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| Feedback on power supply 0-30V 0-4A |
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| xavier60:
--- Quote from: d4n13l on July 27, 2019, 07:30:38 am ---I'm sort of new to electronics so correct me if I'm wrong but you have the high potential (the output of the LM338) and the low potential (-3V rail), why do you need ground? when you connect two batteries in series you use the extremes of the batteries you don't care about the middle. The current flowing throught the divider is very small and compensated by R11, as to not affect the adj pin. IC1A input connects to the divider but as I undertand it no current is flowing through it. The point of IC1B is to not allow the voltage to change at R2 no matter the load. IC1B see in the non inverting input 0.9V tops from the divider. The same voltage is put in the inverting input and so you would allow 0.9V/0.22=~4A max, if you set VR1 to supply 0.1V the max current would be 0.45A.. which is my problem, even thought 0.1 is the low end of the voltage it still supplies high current for small electronic projects, which make it hard to regulate in this circuit. --- End quote --- I don't think I'll ever make sense of the voltage regulation side. I'll just accept that it works for now. It sounds like your current regulation is working but not all the way down to 0V output such as when the output is short circuited. You need to do some testing. Set the current to some low setting like 1A and apply a load with gradually decreasing resistance. I use a 6Ω 300W rheostat. After the 1A limit is reached, IC1B should be capable of pulling the ADJ pin down to -1.2V as the load approaches 0Ω. |
| d4n13l:
Sorry man, but I think you don't get it. The supply works great as is. It goes from 0 to 30V and 0 to 4A. The problem is that I have a coarse current regulation when I want a fine current regulation. If I adjust R10 to output 0.1V VR1 works great now because the output range it was to work with goes from 0 to ~450mA whereas if R10 outputs 1V it has a range of 0 to 4A. What I'm looking for I guess is a way to allow this fine/coarse tunning for VR1 through the whole 0-4A range. Also, I have problems adapting the meter display, if I power it from yet another supply, it works great, but if I feed power it it from B3 with a L7805 or something like that it rises the output voltage a few volts. I would like a suggestion on how to power it without having to add yet another supply. |
| xavier60:
You could add a Fine Pot. One way of doing it is to wire the outer pins in parallel and then sum the wipers with 2 resistors say a 10K for the course and a 100K for the fine. I used 10 turn Pots. They were cheap enough on ebay but I had trouble. I'm not certain if was due to poor quality or bad luck. I explained what happened here. https://www.eevblog.com/forum/projects/linear-lab-power-supply/msg2368746/#msg2368746 https://www.eevblog.com/forum/projects/linear-lab-power-supply/msg2388873/#msg2388873 |
| xavier60:
--- Quote from: d4n13l on July 27, 2019, 06:29:02 pm --- Also, I have problems adapting the meter display, if I power it from yet another supply, it works great, but if I feed power it it from B3 with a L7805 or something like that it rises the output voltage a few volts. I would like a suggestion on how to power it without having to add yet another supply. --- End quote --- How were you powering the meter from B3 as well as U2? The meter would need a + supply? What voltage is there across C2 at the moment? |
| d4n13l:
I just connected the a L7805 in parallele with C2.. I didn't realize before that this causes the voltage to come down.. guess I'll try to connected it somehow to B2 |
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