Phase cut dimming LED driver
A phase cut dimming LED driver includes a rectifier, a phase cut hold, a local regulator, controller, a power switch, a transformer, and a load detector. The phase cut hold is connected to the rectifier, one terminal of the primary winding of the transformer, and the local regulator. The controller includes pins connected to the local regulator, the power switch, and the aux winding of the transformer. The power switch is connected to the other terminal of the primary winding. The load detector is connected between the secondary winding of the transformer and a LED. The load detector sends the voltage or current signal of the LED to the controller, and the controller controls the power switch in an uninterrupted mode to keep the current or voltage in a condition to obtain higher PF and lower THD.
1. A phase cut dimming LED driver, comprising:
a rectifier, comprising a rectifier input for being connected to an AC power source and a rectifier output;
a phase cut hold, connected to the rectifier output;
a local regulator, comprising a regulator input connected to the rectifier output and a regulator output;
a controller, comprising a Vcc pin connected to the regulator output, a phase pin connected to the regulator input, an aux pin, an output pin, a CS pin, a FB pin and a ground pin connected to ground;
a power switch, connected to the output pin and CS pin of the controller;
a transformer, comprising a primary winding connected between the rectifier output and the power switch, a secondary winding, and an aux winding connected between the aux pin and ground; and
a load detector, connected between the secondary winding and a LED, the load detector being connected to the FB pin;
wherein the controller monitors a voltage or a current of the LED from the load detector.
2. The phase cut dimming LED driver of claim 1 , wherein the power switch further comprises:
an OP amplifier, comprising an amplifier input connected to the output pin of the controller and an amplifier output;
a MOSFET, comprising a gate connected to the amplifier output, a source connected to the primary winding, and a drain connected to the CS pin; and
a first resistance connected between the CS pin and ground.
3. The phase cut dimming LED driver of claim 1 , wherein the load detector comprises a diode having an anode connected to the LED anode and a cathode connected to a first terminal of the secondary winding, a second resistance connected between a second terminal of the secondary winding and the LED cathode, and a capacitance connected between the junction of the anode of the diode and the LED anode and the junction of the second terminal of the secondary winding and the second resistance.
4. The phase cut dimming LED driver of claim 3 , further comprising an optical-coupler connected between the load detector and the FB pin.
5. The phase cut dimming LED driver of claim 4 , wherein the optical-coupler is connected between the second terminal of the secondary winding and the FB pin of the controller.
6. The phase cut dimming LED driver of claim 1 , further comprising a filter connected between the AC power source and the rectifier.
7. The phase cut dimming LED driver of claim 1 , wherein the controller monitors the voltage or current to keep the voltage or current constant.
8. The phase cut dimming LED driver of claim 1 , wherein the controller operates in an uninterrupted control mode to control the MOSFET to generate an adjustable load according to the AC waveform provided by the AC power source.