ELECTRONIC CIRCUIT CONTROL ELEMENT WITH TAP ELEMENT

摘要

An example control element for use in a power supply includes a first terminal, a power MOSFET, and a control circuit. The power MOSFET has a drain terminal, a source terminal, a control terminal, and a tap terminal. In operation, a voltage at the tap terminal is less than and tracks a voltage at the drain terminal when the voltage at the drain terminal is less than a pinch off voltage of the power MOSFET. The control circuit includes a PWM circuit and a start-up circuit. The PWM circuit provides a control signal to the power MOSFET to switch the power MOSFET on and off in response to the feedback signal. The start-up circuit charges a bypass capacitor at the first terminal in response to the voltage at the tap terminal until a voltage at the first terminal reaches a first voltage level.

主权项

1. A control element for use in a power supply, the control element comprising:
a first terminal to be coupled to a bypass capacitor and to receive a feedback signal of the power supply; a power Metal Oxide Semiconductor Field Effect Transistor (MOSFET) having a drain terminal, a source terminal, a control terminal, and a tap terminal, wherein the power MOSFET is to be coupled to an energy transfer element of the power supply to control a transfer of energy across the energy transfer element, and wherein a voltage at the tap terminal is less than and tracks a voltage at the drain terminal when the voltage at the drain terminal is less than a pinch off voltage of the power MOSFET; and a control circuit coupled to the power MOSFET, wherein the control circuit includes:
a pulse width modulator (PWM) circuit coupled to provide the control terminal of the power MOSFET with a control signal to switch the power MOSFET on and off in response to the feedback signal; anda start-up circuit coupled to the first terminal of the control element and coupled to the tap terminal of the power MOSFET, wherein the start-up circuit is configured to charge the bypass capacitor in response to the voltage at the tap terminal until a voltage at the first terminal reaches a first voltage level.