yep, i read you on doing a little more research before jumping in. i know that the link i posted was for someting completly different. i was just using it as a reference for a better idea of it in action.

 

I have two SD431 and the circuit is different from what SgtWookie has posted. I am unable to find the data sheet for SD431. Can someone help me in identifying the pins?

I have Suntek Switching Power Supply***Model NO: AM607BS. Is is possible to get the circuit diagram for this model?

Also, in the original link posted by OP the guy is able to adjust the complete voltage range from one of the output. Tom66 chose different outputs for different voltage ranges. What is the difference? I want to use the SMPS as simple power supply in the range 1.5 to 20 @ 3 A max. How can I do this?

Thanks in advance.

 

I have two SD431 and the circuit is different from what SgtWookie has posted. I am unable to find the data sheet for SD431. Can someone help me in identifying the pins?

Did you look at the datasheet for the AZ431 that I posted a link to earlier?
You can also look at TL431 or LM431 datasheets to see if they are similar.

I have Suntek Switching Power Supply***Model NO: AM607BS. Is is possible to get the circuit diagram for this model?

A quick search didn't turn up any schematics, but you might get lucky if you keep looking.

Also, in the original link posted by OP the guy is able to adjust the complete voltage range from one of the output. Tom66 chose different outputs for different voltage ranges. What is the difference? I want to use the SMPS as simple power supply in the range 1.5 to 20 @ 3 A max. How can I do this?

It depends on your supply. Lots of different designs are used in computer power supplies. Although they follow a somewhat similar theme, they still have lots of differences. You have to figure out which ICs are those that control the voltages, and then which are the resistors on your board that supply the feedback voltage to the regulator's feedback input.

 

In my unit I had to disable the overvoltage protection circuit too. This consisted of an SCR on my model. The simplest way to do this is to connect the gate to the cathode pin with a solder bridge, so the SCR can never trigger.

 

Thanks SgtWookie and Tom66 for your replies.

I will check the board again. I would not like to power the board until things are clear to me.

 

I have attached the circuit. could some help me where I should connect the potentiometer?

 

You need to provide more information about the connections to/from the TL494 IC; that's the SMPS controller IC.

 

Sorry, SgtWookie I could not draw the schematic properly. But, I would like to thank you and others for the help. I spent some time in understanding how the SMPS works and I was finally able to add a potentiometer to feed back circuit. I now have 5 - 13 V variable power supply.

Wish I had a power supply up to 20v by deactivating the over voltage protection circuit. I am still trying to fix the issue.

I would like to share with you guys the following link

http://danyk.wz.cz/s_atx_en.html

this has schematics for lot of SMPS models except mine . Hope it is useful for someone.

 

Glad that you were able to figure out the feedback circuit - good job!

Be careful about taking the voltage too high, or it is likely that you will exceed the voltage rating of a number of components, including the capacitors.

That link to the schematics page is indeed very useful - thank you for that!

 

Sgtwookie,

I already changed the filter caps for higher voltages.

 

ok well, i messed someting up. yes wookie ur schematic is correct and the two values of r38 and r40 are correct. i unsoldered them very easily(it was very easy to get to on the edge of the board) i soldered 2 wires in place of one resisitor(as they are in parallel) i used a 20k resistor and a 50k pot. i failed to measure the total resistance before i turned the supply on. turns on for 2 seconds and shuts off. i replaced the origional resistors and same thing....only runs for 2 seconds. not sure if something got fried or what. im open to suggestions and input. i dont give up easily, id like to perfect this, but it may take a few PSUs to get it right! one more question; which rail does this vary? ie, 12v, 5v, 3.3v? ty

In order to vary the voltage you have to fool the ic by inhibiting the three voltage sensors on pins 1,2, &3. Pin 2 is to be connected to the 5v standby,pins 1&3 have to be connected to the 5v standby by means of a 4k7 pot to each pin across the 5v standby supply with the the pins on the wipers, and set the voltages to 3v on pin 1 and 0.5v on pin 3. Also disable the overvolts on pin 4 by connecting it to gnd.

 

Welcome to AAC.

This thread has sat idle for 7 months, and the OP basically solved his issue.

You have practiced the arcane art of necromancy, the revival of a long dead thread.