Simplest SMPS power supply ever - efficient and powerful - from an old CFL

New to power electronics ? Here is your first SMPS project.

But a SMPS from an old/dead CFL ? Yes, it's possible, with a little modification, of course the CFL's ballast is in working condition.

This simple hacked SMPS is not just a toy, quite efficient and powerful too, while the output power depends on the wattage of CFL.

You can also hack an electronics tube light ballast for the same purpose.

What to do ?

The idea is to wind a few turns of enameled copper wire over the resonant series inductor of the CFL ballast and short the two active outputs of the CFL.

Low voltage output is taken out from the secondary, that's all you need to do !

If it's sounding too technical, have a look at the pictures below.

A schematic, which pins you have to short,

Here I'm using point 2 and point 4 just for reference purpose. You have a good chance that the shorting points are jumbled up, but they're easy to find.

Real world example, front side of the CFL ballast.

In my case the Main inductor is connected to the point 2 and the series capacitor is connected to point 4. So I've to short point 2 and 4 .

Few pictures of how I modified the transformer.

Take the two output wires from secondary winding with a pair of long wire.

Calculating the secondary turns

I've made certain assumption that, 2 turns of secondary coil is producing approximate 1 volt, around 0.5V/turn. Got that approximate result after lots of trial and error with different number of secondary turns and connecting the output to different loads. Unfortunately I don't have a multi meter while writing this.

Insulate the primary and secondary well before winding the secondary to prevent AC leakage.

Only use the inductor coil from the same type and model of CFL, else it may not work. As different types of CFL may use different types of coil with different inductance, and they're matched to resonate with the tank capacitor.

Testing the SMPS

The output is high frequency AC, if you're planning to use it as DC, you're going to need a matching high speed Schottky diode like 1N5822.

For lighting or heating purpose, you can use the AC directly.

Running a 12V-35 watt automotive headlamp, approximately 80% of the normal brightness.

I left the setup running for hours, it heats up a bit, as in normal operation.

Transistors are heating a much less than my expectation, but the transformer core is heating more than expected, perhaps that's normal too.

According to my assumption, the above setup with a 25 watt CFL ballast can easily deliver 12 volt at 2 amperes, and it costs almost nothing !

I'll update the tutorial after buying a multimeter with more details about the output voltage, power and voltage regulation.

I'd like to know your experience on this project, so please don't hesitate to leave comments.