Electronics > Beginners
Help me design a PSU
VEGETA:
--- Quote from: Efe_114 on November 14, 2018, 06:49:25 am ---i have a suitable 48v transformer for the banggodd kit i may buy that but i want to learn. a negative bias center tapped etc. transformer is gonna be hard to find in my country . Yes i meant lt3080 . i had some problem troubleshooting my lm317 clrcuits i dont know if my lm317s are fake cuz 1 of them blew up and released a lot of magic smoke and caught on fire at 0.5 amps 12v input 10v output 1 watts heat dissipation
i wonder if i can make a stable build out of 2n2222 and 2n3055 npn power transistor and a jellybean lm358
I can make a darlington pair out of 2n2222 and 2n3055 and use it series pass(?) with the vcc(im. NOT good at transistor configuration names)and a classic error amplifier configuration out of lm358 and pot as a referance and output feedback on the another input i think this can go high currents because i will buy 2n3055 in to-3 package or i might stay away from complexity and use lm317 and i wonder if Putting a zener diode reverse biased in Adj pin will work? i dont think so but just want to ask you does minus voltage regulators need minus voltage in the input? If not i may feed -1.25 to the lm317 otherwise i cant because of the availablity problems i mentioned before .sorry for the complex reply :-//
I just seen some of these questions got answered while i write this thank you ;D
--- End quote ---
Actually, lm317 is not meant to be a lab variable power supply regulator, but it kinda works and cheap.
If you wanna make your own regulator then it is gonna be hard since there is stabilization and so on that you are gonna face like I did previously. I made a floating regulator design but never built it yet.
stick to lm317 + 7660 + lm358 + tl431 like I told you and then you will be fine.
not1xor1:
--- Quote from: Cliff Matthews on November 14, 2018, 01:38:08 am ---Here's one from Banggood (it's about $6). Someone posted a schematic.. Funny drawback of producing a negative rail with a bucket load of cheapo 1N4007's is the 1 amp maximum. Real efficient heater though..
--- End quote ---
It is easy to make a much better (more stable, more efficient) PSU with about the same amount of components (dual opamp and power transistors), but if current regulation is not important even a TL431 + darlington would work.
A negative rail and another TL431 would allow to start voltage regulation from 0V.
It would be wise anyway to add a foldback current limit via an additional BJT and resistor.
VEGETA:
--- Quote from: not1xor1 on November 14, 2018, 08:28:55 am ---
--- Quote from: Cliff Matthews on November 14, 2018, 01:38:08 am ---Here's one from Banggood (it's about $6). Someone posted a schematic.. Funny drawback of producing a negative rail with a bucket load of cheapo 1N4007's is the 1 amp maximum. Real efficient heater though..
--- End quote ---
It is easy to make a much better (more stable, more efficient) PSU with about the same amount of components (dual opamp and power transistors), but if current regulation is not important even a TL431 + darlington would work.
A negative rail and another TL431 would allow to start voltage regulation from 0V.
It would be wise anyway to add a foldback current limit via an additional BJT and resistor.
--- End quote ---
This schematic doesn't seem to have constant current mode. Adding one will make it better since it is already easy schematic. I guess the purpose of Q1 is for short circuit protection, is it correct?
I am not a fan of having negative rails from diodes due to the heat and other issues. My initial suggestion was a TL431 + ICL7660 which is probably the best choice.
Efe_114:
i think that Q1 is for short circuit protection too. But i didnt understand does this circuit have negative output? Can i build this thing with opamps instead of programmable zeners and 2n2222s as transistors
Or bd138 pnps?
VEGETA:
--- Quote from: Efe_114 on November 14, 2018, 10:34:39 am ---i think that Q1 is for short circuit protection too. But i didnt understand does this circuit have negative output? Can i build this thing with opamps instead of programmable zeners and 2n2222s as transistors
Or bd138 pnps?
--- End quote ---
Yes you can build it with LM358 but using tl431 is easier and does the job perfectly without the need for a separate power supply for the op-amp.
This circuit doesn't output a negative voltage but it uses a negative voltage to drive the output to 0v, since tl431 also has 1.25v internal reference similar to lm317 and it is the sole reason why it cannot reach 0v. By using a negative rail, you add -1.25v to the already existing 1.25v to be 0v.
The newer LT3081 and LT3083 has the capability to reach 0v simply because the internal reference is different. It uses a current source instead of a voltage source... that means if you force a voltage at the adjust pin (like you do with lm317), then that forced voltage is the output because there is no voltage drop to compensate for.
You should study the datasheets well before proceeding, and even in using LT3083 there are issues just like Dave's supply didn't work because of circuit oscillation. I think I have seen LT themselves putting a lab power supply reference design based on LT3081 and even that uses a negative rail!
regards
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