Electronics Projects: How to Build an LED Driver Circuit

By Doug Lowe

In this project, you build an electronic circuit that uses a transistor to switch on an LED using a current that’s much smaller than the LED current. When you close the switch, both LEDs light up. However, LED1 is brighter than LED2 because the collector current is larger than the base current.


If you feel like experimenting a bit after you complete this project, here are couple of suggestions:

  • Try replacing R2 with larger resistors, such as 10 kΩ and 22 kΩ, or insert a 100 kΩ potentiometer in series with R2. What effect does the increased resistance have on the brightness of the two LEDs?

  • Measure the base current and the collector current, as follows:

    • To measure the base current, remove the R2 lead in hole F1 and touch your multimeter probes to the lead you removed and the 2X terminal on the switch.

    • To measure the collector current, remove the R1 lead at J15 and touch the multimeter probes to the lead you removed and the LED1 anode.

      image1.jpg image2.jpg