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TO-247-4L Half-Bridge Evaluation Board
User’s Guide
©
2019 ROHM Co., Ltd.
No. 61UG047E Rev.001
August.2019
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Waveform example when clamp-SBD is used
Figure 33 shows the Vgs surge suppression effect at double pulse test when clamp SBD is used. SCT3040KR MOSFETs are
connected in a half-bridge configuration and switching is done on the high side MOSFET. The external Gate resistor is 10
Ω. From
top, the first waveform is the high side MOSFET Vgs, the second waveform is the commutation side (low side) Vgs, the third
waveform is the high side Vds, and the last waveform is the high side Id. From red line waveform, we can notice that there is not a
single Vgs protection circuit being applied as the self-turn on during turn on and the negative surge during turn off is very severe.
On the other hand, with only clamp SBD is applied to the circuit (green line), we can notice that the negative surge disappeared.
However, this clamp SBD does not effective in reducing the positive surge, and does not stop the self-turn on. There is only one way
to reduce the positive surge or stop the self-turn on which is by using Active MOSFET.
No protection
Rg=10
Ω
Clamp-SBD
Only
Miller clamp
MOS Only
Miller clamp
MOS and
Clamp-SBD
Figure 33. Vgs Protection Circuit Effect (SCT3040KR)
