NPN or PNP transistors.. - Electronic Circuits Projects Diagrams Free

Project-X · 10th June 2008, 11:39 AM

just wondering, what is generally better for switching an earth, and whats better for switching a supply?

**Nigel Goodwin** · 10th June 2008, 11:50 AM

You don't mention what polarity the supply is, which makes all the difference.

But you should take the output from the collector, and choose the transistor accordingly.

Hero999 · 13th June 2008, 05:20 PM

To switch the positive, use a PNP transitor and to switch the negative use an NPN transistor.

If you're working on a system where one side of the supply is bonded to earth or the chassis then you should always switch the other side. For example in a negative earth car, switch the positive rail and in a communications system (normally positive earth) switch the negative.

If neither side of the supply is earth or chassis bonded then it doesn't matter, most of the time an NPN transistor is used because negative devices tend to have better characteristics.

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10th June 2008, 11:39 AM	(permalink)
Project-X	NPN or PNP transistors.. just wondering, what is generally better for switching an earth, and whats better for switching a supply?

10th June 2008, 11:50 AM	(permalink)
Nigel Goodwin	You don't mention what polarity the supply is, which makes all the difference. But you should take the output from the collector, and choose the transistor accordingly. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

13th June 2008, 05:20 PM	(permalink)
Hero999	To switch the positive, use a PNP transitor and to switch the negative use an NPN transistor. If you're working on a system where one side of the supply is bonded to earth or the chassis then you should always switch the other side. For example in a negative earth car, switch the positive rail and in a communications system (normally positive earth) switch the negative. If neither side of the supply is earth or chassis bonded then it doesn't matter, most of the time an NPN transistor is used because negative devices tend to have better characteristics. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez