High-Frequency Inverter winding method: First, use a paper box or plastic sheet to make a coil former according to the core area. Then wind the coil on the former. Wind the primary first. After the primary is wound, wrap three layers of capacitor paper or kraft paper as insulation between primary and secondary. Then wind the secondary, with two 54-turn coils (this transformer has an input of 220V and an output of dual 27V). According to this, each turn is 0.5V, meaning the primary is wound with 440 turns. After winding the secondary, wrap two layers of capacitor paper or kraft paper for insulation from the core. Then insert the core, which can be done by interleaving three core pieces at a time. After inserting the core, test with power. If the voltage meets requirements, apply insulating varnish and dry. The layers of the coil can be insulated with capacitor paper or kraft paper. The primary can use thin paper. It can also be omitted.
High-Frequency Inverter resistor selection: The two resistors in series with the 4V coils can be made from resistance wire. The resistor size can be chosen based on the output power, typically a few ohms. When the output power is high, the resistance should be smaller. The bias resistor uses a 1W 300-ohm resistor. It can work without this resistor, but due to inconsistent transistor parameters, it may not oscillate sometimes, so it is best to connect one.
High-frequency inverter transformer fabrication: You can choose a control transformer used in machine tools according to your needs. I used a 100W control transformer. Disassemble the transformer core, then remove the secondary coil. Record the number of turns per volt. Then rewind the secondary coil. Use 1.35mm enameled wire, first wind a 22V coil with a center tap, which is the main coil. Then use 0.47mm enameled wire to wind two 4V coils as feedback coils. Insulate between layers with thick kraft paper. After winding, insert the core. Connect the two 4V secondaries to the main coil respectively, being careful not to reverse the head and tail. Test the voltage with power. If the voltage increases after connecting the 4V coil to the main coil, the connection is correct; otherwise, it is wrong. You can swap the connections. In this way, the transformer is completed.
