Apparatus and method for implementing a multiple function pin in a BCM power supply

摘要

An apparatus and a method for implementing a multiple function pin in a boundary conduction mode power supply, uses a same pin to switch a power switch and to achieve zero current detection to reduce pin count and save cost of a control integrated circuit. A first voltage is applied to the multiple function pin to turn on the power switch, and then a second voltage is applied to the multiple function pin after the power switch has been turned on for a first time, to thereby turn off the power switch. After the power switch has been turned off for a second time, a third voltage is applied to the multiple function pin keep the power switch off. Preferably, a tristate output driver is used to provide the first and second voltages, and a clamping circuit is used to provide the third voltage.

主权项

1. An apparatus for implementing a multiple function pin in a boundary conduction mode power supply including an inductor and a power switch, the apparatus comprising:
a tristate output driver connected to a control terminal of the power switch via the multiple function pin, providing a first voltage to turn on the power switch when being started up, providing a second voltage to turn off the power switch after the power switch has been turned on for a first time, and being turned off after the power switch is turned off for a second time; a zero-current detected signal generator connected to the multiple function pin, detecting a change in an across voltage of the inductor for asserting a zero-current detected signal when a current in the inductor becomes zero, to apply to the multiple function pin; a zero current detector connected to the multiple function pin, detecting a voltage of the multiple function pin for asserting a zero current signal when the voltage of the multiple function pin reaches a threshold, to start up the tristate output driver; and a clamping circuit connected to the multiple function pin, providing a third voltage during an off time of the tristate output driver to turn off the power switch.