I’m investigating transient switch arcing that occurs in a 3 phase switching unit.

I am planning on generating the phase signals with an STM32F4 using DAC and DMA with timing separation for the phase difference.

I need to boost this signal to around 40 V peak with around 3-5A with the ability to provide or than that for short periods.

I was considering a power opamp like the LM675 but I’m not sure if this would be the best or feasible approach.

Is there a typical way of accomplishing this kind of amplification?

I can purchase basic components as required and have lab bench power supplies available.


  • \$\begingroup\$ If these are AC waveforms, you probably need 80 Vp-p, more than a LM675 can provide. I would look at these: powerampdesign.net/poweropamps/100voltmodels.html , but they won't be cheap. \$\endgroup\$ – Mattman944 Apr 21 '19 at 2:13
  • \$\begingroup\$ Ok nice, I thought there would be components like this available. When you say expensive are you talking 10s or 100s of dollars? If I was looking at a smaller scale proof of concept keeping within the limits of the LM675 (or similar opamp) would it work? I’m just making sure I’m on the right path before I sink heaps of time into the idea. \$\endgroup\$ – Krixz Apr 21 '19 at 2:54
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    \$\begingroup\$ I'm not sure whether you really need a linear amplifier to accomplish what you're looking for. If not, consider using a class D switched amplifier instead. This will be a much more power efficient solution. You could even use the STM32's PWM outputs. \$\endgroup\$ – joribama Apr 21 '19 at 7:09
  • \$\begingroup\$ Yes, a power opamp is a reasonable solution. There may be others with higher voltage, but I couldn't find one with a quick search. The modules from powerampdesign are industrial quality and would most likely be 100's of dollars. @joribama, if I was building lots of these, I could consider a more elegant solution, but I wouldn't want the solution to be more complicated than my original problem. \$\endgroup\$ – Mattman944 Apr 21 '19 at 8:53
  • \$\begingroup\$ @joribama I need a solution that approximates a continuous one. If I were to use switching I would need an inductive filter which would change the system model that is seen by the switching unit. Thanks for the info, because its just a testing unit I’m not too worried about efficiency (aside from associated thermals). At this stage I’m think I will use an opamp level shifter to take the MCU output to +- then a non inverting amplifier configuration with the LM675 to boost the signal. This should get me started and I can go to a more expensive solution if this provides results. \$\endgroup\$ – Krixz Apr 22 '19 at 8:06

The opamp or any linear solution will dissipate a lot of power. Also look at the graphs to see how close the output can get to Vcc. Here is an example calculation with the LM675 assuming a constant resistive load. You need to keep the case temperature near ambient to get the most power out. Something like 4 x 4 inches with lots of fins and a fan.

Instantaneous Power Table


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