Overheating on non-isolated tny268

Posted by: rogoman on 03/09/2012

Hi,

I am running a tny 268 in a non isolated form to run a controller for a larger power supply. The drain current is about 10mA, and the controller overheats in about 10 minutes, there are no shorts that I can see. The controller is essentially running off the first image in the schematic on your data sheet, except, there is a 100ohm resistor to limit the current in the opto-coupler.

The transformer is a EE16 24V
Zener diode 22V
Typical output voltage 26V

Snubber circuit:
Diode NUR460
Cap 1840nF
Resistor 150kohm

Output side:
Diode NUR460
cap 330uF

input side:
emi filter
10uF cap
160Vdc

Comments

Could you please post the transformer design and an actual schematic may help too.

Do you have output voltage? if so, how much? is the supply regulating?

When you say the DRAIN current is 10 mA. do you mean Peak current?
Can you post a picture of your DRAIN current waveform?

The transformer:
http://katalog.we-online.de/kataloge/eisos/media/pdf/7491182024.pdf

The output voltage is 26V
It does regulate the voltage

The output current is 10mA to 14mA to run a uc3823, nothing else is attached.

Thanks

I check your schematic and your transformer document

I can not say the transformer you are using in the right transformer to use with TNY268 because the spec does not show the number of turns on each winding. It only shows the turn ratio.

Who told you to use this transformer?

Anyway, you need to check the DRAIN current waveform and see if it is not getting into saturation. If possible, can you post a picture of your DRAIN current?