Intro: 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.
Step 1: Materials
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)
Step 2: Schematic / Plan
This is the circuit diagram, very simple only two transistors.
Step 3: Get Ya Breadboard/perfboard
just get it.....
Step 4: Place Your First Transistor
Just look at the picture, by the way my transistor have a CBE pinout.
Step 5: Place Your Second Transistor
one row down from the first.
Step 6: Place Your 220Ω Resistor
just like in the picture....
Step 7: Place Your 1kΩ Resistor
pictures are worth 1000 words
Step 8: Place Your LED
Place your led or your header.
Step 9: Apply Power
Plug in your power wires/battery snap and you get 10-20ma.
Step 10: Done
Now you have a 20ma led tester. Run it off USB, car battery, 9v it will light your leds!