PNP bipolar junction transistors (BJTs) use an emitter resistor and base voltage to set the collector current. The load from collector to ground won’t influence how much current flows, as long as enough voltage is used.

Diagram

The emitter resistor sets the current based on the voltage at the base.

There is an approx 0.6V difference (higher than ground) between the base voltage and the voltage across the emitter resistor.

The voltage across the emitter resistor and the resistor’s value determine how much current flows from emitter to collector and the load which is in series with it.

There needs to be enough supply voltage to power the current setting resistor, transistor and load, or the current will drop.

Video

2N3906 PNP BJT current source set with trimpot voltage divider circuit build by electronzap



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A lot of the components that I use are in this diode and transistor semiconductor kit.





I really like my 10K trimpot, which is like the ones in the ad above.





Really easy to use USB multimeter tester used in a number of my videos.

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