Descriptions of the normal operation – Diodes ZXGD3104N8 User Manual
Page 6
ZXGD3104N8
Document Number DS35546
Rev. 1 – 2
6 of 13
November 2011
© Diodes Incorporated
A Product Line of
Diodes Incorporated
ZXGD3104N8
Descriptions of the normal operation
The operation of the controller is described step-by-step with reference to the timing diagram in Figure 1.
1. The controller monitors the MOSFET Drain-Source voltage.
2. When, due to transformer action, the MOSFET body diode is forced to conduct there is approximately -0.8V on the
Drain pin.
3. The detector outputs a positive voltage with respect to ground, this voltage is then fed to the MOSFET driver stage
and current is sourced out of the GATE pin.
4. The controller goes into proportional gate drive control — the GATE output voltage is proportional to the on-
resistance-induced Drain-Source voltage drop across the MOSFET. Proportional gate drive ensures that MOSFET
conducts for majority of the conduction cycle and minimizes body diode conduction time.
5. As the Drain current decays linearly toward zero, proportional gate drive control reduces the Gate voltage so the
MOSFET can be turned off rapidly at zero current crossing. The GATE voltage is removed when the Drain-Source
voltage crosses the detection threshold voltage to minimize reverse current flow.
6. At zero Drain current, the controller GATE output voltage is pulled low to V
G(off)
to ensure that the MOSFET is off.
Figure 1. Timing diagram for a critical conduction mode Flyback converter