Thursday, March 8, 2018

Wall Clock Power Supply From USB

Most of the wall clocks that we use usually runs on a single AA cell. It might have more than one cell in case the clock has something fancy like Alarm or bell. For normal clocks however it might be a bit problematic to keep on changing the cells as they often run on disposable ones. Although they do run for a long time but it can be very easy to add a simple circuit that will give us the ability to run the clocks from USB. One drawback of this is it will turn off if the USB power source is off.

Component list:


1 470‎Ω


1 47µF 


3 1N4148


How does it work?
The mechanism is pretty simple but a bit crude. Diode drops a certain amount of voltage across it. This voltage depends on the diode itself and the amount of current through it. For a general purpose diode it is about 0.5V. So three of them will roughly give us 1.5V which should be enough for running a simple wall clock that does not require that much current to run. The resistor here will drop some voltage across it. 


1. Make sure to check the voltage before connecting it to anything.
2. You might have to change the value of the resistor and model of the diodes.
3. You can even change the number of diodes as well. 

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