I have a push pull converter that uses BSC040N10NS5ATMA1 MOSFETs. I have also tried using CSD19533Q5A MOSFETs.

The FETs keep blowing at low power output (about 15W). I am trying to get to 100 W. They fail to a short circuit. When I replace a FET, it happens again. Here is my circuit:

Things I have tried and verified:

• Gate-source resistor: currently set to 10k
• Gate drive resistor: currently set to 1 Ohm, have used as high as 3 Ohm
• The duty cycle, turn-on time, and frequency are such that the gate voltage waveforms are not overlapping, so I do not think cross-conduction is the problem. Acutal duty cycle is still a bit higher than design duty cycle (40% vs. 30%), but the waveforms do not appear to overlap and the driver adds in about 40 ns of dead time.
• The diodes in the snubber are very fast, part number UF4004
• I cranked up the gate drive and current as shown in the circuit and I am pretty sure I am fully turning on the MOSFET
• I also tried to use the FETs in parallel to reduce current per FET, and made sure to apply parallel gate driving, I see the same problem at the same power level (about 15W)

I think the problem is my resistor in the RCD snubber is wrong, but I don't know if it is too large or too small.

Any ideas?

EDIT 1: Inductance Measurement

Leakage inductance is high actually about 4 uH, Primary inductance is actually 280 uH, turns ratio is accurate. Edited in image above.

EDIT 2: V(DS) and V(GS) Measurements

Initially I measured V(DS) using the RCD clamp values above, and I saw that V(DS) was spiking above 100 V at 15W output, which is beyond the allowed value for the BSC040N10NS5ATMA1.

I changed the snubber values in the hopes that this would clamp V(DS). My measurement with C in the clamp replaced with 6.8 nF is shown in the photo. This was also taken at 15 W.

V(DS) is getting pretty close to 100 V. Also R in my RCD clamp was getting so hot that it looked like it was desoldering itself. A measurement of the capacitor shows that it completely discharges and rings during each cycle due to the low time constant.

V(GS) was a nice clean square wave on both MOSFETs with no ringing, foudn to be about 50 ns rise time.

I have a push-pull converter that uses BSC040N10NS5ATMA1 MOSFETs. I have also tried using CSD19533Q5A MOSFETs.

The FETs keep blowing at low power output (about 15 W). I am trying to get to 100 W. They fail to a short circuit. When I replace a FET, it happens again. Here is my circuit:

Things I have tried and verified:

• Gate-source resistor: currently set to 10 kΩ
• Gate drive resistor: currently set to 1 Ω, have used as high as 3 Ω
• The duty cycle, turn-on time, and frequency are such that the gate voltage waveforms are not overlapping, so I do not think cross-conduction is the problem. Acutal duty cycle is still a bit higher than design duty cycle (40% vs. 30%), but the waveforms do not appear to overlap and the driver adds in about 40 ns of dead time.
• The diodes in the snubber are very fast, part number UF4004.
• I cranked up the gate drive and current as shown in the circuit and I am pretty sure I am fully turning on the MOSFET.
• I also tried to use the FETs in parallel to reduce current per FET, and made sure to apply parallel gate driving, I see the same problem at the same power level (about 15 W)

I think the problem is that my resistor in the RCD snubber is wrong, but I don't know if it is too large or too small.

Any ideas?

EDIT 1: Inductance measurement

Leakage inductance is high actually about 4 μH, Primary inductance is actually 280 μH, turns ratio is accurate. Edited in image above.

EDIT 2: V(DS) and V(GS) measurements

Initially I measured V(DS) using the RCD clamp values above, and I saw that V(DS) was spiking above 100 V at 15 W output, which is beyond the allowed value for the BSC040N10NS5ATMA1.

I changed the snubber values in the hopes that this would clamp V(DS). My measurement with C in the clamp replaced with 6.8 nF is shown in the photo. This was also taken at 15 W.

V(DS) is getting pretty close to 100 V. Also R in my RCD clamp was getting so hot that it looked like it was desoldering itself. A measurement of the capacitor shows that it completely discharges and rings during each cycle due to the low time constant.

V(GS) was a nice clean square wave on both MOSFETs with no ringing, found to be about 50 ns rise time.

Fuck this site delete this question

I have a push pull converter that uses BSC040N10NS5ATMA1 MOSFETs. I have also tried using CSD19533Q5A MOSFETs.

The FETs keep blowing at low power output (about 15W). I am trying to get to 100 W. They fail to a short circuit. When I replace a FET, it happens again. Here is my circuit:

Things I have tried and verified:

• Gate-source resistor: currently set to 10k
• Gate drive resistor: currently set to 1 Ohm, have used as high as 3 Ohm
• The duty cycle, turn-on time, and frequency are such that the gate voltage waveforms are not overlapping, so I do not think cross-conduction is the problem. Acutal duty cycle is still a bit higher than design duty cycle (40% vs. 30%), but the waveforms do not appear to overlap and the driver adds in about 40 ns of dead time.
• The diodes in the snubber are very fast, part number UF4004
• I cranked up the gate drive and current as shown in the circuit and I am pretty sure I am fully turning on the MOSFET
• I also tried to use the FETs in parallel to reduce current per FET, and made sure to apply parallel gate driving, I see the same problem at the same power level (about 15W)

I think the problem is my resistor in the RCD snubber is wrong, but I don't know if it is too large or too small.

Any ideas?

EDIT 1: Inductance Measurement

Leakage inductance is high actually about 4 uH, Primary inductance is actually 280 uH, turns ratio is accurate. Edited in image above.

EDIT 2: V(DS) and V(GS) Measurements

Initially I measured V(DS) using the RCD clamp values above, and I saw that V(DS) was spiking above 100 V at 15W output, which is beyond the allowed value for the BSC040N10NS5ATMA1.

I changed the snubber values in the hopes that this would clamp V(DS). My measurement with C in the clamp replaced with 6.8 nF is shown in the photo. This was also taken at 15 W.

V(DS) is getting pretty close to 100 V. Also R in my RCD clamp was getting so hot that it looked like it was desoldering itself. A measurement of the capacitor shows that it completely discharges and rings during each cycle due to the low time constant.

V(GS) was a nice clean square wave on both MOSFETs with no ringing, foudn to be about 50 ns rise time.

I have a push pull converter that uses BSC040N10NS5ATMA1 MOSFETs. I have also tried using CSD19533Q5A MOSFETs.

The FETs keep blowing at low power output (about 15W). I am trying to get to 100 W. They fail to a short circuit. When I replace a FET, it happens again. Here is my circuit:

Things I have tried and verified:

• Gate-source resistor: currently set to 10k
• Gate drive resistor: currently set to 1 Ohm, have used as high as 3 Ohm
• The duty cycle, turn-on time, and frequency are such that the gate voltage waveforms are not overlapping, so I do not think cross-conduction is the problem. Acutal duty cycle is still a bit higher than design duty cycle (40% vs. 30%), but the waveforms do not appear to overlap and the driver adds in about 40 ns of dead time.
• The diodes in the snubber are very fast, part number UF4004
• I cranked up the gate drive and current as shown in the circuit and I am pretty sure I am fully turning on the MOSFET
• I also tried to use the FETs in parallel to reduce current per FET, and made sure to apply parallel gate driving, I see the same problem at the same power level (about 15W)

I think the problem is my resistor in the RCD snubber is wrong, but I don't know if it is too large or too small.

Any ideas?

EDIT 1: Inductance Measurement

Leakage inductance is high actually about 4 uH, Primary inductance is actually 280 uH, turns ratio is accurate. Edited in image above.

EDIT 2: V(DS) and V(GS) Measurements

Initially I measured V(DS) using the RCD clamp values above, and I saw that V(DS) was spiking above 100 V at 15W output, which is beyond the allowed value for the BSC040N10NS5ATMA1.

I changed the snubber values in the hopes that this would clamp V(DS). My measurement with C in the clamp replaced with 6.8 nF is shown in the photo. This was also taken at 15 W.

V(DS) is getting pretty close to 100 V. Also R in my RCD clamp was getting so hot that it looked like it was desoldering itself. A measurement of the capacitor shows that it completely discharges and rings during each cycle due to the low time constant.

V(GS) was a nice clean square wave on both MOSFETs with no ringing, foudn to be about 50 ns rise time.

Fuck this site delete this question