TOP268KG-TL temperature rise

Posted by: Mayur@111 on 06/12/2024

I am using TOP268KG-TL for 4.5 W output. At 19.2V DC converter operating in CCM, But from from 40V above it is operating in DCM.

Input: 19.2 - 373V DC & Universal AC input

output: 12V, 5W

Transformer: Primary 24; Secondary 16; Auxillary 17 ( output voltage 15); Primary magnatizing inductance 240uH

TOP268KG-TL: 1) V pin is shorted 2) At X pin & ground 15K resistor connected

Results: Converter is working fine in entire DC input voltage range

Testing:

At 19.2V & 4.5W output, I have tested this device for 4hours. from supply it is drawing 0.41A average current. Ambient temp is 29 degree Celsius. After 4Hrs,

IC temperature is 81 degree Celsius

Transformer winding temperature is 55 degree Celsius

Transformer core temperature is 55 degree Celsius

loss = 19.2*0.41-4.5 = 3.372W

At 19.2V converter operating in CCM, But from

Questions:

1) If ambient is 70 degree Celsius, How much temperature rise will be there. Whether this maximum temperature will be within junction maximum temperature limit? this converter can work properly wrt temperature?

2) From above loss 3.372W, how to consider IC loss, how to find out junction temperature?

3) At ambient 29 degree Celsius, rise is 52 degree Celsius. If ambient is 70 degree Celsius, then rise will be fixed or not?

Comments

What sort of heat sinking is provided for the part? It has a bottom-side source referred pad that should soldered to a suitably sized PCB land for heat sinking. As a general rule, the RDSon of a mosfet will rise with increasing temperature. This means the switch conduction losses will be higher at 70C ambient. You may find it necessary to choose a larger device (lower RDSon) and change the X pin resistor value, as well as providing adequate heat sinking.