Abstract:
A LED drive circuit for SCR dimming including an external controller configured to receive AC voltage from a power network to convert the AC voltage to an AC voltage with a lacked phase by phase controlling the voltage through a thyristor, and a LED driver that includes a bridge rectifier configured to shape the AC voltage with the lacked phase output into a unidirectional pulse DC voltage, and a phase angle detecting circuit configured to shape the AC voltage signal output with lacked phase from the external controller into a saw-tooth wave pulse signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of Chinese Patent Application No. 200910100298.2 filed Jul. 6, 2009, which is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present invention generally relates to an LED drive circuit for SCR dimming. More specifically, it relates to an LED drive circuit for SCR dimming by detecting phase angle and controlling current. 
       BACKGROUND OF THE INVENTION 
       [0003]    With the increasing of energy consumption, the requirements on energy saving are getting higher and higher. The illumination consumption is an important part of the energy consumption. LED illumination, as an energy saving and green illumination, will replace the traditional gas discharge lamps and the incandescent lamps. LED has the advantages of long life, high luminous efficiency, and energy saving besides which, its simplicity in driving and controlling of the LED makes it easy and flexible to adjust the illumination intensity, which is particularly suitable in the situation when we need to adjust the illumination intensity according to the different conditions. For example, in the road illumination, the plaza illumination and other outdoor or indoor illumination, when there is no need for 100% illumination intensity, dimming can save a lot of energy. 
         [0004]    Since the LED power supply is the AC/DC switching power supply with high efficiency and wide input voltage range, the traditional dimming mode such as controlling input voltage or phased angle, can not adjust the output voltage or current, and can not achieve the purpose of illumination intensity adjustment of LED. Currently, there are a variety of driving circuits for dimming. In some circuits, the automatic timing dimmer is added to the LED driver, which means the lighted LED will be dimmed after a fixed time period. This kind of dimming circuit is under the control of timing dimming circuit and built-in device for detecting illumination intensity, which can not be controlled flexibly. In some other circuits, a control circuit is added to the LED driver in order to receive the radio signal or the power line carrier signal sended by controller, and the signal is used to control the illumination intensity of LED. But the shortages of this mode are expensive cost, complex circuitry, and low reliability (shown in  FIG. 1 ). 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention intends to solve the aforesaid drawbacks of the prior art by providing an LED drive circuit for SCR dimming in order to obtain a good dimming result. 
         [0006]    To settle the drawbacks of the prior art as described above, the present invention adopts an LED drive circuit for SCR dimming which comprises an external controller and an LED driver. It has the following features: 
         [0000]    The LED driver comprises a bridge rectifier, a main circuit, a phase angle detecting circuit and a current controlling circuit. 
         [0007]    The external controller coverts the AC voltage from power network to AC voltage with lacked phase, by phase controlling through thyristor; 
         [0008]    The bridge rectifier shapes the AC voltage with lacked phase output from an external controller into a unidirectional pulse DC voltage, and then feeds it to the main circuit. 
         [0009]    The main circuit receives the pulse DC voltage signal output from bridge rectifier and the current reference signal output from current detecting circuit, and after modulated by the PWM circuit, the main circuit coverts its voltage and outputs DC voltage to LED load and current detecting signal to the current controlling circuit. 
         [0010]    The phase angle detecting circuit is used to shape the AC voltage signal output with lacked phase from an external controller into a saw-tooth wave pulse signal, whose peak value changes according to the variation of thyristor trigger phase angle. Then the saw-tooth voltage signal is converted to a level signal, which changes in proportion to the peak variation of the saw-tooth wave pulse signal, and then outputs the level signal to the controlling current circuit as the output controlling signal from the phase angle detecting circuit. 
         [0011]    The current controlling circuit processes the current detecting signal output (which is from the main circuit) and the controlling signal output (which is from the phase angle detecting circuit), and then outputs a current reference signal to the main circuit to control and adjust the current. Thereby, the main circuit can control the constant current and adjust the output current, which makes it possible to regulate the output current and adjust the illumination intensity of LED. 
         [0012]    The thyristor trigger angle phase is detected by the phase angle detecting circuit and the controlling current circuit, while the illumination intensity of the LED light changes with the phase. The LED light will be brightest when the thyristor trigger angle is smallest, and the LED light will be darkest when the thyristor trigger angle is biggest. With the increasing thristor trigger angle, the peak of the saw-tooth wave and the level signal will increase, which will be fed back by the current controlling circuit to the main circuit, whose output current will be reduced, and the LED light will start to dim, and vice versa. When the thyristor trigger phase angle is increased to a certain maximum angle, the output current of the main circuit is reduced to zero. Thus, the LED light goes out. 
         [0013]    As the present invention adopts an LED drive circuit for SCR dimming, the phase angle detecting circuit and the controlling current circuit are ideal for all applications where an LED drive circuit for SCR dimming is employed. Whenever the external controller of the front-end dimming circuit sends out a dimming signal, the phase angle detecting circuit can detect the signal, and the current controlling circuit can adjust the output current according to the signal by the main circuit. The illumination intensity of LED will be adjusted by wide range, even with the small variation of the thyristor trigger phase angle in the external controller. The present invention features simple structure and low cost. It is able to generate good dimming effect without using complicated modems or wireless transmitters and receivers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a block diagram of the LED drive circuit for dimming circuit in prior art. 
           [0015]      FIG. 2  is a block diagram of the LED drive circuit for SCR dimming circuit in the present invention. 
           [0016]      FIG. 3  is the first embodiment of the isolated LED drive circuit for SCR dimming circuit in the present invention. 
           [0017]      FIG. 4  is the second embodiment of the isolated LED drive circuit for SCR dimming circuit in the present invention. 
           [0018]      FIG. 5  is the third embodiment of the isolated LED drive circuit for SCR dimming circuit in the present invention. 
           [0019]      FIG. 6  is the first embodiment of the non-isolated LED drive circuit for SCR dimming circuit in the present invention. 
           [0020]      FIG. 7  is the second embodiment of the non-isolated LED drive circuit for SCR dimming circuit in the present invention. 
           [0021]      FIG. 8  is a typical schematic diagram based on the third embodiment of the isolated LED drive circuit for SCR dimming circuit in the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    As shown in  FIG. 2 , the LED drive circuit for the SCR dimming circuit comprises an external controller and an LED driver, and the LED driver comprises a bridge rectifier, a main circuit, a phase angle detecting circuit and a current controlling circuit in the present invention. 
         [0023]    In  FIG. 3 , the first embodiment comprises an isolated phase angle detecting circuit and an isolated current controlling circuit, and an isolated main circuit with constant current output. The input of the external controller is the power network, and the output of the external controller is the input of the bridge rectifier and the phase angle detecting circuit. 
         [0024]    The phase angle detecting circuit consists of resistor R 1 , resistor R 2 , resistor R 8 , capacitor C 1 , capacitor C 2 , diode D 1 , diode D 2 , diode D 3 , transistors Q 2  and optocoupler U 1 . 
         [0025]    The anodes of D 1  and D 2  are connected to the two output ends of the external controller respectively. The cathodes of D 1  and D 2 , and one end of R 1  are connected. The other end of R 1  is connected to the base of Q 2 , while the emitter of Q 2  is connected to the power ground. The cathode of the LED in U 1  is connected to the collector of Q 2 , while the anode of U 1  is connected to one end of R 8 . The other end of R 8  is connected to the Vref 3  end of the third reference power supply. The collector of photistor in U 1  is connected to the anode of D 3 , the ends of the R 2  and C 1 . The other end of R 2  is connected to the Vref 1  end of the first reference power supply. The emitter of photistor in U 1  is connected to the signal ground. The cathode of D 3  is connected to one end of C 2 , while the other end of C 2  is connected to the other end of C 1  and the signal ground. The aforesaid circuit can detect and shape signal on the phase angle signal. 
         [0026]    The current controlling circuit consists of resistor R 3 , resistor R 4 , resistor R 5 , resistor R 6 , resistor R 7 , capacitor C 3 , capacitor C 4 , transistors Q 1 , and integrated operational amplifier IC 1 . 
         [0000]    The base of Q 1  is connected to the cathode of D 3  and one end of C 2 , the collector of Q 1  is connected to the Vref 1  end of the first reference power supply, and the emitter of Q 1  is connected to one end each of R 3  and R 4 . The other end of the R 3  is connected to the signal ground, while the other end of R 4  is connected to the negative input terminal of IC 1 , and one end each of R 5 , R 6  and C 3 . The other end of R 5  is connected to one end of R 7 , and the other end of R 7  is connected to the signal ground. The positive input terminal of IC 1  is connected to the Vref 2  end of the second reference power supply. The other end of R 6  is connected to one end of C 4 , while the other end of C 4  is connected to the other end of C 3  and the output terminal of IC 1 . The signal in the output terminal of IC 1  is the current reference signal, and the output current of LED driver is controlled by the main circuit. 
         [0027]    In  FIG. 4 , the second embodiment comprises an isolated phase angle detecting circuit, an isolated current controlling circuit, and an isolated main circuit with constant current output. The input of the external controller is power network, and the output of which is the input from the bridge rectifier and the phase angle detecting circuit. 
         [0028]    The phase angle detecting circuit consists of resistor R 1 , resistor R 2 , capacitor C 1 , capacitor C 2 , diode D 3 , transistors Q 1 , optocoupler U 1  and optocoupler U 2 . 
         [0029]    A branch consists of the LEDs in U 1  and U 2  using an anti-parallel connection, and R 1  in series. The two ends of the branch are connected to the two output ends of the external controller respectively. The collectors of the photistors in U 1  and U 2  are connected together, and then connected to the anode of D 3 , the ends of R 2  and C 1 . The other end of R 2  is connected to the Vref 1  end of the second reference power supply. The emitters of photistors in U 1  and U 2  are connected to the signal ground. The cathode of D 3  is connected to one end of C 2 , while the other end of C 2  is connected to the other end of C 1  and the signal ground. The aforesaid circuit can detect and shape signal on the phase angle signal. 
         [0030]    The current controlling circuit consists of resistor R 3 , resistor R 4 , resistor R 5 , resistor R 6 , resistor R 7 , capacitor C 3 , capacitor C 4 , transistor Q 1 , and integrated operational amplifier IC 1 . 
         [0031]    The base of Q 1  is connected to the cathode of D 3  and one end of C 2 , the collector of Q 1  is connected to the Vref 1  end of the first reference power supply, and the emitter of Q 1  is connected to one end each of R 3  and R 4 . The other end of R 3  is connected to the signal ground, while the other end of R 4  is connected to the negative input terminal of IC 1 , one end each of R 5 , R 6 , and C 3 . The other end of R 5  is connected to one end of R 7 , and the other end of R 7  is connected to the signal ground. The positive input terminal of IC 1  is connected to the Vref 2  end of the second reference power supply. The other end of R 6  is connected to one end of C 4 , while the other end of C 4  is connected to the other end of C 3  and the output terminal of IC 1 . The signal in the output terminal of IC 1  is the current reference signal, and the output current of LED driver is controlled by the main circuit. 
         [0032]    In  FIG. 5 , the third embodiment comprises an isolated phase angle detecting circuit and an isolated current controlling circuit use isolated circuit, and an isolated main circuit with constant current output. The input of the external controller is power network, and the output of the external controller is the input of the bridge rectifier and the phase angle detecting circuit. 
         [0033]    The phase angle detecting circuit consists of resistor R 1 , resistor R 2 , capacitor C 1 , capacitor C 2 , diode D 1 , diode D 2 , diode D 3 , optocoupler U 1 . 
         [0034]    The anodes of D 1  and D 2  are connected to the two output ends of the external controller respectively. The cathodes of D 1  and D 2 , and one end of R 1  are connected. The other end of R 1  is connected to the anode of the LED in U 1 . The cathode of the LED in U 1  is connected to the power ground. The collector of the photistor in U 1  is connected to the anode of D 3 , one end each of R 2  and C 1 . The other end of R 2  is connected to the Vref 1  end of the first reference power supply. The emitter of photistor in U 1  is connected to the signal ground. The cathode of D 3  is connected to one end of C 2 , while the other end of C 2  is connected to the other end of C 1  and the signal ground. The aforesaid circuit can detect and shape signal on the phase angle signal. 
         [0035]    The current controlling circuit consists of resistor R 3 , resistor R 4 , resistor R 5 , resistor R 6 , resistor R 7 , capacitor C 3 , capacitor C 4 , transistors Q 1 , and integrated operational amplifier IC 1 . 
         [0036]    The base of Q 1  is connected to the cathode of D 3  and one end of C 2 , the collector of Q 1  is connected to the Vref 1  end of the first reference power supply, and the emitter of Q 1  is connected to one end each of R 3  and R 4 . The other end of R 3  is connected to the signal ground, while the other end of R 4  is connected to the negative input terminal of IC 1 , one end each of R 5 , R 6 , and C 3 . The other end of R 5  is connected to one end of R 7 , and the other end of R 7  is connected to the signal ground. The positive input terminal of IC 1  is connected to the Vref 1 , end of the second reference power supply. The other end of R 6  is connected to one end of C 4 , while the other end of C 4  is connected to the other end of C 3  and the output terminal of IC 1 . The signal in the output terminal of IC 1  is the current reference signal, and the output current of LED driver is controlled by main circuit. 
         [0037]    In  FIG. 6 , the first embodiment comprises a non-isolated phase angle detecting circuit and a non-isolated current controlling circuit, and a non-isolated main circuit with constant current export. The input of the external controller is power network, and the output of the external controller is the input of the bridge rectifier and the phase angle detecting circuit. 
         [0038]    The phase angle detecting circuit consists of resistor R 1 , resistor R 2 , capacitor C 1 , capacitor C 2 , diode D 1 , diode D 2 , diode D 3 , transistors Q 2 . 
         [0039]    The anodes of D 1  and D 2  are connected to the two output ends of the external controller respectively. The cathodes of D 1  and D 2 , and one end of R 1  are connected. The other end of R 1  is connected to the base of Q 2 , while the emitter of Q 2  is connected to the ground. The collector of Q 2  is connected to the anode of D 3 , one end each of R 2  and C 1 . The other end of R 2  is connected to the Vref 1  end of the first reference power supply. The cathode of D 3  is connected to one end of C 2 , while the other end of C 2  is connected to the other end of C 1  and the ground. The aforesaid circuit can detect and shape signal on the phase angle signal. 
         [0040]    The current controlling circuit consists of resistor R 3 , resistor R 4 , resistor R 5 , resistor R 6 , resistor R 7 , capacitor C 3 , capacitor C 4 , transistors Q 1 , and integrated operational amplifier IC 1 . 
         [0041]    The base of Q 1  is connected to the cathode of D 3  and one end of C 2 , the collector of Q 1  is connected to the Vref 1  end of the first reference power supply, and the emitter of Q 1  is connected to the ends of R 3  and R 4 . The other end of R 3  is connected to the ground, while the other end of R 4  is connected to the negative input terminal if IC 1 , the ends of R 5 , R 6 , and C 3 . The other end of R 5  is connected to one end of R 7 , and the other end of R 7  is connected to the ground. The positive input terminal of IC 1  is connected to the Vref 2  end of the second reference power supply. The other end of R 6  is connected to one end of C 4 , while the other end of C 4  is connected to the other end of C 3  and the output terminal of IC 1 . The signal in the output terminal of IC 1  is the current reference signal, and the output current of the LED driver is controlled by the main circuit. 
         [0042]    In  FIG. 7 , the second embodiment comprises a non-isolated phase angle detecting circuit and a non-isolated current controlling circuit, and a non-isolated main circuit with constant current output. The input of the external controller is power network, and the output of the external controller is the input of the bridge rectifier and the phase angle detecting circuit. 
         [0043]    The phase angle detecting circuit consists of resistor R 1 , resistor R 2 , resistor R 8 , resistor R 9 , resistor R 10 , capacitor C 1 , capacitor C 2 , diode D 3 , transistors Q 2 , and transistors Q 3 . 
         [0044]    The ends of R 1  and R 9  are connected to the two output ends of the external controller respectively. The other end of R 1  is connected to the base of Q 3  and one end of R 8 , while the other end of R 9  is connected to the base of Q 2  and one end of R 10 . The other ends of R 8  and R 10 , and the emitters of Q 3  and Q 2  are connected to the ground. The collectors of Q 2  and Q 3  are connected to the anode of D 3 , one end each of R 2  and C 1 . The other end of R 2  is connected to the Vref 1  end of the first reference power supply. The cathode of D 3  is connected to one end of C 2 , while the other end of C 2  is connected to the other end of C 1  and the ground. The aforesaid circuit can detect and shape signal on the phase angle signal. 
         [0045]    The current controlling circuit consists of resistor R 3 , resistor R 4 , resistor R 5 , resistor R 6 , resistor R 7 , capacitor C 3 , capacitor C 4 , transistors Q 1 , and integrated operational amplifier IC 1 . 
         [0046]    The base of Q 1  is connected to the cathode of D 3  and one end of C 2 , the collector of Q 1  is connected to the Vref 1  end of the first reference power supply, and the emitter of Q 1  is connected to one end each of R 3  and R 4 . The other end of R 3  is connected to the ground, while the other end of R 4  is connected to the negative input terminal of IC 1 , one end each of R 5 , R 6 , and C 3 . The other end of R 5  is connected to one end of R 7 , and the other end of R 7  is connected to the ground. The positive input terminal of IC 1  is connected to the Vref 2  end of the second reference power supply. The other end of R 6  is connected to one end of C 4 , while the other end of C 4  is connected to the other end of C 3  and the output terminal of IC 1 . The signal in the output terminal of IC 1  is the current reference signal, and the output current of LED driver is controlled by main circuit. 
         [0047]      FIG. 8  is a typical schematic diagram based on the third embodiment of the isolated LED drive circuit for SCR dimming circuit in the present invention. A detailed introduction is as following: The input of external controller is power network. The external controller comprises thyristor SCR, bridge rectifier BD 1 , resistors R 8 , variable resistors R 9 , capacitor C 5 , and capacitor C 6 . The AC input terminal of bridge rectifier BD 1  is connected to the null line, the positive output terminal of it is connected to the anode of the thyristor SCR and one end of the variable resistor R 9 , the negative output terminal of it is connected to the cathodes of the thyristor SCR and the ends of the capacitor C 5  and capacitor C 6 . The other end of the capacitor C 6  is connected to the other end of the resistor R 9  and one end of the resistor R 8 . The other end of the capacitor C 5  is connected to the other end of the resistor R 8  and the gate of the thyristor SCR. The output of the external controller is the input of the bridge rectifier and the phase angle detecting circuit. 
         [0048]    The phase angle detecting circuit and the current controlling circuit are exactly the same as that shown in  FIG. 5 . 
         [0049]    The topology of the main circuit is FLYBACK. The main circuit comprises transformer T 1 , MOSFET Q 2  with drive circuit, diode D 4 , output electrolytic capacitor C 7 , and resistor R 7 . The dotted terminal of primary winding of the transformer T 1  is connected to the drain of the MOSFET Q 2 . The source of the MOSFET Q 2  is connected to the power ground, and the gate of the MOSFET Q 2  is connected to the drive circuit of the MOSFET. The dotted terminal of secondary winding of the transformer T 1  is connected to the anode of the diode D 4 , and the cathodes of diode D 4  is connected to the positive terminal of the electrolytic capacitor C 7 , and the positive output terminal of the main circuit. The negative terminal of the electrolytic capacitor C 7  is connected to one end of the resistors R 7 , and the other end of the resistors R 7  is connected to the negative output terminal of the main circuit. 
         [0050]    Finally, it should be understood that the above mentioned embodiments are just the illumination of the present invention, but not limited to the invention. All extended solutions or substitutions based on the principle and content of this invention should be regarded as Inventors&#39; claims to be protected.