Converting a Dead CFL into an LED Tubelight

You might have already read about this interesting idea in many different sites. It's about converting a dead CFL into a sleek LED tube light circuit. In this post we learn the procedures with more details.

How many times did you throw away a dead or over used faulty CFL unit into the dust bin? Well, we do this quite often whenever we find one of our home CFL lamps no longer illuminating or illuminating dimly.

You would be surprised to know that the circuit inside the lamp in fact never blows of or becomes weak. It's the tube portion which gets blackened, and unresponsive. It means the circuit of most of the discarded CFL units never goes faulty, and can be recycled through some other means.

For a layman this might look pretty tough....but actually it's quite easy. The tube portion of the CFL may be simply replaced with LEDs, and reused for getting the same illumination that your previous CFL used to give... well almost the same.

Let's learn the procedures.

How to Convert CFL into LED Bulb

Find a dead CFL unit, and very carefully open up the lid which holds the tube from the lower cup type enclosure.

You must do this very carefully using a screwdriver equipment, making sure you don't damage the internal circuit while doing this.

If  you find it difficult to insert the screwdriver end across the joint opening, use a fine hacksaw to make a small section of the opening wider by sawing it some. Now you can force open the lid by using the screwdriver.

This will immediately expose the internal circuit and the connections.

You will find the tube ends terminating with a pair of wires and connecting with the circuit board at four points arranged in a row through fine wire links. Cut these connections with a sniper so that the tube portion gets separated from the circuit board.

Join the above terminals from the ends so that only two terminals end up as the output.

Next using 4 nos 1N4007 diodes build a bridge rectifier, and connect it to the above terminals as shown in the diagram.

Now through a suitable holder and plug device connect the above system to mains and check the voltage a the output of the above connected rectifier.

It should be around 100 to 150 volts DC.

You have just transformed a dead CFL into a small transformerless power supply ideally suitable for illuminating LEDs (white).

Now comes the LED assembly part which may be constructed in the following manner:

To figure out the number of LEDs that would fit inside the output voltage of the above unit, we need to divide the measured voltage with 3.3V. Suppose the measured voltage was 120V, dividing this by 3.3 would give around 36 (numbers).

Use the derived number of LEDs and connect all of them in series with a 5 Ohm, 1/4 watt series resistor.

Done! Now simply connect the LED assembly end terminals with the bridge output of the modified CFL power supply.

You can test the system  by providing mains supply to it....the LEDs should illuminate with dazzling light.

Now fix the assembly appropriately so that the CFL circuit gets inside its original holder while the LEDs may be integrated to the holder over a suitable rectangle type of box, or inside any other decorative cabinet as per user preference.

WARNING: THE IDEA IS BASED ON A SIMILAR CIRCUIT WHICH WAS PUBLISHED IN A DIFFERENT WEBSITE, IT HAS NOT BEEN VERIFIED BY THE AUTHOR.

THE CIRCUIT IS NOT ISOLATED FROM MAINS, AND THEREFORE IS EXTREMELY DANGEROUS IN UNCOVERED, POWERED POSITION.

Another Idea

The method of converting a blown CFL into an LED lamp as explained above looks unnecessarily complex and risky. A better and a foolproof technique would be to salvage a few of the useful parts from the CFL PCB and then apply them to build a simple tranformerless LED driver.

The parts which needs to be extracted can be learned from the following explanation.

Typically, you will find a few PPC capacitors present (which look like chewing gums), check the values and pick up the one which has the highest value in terms of uF and also the voltage value.

The voltage is more important, and make sure the picked one is rated above the supply value of your home AC. So if the supply AC is 220V, the capacitor should be above 250V minimum, and likewise.

Next, remove the filter capacitor, which would be in electrolytic form, and also the 4 diodes from the bridge rectifier.

After collecting these de-soldered  items, assemble them back over a separate stripboard or piece of general purpose board with the help of the following schematic:

Once you have built this, the rest of the parts and the CFL PCB could be removed and thrown away, we don't need it anymore.

After this, procure around 50 LEDs @ 20mA  , preferably SMD type as shown below, and assemble them in series over a circular PCB.

Finally connect the +/- ends of this series LED assembly with the "LED board" points of the above explained power supply circuit.

Feed the 220V input to the capacitive supply and watch the LED dazzle up with mind blowing brightness.

That's it, you have just converted a dead CFL into a high bright LED bulb. Enclose the whole thing inside the CFL box, and glue the PCB appropriately, plug it in your home bulb AC socket for the preferred use

Note: The quantity of LEDs is intentionally selected to be 50nos to get an increased brightness and also better surge control.

Remember here we are assuming the input PPC capacitor to be not more than 0.22uF. If its more than this value then you may have apply a series resistor with the LED assembly to enable an improved surge restriction.

About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!