Solution Finder Get Tech Support

TINYSWITCH III

Posted by: bren on
I am trying to design a smps with an output of 18Vdc 1.25Amps. The software uses tinyswitchIII using TNY277PN + 1(what is + 1 mean?). Based on the application note, for open frame it can handle 23.5watts, but for adapter, it can only handle 13W. My question is, the ambient temperature of the TNY277PN is around 60degrees centigrade, can i still use it? My input voltage is 170Vac to 265Vac. Please advice me of the best possible and cheapest solution.Bren BY THE WAY, THE SMPS WILL BE USED TO CHARGE A NIMH BATTERY. 12V 1200MAH

Comments

Submitted by John Carpenter on 10/09/2008
By placing a 10uF capacitor on the BP/M pin, the device increases the drain current limit. This is referred to as a +1 mode or increased current limit mode. Please refer to the datasheet section labeled Circuit Protection to determine the actual current limit for each device vs mode of operation. By the way, there is also a -1 mode or reduced current limit mode as well as a normal mode. I am concerned about the thermal aspect especially operating in a 60 Deg C environment in a +1 mode. If the charger is enclosed in a non-vented case, I expect the TinySwitch will become too hot and go into thermal shutdown. In this situation, I would recommend using a TNY279 or 280 and use it in a -1 mode. Also you will need a minimum of 3/4 of a square inch of copper ground plane connected to the source pins of the device to heat sink the TinySwitch. This will give you the best chance of meeting your thermal requirements without the addition of a costly heat sink. Z. Cochrane
Submitted by bren on 10/09/2008
Thanks a lot. I really appreciate it.