Help me design a PSU

[Efe_114]

I want to make a small psu that could go up to 15 volts and DOWN TO 0 VOLTS (because i like hard projects) .no current limit needed. i want to make it out off jellybean parts and not copy it from a random website. And most importantly im a beginner(i have been in hobby for 3 years but since 90% of my projects fail i call myself beginner)Can anyone help me about this? Also this is my first post in this forum so forgive my mistakes please

[wraper]

Does it really need to go down to zero? If minimum of 1.2V is fine, simplest LM317 based schematics would do the job. Also what maximum current is needed?

[Efe_114]

Half an amp or 1 amp will do the job for me. my main purpose of building this is to make a project that i will use . I want to improve my design skills and also improve this circuit over time. I dont want to just lm317 on its own cuz as i said i dont like simple stuff. I want to go a little bit more complicated. And also i want to make it dual tracking if possible.

[Efe_114]

Efficiency is not an issue since i will use it on low power.

[wraper]

I dont want to just lm317 on its own cuz as i said i dont like simple stuff. I want to go a little bit more complicated.

Then why you don't need current limit? Generally it's way more useful than going down to 0V. Tracking generally is not very useful and quite complicated to do on isolated channels. Generally it would be better to just have 2 isolated independent channels or 2 separate PSUs rather than having 2 channels with common GND and tracking.

[wraper]

Performance wise, if you don't need current limit or high output current or voltage, it will be quite hard to beat LM317, LT108x or similar ICs. By adding a few volt low current negative supply voltage rail you can also make them going down to 0V.

[Efe_114]

I decided to use LT1080 before but it isnt available in my country. What if i put a reverse biased 1.25 volt zener diode in output of the Lm317 what will happen? Genius or dumb? (Dumb i guess)
I wonder if i can copy inside circuitry of the lt1080... that would be awesome! (i guess) 

[rstofer]

As a place to start:
https://electronics.stackexchange.com/questions/244354/making-lm317-output-voltage-adjustable-down-to-0-v

Google has a lot of LM317 projects

[SiliconWizard]

I decided to use LT1080 before but it isnt available in my country. What if i put a reverse biased 1.25 volt zener diode in output of the Lm317 what will happen? Genius or dumb? (Dumb i guess)
I wonder if i can copy inside circuitry of the lt1080... that would be awesome! (i guess) 

You probably mean LT3080, as the LT1080 is something else?
https://www.analog.com/en/products/lt1080.html
https://www.analog.com/en/products/lt3080.html

The LT3080 would be the simplest solution indeed.

Something like the following schematic would probably fit your requirements with discrete parts, and is a close match.
You can use another NPN transistor, it just has to be able to handle at least 20V and 1A. I showed a 19 V DC input power supply, so that you could use any 19 V laptop adapter as an input.
You can use a 1 Meg linear pot. for R1/R2. The transistor will require proper heatsinking.
Do not use a ceramic capacitor at the output as the regulator would tend to oscillate, a tantalum or electrolytic is preferred here.
Note that the set voltage is referenced to input voltage for simplicity's sake. If you want a more precise reference, you can always insert a fixed 15V LDO.

[Cliff Matthews]

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..

[FriedMule]

I would look at some of the videos from Mr. EEV and after that, try to search google for what you decide to make, then put it together and see what happens. If you hit a wall then show your design here on this forum and ask what's wrong.

[xavier60]

This regulator circuit works well for me. It is possible to just make the positive side only.
The current limit is about 600ma. It can be set higher.
 https://www.eevblog.com/forum/beginners/diy-power-supply-129692/msg1784705/#msg1784705

[james_s]

There are lots of linear power supply circuits out there. If you want it to go down to zero, you need a negative bias supply, it doesn't have to deliver much current. Usually there's a separate winding on the transformer for this.

[VEGETA]

To make it go down to 0v you would need a negative rail. To make this very easy for you, get ICL7660 charge pump IC. Feed it with say 5v and it will output -5v with low current of course.

This will be the negative rail of your op-amp which sets the output voltage... it could be something like +25v positive rail and -5v negative rail which will ensure 0v output.

It is better to put more filtering caps on 7660 output since it generates lots of noise, or better yes as I did in my dummy load design.. which is to give 9v to 7660 so it outputs -9v (or -8v with losses) then put TL431 after it which generates 2.5v in my case (you can make it anything via 2 resistors) with very low noise, now add another 100uF cap after it and you'll be done.

I hope this helps you.

[Efe_114]

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

[VEGETA]

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

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]

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..

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]

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..

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.

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]

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?

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

[rstofer]

There is mention of a 48 VAC transformer above and the output, when rectified, is about 62V (plus or minus the filter capacitor and current draw/voltage drop.  Nevertheless, a really big number.

When the PS is outputting, say, 1A at 1V, the pass transistor(s) drops 62V - 1V and dissipates 61 Watts (more or less).  That's also a really big number.

That's why real power supplies use transformers with tapped secondaries and some number of relays that kick in at various voltage settings.

If you want to output 5V, there is no point in having more than 8v DC going into the pass transistor (more or less).  Clearly, not 62V...

[Efe_114]

There is mention of a 48 VAC transformer above and the output, when rectified, is about 62V (plus or minus the filter capacitor and current draw/voltage drop.  Nevertheless, a really big number.

When the PS is outputting, say, 1A at 1V, the pass transistor(s) drops 62V - 1V and dissipates 61 Watts (more or less).  That's also a really big number.

That's why real power supplies use transformers with tapped secondaries and some number of relays that kick in at various voltage settings.

If you want to output 5V, there is no point in having more than 8v DC going into the pass transistor (more or less).  Clearly, not 62V...

thats more than some heaters i cant imagine running it at full power 3A 1v which would create 183 watts heat my aquarium heater is 60 watt 

[Efe_114]

I dint know how but i made a lm317 circuit go under 1.25 volt without anything
I just connected like this:
Pot pins at the outwards go to ground and output
Slider goes to adj
Vcc goes to Vin
I wonder how did it work i will probe everywhere and test it under load when (if) i find out whats going on i will post here

[wraper]

I dint know how but i made a lm317 circuit go under 1.25 volt without anything
I just connected like this:
Pot pins at the outwards go to ground and output
Slider goes to adj
Vcc goes to Vin
I wonder how did it work i will probe everywhere and test it under load when (if) i find out whats going on i will post here

Dunno what you made but LM317 won't go below 1.25V without negative voltage on ADJ pin.

[VEGETA]

I dint know how but i made a lm317 circuit go under 1.25 volt without anything
I just connected like this:
Pot pins at the outwards go to ground and output
Slider goes to adj
Vcc goes to Vin
I wonder how did it work i will probe everywhere and test it under load when (if) i find out whats going on i will post here

That cannot be, please post schematic and pictures if possible.

I explained to you why it happens and you could see its internal schematic to see it.

Dunno what you made but LM317 won't go below 1.25V without negative voltage on ADJ pin.

Yes because you need to compensate for the +1.25v of its internal reference.