LED Tester (20ma Constant Current Source)

Are you tired of having to change the resistor every time you change the voltage to power your LED??

Here is your solution! a constant current source. Built with only two transistors, fits in a 3 by 5 perfboard.

You are going to need:

• NPN Transistors (2)
• 1kΩ Resistor (1)
• 220Ω Resistor (1)
• 9v Battery Snap / Power (1)
• LED / Header (1)
• Breadboard / Perboard (1)

This is the circuit diagram, very simple only two transistors.

just get it.....

Just look at the picture, by the way my transistor have a CBE pinout.

one row down from the first.

just like in the picture....

pictures are worth 1000 words

Place your led or your header.

Plug in your power wires/battery snap and you get 10-20ma.

Now you have a 20ma led tester. Run it off USB, car battery, 9v it will light your leds!