[quote=“waqar789, post:, topic:”]
Aoa friends, please suggest me some good power transistors for my 1000W UPS, Presently I'm using 16 transistors with following descriptions 80NF 70 , GKOR5 V6, CHN247 ( all that written on transistor) but the problem is that 2-3 transistors always blow out after every 1-2 months and I'm really fed up to replace them again and again, so friends please suggest me some good transistors or could you please tell me specifically whats the problem is that cause them to blow, Thank you, Jazak Allah Sent from my LT22i using Tapatalk
Is this a 24V or 12V UPS ?
Do the same MOSFETs blow up every time ? Or at least on the same side or is it random ?
Do the MOSFETs blow only when UPS is operating at near full load conditions ? Have you observed ?
80NF70 is a MOSFET. This is a type of transistor which has some obvious advantages over the Bipolar Junction Transistors. But there is difference between driving both types i.e. MOSFET Vs BJT. The kit installed in the UPS seems to be designed for BJT types. MOSFETs require some different arrangement. You need to have a series resistor (10-47 Ohm typically) between "gate" terminal of each MOSFET when they are in parallel.
Without going into further details of driving MOSFETs, I will suggest to:
1) Change all the MOSFETs in a parallel bank when few of them blow up. If your UPS is 24V, then I would suggest to use a MOSFET with higher voltage rating. This is required because of the back EMF due to transformer winding. Chose something near or above 100V rating. This 80NF70 is merely 68V.
2) Add a suitable snubber/clamping circuit to protect the MOSFETs.
3) Insulate each MOSFET individually using a mica insulator from heatsink plate and mount the plate directly to the casing rather than using a wooden strip as insulator. This will dramatically reduce the junction temperature of MOSFETs when they are operating as compared to the present arrangement.
4) Use thermal grease under each MOSFET. This increases the contact area by filling in the micro sized uneven areas which are not visible to naked eye.