I need help choosing a transistor

Thread Starter

threepwood

Joined Jun 4, 2015
20
ok, thank you, because i have tons of those SMD resistors that i would be very happy to use. If i remove the resistor the bulb turns on dimmed and the transistor gets lava hot.
 

ian field

Joined Oct 27, 2012
6,536
The collector-to-emitter voltage will be higher on a bipolar, hence it will get hot, as you have already learned.
The huge quest for ultra low RDSon with MOSFETs was because on early devices it was difficult to match the typically 0.4 VCEsat that an average transistor could do, there were special low VCEsat types with around 0.2V.

That was the whole point of developing the IGBT, being a MOSFET/bipolar Sziklai hybrid with effectively an emitter follower output, so it was slower than a straight MOSFET but got nearer to a transistor VCEsat.

As one or two others mentioned - its a common problem that people don't meet the VGSthr requirement in their designs, the MOSFET isn't switched fully on and dissipates a lot of power.

Unless its a logic level MOSFET, they usually need at least about 8V. The oxide layer is very thin, so most types can't stand VGS more than about 18 - 20V.
 
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