Current sources 101

Have you found part 2?

Hi John, think that comes out next month

martin

I must admit I use the simple R and LED, and hadn't thought about it that much. But I've never seen the emiitter to ground R before (I'm assuming a pnp).

and, yes, maybe a part 2....

martin

For the simple LED or 2-diode type sources, a major error is the voltage divider formed by the bias resistor and the dynamic impedance of the led or diodes. A resistor from the transistor emitter to ground can cancel this error. Or drive the led/diodes with a very simple, ground-referenced current source. Or bypass the hell out of them.

He doesn't show using an opamp to close the loop around a transistor or fet, which gives better dynamic and temperature performance; maybe in part 2?

John

are you

martin

Well, I just invented it!

John