| Electronics > Projects, Designs, and Technical Stuff |
| Bench CC/CV PSU Based on Daves uSupply (Not Anymore) |
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| Kleinstein:
The minimum current setting could be due to the LM324 like nearly all OPs can not get it's output all the way to the output when there is a load at the output. Just a little of negative supply should do the trick. Alternatively one could add an offset to the divider, so that zero current could be shifted to some 10 or 50 mV as needed. No need to have the offset at the shunt. Without a negative supply the constant current load would also not work well, when the output voltage is low. The simulation already includes a constant load before the shunt, so it would not interfere with the current measurement. A LMP7705 or similar could be an option, though a little tricky to solder (VSSOP 8 case). As there is likely enough voltage to spare, I would consider a diode (like 1N5403) for the negative side current to drop something like 0.6 V from the negative side. Usually the laptop supplies are isolated, and thus no need to have the negative side of the input to be also the negative side (ground) of the output. |
| iMo:
A small modification of small_psu 50mV-20V/2.5A.. Added "Green LED" current sources and with junkbox transistors. Needs a negative supply as well, -5V for example, or similar. Simulates stable with min 10uF at the output. PS: Q3 requires a heatsink as well.. |
| KC0PPH:
I do not have a Laptop supply to use yet, but I was thinking I could easily get one in the 18V range. I can use a diode to create a negative voltage rail for the op-amps. This should be ok without causing any issues to the rest of the circuit. I need to still figure out how to use LTSpice so I can play before I build. I have parts on order to breadboard this up. As for OpAmp selection if a 324 works well I would like to use it as I have a bunch laying around. It will also be interesting to see how this likes being fed from a homebrew switchmode PSU as I will keep the voltage supply to this right above the cutoff threshold to reduce heating. |
| iMo:
I get almost identical results with LM324. Of course, it is a simulation only.. |
| Kleinstein:
A LM324/LM358 should work though relatively slow. My usual bench supply is build similar with an LM324, though with the low side shunt, as only single channel. As most of the OPs have a standard pinout there is a chance to use a different OP for better accuracy, higher speed (could be a factor for the current regulation). For the current sources I would not use green LEDs, as quite some voltage is lost. The more usual choice would be a red LED. One could still use a divider to reduce the voltage drop even further - so that some -0.5 V would be sufficient. |
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