Hello,
I'm building a high voltage push-pull converter running at 100 kHz and I have some questions about snubbers.
Part of schematic
Transformer was build with following characteristics:
- inductance : 250 mH;
- induction : 0.2 T;
- primary Cu losses : 0.2 W;
- secondary Cu losses : 0.3 W;
- Fe losses : 0.4W.
Transformer contains two primaries :
- T-/TN ;
- T+/TN.
TN is around 28Vdc and current in primary can reach 12A.
On secondary side, I only have installed a four high voltage diodes redressor (with CLC filter).
CMD1 et CMD2 are generated by a dedicated subcircuit that runs es expected. Signal on gates are also as expected (very clean fronts between 0.2V and 14.5V). I see some ringing on MOSFET drains. Thus, I have added two snubbers (R109/C74 and R110/C75). Whith these snubbers, signals on both drains are correct but snubbers consume a lot of power (42W !).
I am quite surprised as application design show (when they deal with snubbers) very little value for C (100 to 330 pF). In my case, I measured 68 nF ! Other applications designs only show a unique snubber between T+ and T-.
I suppose I have done a mistake somewhere. Help will be welcome.
Best regards,
JB
I'm building a high voltage push-pull converter running at 100 kHz and I have some questions about snubbers.
Part of schematic
Transformer was build with following characteristics:
- inductance : 250 mH;
- induction : 0.2 T;
- primary Cu losses : 0.2 W;
- secondary Cu losses : 0.3 W;
- Fe losses : 0.4W.
Transformer contains two primaries :
- T-/TN ;
- T+/TN.
TN is around 28Vdc and current in primary can reach 12A.
On secondary side, I only have installed a four high voltage diodes redressor (with CLC filter).
CMD1 et CMD2 are generated by a dedicated subcircuit that runs es expected. Signal on gates are also as expected (very clean fronts between 0.2V and 14.5V). I see some ringing on MOSFET drains. Thus, I have added two snubbers (R109/C74 and R110/C75). Whith these snubbers, signals on both drains are correct but snubbers consume a lot of power (42W !).
I am quite surprised as application design show (when they deal with snubbers) very little value for C (100 to 330 pF). In my case, I measured 68 nF ! Other applications designs only show a unique snubber between T+ and T-.
I suppose I have done a mistake somewhere. Help will be welcome.
Best regards,
JB