ZXGD3101T8 Datasheet, PDF (5/14 Pages) Zetex Semiconductors – Synchronous rectifier controller for flyback converters

ZXGD3101T8
Operation
Normal Operation
The operation of the device is described step-by-step with reference to the timing diagram below.
1. The detector monitors the MOSFET Drain-Source voltage.
2. When, due to transformer action, the MOSFET body diode is forced to conduct there is
approximately -0.6V 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 GATEH pin.
4. The current out of the GATEH pin is sourced into the synchronous MOSFET Gate to turn the
device on.
5. The GATEH output voltage is now proportional to the Drain-Source voltage drop across the
MOSFET due to the current flowing through the MOSFET.
6. MOSFET conduction continues until the drain current reaches zero.
7. At zero current the detector output voltage is zero and the synchronous MOSFET Gate voltage
is pulled low by the GATEL, turning the device off.
Body D iode
2 ^{C onduction}
MOSFET
D rain Voltage ₁
D rain
current
zero
MOSFET
Gate Voltage ₃
6
5
MOSFET
7
Gate Current ₄
Issue 4 - January 2009
5
© Diodes Incorporated 2009
www.zetex.com
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