The article explains a simple variable voltage bench power supply circuit which utilizes just a single transistor. The design can be very handy for the new electronic hobbyist
What's a Bench Power Supply
A bench power supply having an adjustable voltage feature is an essential tool for every electronic enthusiast. However making one such power supply within minutes using a handful of components might look difficult.
The circuit of a simple variable voltage bench power supply referred here shows us how to build one such unit quickly using common parts from your junk box.
The Bench Power Supply is easy to construct. It takes less than an hour on a piece of copper-laminate.
All the components can be mounted as show in the aforesaid diagram, cutting the strips for placement.
Moreover the board also acts as a heat-sink. Enamelled wires are used to connect the components and the transistor gets bolted to the board, acting as a cooling agent.
Circuit Operation
The circuit is designed for use with old C," "D", and even lantern batteries. That’s the reason for no diodes or electrolytic. Get some old batteries and connect together to receive 12v – 14v, at least.
The power for this output is controlled by a 10v zener, made by following the characteristic of zener voltage of 8.2v in between the base-emitter leads of a BC547 transistor, in a reversed bias, and 1.7v approx. across one Red LED. The circuit is designed to deliver 0v-9v at 500mA.
However the deliverance depends upon the life of the cells being used. The 10k pot works to adjust the output voltage and thereby the LED circuit goes in ON state.
A good part is that the circuit is well designed to fetch the last leg of energy from old cells.
Submitted By: Dhrubajyoti Biswas
Circuit Diagram
Thank u sir
Hai sir….
Output it will give constant current 1v to 9v…
For example 1v 200ma 5v 290ma 9v 500ma…
While varying voltage the current will be constant or it will vary…
1v to 9v same constant current
Or it will change ?
Hi Kesav, if your transformer is rated at over 500mA @ 9V then the output from the circuit will be constant 500mA throuout 0-9V range
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