LED AC driving circuit capable of adjusting operating voltage

摘要

An LED AC driving circuit capable of adjusting operating voltage has a rectifying unit, an LED unit, a voltage-controlled transistor, a current detecting unit and a current regulating unit to form a power loop. Further, a resistance adjusting unit is connected to the voltage-controlled transistor in parallel. The current regulating unit detects the operating power of the voltage-controlled transistor. When the detected operating power is zero, the resistance of the resistance adjusting unit is increased for increasing the current flowing through the voltage-controlled transistor. When the detected operating power becomes larger than a maximum rated power, the resistance of the resistance adjusting unit is decreased to reduce the current. Thus, the operating power is maintained between zero and the maximum rated power.

主权项

1. An LED AC driving circuit capable of adjusting operating voltage, comprising:
a rectifying unit receiving and converting AC power to pulsed DC power and output the pulsed DC power through an output; an LED unit connected to the output of the rectifying unit to form a power loop and comprising multiple LEDs; a voltage-controlled transistor for adjusting a loop current of the power loop, wherein the voltage-controlled transistor connects to the power loop in series and has a control terminal, a first pole and a second pole; a current detecting unit connecting to the power loop in series and converting the loop current to a voltage signal; a low frequency filter connecting to the current detecting unit and outputting a voltage based on the voltage signal; a resistance adjusting unit connecting to the voltage-controlled transistor and being capable of adjusting a resistance across the voltage-controlled transistor; and a current regulating unit having
an input terminal receiving the voltage from the low frequency filter;a reference input terminal receiving a reference voltage; andan output terminal connected to the control terminal of the voltage-controlled transistor; wherein the current regulating unit compares the voltage from the low frequency filter with the reference voltage to produce a control signal applied to the control terminal of the voltage-controlled transistor for stabilizing the loop current, and detects operating power of the voltage-controlled transistor for controlling the resistance adjusting unit to change the resistance across the voltage-controlled transistor.