Yet Another Flyback Transformer Project

I was looking for some parts a couple of weeks ago and came across an old TV flyback transfomer, so I thought I would build a project with it.

Of course, using a flyback transformer for high voltage generation is probably one of the easiest project for people just waded into the electronics DIY world. Not only is the involved circuitry very simple, but the generated high voltage is considered relatively safe as well. Plus, looking at the bright blue spark is quite a unique but satisfying experience. So, here I will show you my version of the circuit (well it’s not that much different than the many designs found on the internet).

Flyback Driver Circuit

Flyback Driver Circuit

In this circuit, I used a pair complementary power transistors (TIP31C, TIP32C) to form a totem pole driver. For the output stage, you can use a TIP41C power transistor. In my implementation (see picture below), I used two parallel TIP31C’s since I have many of these lying around.

Flyback Driver

Flyback Driver

When using the above mentioned transistors, the supply voltage used can be from 9V to 18V. It is always a good idea to start with a lower voltage to minimize the possibility of damaging the power transistors or the flyback transformer in case there was a wiring issue.

Here is a picture of the spark generated with the above circuit when driven by an 20Khz 50% duty cycle square wave from a 555 pulse source.

Spark

Spark

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6 Comments

  1. maurizio says:

    Is that an unmodified flyback transformer? Or did you rewind the primary?

  2. max says:

    What were the pins you used on the flyback transformer? I have two old transformers from monitors but I haven’t been able to find the right pins to use because each has about 10
    (I’m guessing 2 pins on the bottom for input voltage and then one pin connected to the red output wire..)

    • kwong says:

      Different Flyback transformers have different pin out. If you can’t find it in the datasheet, the best way to do is by to try the following:

      Identify all pins that have relatively low resistance among them and write down their locations (as these would be primary windings). Apply the drive voltage from the circuit to two of these low resistance pins at a time and while powered on, try connecting the HV wire (the long wire with the rubber cap) to the remaining unconnected pins one by one (one of these would be ground pin) to see which connection generates a spark.

      Repeat this operation until you find the primary pair that generates the largest spark.

  3. Jim says:

    You for got to mention that the voltage generated from this “experiment” could kill you.

  4. Thalion says:

    I’ve been wondering-

    I understand that there are AC flyback transformers and DC flyback transformers. What happens if I were to use DC current with an AC flyback? Would I break something, or would it simply output several kV of DC current?

    Thanks! I tried looking all over the web, but I guess I don’t yet know enough to be able to find this answer. :-D

    -T

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