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How is the output circuit of a switching regulator configured?

Latest Updated:12/01/2011

Question:

How is the output circuit of a switching regulator configured?

Answer:

There are three types of configurations.

  • Totem pole
  • Open collector/open drain
  • Push-pull

(1) Totem pole
A power MOS FET is generally used as the main switching element of a switching power supply. In order to drive a power MOS FET at high speeds, the gate capacitor of the power MOS FET must be charged and discharged very quickly.
A totem pole circuit is a pre-driver circuit that can supply a large peak current to enable the power MOS FET's gate capacitor to be charged and discharged as quickly as possible.
A simple switching power supply circuit can be configured by incorporating a totem pole circuit in the control IC.

Totem Pole Driver



(2) Open collector/open drain
Using this type of configuration makes it possible to design a driver that ideally matches the characteristics of the main switching element.

Open Collector and External Driver



(3) Push-pull
"Push-pull" is the name of a switching power supply circuit system. With this system, two main switching elements are used and the switching transformers are driven alternately. This system raises the utilization ratio of the transformers, making it ideal for switching power supplies with large outputs.

In push-pull switching power supplies, dead time is built in to prevent two transistors turning on at the same time. Setting this dead time is easy in the uPC494.

Suitable Products
Power Management Linear