Temporary LED Lamp/Illuminator

This temporary lamp circuit is very helpful in emergency situation or in any application where we don’t have much time to turn off the lamp. Just press the push button, do a little fast task, and then leave it. This circuit hold the LED light for about 10 seconds, which should be enough for most simple tasks.  Here is the schematic diagram of the circuit:

This circuit works like this: when the push button S1 is pressed, the C1 will be fully charged instantly.  Not only charging the capacitor, the current will supply the bias current for transistor’s base as well. This base current will activate the transistor to turn on the LED. After the push button is depressed, the capacitor C1 will keep supplying the base current for about 10 seconds, holding the LED lamp on.  If you think this period is too short then you can try with different C1 values, try 47uF or 100uF and you’ll see the difference. You can use almost any type of small transistor since almost all small transistors will be capable of driving LED lamp which draw current less than 20 mA.