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Constant Current Source

A custom design for a constant current source. This was build for the Laser-pop project.


  • In: Power supply voltage (Vcc), 0 to 30V
  • In: Logic supply voltage (Vdd), 0 to Vcc+1.5V
  • In: Contol voltage, 0 to 5 volts
  • Out: Constant current (Ic). Max 2.1A. Vmax = Vcc-400mV.

The Current Source is designed to supply current according to a 0 to 5V input voltage control signal. The current scales linearly with control voltage. This signal can be a PWMed signal of a microcontroller (in my case an Arduino PWM signal at around 500Hz) or a constant voltage. How much current will be supplied when the 5V control signal is 5 volts can be set by a variable resistor from approximately 800 to 2100mA.

The board uses a LT3086 regulator which has a 400mV voltage drop. So maximum voltage output is the supply voltage minus the 400mV. In the case of the LaserPop project, the 5V rail will drive the laser at a maximum of 4.6V.

Besides the supply voltage a different logic voltage can be supplied. A separate logic voltage (Vdd) is required if the maximum ouput voltage of the constant current source is within 1.5V of the Power supply voltage.


The boards circuit were designed with LTSpice. Layout was done with Eagle.