Hi,

We have SMPS 5V,26A but we need to use the voltage from 3V to 4V(use as a dimmer ckt.).We tried to drop the voltage from inbuilt potentiometer but it goes maximum 4Vdc.
Kindly help us to resolve the issue.How we can drop it?

 

You will need to adjust the output voltage feedback of the PWM control. And the under voltage cutoff too.

Can you get a schematic?

What are the Heat sinked transistors?

What are the IC's used?

Ramesh

 

Sorry we don't have schematic.

the heat sink diode is SBL3040PT (2NO'S)

 

Sorry we don't have schematic.

the heat sink diode is SBL3040PT (2NO'S)

What about the control IC's? Make an effort to trace the voltage feedback line.

Else, use a Hi Power Linear Regulator.

Ramesh

 

Sorry we don't have schematic.

There is no way to defeat the regulator externally. You can only adjust it on the circuit board. I have done this. I had a 6 volt smps and wanted 6.3 volts for vacuum tube filaments. Easy as changing one resistor...right after you read the schematic and know where to do the adjustment.

 

Hi,

We have SMPS 5V,26A but we need to use the voltage from 3V to 4V(use as a dimmer ckt.).We tried to drop the voltage from inbuilt potentiometer but it goes maximum 4Vdc.

There is your clue; the "inbuilt potentiometer" adjusts the feedback loop to the internal regulator. Either the potentiometer's value needs to change, or a fixed resistor next to the potentiometer needs to be replaced with a different value. You need to see what is attached to that potentiometer, and draw a schematic.

 

There is no way to defeat the regulator externally. .

If you substitute an ATX PSU, that may not be strictly true.

The 3.3V output usually has a sense line wire crimped into one of the 3.3V wires to sense the voltage a little closer to the actual load.

BEWARE though; if you let the sense wire float the PSU will go bang!!!

You also have to put a load on the 5V rail for everything to work correctly - but its in the right ballpark for the 26A the OP mentioned.

If a lower current capability is acceptable - the surplus market used to be awash with small open-frame switchers, pick one with a TL431 error amp circuit and the voltage sensing resistors are easy to trace out.