Do anyone know how to convert atx psu to varible power supply?

Thread Starter

Dzoro

Joined Feb 1, 2019
161
I would like to convert my old atx power supply to give varible output but i don't want to put buck or boost converter or some other pcb in it.
 

Papabravo

Joined Feb 24, 2006
14,684
If you can ship it i would appreciate it,but can you tell me more specific what that is
You sprinkle it on an impossible problem and the problem is solved by magic. It helps if you believe in magical thinking.

The best way to solve your problem is to hack the design of the existing PCB, by adding additional components. The best way to add additional components is to put them on a new PCB so you can continue to use as many of the original components as possible.

It seemed to me you were looking for a solution that involved magic.
 

Thread Starter

Dzoro

Joined Feb 1, 2019
161
This is an electronic page not a joking page,so if you have something that is based on the question than share it,otherwise i don't need stupid replays
 

Thread Starter

Dzoro

Joined Feb 1, 2019
161
Then don't ask ridiculous questions
It's not a ridiculous question,it's a simple question and it's a doable thing but i don't have the knowlege to do it so i asked for someone to help me not to judge me about my questions.
 

Papabravo

Joined Feb 24, 2006
14,684
It's not a ridiculous question,it's a simple question and it's a doable thing but i don't have the knowlege to do it so i asked for someone to help me not to judge me about my questions.
If you had a schematic diagram of the particular ATX power supply we could tell you if it is doable or not. It is not doable, a priori, without looking at the design. It is not a simple question, nor is it a particularly simple thing to do. You have listed no REQUIREMENTS for this variable supply: such as voltage ranges or current requirements.
 

Thread Starter

Dzoro

Joined Feb 1, 2019
161
It uses tl494 chip that's all that i can say about it i can't find chematic for it beacose it's old
 

Papabravo

Joined Feb 24, 2006
14,684
It uses tl494 chip that's all that i can say about it i can't find schematic for it because it's old
It would be well worth your time to take the PCB and create your own schematic of the existing board. Once you have the schematic we can advise you on what you would need to do to convert the fixed output to a variable one. I still don't see how you expect to get away without using additional components. Maybe you can use "flying component" or "dead bug" construction on the existing board. Would that meet your requirement of not having a "new" PCB?

Do you have any TL494 reference designs that you can study for information or ideas?
http://www.ti.com/lit/an/slva001e/slva001e.pdf
 
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Thread Starter

Dzoro

Joined Feb 1, 2019
161
First of all i have a lot of components.
Second i didnt mean pcbs that i make i mean like i don't want to buy buck or boost converter and put on the output.I think you get what i want to say.
I have this picture but i don't know if it works
 

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Papabravo

Joined Feb 24, 2006
14,684
First of all i have a lot of components.
Second i didnt mean pcbs that i make i mean like i don't want to buy buck or boost converter and put on the output.I think you get what i want to say.
I have this picture but i don't know if it works
No, I have no clue what you are trying to say. An ATX power supply has one or more fixed output voltages. Usually these are +5VDC, ±12VDC, and maybe 3.3VDC. You are correct in saying that you can use these fixed voltages as INPUTS to buck or boost regulators to get other fixed and/or variable voltages. You can also go into the internals of the ATX power supply and modify it from fixed to variable output. Trying to do this on the basis of a YouTube video, without a schematic diagram, is foolish beyond words. There is no guarantee that the design you have is in any way related to the design in the video. Any suggestion that we are talking about a simple modification without understanding the design we are starting from is nonsense. If you want to do this for your own satisfaction, or as a learning experience, there is a way to do it. Trying to do it with a couple resistors and or potentiometers is doomed to failure because the voltage will change as soon as you connect a load and will bounce up and down as the load changes.
 

BR-549

Joined Sep 22, 2013
4,938
There might be newer designs now.....but the problem with your idea is that the ATX has one switch......and all output voltages are controlled by that one switch. So if you dittle inside with that control......it varies all the other outputs. AND the atx was designed to operate at a defined range.

So......there is a lot working against your idea. That's why when someone wants to vary a ATX supply......they build an adjustable switcher and connect it to an existing output.

Does that make any sense to you?
 

Thread Starter

Dzoro

Joined Feb 1, 2019
161
There might be newer designs now.....but the problem with your idea is that the ATX has one switch......and all output voltages are controlled by that one switch. So if you dittle inside with that control......it varies all the other outputs. AND the atx was designed to operate at a defined range.

So......there is a lot working against your idea. That's why when someone wants to vary a ATX supply......they build an adjustable switcher and connect it to an existing output.

Does that make any sense to you?
Yes and i know how to build an ajustable switcher
For example i could use two lm371 one to regulate the voltage and one to regulate the current.I could use biger transistor on the current side beacose lm 371 can output 1A and i use more than 1A in my projects and i don't even have to spend money beacose i have all this components in my workbench beacose i work with electronics for 4 years and i ghaterd a lot of components over the years
I have a lot of knowlege about some circuits like that but i wanted to do something whit the main chip of the psu and i found this on the internet
 

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Thread Starter

Dzoro

Joined Feb 1, 2019
161
And also on that site i found that picture said that i need to somehow trick the safty future (when turns the psu off)and as i know that can be achived by bridging the optocoupler on the primary side but on mine psu there are 4 optocouplers so those that mean that i should bridge all of them or i should bridge the one that is responsable for the safty future
 

Thread Starter

Dzoro

Joined Feb 1, 2019
161
I have never designed a switcher. I was considering modification strategy only.
That means that we didn't understand.But when you think of a switcher that's a different pcb.
I am going to try the methode that the site said and if that don't work i am going to build a regulator whit the two lm317 and that's going to work 100% but thanks for the replays
 

Papabravo

Joined Feb 24, 2006
14,684
And also on that site i found that picture said that i need to somehow trick the safety future (when turns the psu off)and as i know that can be achived by bridging the optocoupler on the primary side but on mine psu there are 4 optocouplers so those that mean that i should bridge all of them or i should bridge the one that is responsible for the safety future
I don't know WTH you expect from us. You ask us how to modify a power supply with no part number and no schematic and no useful information. The answer is that without a speck of useful information I have no freaking idea how to do anything remotely connected to your requirements which you have also failed to mention.
 

Dodgydave

Joined Jun 22, 2012
9,664
Yes it's easy with a TL494, you need to ground pin 4 to override the cutout, then pins 1,2 are for votage regulation control.


http://www.pavouk.org/hw/en_atxps.html


Pin 1 is the reference input, and Pin 2 is the output feedback pin, looking at this diagram they have set the output using fixed resistors on pin 2. If you remove all resistors on pin 2, and connect a 10K potentiometer across the 12V rail (yellow black) and put the wiper to pin 2, you will have a Variable output.

If all is working it should go from 5V to 28V on the 12V rail, replace the output capacitors to 35V or 63V..
 
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