Flyback transformers, also called line output transformers, are used to supply power to electrical circuits and to generate high-voltage signals at a high frequency. Flyback transformers are power inductors. They take energy from an electrical source such as a battery, then briefly store the electrical energy in the magnetic field created by coils wrapped around a ferrite core. The energy is then transferred to a circuit to power it.
- Skill level:
Things you need
- Plastic coil form
- Plastic wire insulating sheet
- Insulating electrical tape
- #16 gauge insulated wire
- #20 gauge insulated wire
- 2N3055 NPN transistor with mounting kit
- Large transistor heat sink
- 240-ohm 5W resistor
- 27-ohm 1W resistor
- Soldering wire
- Small breadboard printed circuit board
Find the two wire coils located on the back of the flyback transformer. One is the feedback coil, the other is the primary coil. They should be covered and "potted" inside the flybacks. If they are not insulated, attach a plastic coil form to them. Wrap plastic sheet around the plastic coil form, then cover it in electrical insulating tape.
Find two pairs of interconnected wire coils attached to the horseshoe-shaped connection pins. This is done by testing the flyback pins. There may be more than two pins on a single curve of a transformer coil. Measure the resistance of each wire with an ohmmeter to find the high-voltage output pins, which will have a resistance between 100 to 1000 ohms compared to single-digit readings and less for the others. These are the coiled wires that are going to have wire attached to them.
Wind four pieces of the #16 gauge insulated wire four to six turns around the coil of the flyback. Glue them in place. Wrap insulation tape over the connection. It doesn't matter which way you wind them, as long as you wind both of them in the same direction.
Connect the wires at the centre-tap terminal of the flyback located near the coils on the back of the transformer. Insulate the connection with electrical tape. Hook them up to the circuit in any polarity or position. If you don't hear humming electricity, switch the leads to reverse the polarity of one of the coils.
Mount the transistor onto the large heat sink. The transistor mounting kit comes with a mica isolator, thermal compound, mounting bracket, screws and plastic spacers. Insert the plastic spacers between the mounting bracket screws and the transistor. Place a mica isolator between the transistor and the heat sink. This protects you from accidental shock. Place thermal compound between the transistor case, the mica isolator and the heat sink. Tighten the screws to secure the mount.
Connect the flyback transformer to the transistor, at the top of the which are B, C and E terminals. B is the base terminal, C is the collector terminal, and E is the emitter terminal. Connect one of the feedback coil wires to the B terminal of the transistor and solder into place. Connect the negative end of the primary coil to the C terminal at the top of the transistor and solder into place. Place a new wire on the E terminal and solder into place. Lead the end of the E wire to the negative terminal of the battery and secure it to the battery terminal.
Insert the wires of the 5W resistor to the printed circuit board and solder them into place. Position the 1W resistor on the circuit board so that the positive end of the 1W resistor leads to the negative end of the 5W resistor. Solder the 1W resistor wires or pins to the printed circuit board. Attach the positive end of the feedback coil to the wire of the printed circuit board that leads from the 5W resistor and the 1W resistor and solder into place.
Connect the positive end of the primary coil to the positive end of the battery and secure it. Solder a wire to the positive end of the 5W resistor. Lead this wire to the positive terminal of the battery and secure it.
Tips and warnings
- Place a small layer of flux on the terminals and the wire before soldering. Add only a small amount of melted solder wire to solder them into place.
- Flyback circuits transmit a lot of high-voltage electricity and can create fires or shock you, so use with caution.
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