Interpretation of Transistor Datasheets

Aug 04, 2006 2 Replies
J

Hello All,



This along the lines of my previous 'High Side MOSFET' switch post yesterday but in relation to transistors.



In some situations I'd like to use a PNP as a high side switch. I see that some PNPs are -V & -I, and some are +V & +I. Visually, with the base to the left, emitter up, and collector down... what is considered



+I vs. -I? I would assume E--->C is considered positive flow?

Also, that leads to datasheet data such as Vceo (collector emitter voltage) of 40V. I assume the max V present at the collector is Ve +



40V? Or... Vceo of -40 is emitter can be Vc + 40?

Thanks,



John



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R

I've moved this thread over to .basics, because this is a basic question.

For one thing, it depends on if you're using conventional current flow or electron flow. Generally, college guys use conventional, and techs use electrons.

Anyway, the easy way to remember how current flows in a semiconductor is that conventional current (which flows from positive to negative) always flows in the direction the arrowhead is pointing. (well, except in a Zener, and other unusual cases.)

As far as which they use on the data sheet, it's pretty much up to the data sheet designer, although strictly speaking, all of the parameters that are positive for an NPN become negative for a PNP, and vise versa.

Hope This Helps! Rich

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E

I think you know which way round to collect a pnp transistor. Some manufacturers state the polarity of the voltage, some don't bother. I guess they assume you know it'll be negative.

Graham

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