A simple circuit of variable power supply and charger is described here. It is useful when the main power supply is available or when there is no power supply.This circuit can be used for testing electronic projects at your work bench. It can be used to charge your mobile battery. It can be used as an emergency light. In this circuit you can take outputs by flipping the different switches according to your requirement. Engage switch S3 if you want a variable power supply as output. For variable power supply, we have used variable voltage regulator LM317whichis a 3 terminal adjustable positive voltage regulator. It will provide an output voltage in the range of 1.2V to 37V. For obtaining different voltages, adjust the variable resistor to see the output on the multimeter and set the required voltage. Range of power supply varies from 1.5V-12V.
Described here is a CD 4027 hearted, battery employed circuit that serves as a solution for light and fan during the times of extreme humidity or power cuts. The circuit consists of a LED light and small DC fan which can sufficiently work for one person. The main advantage of this circuit is one can use any one or both devices at a particular time. The circuit does not consume much power so one can expect it work for a good amount of time. This circuit is based on CD4027 IC which is the most commonly used JK flip flop IC. CD4027 is the master slave JK flip flop IC which works in toggle mode. Here, this IC can be used to change the state by signal applied to one or more control inputs and will have one or two outputs. In this circuit, output is only depended upon the current input.