While experimenting with flyback transformer circuits I found a simple induction heater circuit and decided to give it a try.
Induction heating uses a high frequency electromagnetic field to induce eddy currents in a piece of conductive material. The current and the resistance of the material lead to ohmic heating. To generate the high-frequency field a self resonant oscillator is used. The circuit mainly consists of two MOSFETs, a tank capacitor and a center tapped coil.
For a detailed description of the circuit operation see the source page.
I did not make a PCB for this circuit but instead soldered it on a piece of perfboard. This is not optimal in regard to trace resistance because the solder has about 7.5 times the specific resistance of copper, but it works ok. An improvement would be to solder some thick copper wires between the components.
My circuit resonates at approx. f=115 kHz (no load inside the coil). With a capacitance of C=440 nF the inductance L of the coil can be calculated by the following formula
to be approx. 4.3 µH.
With an input of 15 V at 660 mA the voltage over the coil is 92 Vpp.
Heating a bolt or nail to a red glow takes about 5 minutes with an increased current draw of approx. 3 A.