Constant current source

VCC = Voltage of the voltage source VLED = adding all LED voltages VBE = base/emitter voltage of a transistor Current is constant until voltage VLED + (2 * VBE) reaches or exceeds VCC. Tested in real with 2N2222 transistors and white LED with a blocking voltage of 2.95V. If voltage of the current source drops below 15V the current decreases. The constant current (I) through the LED's is calculated by R = VBE / I. In my real life example it was 630mV / 20mA = 31.5 Ohm. I used a 33 Ohm resistor and the current measured was 18mA. I saw this circuit at the YouTube channel from Qualiflyer.

published 4 years ago