Adjustable Power Supply (1.2 V 1.5 A)


We present a very simple but efficient power supply for those who are doing their first steps in the fascinating field of electronics.

At first sight, nothing more simple than a power supply for small projects.

We can buy it, and then forget about it or, we can build it by ourselves and so our satisfaction will be much greater.

So, we decide to build our power supply in order to be able to experiment.

It is obvious that it must be adjustable and that the current must be important enough to cover the necessities of our small projects. But, in that case, we are speaking already about a schematic that includes a transformer (quite expensive), and some regulator circuitry.

Now, here we are with a schematic that offers satisfaction when we do not dispose of very important possibilities :

As we can see, the transformer, the heaviest part and the most difficult to find, was replaced by a 12 v/7Ah battery. This helps a lot the filtering and the current is more than enough for a large variety of circuits. Needless to say the battery can be charged from time to time with an ordinary car battery charger.

When it comes about adjusting the output tension level , we chose to use a system of three potentiometers, two on the same shaft of a 10 kOhm value and the third of 500 Ohms value (of course we should rather prefer to use linear potentiometers, this way the output value of the tension versus the angle of rotation of the potentiometers will be a constant). As it is shown in the schematic, we have to pay attention to the connections in order to get the desired effect . Turning the 10 kOhm potentiometers, we will have the coarse adjustment, and turning the 500 Ohm potentiometers, we will have the fine adjustment .

As a regulator element we used the : LM 317 ( ECG 956 ), so we can vary the output level between : 1.2 v and 12 v (we are limited only by the battery level , because the regulator can go up to 37 v ), and the current up to 1.5 A, which is generally enough for low power circuits .

If we ad to our schematic two indicators (1 voltmeter and 1 ampermeter), we get a ready to use adjustable power supply.

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