? so you dont have to mess with low tech stuff, using up your time building one or risk damaging your DG1022.fromArbitrary/Function PSU Idea. Usefull or Not?Quote from: HackedFridgeMagnet on October 01, 2012, 01:24:03 pmthats sensible, thanks for the idea.

author: robrenz
author_rank: Super Contributor
timestamp: October 01, 2012, 04:06:42 pm
content: Thanks Mechatrommer, The Rigol PA1011 does not have much of a following and a chinese forum did not have much good to say about it.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 01, 2012, 05:14:38 pm
content: Quote from: robrenz on October 01, 2012, 04:06:42 pmi believe there should be very little can go wrong with simple circuit above as long as you take care the limiting resistor R5 there (1KOhm) to protect your FG. for higher wattage i think paralleling mosfets and adding balancing resistor at output of each mosfet will do the trick? i've never tried. but adding current (rms) limiting should be more involved than that.