Variable Flashing LED ( single transistor circuit)

It is possible to blink or flash an LED using just a transistor. This interesting circuit makes use of a rarely used property of the transistor known as the reverse avalanche breakdown. Since this is a non-standard feature, this may not work on all NPN transistors. Also, note that you may need more than 12 voltage for this to get working on most transistors.

In reverse avalanche mode, the collector to emitter circuit of the transistor is connected in reverse polarity. Hence positive terminal of the power source is connected to the emitter and the collector is connected to the negative terminal. In usual operation, very little current will flow from emitter to collector in this configuration. However, if we increase the voltage of the power source, beyond a specific value, the emitter to collector junction breaks down and a large current will flow through the circuit. The base of the transistor is not used at all in this configuration.