016 NPN BJT current source – Zener – Trimpot – LDR Light Dependent Resistor

NPN bipolar junction transistors make a good current source (technically a current sink). First off, a resistor from the emitter to ground will set the current based on it’s value and the voltage across it (Ohms law). The voltage across the emitter resistor will be the voltage at the base, minus the 0.6V base to emitter drop.

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The current through the resistor though, comes primarily from the collector. A load on the collector side will not change how much current flows as long as the power supply voltage is high enough to meet the demand. Therefor the collector current, including the load, will have almost exactly the same current going through it as the emitter.

Video covering NPN BJT current source and diagram

Electronics course 16 current source circuit NPN BJT zener diodes trimpot light dependent resistor

Basic electronics circuit fragments and simple circuits 14 NPN BJT current source using zener diodes trimpot potentiometer and light dependent resistor LDR diagram by electronzap electronzapdotcom
Basic electronics circuit fragments and simple circuits 14 NPN BJT current source using zener diodes trimpot potentiometer and light dependent resistor LDR diagram by electronzap electronzapdotcom
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