Variable Power Supply





Introduction: Variable Power Supply

About: I did my Bachelors in Electrical Engineering with majors in Electronics. I have designed and implemented a lot of projects. I plan to share them with the community soon InshaAllah!

Now this is one of the most important thing for any electronic hobbyist. Every project you make requires a power source. And as these supplies tend to be expensive its better to make them using cheap parts. So what I did was I made two power supplies.

The first power supply I made is for voltages lower than 9 V. I made it by using a power adapter for PS2. The adapter is rated at 8.5 V and 5.6 A.

The second power supply was for voltages lower than 15 V. I made it by using a power adapter of my old laptop. The adapter is rated at 15.6 V and 5 A.

So lets begin.

Step 1: Parts Acquisition

For the first circuit using the PS2 adapter of 8.5 V:

1) Electrolytic Capacitor of 10uF (This is for filtering the ripple).

2) Ceramic Capacitor of 100nF.

3) Regulator IC L200.

4) 1.5 K Resistor

5) 5 K or 10 K Potentiometer.

For the second circuit using the laptop adapter of 15.6 V:

1) Ceramic Capacitor of 100 nF (This is for filtering the ripple).

2) Electrolytic Capacitor of 10 uF & 1 uF.

3) Regulator IC LM350.

4) 240 ohms Resistor

5) 5 K or 10 K Potentiometer

6) Diode (This is for discharging the output capacitor).

General things:

1) Veroboard

2) Soldering Iron

3) Solder Wire

4) Heat Sinks for the ICs.

5) Two Conectors,

6) Two Voltmeters.

Step 2: Making the Circuit

Making the circuits is a fairly easy and simple task.

The first thing to do is to peel of the wire from the output end of the adapter. You must also separate the two wires and determine which of them is the positive and which one of them is the negative.

Then connect the wires to the connectors and solder them onto the veroboard. After that make the respective circuit shown in the figure above. The figures with the axis shows the circuit you want to make and their connections.

The final result is shown in the image above. Once done then it is time for testing.

The voltage of the first circuit will max reach 6 volts and can supply up to 5 A. The voltage of the second circuit will reach 14 V and can supply up to 5 A.

Step 3: Making Changes in the Circuit

Now what to do if you don't have the adapters that I have used. Then you should use whichever adapter you have with you. You can then use any one of the circuit you want and just change the power adapter the output voltages will vary accordingly.

Caution! But before you connect the adapter make sure to read the data sheets of all the components to see that they can withstand the power of your adapter. Otherwise your circuit might get overheated and eventually burn up. So be careful at all times. Also make sure while operating that no loose connection should exist.

Proteus Simulation file is included if you want to see your changes before actually making them. This helps a lot.

Waiting for you feedback!



    • Oil Contest

      Oil Contest
    • Water Contest

      Water Contest
    • Creative Misuse Contest

      Creative Misuse Contest

    10 Discussions


    1 year ago

    (1) If you connect the regulators like that you will inly get around 2A (L200)/ 3A (LM350).

    (2) I didn't do calculations yet but those heat sinks look quite small for this purpose.

    (3) For safety reasons I'd add some fuses.

    5 replies

    Well I haven't actually measured the current supplied. Well only the heat sink on the 15 V looks small. The other one is fine. And the fact is that I don't need more than 2 A. You are right that I should consider to put fuses there for safety.

    Well if you need 5A at say 4V you will put (19-4)*5=75W into the heatsink. The one on the picture won't cut it. Use a 1K/W or lower one.

    If I need 4 V at 5 A then I will use the first circuit of course. And so 8 - 4 is 4 V * 5 A = 20 W. So that is less compared to using the second circuit in which 15 - 4 is 11 V * 5 A = 55 W. So I have made two different power circuits for different purposes. The first circuit serves the purpose to provide Vcc. The second circuit is to use for voltages in the range 10 - 15 V. So the maximum power dissipated by any circuit is less than 25 W. But you are still right for safety purposes I should consider to put bigger heat sinks.

    Oh, didn't read carefully, you use a less standard laptop supply. Most of them are 19V.

    But yes, it's best to choose a supply with lowest difference between in and out. Less heat, more profit! :) If you take it up one more level you can build one with much lower loss. Look for switching or switchmode power supply schematics. I am currently "building" a 42V 350A one out of old power supplies. See for info's.

    I had the Buck Boost supply in mind but it is much restrictive. I wanted a supply with a longer range. The supply range I need is from 3.5 V to 15 V. If you no any good way to make a switching power supply then please inform me.

    That looks good, thanks for sharing :)


    1 year ago

    If that first picture you posted is your own built power supply, I have to say you built an amazing looking power supply. Where did you get the case for it?

    2 replies

    Thanks for the positive feedback. This is my first instructable, and I tried my best to make it easy for understaning.