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Secondary Side Switch-Mode Power Supply Control Slide 30

The next few slides discuss the dual low-side MOSFET driver, the PM8834. It is a device that can be used in all configurations where MOSFETs with high capacitance gates are referenced to ground and need to be switched with a high peak current. This is a different type of driver, not like the half bridge drivers that have a floating high-side driver. These devices are meant for low-side referenced driving of MOSFETs or where MOSFETs might be paralleled. They are also used to drive very large MOSFETs with high gate charge requirements. The PM8834 can be used for driving synchronous rectification MOSFETs in DC/DC bricks and telecom, or a Power Factor Correction boost MOSFET in a large power supply. In this case the MOSFET of the boost PFC stage, is ground referenced. They may also be used to drive MOSFETs in a push/pull topology for a UPS, or as a driver for gate transformers in half bridge and full bridge topologies. The two outputs can be used for this and by logically alternating the inputs, a full bridge is created that can drive a capacitively coupled pulse transformer, creating a carrier drive that will provide gate drive where needed to float it and have isolation. The output of the gate drive transformer is subsequently rectified and filtered and then drives the high-side MOSFET. This circuit utilizes a bipolar pull down transistor for MOSFET turnoff.

PTM Published on: 2015-04-06