W
webber
- Jan 1, 1970
- 0
I have a question about the magnetizing energy changing during the
transition between the turn off of MSOFET and the turn on of the
output rectifier.
When the power MOS is turned on, the input energy is stored into the
magnetizing inductance, and the current on the inductor increases
linearly. After the MOS is turned off, the inductor current starts to
charge the output capacitance of the MOS (Coss), and the Vds voltage
starts to increase. Once the voltage on the Vds is high enough to let
the secondary rectifier becomes forward biased, the energy starts to
transfer to the secondary. And, thing keep happens on the primary side
is that the energy on the leakage inductor continuous to transfer to
the Coss and the Vds will increase to high level until the primary
snubber diode is on.
The above is my understanding of the flyback converter.
Based on this understanding, the difference between the energy stored
in the magnetizing inductor and the left energy in this inductor
during the period after the MOS is off and the secondary rectifier is
on, is used to charge the Coss to the point to let the secondary
rectifier becomes forward biased.
But, my measured data is quite different.
The energy difference on the inductor (5.7W) during this small period
is much larger than the energy transfer to the Coss (0.36W).
Can anyone tell me what's wrong ??
Thanks a lot.
Webber.
transition between the turn off of MSOFET and the turn on of the
output rectifier.
When the power MOS is turned on, the input energy is stored into the
magnetizing inductance, and the current on the inductor increases
linearly. After the MOS is turned off, the inductor current starts to
charge the output capacitance of the MOS (Coss), and the Vds voltage
starts to increase. Once the voltage on the Vds is high enough to let
the secondary rectifier becomes forward biased, the energy starts to
transfer to the secondary. And, thing keep happens on the primary side
is that the energy on the leakage inductor continuous to transfer to
the Coss and the Vds will increase to high level until the primary
snubber diode is on.
The above is my understanding of the flyback converter.
Based on this understanding, the difference between the energy stored
in the magnetizing inductor and the left energy in this inductor
during the period after the MOS is off and the secondary rectifier is
on, is used to charge the Coss to the point to let the secondary
rectifier becomes forward biased.
But, my measured data is quite different.
The energy difference on the inductor (5.7W) during this small period
is much larger than the energy transfer to the Coss (0.36W).
Can anyone tell me what's wrong ??
Thanks a lot.
Webber.