This is an instructable for making your own PWM (Pulse Width Modulated) flyback driver!
The design is relatively simple and easy to make if you have basic electronic skills.
In fact, you don't even have to know how a transistor or a MOSFET works to make this. You only have to follow the instructions.
What the PWM driver does:
The driver is fed by a 12V power supply (a regular DC adapter). This DC voltage is chopped into pieces by our MOSFET because it rapidly switches the 12V on and off. This switching is controllable by two potentiometers. One for the ON-time and one for the OFF-time.
If the ON-time and the OFF-time are equal, the output voltage will be 6V.
If the ON-time is larger then the OFF-time, the output voltage will be between 6V and 12V
If the ON-time is smaller then the OFF-time, the output voltage will be between 0V and 6V.
So with this feature, we can control the average voltage that our primary Flyback coil gets. This will change the output voltage.
When we make sure both potentiometers have the same resistance value, we'll create a block-wave signal that has the same ON- as OFF-time. Decreasing the resistance (of both potentiometers, at the same time) will increase the frequency of the output signal. Increasing the resistance will decrease the frequency.
We now have controllable ON- and OFF-time, and controllable frequency, so this driver is perfect for Any flyback transformer! (Each flyback transformer works better on another frequency).
The operating frequency of the flyback transformer goes somewhere from 15kHz to 50kHz. My flybacks operate best at 20kHz.
(oh, and the power supply doesn't need to be exactly 12V. You can also use a 30V supply or something a little lower then 12V).
Preview video of the PWM driver:
Step 1: Requirements
- a PCB
- a power supply (DC adapter 12V to 20V)
- a heatsink (the size of the heatsink depends on the flyback and on the type of MOSFET, you'll have to experiment)
- a MOSFET (I used an IRFB17N50L because they're awesome)
- wire for making connections at the bottom of the PCB
- 2x potentiometer 100kohm
- 2x resistor 260ohm 250mW
- 2x resistor 1kohm 250mW
- 1x resistor 4k7ohm 250mW for the LED (high resistance so that we can also use greater power supplies)
- 2x capacitor 3.3nF polyester film or something close to that
- 2x NPN transistor (regular transistor)
- a small pushbutton (not required)
- a flyback transformer (not required)
- a FAN connector for inserting the MOSFET (not required, you may solder it directly on your PCB)
The picture above here shows how the components look like.
Step 2: The schematic
Use of the small pushbutton:
Sometimes, the circuit doesn't seem to start up immediately after connecting the power supply to it. When you push this button, it'll start working.
However, I never seem to have this problem any more now.
Notice that the uper right and upper left connection are the same. We only have to make this connection once.
You can also see in the other pictures that the PWM driver only has 3 connections. +, - and output signal.
The cross in the middle of the schematic is NOT a connection.
Step 3: Soldering all components to the PCB
There's not much to explain in this step; All a can tell you is how-to-solder but there are lots of other instructables that explain that.
About the potentiometers:
You only have to connect two of the three pins. Use the middle pin and one of the outer pins. It doesn't really matter which outer pin you choose.
It only changes weather you want to rotate clockwise or anti-clockwise for increasing the frequency.
Step 4: Testing the PWM driver
- Connect the negative connection from the power supply to the - connection (GND) from the PWM (see schematic)
- Connect the + connection from the PWM to one of the 2 pins of the primary coil of the flyback transformer
- Connect the 'output' or 'signal' connection from the PWM to the other pin of the primary coil from your flyback transformer.
- If nothing happens, try pushing the small pushbutton or change the potentiometer's positions.
- If still nothing happens, reverse the two connections of the primary flyback transformer coil.
- If still nothing happens, leave a reply here with a description of the problem.
The picture above also shows how the connections should be made. The black aligator clip is the negative and the yellow clip is the positive connection of the power supply.
You can also add other things than a flyback transformer, such as a DC motor, a light bulb, LED's, ... just anything, and see how they react to the pulse width controlled signal ;)