TNY280 how can I lower heat?

Posted by: Shawn_Gibson on 01/15/2015

I have a 5volt 4.2 Amp design based on the TNY280. At the full load of 4.2 Amps the TNY280 gets hot enough to shut off. What can I do to generate less heat? I have already heatsinked the controller IC but eventually the enclosure traps enough heat for it to shut down.

I have attached the original design I started with from PI Expert., The Transformer that I am using, and the actual circuit that I am using on my prototype.

The Schottky diode and R7 also are creating quite a bit of heat.

Thanks,
Shawn

Files

4p2amp_Proto.pdf (10.79 KB)

4_2ampUniversal_mod.pdf (57.52 KB)

4_2ampUniversal_mod_TXFMR.pdf (101.27 KB)

Comments

TNY280 overheating

Hi,
Basically the heat is generated because of the loss in the device. For a power switch like MOSFET, the loss includes the switching loss and conductive loss. The method to reduce the heat is to find a way to decrease the loss on the devices either by decreasing the conductive loss or switching loss. Here are some general rules:
1. Using bigger device to get lower Rdson normally improve the conductive loss, but may increase switching loss.
2. Designing transformer with more lower KP, which is more CCM (Continuous Conduction Mode) will help to decrease the primary rms current under the same output put, which could also improve the loss/
3. Design transformer with lower leakage inductance. You could use the sandwich transformer structure, which usual improve the coupling between primary to secondary. This will also help the get lower loss in R7.
4. Use bigger heatsink to cool the device if there is no way to decrease the loss.
5. For the R7, the value is kind of low in this design. If there is still margin on the Vds voltage in the worst case situation (startup full load and highest input voltage), you can increase the R7 resistor value. By using transformer with lower leakage inductance, you should be able to use high resistor value. The other way to improve the temperature is to use several resistor in series or in parallel to distribute the heat.

Hope this is helpful

Terry,
Thanks for your reply.
I will be looking at all of these for lowering the heat inputs into my system.
Shawn