This is a very simple LED dimmer circuit which has 2 transistors, 1 resistor and 2 potentiometers. Typical segment displays LEDs consume around 25 mA for each segment and should be limited to this ...

Like the circuit in Figure 1, it operates with 3.6 to 6.5V inputs and drives one LED with currents as high as 1A. For the single-LED circuit of Figure 3, the starting voltage of the MAX1685 defines ...

With the circuit values shown, R2 will drop a bit less than 5 V before D3 turns on. Prior to turn on, D2 remains back-biased and no current flows through the LED (D1).

Find out how you can change a circuit by adding items like switches with this Bitesiz KS2 science animation and a fun activity.