1.5V LED FLasher Using 3 Transistors

LED flasher circuit here will flash a LED using only 1.5 volts  supply voltage. Normally, to make any LED lamp works, you need more than 2 volts power supply. This because LED will work only when the supply voltage is higher than its forward bias voltage, around 2 volts  for red LED, and slightly lower for other color (but still higher than 1.5V).  Using this LED flasher circuit, you can blink a LED with only single 1.5V cell battery. Here is the schematic diagram of the circuit:


This LED flasher works using capacitor charge pump principle. The final LED driver is 2N3904 transistor connected to a 330 ohm resistor and 220uF capacitor.  When this transistor is switched off, the capacitor is charged through two 330 resistors, and when the transistor is swithed on, the capacitor will be discharged through the LED , the transistor and the power supply. At the point of view of the LED, the voltage of capacitor and the power supply is added when trying to flow through the LED, so the peak voltage when the LED is triggered is around 3 volts (but this won’t be observed since the LED will drop this voltage to its forward bias voltage value).