Electronics > Projects, Designs, and Technical Stuff
Bench CC/CV PSU Based on Daves uSupply (Not Anymore)
jaycee:
--- Quote from: KC0PPH on March 20, 2019, 03:49:57 am ---So if I am getting the theory right C6 begins to look like a "short" as the frequency goes up. Even though this is a DC circuit the transients are AC and thus this AC "noise" gets pushed right through C6 into the OA.
--- End quote ---
Correct.
--- Quote from: KC0PPH on March 20, 2019, 03:49:57 am ---The thing I am confused about is why the feedback Resistors and Capacitors are required in a steady state system? I would think that oscillation would not happen with a fixed load, and without oscillation there would be no "AC" transients to go through the feedback loops.
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It's one of these cases where the real world is a drag... there isn't really any such thing as "pure DC" or a "steady state" - there is always noise and ripple.
KC0PPH:
Well I guess I can accept that lol.. Well I have the circuit all wired up excluding the current limit. I need to get re acquainted with my Analog Discovery and start to look at the waveforms. I added 2 diodes in the common to cheat a negative voltage for the OA.
Measuring from the DC Common to Output I get a Max of 9.58V and a low of 796mV
Measuring from my Diodes to Output I get a Max 8.888 of and a min of 130mV.
I am using 1N400. My guess Is i am not running enough current through them to drop the voltage enough.
All testing is being done with no additional load, just the 20mA CC load.
KC0PPH:
I am also not sure what the purpose of the .16 ohm resistor is (R15)
jaycee:
Im assuming you are referring to CV_CC_PSU_2xLM358_TIP120_FASTCC_LOAD_TEST.PNG
The resistor is an emitter resistor which is acting as a local sense resistor. This is the voltage that Q5 is monitoring in order to provide the fast current limit. If you were to add extra pass transistors in parallel, this resistor would also act as a "ballast" resistor to ensure the transistors share the load equally.
iMo:
FYI- Mike_Mike has done an FastCC/SlowCC measurement with the "PSU Shorter" in his HW, it can work for PSU stability testing as well.
https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg2283144/#msg2283144
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