How to measure transistor current? - Electronic Circuits Projects Diagrams Free

menirva · 2nd March 2008, 07:41 AM

I'm designing a current source. In reality, how to measure the current flow thru E to C of the PNP, with ammeter? Is it the same with NPN?

Cut off the wire from (+ve VDC) to the E, then connect probe A to (+ve VDC), and probe B to the E? But i get different value displayed, when compare to the simulation reading.

Thanx!

forum6.GIF

p/s: sorry, ignore this post, i got it already, just a minor mistake.

Hero999 · 2nd March 2008, 10:06 AM

I know you've got it but, for anyone that doesn't, it's the same as measuring current in any situation. Just break the circuit and connect the ammeter in series with it.

That isn't a very good constant current source, the current will vary hugly depending on the power supply and transistor's gain.

A better onstant current source can be made from an LM317, see the datasheet.

2nd March 2008, 07:41 AM	(permalink)
menirva New Member	How to measure transistor current? I'm designing a current source. In reality, how to measure the current flow thru E to C of the PNP, with ammeter? Is it the same with NPN? Cut off the wire from (+ve VDC) to the E, then connect probe A to (+ve VDC), and probe B to the E? But i get different value displayed, when compare to the simulation reading. Thanx! forum6.GIF p/s: sorry, ignore this post, i got it already, just a minor mistake. Last edited by menirva; 2nd March 2008 at 04:19 PM.

2nd March 2008, 10:06 AM	(permalink)
Hero999 Experienced Member	I know you've got it but, for anyone that doesn't, it's the same as measuring current in any situation. Just break the circuit and connect the ammeter in series with it. That isn't a very good constant current source, the current will vary hugly depending on the power supply and transistor's gain. A better onstant current source can be made from an LM317, see the datasheet. __________________ What's so bad about Microsoft? Get Opera it's simply a superb browser.

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