Online Constant Current Source Calculator
A constant current source consists of a signal source and a voltage-controlled current source (VCCS), producing an output current that stays constant. A basic constant current source has an input stage that provides the reference current and an output stage that delivers the required constant current.
1. Input parameters
mA
mW
V
3. Output results
=
kΩ
=
kΩ
=
kΩ
=
kΩ
=
mW
2. Circuit diagram
Formula
R1 (bias resistor)
R1 = (0.1 × V) / I
R2 (feedback resistor)
R2 = 10 × R1
R3 (emitter resistor)
R3 = (V - (I × R1 + 0.7)) / (0.1 × I)
Ro (output resistor)
Ro = (100 - I/100) × (1 + 1000 × R1 × I / 26)
Px (Q1 power dissipation)
Px = (V - I × R1) × I
Note:If the calculated Px exceeds Q1's rated dissipation Ptot, Q1 is overloaded — lower the supply voltage or output current, or use a higher-power transistor.