TRIAC dimmable LED driver circuit

Abstract

A TRIAC dimmable light-emitting diode (LED) driver circuit is disclosed, compromising: An alternating-current (AC) voltage connected to a rectifier bridge; An LED load, which is connected to an inductor or a transformer, a power MOS transistor, a low voltage MOS transistor and a current sensing resistor. The LED driver also compromises: a peak current comparator which is used to compare the voltage between a current sensing resistor and a reference voltage; a maximum on-time timer, which is used to detect the on time of the low voltage MOS transistor. When the voltage on the current sensing resistor is higher than the reference voltage or the on time of the low voltage MOS transistor reaches the preset time of the maximum on-time timer, the low voltage MOS transistor is turned off.

What is claimed is: 
     
       1. A TRIAC dimmable LED driver circuit comprises an input AC voltage source connected to a rectifier bridge and an LED load, the LED load is connected to an inductor or a transformer, a power MOS transistor, a low voltage MOS transistor and a current sensing resistor, the inductor or transformer includes at least two windings, the first winding is connected to the power MOS transistor, the auxiliary winding is connected to the positive terminal of a supplying diode, the negative terminal of the supplying diode is connected to a supplying capacitor, the LED driver further includes two resistors and an over voltage protection circuit, the resistors are in series and are connected to the auxiliary winding of the inductor or transformer, and the middle point of the resistors are connected to the over voltage protection circuit, the LED driver is characterized in that,
 a peak current comparator, which is used to compare the voltage between the current sensing resistor and a reference voltage; 
 a maximum on-time timer, which is used to detect the on time of the low voltage MOS transistor, 
 when the voltage on the current sensing resistor is higher than the reference voltage, or the on time of the low voltage MOS transistor reaches the preset time of the maximum on-time timer, the low voltage MOS transistor is turned off. 
 
     
     
       2. The TRIAC dimmable LED driver circuit of  claim 1 , characterized in that one input terminal of the peak current comparator is connected to the current sensing resistor, another input terminal is connected to the reference voltage. 
     
     
       3. The TRIAC dimmable LED driver circuit of  claim 1 , characterized in that the LED driver circuit further includes an OR logic gate and a RS flip-flop, the input signal of the maximum on-time timer is the output signal of the RS flip-flop, the input signal of the OR logic gate is the output signal of the maximum on-time timer and the output signal of the peak current comparator, the output signal of the OR logic gate is connected to the reset terminal of the RS flip-flop. 
     
     
       4. The TRIAC dimmable LED driver circuit of  claim 3 , characterized in that the LED driver circuit further includes a first voltage sensing network, a second voltage sensing network and a demagnetization comparator, the input terminal of the first voltage sensing network is connected to the gate of the power MOS transistor, the input terminal of the second voltage sensing network is connected to the source of the power MOS transistor, the output of the first voltage sensing network and the second voltage sensing network are connected to the input terminals of the demagnetization comparator, the output of the demagnetization comparator is connected to the reset terminal of the RS flip-flop. 
     
     
       5. The TRIAC dimmable LED driver circuit of  claim 4 , characterized in that the first voltage sensing network is composed by resistors and capacitors; and the second voltage sensing network is composed by resistor and capacitors. 
     
     
       6. The TRIAC dimmable LED driver circuit of  claim 3 , characterized in that the LED driver further includes a switch driver, the input terminal of the switch driver is connected to the output of the RS flip-flop, the output of the switch driver is connected to the gate of the low voltage MOS transistor. 
     
     
       7. The TRIAC dimmable LED driver circuit of  claim 1 , characterized in that the supplying capacitor is paralleled with a zener diode. 
     
     
       8. The TRIAC dimmable LED driver circuit of  claim 1 , characterized in that the LED driver is one of a buck-boost TRIAC dimmable LED driver, a buck TRIAC dimmable LED driver, or a flyback TRIAC dimmable LED driver.