Abstract:
A LED control circuit is disclose which comprises a silicon-controlled rectifier (SCR) configured to control a first current supplied to a LED light bulb, and a dynamic current maintenance module serially coupled to the SCR and configured to draw a second current from the SCR, the second current being inversely proportional to the first current.

Description:
BACKGROUND 
     The present invention relates generally to switching of electrical power supply, and, more particularly, to LED control system. 
     Light emitting diode (LED) as a light source has the advantage of lower power consumption and excellent shock resistance. Conventionally, LED light is merely turned on and off, without dimming function and cannot be adjusted to match the needs at different seasons and at different ambient light situations. 
     Silicon controlled rectifier (SCR) has been used to efficiently adjust light output of resistive incandescent light bulbs. However, the SCR cannot be adequately used with LED light bulbs, because LED light bulbs generally include a switching power supply, which may have hundreds or even thousands of pulses, i.e., current cut-off periods, per cycle of an alternating current (AC). Even if the current is not completely cut off at valleys of the pulses, the reduced current may not be able to sustain SCR&#39;s conduction and cause the SCR to unexpectedly shut off, especially when the LED light bulb is of lower power rating or being adjusted to lower power output. The SCR can only be turned back on by next trigger. As a result, the LED light may exhibit abnormal light output or blink. 
     As such, what is desired is a control system that can efficiently adjust LED light output. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a block diagram illustrating a LED control system according to an embodiment of the present invention. 
         FIG. 2  is a schematic diagram illustrating an embodiment of the current measurement module. 
         FIG. 3  is a schematic diagram illustrating an embodiment of the SCR module. 
         FIG. 4  is a schematic diagram illustrating an embodiment of the SCR start current module. 
         FIG. 5  is a schematic diagram illustrating an embodiment of the zero detection module. 
         FIG. 6  is a schematic diagram illustrating an embodiment of the dynamic current maintenance module. 
         FIG. 7  is a block diagram illustrating an embodiment of the interface module. 
     
    
    
     The drawings accompanying and forming part of this specification are included to depict certain aspects of the invention. A clearer conception of the invention, and of the components and operation of systems provided with the invention, will become more readily apparent by referring to the exemplary, and therefore non-limiting, embodiments illustrated in the drawings, wherein like reference numbers (if they occur in more than one view) designate the same elements. The invention may be better understood by reference to one or more of these drawings in combination with the description presented herein. 
     DESCRIPTION 
     The present invention relates to a LED control system utilizing silicon controlled rectifier (SCR) to efficiently adjust output of LED light bulb. Preferred embodiments of the present invention will be described hereinafter with reference to the attached drawings. 
       FIG. 1  is a block diagram illustrating a LED control system  100  according to an embodiment of the present invention. The LED control system  100  includes a current measurement module  105  and a SCR module  110  serially coupled to a LED light bulb  102  between a live wire L and a neutral wire N of an alternating current (AC) power supply. The current measurement module  105  measures current flowing through the LED light bulb  102  and provides a control signal C-INT generated from the measured current to a controller  120 . The SCR module  110  having one or more SCR units adjusts the current flowing through the LED light bulb  102  and hence light output under the control of the controller  120 . A control signal S-INT is coupled from the controller  120  to the SCR module  110 . The controller  120  also communicates with an interface module  130 , which interacts with environment as well as operators 
     Referring again to  FIG. 1 , the LED control system  100  further includes a SCR start current module  113 , a zero detection module  115  and a dynamic current maintenance module  118  all are parallelly coupled to the LED light bulb  102  between the neutral wire N and a live wire B. The SCR start current module  113  provides initial conduction current to the SCR module  110  upon the SCR units being triggered. The zero detection module  115  detects the AC current and provides a signal X-INT to the controller  120  indicating a moment when the AC current crosses zero. The dynamic current maintenance module  118  provides a current to the SCR units to maintain their conduction. The dynamic current maintenance module  118  is controlled by the controller  120  through a control signal D-INT. 
     Referring again to  FIG. 1 , the LED control system  100  further includes a power adapter  112  connected directly to the live wire L and the neutral wire N, and drawing AC power directly from the live wire L. The power adapter  112  converts AC power to DC power which is supplied to the controller  120  and the interface module  130 . By connecting directly to the live wire L, the power adapter  112  is not affected by the SCR module  110 , therefore, the power supply to the controller  120  and the interface module  130  will not be interrupted. 
       FIG. 2  is a schematic diagram illustrating an embodiment of the current measurement module  105 . The current measurement module  105  employs a Hall effect transducer U 1  for converting an AC current flowing through the live wire L and a node A to a voltage which is coupled, through a capacitor C 10  and a resistor R 12 , to a rectifier comprising diodes D 1  and D 2  and an operational amplifier U 3  and associated resistors R 15 , R 18  and R 25 . As shown in  FIG. 1 , the current flowing through the live wire and the node A is the same current that flows through the LED light bulb  102 . An output of the operational amplifier U 3  is amplified by another operational amplifier U 5  and associated capacitor C 15  and resistor R 23 . Resistors R 28  and R 32  serially connected between a high direct current voltage (Vcc) and a ground provide a reference voltage to the operational amplifiers U 3  and U 5 . An output (C-INT) of the operational amplifier U 5  is a full wave rectified signal with amplitude proportional to the current flowing through the LED light bulb  102 . 
       FIG. 3  is a schematic diagram illustrating an embodiment of the SCR module  110 . The SCR module  110  includes a SCR unit U 9  coupled between a node A and a node B. Referring back to  FIG. 1 , the node A is coupled to the live wire L through the current measurement module  105 ; and the node B is coupled to the neutral wire N through the LED light bulb  102 . The SCR unit U 9  is controlled by an optocoupler SCR device U 12  which is in turn controlled by a transistor T 1  through its associated resistors R 32 , R 35  and F 38 . In one embodiment, the transistor T 1  is a NPN type bipolar transistor with the control signal S-INT coupled to a base terminal of the transistor T 1  through the resistor R 38 . When the control signal S-INT is at high voltage level, the transistor T 1  will be turned on which will then turn on the optocoupler SCR device U 12  and the SCR unit U 9 . When the control signal S-INT is at low voltage level, the transistor T 1 , the optocoupler SCR device U 12  and the SCR unit U 9  will be turned off. 
       FIG. 4  is a schematic diagram illustrating an embodiment of the SCR start current module  113 , which includes a resistor R 42  and capacitor C 44  parallelly coupled between the node B and the neutral wire N. As shown in  FIG. 1 , the LED light bulb  102  is also coupled between the node B and the neutral wire N. In operation, the capacitor C 44  stores and releases energy following the AC current cycles between the live wire L and the neutral wire N. The released energy provides a start current for the SCR unit U 9  of  FIG. 3  when the SCR unit  9  is triggered by the signal S-INT to conduct. 
       FIG. 5  is a schematic diagram illustrating an embodiment of the zero detection module  115 . The zero detection module  115  is coupled between the live wire L and the neutral wire N through resistors R 51  and R 53 , respectively, and includes an optocoupler U 7 , a NPN transistor T 3  and resistors R 55 , R 57 , R 59  and R 88 . The optocoupler U 7  produces an output voltage during both positive half cycle and negative half cycle of the AC current, which in turn turns on the transistor T 3  and pulls the output signal X-INT to ground. However, when the AC current crosses at zero, the U 7 &#39;s output voltage becomes zero, and turns off the transistor T 3 . Therefore, the zero detection module  115  produces a positive pulse signal at X-INT at the moment of the AC current crossing at zero. 
     Referring back to  FIG. 1 , the signal X-INT is coupled to the controller  120 , which generates the control signal S-INT from the signal X-INT. The control signal S-INT is also a positive pulse but there is a predetermined time delay from the pulse signal X-INT to the control pulse signal S-INT. The positive pulse of control signal S-INT triggers the SCR unit U 9  to start conducting. The predetermined time delay may be empirically determined and then stored in the controller  120 . 
       FIG. 6  is a schematic diagram illustrating an embodiment of the dynamic current maintenance module  118  which includes a full-wave rectifier J 1  with inputs coupled between the node B and the neutral wire N. Outputs of the rectifier J 1  are coupled between a source and a drain of a NMOS transistor T 5  through resistors R 61  at the drain side and resistors R 63  and R 65  at the source side thereof. The amount of current flowing through the NMOS transistor T 5  determines the amount of current flowing between the node B and the neutral wire N. The NMOS transistor T 5 &#39;s conduction current is in turn determined by voltage at a node C. 
     Referring to  FIG. 6  again, the dynamic current maintenance module  118  further includes a PMOS transistor T 7  with a source connected to a constant voltage source provided by a Zener diode D 5 , a diode D 6 , a resistor R 72  and a capacitor C 68  coupled to the outputs of the rectifier J 1 . A drain of the PMOS transistor T 7  is coupled to the node C through a resistor R 76 . A resistor R 74  connected between the source and a gate of the PMOS transistor T 7  turns the PMOS transistor T 7  on if an optocoupler U 15  coupled between the gate of the PMOS transistor T 7  and the ground is on. The optocoupler U 15  is controlled by a signal D-INT from the controller  120 . When the signal D-INT is at high logic voltage level, the optocoupler U 15  is on to pull the gate of the PMOS transistor T 7  to ground to turn it on. When the signal D-INT is at low logic voltage level, the optocoupler U 15  is off and the PMOS transistor T 7  is off, too. Then the node C voltage is at the ground voltage level due to the capacitors C 62 , C 64  and C 66  coupled between the node C and the ground, and the NMOS transistor T 5  is turned off. Therefore, when the dynamic current maintenance module  118  is not expected to draw current between the node B and the neutral wire N, the controller  120  can set the controller signal D-INT to low logic voltage level. 
     Referring to  FIG. 6  again, the dynamic current maintenance module  118  further include a shunt regulator diode D 9  with a cathode coupled to the node C through a resistor R 69 , an anode connected to the ground and a reference terminal connected to the signal C-INT. When voltage at the reference terminal increases, resistance of the shunt regulator diode D 9  decreases proportionally. As depicted in  FIG. 2  and associated description, voltage at the signal C-INT reflects the current flowing through the LED light bulb  102 . When the current at the LED light bulb  102  runs low, the voltage at the signal C-INT is relatively low, and the resistance of the shunt regulator diode D 9  is relatively high, and so is the node C. As a result, the NMOS transistor T 5  becomes more conductive causing the dynamic current maintenance module  118  to draw more current from the node B and thus from the SCR module  110 . In this way, the SCR module  110  will maintain an adequate conduction current level even when the LED light bulb  102  does not draw sufficient current. 
     On the other hand, when the LED light bulb  102  draws a relatively high current, voltage at the signal C-INT is relatively high, then the resistance of the shunt regulator diode D 9  is relatively low, which in turn causes voltage at the node C to drop and so is the conduction of the NMOS transistor T 5 . As a result, the dynamic current maintenance module  118  draws less current in this situation. In summary, the current drew by the dynamic current maintenance module  118  is inversely proportional to the current flowing through the SCR module  110  and the LED light bulb  102 . 
     Referring to  FIG. 6  again, the dynamic current maintenance module  118  further includes a Zener diode D 7  connected between the signal C-INT and the ground. The Zener diode D 7  serves to protect the shunt regulator diode D 9  from damage by surging voltage at the signal C-INT. 
       FIG. 7  is a block diagram illustrating an embodiment of the interface module  130  which includes a central processing unit (CPU)  702 , an infrared (IR) body sensor  711 , a temperature and humidity sensor  713 , a video camera  715 , an ambient light detector  717 , a touch sensor  719 , and Wi-Fi unit  722 , a microphone and speakers unit  725  and a display  728 . The IR approach sensor  711 , generally placed near the LED light bulb  102  senses the presence of a person in the vicinity thereof, and sends such information to the CPU  702  and then the controller  120  for controlling the LED light bulb  102 . In operation, the LED light bulb  102  is turned on when the presence of a person is detected, and turned off when nobody is present after a certain period of time. 
     The temperature and humidity sensor  713  measures the environment temperature and humidity for being displayed in the display  728 . In some embodiments, the display  728  employs a LED display panel. 
     The video camera  715  captures images and can be used as a security instrument. Captured images can be transmitted over the Internet through the Wi-Fi unit  722 . 
     The ambient light detector  717  sense the ambient light intensity and sends the information to the controller  120  through the CPU  702  for automatically adjusting output of the LED light bulb  102 . For instance, when the ambient light is relatively bright, the controller  120  controls the SCR module  110  to reduce the current supply to the LED light bulb  102 . 
     The touch sensor  719  is for an operator to enter commands or settings to the CPU  702 . In some embodiments, the touch sensor  719  employs a capacitive or a resistive touch panel, and overlays the display unit  728 . 
     The above illustration provides many different embodiments or embodiments for implementing different features of the invention. Specific embodiments of components and processes are described to help clarify the invention. These are, of course, merely embodiments and are not intended to limit the invention from that described in the claims. 
     Although the invention is illustrated and described herein as embodied in one or more specific examples, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention, as set forth in the following claims.