STEP-DOWN DC/DC CONVERTER

摘要

A bootstrap power supply circuit generates a constant voltage VCCBST for charging a bootstrap capacitor. An output transistor is configured as an N-channel MOSFET arranged such that its drain is connected to an input line and such that its source is connected to an output line. A constant voltage circuit connected to the gate of the output transistor stabilizes the gate voltage VG to a constant value. A variable impedance circuit is arranged between the input line and the gate of the output transistor, in order to provide a variable impedance. An impedance controller controls the impedance of the variable impedance circuit according to the state of a step-down DC/DC converter.

主权项

1. A control circuit for a step-down DC/DC converter comprising an N-channel switching transistor, the control circuit comprising:
a pulse generator structured to generate a pulse signal for instructing the switching transistor to turn on and off such that a state of the step-down DC/DC converter or otherwise a state of a load approaches a target value; a bootstrap power supply circuit structured to generate a constant voltage for charging a bootstrap capacitor; a rectifier element arranged between an output of the bootstrap power supply circuit and one end of the bootstrap capacitor; and a driver having its upper-side power supply terminal coupled to receive a voltage at the one end of the bootstrap capacitor, and structured to drive the switching transistor according to the pulse signal, wherein the bootstrap power supply circuit comprises:
an input line which is to be coupled to receive a DC voltage;an output line at which the constant voltage is generated;an output transistor configured as an N-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor), having a drain connected to the input line and a source connected to the output line;a constant voltage circuit coupled to a gate of the output transistor and structured to stabilize a voltage at the gate of the output transistor;a variable impedance circuit arranged between the input line and the gate of the output transistor, and having an impedance that can be changed; andan impedance controller that controls the impedance of the variable impedance circuit according to a state of the step-down DC/DC converter.