LM334 Three Terminal Adjustable Current Source

LM334 lets current through its V+ and V- pins based on the resistance between it’s R and V- pin.

Simple LM334 three terminal adjustable constant current source circuit schematic diagram by electronzap electronzapdotcom
Simple LM334 three terminal adjustable constant current source circuit schematic diagram by electronzap electronzapdotcom
  • 0.064V is held across the resistance between R and V-pin. That is no matter what the supply voltage is, as long as it is high enough to provide power to all series components. Current through that resistor (and all other series components) is calculated by using the Ohms law formula I = V/R.
    1. 6.4Ω provides 0.064V/6.4Ω = 0.01A of current. Which is the same as 10mA
    2. 10Ω provides 0.064V/10Ω = 0.0064A of current. Which is the same as 6.4mA.
    3. 64Ω provides 0.064V/64Ω = 0.001A of current. Which is the same as 1mA
    4. 100Ω provides 0.064V/100Ω = 0.00064A. Which is the same as 0.64mA, or 640µA.
LM334 three terminal adjustable current source set voltage schematic diagram by electronzap
LM334 three terminal adjustable current source set voltage schematic diagram by electronzap

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LM334 current source fixes voltage across zener diode without a load schematic diagram by electronzap
LM334 current source fixes voltage across zener diode without a load schematic diagram by electronzap

The best way to hold a steady current through a zener diode is to use a current source. A zener diode relies on a steady current through it, to keep the zener voltage across it from drifting a bit.

Of course, you don’t have to use a LM334. There’s Bipolar Junction Transistor (BJT) based current source circuits that will work.

Junction Field Effect Transistors (JFETs) also make for easy current sources.

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