Power converter for interfacing a fluorescent lighting ballast to a light emitting diode lamp

摘要

An AC/DC power converter is coupled between a fluorescent ballast circuit and a set of light emitting diodes (LEDs) forming an LED lamp. The power converter converts an AC output from the ballast circuit to a DC current applied to drive operation of the LEDs. The power converter transforms and rectifies the AC output from the ballast circuit to generate a DC output current. An open load protection circuit is coupled to protect the ballast circuit when the LED lamp is not connected. Current control is provided by a transistor having a source/drain conduction path coupled to shunt the DC output current in response to a control signal having a duty cycle generated as a function of a zero-crossing of the AC output and a sensed value of the DC output current applied to the LED lamp.

主权项

1. An apparatus, comprising:
a rectifier circuit having input terminals coupled to receive an AC signal and output terminals configured to generate a DC signal; a diode coupled between one output terminal of the rectifier circuit and a first converter output terminal; a capacitor coupled between the first converter output terminal and a second converter output terminal; a switched shunt circuit coupled between output terminals of the rectifier circuit; and a control circuit configured to control actuation of the switched shunt circuit using a PWM control signal having a duty cycle set dependent on a comparison of a current error signal to a ramp signal, wherein the current error signal is generated by a circuit which integrates a difference between a sensed current flowing at the first and second converter output terminals and a threshold.