ZVS Induction Heater + Tank Calculator

Let us build a full ZVS driver + tank circuit simulator super useful for trying different values of voltage, frequency, inductor, capacitor, and seeing how your ZVS-based induction heater behaves.

What This Simulator Does:

Calculates:

• Resonant frequency (f)
• Required inductance (L)
• Tank current (approximate)
• Reactive power (Q-factor)
• Heating efficiency range estimate
• Shows warnings if parameters are unsafe

How It Works Behind the Scenes:

• Z = Xl - Xc → reactance difference creates the LC resonance tank
• I = V / Z → approx current in the LC loop (not including switching losses)
• Q = Xl / Z → higher Q means sharper resonance and better energy recycling
• Reactive Power shows how much VA is circulating (not real power)

Design Tips for Best Results:

How You Can Keep Tank Current Below 30 Amps:

Move Slightly Away from Resonance (Detuning)

Tank current goes to peak only at exact resonance. If you shift the frequency a bit above or below resonance then current drops without killing heating.

Example:
Resonance at 100 kHz
Try operating at 105–110 kHz or 95–90 kHz

This reduces I = V / (Xl - Xc) because Xl ≠ Xc anymore.

Increase Net Reactance (Z = Xl - Xc)

Your current is high because:

Z = |Xl - Xc| is very small → I = V / Z becomes very very big...

To increase Z and reduce current, you can:

a. Reduce Capacitance

Use lower value capacitor. For example:

• Instead of 0.33 µF, Try 0.1 µF.
  This increases Xc which increases |Xl - Xc| → lowers current

b. Increase Inductance

Use slightly more turns or wider coil

• Instead of 7.6 µH, Try 15 µH.
  This increases Xl which helps in detuning and results in less current.

Try keeping Z around 0.8 Ω minimum

So for 24V:

I = 24 / 0.8 = 30 A

Lower the Supply Voltage

Tank current is directly proportional to voltage:

I = V / Z

So instead of 24V we can use 12V:

• 12V supply
  Same Z = 0.05 Ω
  Now I = 12 / 0.05 = 240 A (still high, but 50% lower than 24V case)

But better if you combine lower voltage + detuning → then real current can go under 30A.

Add a Small Series Resistance (Lossy Method)

This is a crude method but works:

• Add 1 to 2 Ω high-watt resistor in series with tank.
• Will limit current but waste energy as heat.
• Use only for small systems, not recommended for powerful heaters.

Use PWM Controlled Supply Instead of Constant Voltage

If you use a PWM buck converter to softly power the ZVS circuit then you can:

• Limit the average input voltage
• Use a current sensor to cut power at 30A
• Gradually ramp up to avoid peak surges

This gives full control like a professional induction heater.

Is Resonant Frequency Automatically Set in ZVS Circuit

In a ZVS (Zero Voltage Switching) circuit, the resonant frequency is kind of automatically followed by the circuit but not exactly adjusted. Let me explain...

So in a ZVS circuit, like the one using push-pull MOSFETs with an LC tank, we see that the circuit is designed in such a way that it tries to naturally oscillate at the LC resonant frequency because that is the point where the circuit works most efficiently with minimum switching loss and smooth current flow.

Now when we power the circuit, then switching action actually starts because of some imbalance or stray oscillation and that oscillation begins near the natural resonant frequency of the LC tank. After that the gate driver (like through diodes, resistors, and transformer feedback) keeps pushing the MOSFETs in that same rhythm. So the switching waveform gets locked with the tank's resonant cycle.

That means the frequency of the oscillation is not fixed by us using any external signal, like in a PWM circuit, but instead the circuit kind of follows and settles around the natural frequency of the LC parts.

But if we change the inductor or capacitor values while it is running then also the oscillation frequency will shift automatically because the whole system is self-resonating. So yes, we can say the resonant frequency is not forcefully adjusted by the circuit but it is automatically tracked by the self-oscillating behavior of the ZVS setup.

So the ZVS circuit does not need an external clock because it itself oscillates at the correct frequency which suits the LC tank.

Does that mean we can just use any LC tank circuit in a ZVS, without calculations

Yes it looks like that at first but actually it's not safe to just use any LC tank blindly in a ZVS circuit without doing proper calculations, let me explain clearly...

So yes, it is true that ZVS circuit will automatically try to oscillate at the natural resonant frequency of whatever LC tank we connect. But still we must calculate and design the LC tank carefully because if we choose wrong values then the whole circuit can misbehave or even damage the MOSFETs.

Like suppose we choose a very small capacitor then the resonant frequency will go too high and the switching speed will become too fast for the MOSFETs to handle, so they can heat up or fail.

Or if we use a very large inductor then the circuit may not get enough current boost for maintaining resonance and the ZVS action will break.

Also the power level we want to transfer, that also depends on the LC values because higher current needs lower reactance which again needs careful tuning of L and C.

So what we do is, we first calculate the resonant frequency we want based on our power supply voltage, MOSFET speed and transformer design. Then we calculate the capacitor and inductor using the formula:

f = 1 / (2 * π * √(L * C))

After that we build the LC tank using these values so that the ZVS circuit can resonate smoothly without overheating or misfiring.

So in short ZVS may follow the LC frequency by itself but still we must calculate and design that LC properly otherwise the circuit will not work safely or efficiently.