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Leakage spike smaller than scope shows?

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cupoftea

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Hi,
We have been sent a Pushpull 300wout, 24vin, 32vout, 300khz.
The output diodes are 200v rated and the leakage spike is seen to go up to 200V.
But the peak of the leakage spike is read off the scope where a sope probe with dangling ground clip was used. Do you agree, that when we measure it with a coaxial probe, (on x1) and directly solder centre conductor and "wire twizzled" outer braid to the circuit, we will see 10 or 20v less spike, due to less common mode noise injection into the scope probe leads?

By the way, the output diodes are actually FETs 200v (IPTF111N20NM3) with series gate drive resistor not fitted, and gate and source shorted.....do you think the internal diode is already 200v rated?...datasheet doesnt say.

IPTG111N20NM3

BTW, the secondary side leakage snubber is 3 x SMCJ36A in series, and a UF diode into the three....and all this in parallel with a 3W, 100R in series with 1n , 630V. The snubbers are connected from diode cathode to vout.
LTspice and scm attached.
 

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  • 230106_pushpull.jpg
    230106_pushpull.jpg
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  • pupull300w_LT1431_fromu.zip
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