DPA-Switch with one isolated and one not-isolated output

Posted by: tronic on 01/27/2009

Dear Ladies and Gentlemen,
we plan to use DPA-Switch for a power supply. The input voltage is 16V to 32V dc and the outputs are 8V/1.5A and 5.3V/1A. The 5.3V output is the regulated one.
The simple schematic attached is taken out of the PI Expert-software.
Referring to it, we need to connect GND_IN and GND_5.3 together. That means we want the 5.3V output to be not isolated but the 8V output has to be isolated.
Is there a possibility to replace the optocoupler by an other circuit without affecting the regulating behaviour?
If it is, could you please give a suggestion for a replacement circuit?
Thanks a lot!

Files

Schematic_0.pdf (12.53 KB)

Comments

You can replace the optocoupler with a PNP transistor. Please refer to page 5 of our design example DER-105 for its feedback portion. http://www.powerint.com/sites/default/files/PDFFiles/der105.pdf. However, the gain of the transistor is much higher than the optocoupler. Please adjust the gain accordingly to avoid instability. Regards, PI-Scotty

how do we adjust the gain?

Hi,

you can insert a resistor in series with the Q2's emitter in order to reduce the gain. Please read section 4.4 in page no. 6 for the same.

Regards,

PI-Nano

You can connect capacitor between 5.3V gnd and Gnd[n)

I have used top 244 - Input 24V , o/p1 5v , o/p2 = 5V . both are isolated. input side As per your design connected cap across D2 and 5V Gnd