whats a good way to prevent high voltage primary kick back spikes

[Zak28]

i wrapped 3 turns around a MOT coil which is ~1mH the aircore transformer yeilds high voltage spikes - 1-3kv on the primrary. the primary is pulsed 200Hz square 50% duty with 5amps with a FET. This kickback can destroy test equpment along with the FET so I need an ideal method to suppress the high voltage spikes on the primary to harmless levels. What component/topology is ideal for this?

 

[Udit_agarwal]

Flyback diode? like the one here: https://www.elprocus.com/freewheeling-or-flyback-diode-circuit-working-functions/
Probably you also need to put a high wattage resistance in series with diode to limit current through it

 

[BradtheRad]

Many schematics have a diode-capacitor-resistor snubbing network. It appears to be a reliable common method. The capacitor absorbs the spike rapidly, then discharges through the resistor during the remainder of the cycle. Values need to be adjusted so capacitor voltage does not rise too high.

The thread below discusses a similar topic. (See my post which has a schematic simulating the above DCR snubber.)

"Need-help-to-design-a-snubber-design-for-my-SMPS"

https://www.edaboard.com/showthread.php?353435

 

[FvM]

Clamping the inductive kick-back to a certain level also affects the wanted operation of your circuit - whatever it is.

Can you give as an idea about the circuit purpose?

 

[Zak28]

Clamping the inductive kick-back to a certain level also affects the wanted operation of your circuit - whatever it is.

Can you give as an idea about the circuit purpose?

I was hoping to attain some degree of mutual inductance without high volt kickback in the primary winding. I was not expecting the high voltage in the primary, I was hoping that would only be present in the secondary coil.

 

[FvM]

An ideal transformer (k=1) can achieve proportional relation of primary to secondary kick back voltage according to winding ratio. With a non-ideal transformer, the primary kick voltage will be higher, because the interruption of primary current is the voltage source. Clamping the primary voltage clamps also secondary voltage.

 

[BradtheRad]

In my simulation experiments, I have seen high-voltage spikes get worse if I try to push the transformer 'too much'. That is, if I set too high step-up ratio, or try to set a low Henry value for the windings, or depart too wildly from a 50% duty cycle.

It is instructive to install a full diode bridge at the secondary. Observe which diodes conduct while the primary is On. The aim is to adjust things so the secondary only conducts during the latter half of the cycle when the primary is Off. Then you are running efficiently.

 

[Easy peasy]

A ha, MOT = microwave oven transformer, you are trying to make sparks with or without a connected Tesla coil.

the coupling is not great in an MOT, so ideally use a 1200V igbt or mosfet to do the pri side switching and get some 150V zeners, 5W ea, say 7 of in series across the D-S to limit the turn off spike ....

however - this will likely limit the peak volts on the other winding ...