Hi,
My customer is using LM5015 in a two-switch Flyback circuit, part of the schematic is as following figure. Output 5V and Input is 24V.
The problem they are facing is: when in DCM mode and 2 Mosfets are both turned off, Vds of two Mosfets is not the same. Yellow line is the Vds of upper Mos and red one is the Vds of lower Mos. With Diodes D30 and D36, the waveform shows as in figure 2, without diodes as in figure 3.
Could you help me to explain:
1. Why the Vds of 2 Mosfets are not the same as (Vin+Vf)/2 when working in DCM and all Mosfets are turned off ?
2. Why there are a difference when adding 2 diodes but the Vds are still not the same ?
Figure1 schematic LM5015
Figure2 with diodes D30 and D36 yellow: upper Vds; red: lower Vds
Figure3 with diodes D30 and D36 yellow: upper MOS Vds; red: lower MOS Vds
Manu Chang