Ok i will put snubber circuit across mosfetUsually a capacitor is installed across the inductive load. The value needs to be selected so C & L values create a resonant frequency which matches the AC supply frequency.
It may be difficult to find the proper solution. This problem is a cousin of the voltage spike generated by the inductor when current is abruptly shut off. The spike can be strong enough to destroy mosfets. Some kind of snubber network reduces the problem. The AC waveform requires a snubber which reduces spikes in both directions.
You need some large caps across the power supply rails near your mosfet totem poles. 4148 is a bit small for the app, the 4007 should be 45V 1A schottkies, 10 ohm gate drive may be too small to stop high dv/dt affecting your controller...
The 200mA to 400mA is DC current.1n4148 = 200mA to 400mA, depending on the datasheets I've seen. Is that enough?
You say 1kW...but when i connected to 1kW motor (at 20v and 10amp supply) the mosfet gets heated up above 60C.
--> what is your commutaion scheme?
--> Measure the MOSFET current with a scope and show us the picture.
From your above informations it seems you switch 20V/100ns.A capacitor directely connected to a "switched" output is no good idea??
I didn't get it.
Hi,
Again:
Klaus
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Hi,
From your above informations it seems you switch 20V/100ns.
Now what capacitance do you intend to use?
Usually 100nF are not enough to compensate for the motor inductance.
Can you calculate the current for a 100nF capacitor and 20V/100ns?
Now for 1uF...
and then you have 3 phases...
With this new current re-calculate the switching loss. And the radited EMI will cause new problems.
Klaus
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