Hi,
I'm investigating a circuit based on diodes, for protecting a mosfet switch from back emf due to transformer leakage inductance (in lieu of a snubber).
The basic idea is to (a) block off the mosfet's body diode, because this is too slow even though it is correctly oriented to conduct the back emf (b) to provide an additional, reverse biased, diode, parallel to the mosfet, to conduct the back emf. I'm using the 16A, 600V 45nS MUR1660CT diode for both (a) & (b). I have uploaded my LTSpice schematic for this circuit as well as spice file for the diode. Below is a screendump of the LTSpice simulation of this circuit:
My questions are: (1) Why am I seeing a drain-source voltage spike of ~600V in the opposite direction to what the back-emf polarity should be ?
(2) why are the external diodes not shielding the mosfet from the back emf spike? Many thanks in advance.
I'm investigating a circuit based on diodes, for protecting a mosfet switch from back emf due to transformer leakage inductance (in lieu of a snubber).
The basic idea is to (a) block off the mosfet's body diode, because this is too slow even though it is correctly oriented to conduct the back emf (b) to provide an additional, reverse biased, diode, parallel to the mosfet, to conduct the back emf. I'm using the 16A, 600V 45nS MUR1660CT diode for both (a) & (b). I have uploaded my LTSpice schematic for this circuit as well as spice file for the diode. Below is a screendump of the LTSpice simulation of this circuit:
My questions are: (1) Why am I seeing a drain-source voltage spike of ~600V in the opposite direction to what the back-emf polarity should be ?
(2) why are the external diodes not shielding the mosfet from the back emf spike? Many thanks in advance.
Attachments
-
667 bytes Views: 37
-
2.7 KB Views: 40