Electronics > Beginners
Linear lab bench power supply - Advise Needed
UltraRC:
Thanks again for the help
I have done a bit of reading, thinking and tinkering and have made the following changes (Sorry but the component prefixes have changed in the new schematic because I pressed a wrong button):
- Added current limiting indicator LED
- Added power on indicator LED
- Opamps, voltage set and current set pots now powered from before the current shunt
- Changed output cap from 1000uF to 100uF
- Added 10K resister in series with the emmitter of Q2
Questions:
- Will Q3 interfere with the loop?
- I read that I may need a negative supply for the opamp, is this needed?
- Also thinking that the inputs of U2 may need switching?
Thanks, am excited to get this thing working
xavier60:
--- Quote from: UltraRC on January 21, 2020, 07:55:35 am ---Thanks again for the help
I have done a bit of reading, thinking and tinkering and have made the following changes (Sorry but the component prefixes have changed in the new schematic because I pressed a wrong button):
- Added current limiting indicator LED
- Added power on indicator LED
- Opamps, voltage set and current set pots now powered from before the current shunt
- Changed output cap from 1000uF to 100uF
- Added 10K resister in series with the emmitter of Q2
Questions:
- Will Q3 interfere with the loop?
- I read that I may need a negative supply for the opamp, is this needed?
- Also thinking that the inputs of U2 may need switching?
Thanks, am excited to get this thing working
--- End quote ---
Q2 is over driven, 10K for R15 is too high anyway to pull the Gate voltage down.
R11 needs to be 10K and about 100Ω for R15. R15 needs to be just low enough so that the Gate can be pulled below the MOSFETs threshold voltage.
The CC loop will still likely be unstable. Adding compensation feedback to U2 might help.
Preferably, U2 should be configured as inverting with series RC feedback and be able to pull down the Gate voltage without adding extra gain.
So far I have not been able to figure out a way that will pull the Gate voltage low enough without causing other complications.
Might need to consider an alternate output configuration that is easier to control and has a much lower dropout voltage so that over 14V max output will be possible.
I have good success with the PNP Sziklai Transistor Pair type output, https://circuitdigest.com/electronic-circuits/sziklai-transistor-pair
Extra: A negative rail can make things easier but not essential with careful design.
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