BJT Transistors - Electronic Circuits Projects Diagrams Free

jack23 · 15th October 2007, 06:05 PM

Hello,

Someone asked me a simple question that I was not able to answer. In general, why would several BJT transistors be connected in parallel??

Does anyone know why??

j.p.bill · 15th October 2007, 06:14 PM

If you need to control more current than one device can pass, the paralleling transistors is the way to go. You have to be careful and use equalizing resistors in the emitter runs to keep things in balance, or one transistor is likely to get a bit warmer than the other/s and go into runaway.

jack23 · 15th October 2007, 08:03 PM

Yeah, that's what I had in mind. Thanks.

But, what does the term "runaway" mean?

audioguru · 15th October 2007, 09:20 PM

Thermal runaway is when a transistor conducts more current which makes it hotter, which makes it conduct more current, which makes it hotter, which makes it conduct more current, which makes it hotter, etc.

jack23 · 15th October 2007, 10:42 PM

I see. Alright, thanks for all the good info.

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15th October 2007, 06:05 PM	(permalink)
jack23	BJT Transistors Hello, Someone asked me a simple question that I was not able to answer. In general, why would several BJT transistors be connected in parallel?? Does anyone know why??

15th October 2007, 06:14 PM	(permalink)
j.p.bill	If you need to control more current than one device can pass, the paralleling transistors is the way to go. You have to be careful and use equalizing resistors in the emitter runs to keep things in balance, or one transistor is likely to get a bit warmer than the other/s and go into runaway.

15th October 2007, 08:03 PM	(permalink)
jack23	Yeah, that's what I had in mind. Thanks. But, what does the term "runaway" mean?

15th October 2007, 09:20 PM	(permalink)
audioguru	Thermal runaway is when a transistor conducts more current which makes it hotter, which makes it conduct more current, which makes it hotter, which makes it conduct more current, which makes it hotter, etc. __________________ Uncle $crooge

15th October 2007, 10:42 PM	(permalink)
jack23	I see. Alright, thanks for all the good info.