Building a high voltage power supply

[Lance]

I'm feeling generous and bored so I wrote this guide to driving a flyback transformer.

 

First you will need a broken TV or computer monitor. After you find one the first step will be to tear it apart. After you remove the case look for a large capacitor that looks something like this and put a screw driver between its leads to discharge it. You're looking for the flyback transformer which looks something like this:

 

 

After you spot the flyback you will need to remove it. In my experience the best way to do this is to tear the board apart around its leads then cut as much off as possible and using a soldering iron remove the excess solder/board from the leads.

 

Next you will need to locate the rest of the parts for this project. We will be using this schematic:

 

 

The most important component is the NPN transistor. The transistor will have to be able to withstand the inductive kick back from the flyback. The transistor will see at LEAST a few hundred volts. If you look around on the web you will see that most people will suggest using the 2N3055 from Radioshack, which is the largest transistor they sell. However, if you look at the data sheet you will see that its only rated for 60 volts. Obviously this is not the best choice for this project. You can use the 2N3055 but it will die eventually. I would suggest the MJE13009, but you would need to order it. If you decide to buy one then go to digikey.com and do a search for it.

 

You will also need a pair of resistors. One should be around 240ohms and the should be around 27ohms. You should be able to find these in the TV or monitor you took apart. You will not be able to find the exact resistors but the value is not critical. You can also put these in series to get the value you want. For example, If you find a 110, 10, 2, 50, 20 and 15 ohm resistors you can but the 110, 50 and 20 in series to get a total value of 180ohms which will be fine for the 240ohm resistor. The rest can then be put in series for the lower value. Note that they also must be high wattage resistors. You're looking for the large wire-wound potted resistors that look something like this:

 

 

Along with your transistor you will need a a heatsink. The heat sink attaches to the back of the transistor and helps dissipate heat when power is flowing. You should be able to find a suitable transistor in your TV or monitor. Simply screw the heatsink on to the transistor and you're all set.

 

Next we are going to wind our own primary on the flyback. If you examine the flyback you will notice that the ferrite core is protruding from the transformer. Obviously the flyback already has a primary, several in fact, but these were wound for a 120 (or 240) volt input. We will wind our own primary directly on the ferrite core for 12v input. For this we will use magnet wire from Radioshack. The wire comes in packages of 3 spools of different colors. We will use the largest(orange) wire. Simply wind 5 turns onto the core and put tape or glue over it to hold it in place. If you look at the schematic again you will see that the circuit actually has two primarys. One of them is labeled “feedback”. This will be wound right next to the primary but will be only 2 turns.

 

Now that we have all the parts ready we can now put together the circuit. The hardest part of this stage will be looking up the data sheet for whatever transistor you chose and finding the pin out. If you connect the transistor wrong it will not work!

 

Now we must find a power supply. If you have never made any electronic projects then this will probably be the hardest part. You will need a 12vdc supply that can supply the current needed for the circuit which is several amps. Radioshack sells a suitable 13.8 supply but not for cheap. If you have a computer power supply around this will also work. You can also get one on ebay for cheap.

 

After you put this all together test it by bringing the thick output lead near the pins at the bottom if you get spark/arcs to any of them then your circuit is functioning properly. If not then reverse the primary OR feedback finding, not both.

 

You now have a working relativity safe high voltage power supply. If your flyback is not internally rectified then you can use it for making a plasma globe out of a light bulb. Most modern flybacks are rectified though and will not work for This purpose.

 

 

This project is dangerous and can result in injury or death. This article is given solely for information purposes. Neither I or SFN will take responsibility for your actions.

[mmalluck]

Yeah that's a good simple flyback driver. It's not a bad driver for someone just getting into high voltage stuff.

 

If you want something a little more involved and stable, I'd try scopeboy's flyback driver. It also makes a fairly decent tesla coil driver for small coils.