| Electronics > Projects, Designs, and Technical Stuff |
| Power supply topology - will it work? (Control theory, stability) |
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| Kleinstein:
30 mA of current is already quite a lot, already more than an typical OP deliver. So at least with such a high threshold the resistor should be ok. One could even use an emitter-follower NPN+PNP push - pull stage, driving the PNP from the diodes. |
| Yansi:
Yes I have also thought about that. I think the PP stage should be with at least some base-to-base voltage or ideally some bias current, otherwise I am afraid the "hysteresis" or "crossover distortion" or how to name that might be a trouble for the control loop. But this complicated current boost stage might be more complicated than what is really needed, so I'll try the simple first. If I weren't so tired today... yaay. Still just writing here and doing nothing, the soldering iron is cold. :=\ |
| Yansi:
With a little help of coffee, the circuit mod is finally done. Rb=2K2 (round about 2.5mA to the opamps), Re=150 (did want to try 180, but couldn't find any >:( ) Circuit still stable, step responses hasn't changed much, if at all. Now I should cobble together the current regulator on the veroboard, so we can have some other thing to play with. >:D |
| Yansi:
What an epic win! :o I have put there another opamp as the current regulator. Did not bother to connect any feedback cap across the opamp, turned it on to see if it at least works, while expecting it to oscillate wildly when the current limiter kick in. And guess what: Nothing! And then I noticed it does limit current and is stable without any additional R/C. (Only 22k resistor in the inverting input) So the high voltage PSU prototype finally works! Tomorrow I will test step responses of the current regulator and the CC/CV switch over. Thanks so far very much for help, now some bed time is needed! :=\ Here is the photo of the little bastard. |
| salbayeng:
Step response testing: I just connect a small relay coil to a signal generator set at ~ 1Hz (10v output into 600ohm drives a 12v 1000ohm coil nicely) use this to switch your dummy load, really only good for 100vDc per contact, 2 in series will get you 200VDc, more than that and you will need MOSFET. Note that 0-10% transient responses are different to 10% TO 100% transients. Note re current limiting: if you have integrators in your voltage loop, then applying current limiting after the integrator will cause the capacitors to charge up fully, at that point the inputs of the opamp will float away from each other, and it will take a loooong time to recover. |
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