What is the function of high current induction heater circuit elements?

Thread Starter


Joined Apr 8, 2022
Note: English translation is below.

Herkese merhaba,
Bu devrede komponentin görevleri nelerdir?
- Dirençler ne işe yarar?
- Bu devrede diyotlar ne işe yarar?
- Toroid sargılarının sayısı artarsa ne olur?
- Birden fazla kondansatör paralel bağlanırsa ne olur?
- Devrenin verimli çalıştığını nasıl anlarız?
Bu tür soruları açıklayabilirseniz çok minnettar olurum. Teşekkür ederim.

Moderation translation, Please use English Text.

Hello everyone,
What are the functions of the component in this circuit?
- What do resistors do?
- What do diodes do in this circuit?
- What happens if the number of toroid windings increases?
- What happens if more than one capacitor is connected in parallel?
- How do we know that the circuit is working efficiently?
I would be very grateful if you could explain such questions. Thank you.

Devre Resmi.jpg
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Joined Jun 22, 2012
This circuit diagram is a Royer Oscillator, a type of multivibrator that pulses the transformer across the supply to create a larger voltage output.
The transformer primary and the parallel capacitor are tuned to the best frequency to give the maximum amount of output with minimal current drain.


Joined Jan 23, 2018
To determine efficiency you will need to determine the electrical power input and the electrical power delivered to the output
of the oscillator circuit.

Because the circuit is not connected to any load, the efficiency as shown is zero, unless the output of the circuit is the magnetic energy produced by the coil. But that is not mentioned.
All four of the resistors are to provide the correct gate bias for the transistors. The diodes are to provide feedback so that the circuit will oscillate.
The capacitance across the inductance of the coil determines the resonant frequency. Adding capacitance will lower the resonant frequency.

And while the impression is that it may be an induction heater circuit, the low voltage supply hints that this may be a homework assignment or a test question.
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Joined Sep 2, 2020
To gain some understanding of the circuit you may enter it into a circuit simulator. Just be aware, that such an oscillator needs some excitation through ramping up the power and some minor mismatch between R2 and R1 . In reality any noise present here starts the oscillations.
Increasing the capacitor lowers the switching frequency. But be aware that it maybe quite difficult to get a good model for the coil. If you just measure the coil it is the unloaded behavior. The circuit will heat up metal parts close to or inside the coil, but the influence of that to the q-factor of the coil maybe difficult to measure or estimate.
So the approach maybe measure and simulate, then check the supply voltage / current consumption in simulation and measurement. Putting some metal object close to the coil will change the current consumption because now some electromagnetic field energy is transformed to heat. A first approach maybe simulate it by a resistor across the coil. The resistor should be chosen that current consumption in simulation and measurement matches again.

Another word of caution: trying to measure around in this circuit can be dangerous because the voltage on the coil maybe higher than the supply voltage and attaching a wire to measure the voltage may work like an antenna connected to a transmitter and you emit some electromagnetic waves. So maybe the frequency of this oscillator is not chosen for technical reasons but for regulatory reasons and tampering around with this circuit can modify the frequency to a value where interference with some services brings you in severe trouble.