dual output

Posted by: tolgaaladag on 07/31/2012

I ve designed two output design that are 4V,2A and 5.5V,04A . But 4V output is fixed but second output changing with load.

For example without load 12V, load with 220R output is about 6V.

Why is output changing with load? is Attached schematic true?

Comments

Hi,

You problem is cross-regulation. 4V output is the regulated one since it has feedback to the controller, but the 5.5V does not

have any feedback and its regulation depends on its coupling to 4V winding.

Here are few things you can do.

Trying adding a small preload to 5.5V output.This will effect your no-load power

Reduce turns on 5.5V winding.

Try DC stacking( connect the 5.5V winding from the Cathode of 4V output diode).

rgds..

hi thank you replies ,

I take second feedback from second output and now I achieve to limit output up to 5.5V that I want to. But now when I load to both of two output adequately to design, +4V output robust but 5,5 V output drop to 3.5V. As if there is regulation problem in my design.

Hi,

Please send me the schematic after the changes you made.

rgds..

Hi PI-Scotty,

I attached schematic.

Hi,

18 ohm resistor seems too small for the second feed-back. Also it doesn't make sense that on a stacked winding you are seeing a lower voltage on the 5.5V winding compared to 4V winding. You have more number of turns so you must have higher voltage (Vots/turn). I assume you are measuring both the voltage with reference to gnd.

rgds..

Hi,

What should i put as preload?

I can not afford to use DC Stacking as i need completely isolated supply so how to do so?

Could you please send the Schematic , i didn't see any attached schematic. Whats the Capacitance value that you are using 5.5V output? Pre-load in the sense you should put 10mA or less than 10mA Load on slave winding in the form of resistance value?