Abstract:
An LED driver circuit includes a primary circuit and a circuit electrically isolated from the primary circuit, a transformer having a primary winding configured to receive power from an alternating current source and to generate power in a first secondary winding configured to provide power to the electrically isolated circuit, and to generate power in a second secondary winding configured to provide power to the primary circuit, and a conductor connected to an end of the first secondary winding and configured to connect a winding driver signal to the first secondary winding to generate power in the second secondary winding.

Description:
FIELD 
       [0001]    The disclosed exemplary embodiments relate generally to lighting control systems, and more particularly to structures and techniques for applying power to at least a portion of a lighting driver circuit. 
       BACKGROUND 
       [0002]    Incandescent light bulbs create light by conducting electricity through a resistive filament and heating the filament to a very high temperature to produce visible light. Incandescent bulbs are made in a wide range of sizes and voltages. The bulbs typically include an enclosure with a tungsten filament inside and a base connector that provides both an electrical and structural support connection. Incandescent bulbs generally mate with a lamp socket having a threaded Edison base connector, bayonet base connector, pin base connector, or any suitable connector for providing electrical power to the bulb. However, incandescent light bulbs are generally inefficient and require frequent replacement. These lamps are in the process of being replaced by more efficient types of electric light such as fluorescent lamps, high-intensity discharge lamps, and, in particular, lamps with light emitting diode (LED) light sources. 
         [0003]    LED technology continues to advance resulting in improved efficiencies and lower costs with LED light sources found in lighting applications ranging from small pin point sources to stadium lights. An LED light source is generally powered by an LED driver circuit that converts alternating current (AC) mains power to a constant current applied to LEDs within the LED light source. The LED driver circuit typically includes support circuitry and a microcontroller that may be programmable for different AC mains input requirements and different output voltages and currents. 
         [0004]    The LED driver circuit may also include a primary circuit connected to an AC supply and a control side, isolated from the primary circuit. In some implementations, the control side may be isolated from the primary circuit in accordance with certain industry standards, for example, International Electrotechnical Commission (IEC) Class II, where the secondary side may also be referred to as being double insulated. In many implementations, the microcontroller for controlling the LED driver circuit may be located on the primary circuit in order to more efficiently monitor line input voltage and current, control the power factor presented to the AC supply, and perform other maintenance functions. However, as a result, programming the microcontroller, or reading data stored in the microcontroller memory, normally requires application of AC power to the primary circuit of the LED driver circuit in order to supply power to the microprocessor. This in turn may require incorporating additional procedures and additional safety measures, in particular when programming the microcontroller or attempting to read data from the microcontroller memory during production, installation, or service operations. For example, access to the primary side of the LED driver with wiring other than the AC line to provide power can be unsafe since the circuit is class  1  rated. Such access would require additional certification and installations guidelines to insure safety. 
         [0005]    It would be advantageous to provide power to a microprocessor of an LED driver circuit without applying AC power to the primary circuit. 
       SUMMARY 
       [0006]    The disclosed embodiments are directed to an LED driver circuit including a primary circuit and a circuit electrically isolated from the primary circuit, a transformer having a primary winding configured to receive power from an alternating current source and to generate power in a first secondary winding configured to provide power to the electrically isolated circuit, and to generate power in a second secondary winding configured to provide power to the primary circuit, and a conductor connected to an end of the first secondary winding and configured to connect a winding driver signal to the first secondary winding to generate power in the second secondary winding. 
         [0007]    The winding driver signal may be generated by a frequency generator. 
         [0008]    The frequency generator may include a timer configured to produce the winding driver signal at a predetermined frequency and duty cycle. 
         [0009]    The predetermined frequency and duty cycle may be determined by characteristics of one or more of the transformer, first and second secondary windings, an electrical load presented by the primary circuit, and an electrical load presented by the electrically isolated circuit. 
         [0010]    The frequency generator may include one or more power drivers for providing the winding driver signal at a specified voltage and current. 
         [0011]    The specified voltage and current may be determined by characteristics of one or more of the transformer, first and second secondary windings, an electrical load presented by the primary circuit, and an electrical load presented by the electrically isolated circuit. 
         [0012]    The frequency generator may be part of the LED driver circuit. 
         [0013]    The frequency generator may be part of a test apparatus configured to be coupled to the LED driver circuit. 
         [0014]    The LED driver circuit may include a communication port configured for exchanging data with a microcontroller of the primary circuit. 
         [0015]    The data may be read from a memory that may be internal or external to the microcontroller. 
         [0016]    The data may be stored in a memory that may be internal or external to the microcontroller. 
         [0017]    The data may include commands to be executed by the microcontroller. 
         [0018]    The disclosed embodiments are further directed to a method of providing power to an LED driver circuit including applying a winding driver signal to a first secondary winding of a transformer to generate power in a second secondary winding of the transformer, the transformer having a primary winding configured to receive power from an alternating current source and to generate power in the first and secondary windings, using power generated in the second secondary winding to provide power to a primary circuit of the LED driver circuit, and using power generated in the first secondary winding by applying the winding driver signal to the first secondary winding to power a circuit electrically isolated from the primary circuit. 
         [0019]    The method may include using a frequency generator to generate the winding driver signal. 
         [0020]    The frequency generator may include one or more of a timer configured to produce the winding driver signal at a predetermined frequency and duty cycle, and one or more power drivers for providing the winding driver signal at a specified voltage and current. 
         [0021]    The method may include determining the predetermined frequency and duty cycle from characteristics of one or more of the transformer, first and second secondary windings, an electrical load presented by the primary circuit, and an electrical load presented by the electrically isolated circuit. 
         [0022]    The method may include determining the specified voltage and current from characteristics of one or more of the transformer, first and second secondary windings, an electrical load presented by the primary circuit, and an electrical load presented by the electrically isolated circuit. 
         [0023]    The method may include exchanging data with a microcontroller of the primary circuit using a communication port of the LED driver circuit. 
         [0024]    Exchanging data with the microcontroller may include reading data from a memory that may be internal or external to the microcontroller. 
         [0025]    Exchanging data with the microcontroller may include storing data in a memory that may be internal or external to the microcontroller. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  shows a block diagram of an exemplary auxiliary bias supply of an LED driver circuit according to the disclosed embodiments; 
           [0027]      FIG. 2  shows a schematic diagram of at least a portion of the auxiliary bias supply; 
           [0028]      FIG. 3  shows a schematic diagram of an embodiment of a microcontroller according to the disclosed embodiments; 
           [0029]      FIG. 4  shows a schematic diagram of an embodiment of control and communication circuitry of the disclosed embodiments; 
           [0030]      FIG. 5  shows an exemplary frequency generator for producing an external power signal; 
           [0031]      FIG. 6  shows an exemplary external communication circuit for exchanging data with a microcontroller of the disclosed embodiments; 
           [0032]      FIG. 7  shows an equivalent circuit used for simulating the performance of the disclosed embodiments; and 
           [0033]      FIG. 8  shows the results produced by the simulated circuit. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    The embodiments of the present disclosure are directed to providing power to components of an LED driver circuit without supplying AC power to the primary circuit of the LED driver circuit. 
         [0035]      FIG. 1  shows a block diagram of an exemplary auxiliary bias supply  100  of an LED driver circuit having a primary circuit  105  and an isolated circuit  110 . The primary circuit  105  may be isolated from the isolated circuit  110  by a transformer  115  and the primary circuit  105  may provide isolated power to the control side using the transformer  115 . The primary circuit may include a switching unit  120  that switches power to a primary winding  125  of the transformer  115 . Secondary windings  130 ,  135  of transformer may provide power to control side auxiliary power circuit  140  and primary side auxiliary power circuit  145 , respectively. Control side auxiliary power circuit  140  may provide power to control and communication circuit  150 . The control and communication circuit  150  may provide a communication port  160  that may include a power signal  165 , a communication bus  170 , a dimming signal  175  and a ground signal  180 . In some implementations the communication bus  170  may be a single wire, bidirectional communication bus. 
         [0036]    Primary side auxiliary power circuit  145  provides power to a microcontroller  155  on the primary circuit  105 . The microcontroller  155  may be coupled to the control and communication circuit  150  by control and communication signals  185 . The control and communication signals  185  may be coupled between the microcontroller  155  and the control and communication circuit  150  using electrical isolators  192 ,  194 ,  196  which may be embodied as, for example, one or more amplifiers, optical couplers, transformers, capacitive couplers, or any other suitable isolation devices. As mentioned above, the control side  110  may be isolated from the primary circuit  105  in accordance with any suitable electrical isolation standard, for example, International Electrotechnical Commission (IEC) Class II. 
         [0037]      FIG. 2  shows a schematic diagram of at least a portion of the auxiliary bias supply  100  in greater detail, in particular, the isolated control power side auxiliary circuit  140  and the primary side auxiliary power circuit  145 . The primary side auxiliary power circuit  145  may convert AC power from secondary winding  135  to various direct current (DC) outputs for the microcontroller  155  and associated support circuitry, for example, a 15 volt output  210 , a 5 volt output  215 , and a regulated 15 volt output  220 . The primary side auxiliary power circuit  145  may also provide a ground signal  225 . 
         [0038]      FIG. 3  shows a schematic diagram of an embodiment of the microcontroller  155  of the primary circuit. The microcontroller  155  may include a microprocessor  310  and a memory  315 . The microprocessor  310  may execute computer readable code stored in the memory  315  to operate and perform the functions of the auxiliary bias supply  100 . The memory may also be used to store characteristics of the auxiliary bias supply  100 , for example, a programmed current output, serial number, date of manufacture, hardware and software revision numbers, test jig information, production test results, customer information, installation information, information related to performance in the field, or any other suitable information. In some exemplary embodiments, the memory  315  may be incorporated in the microprocessor  310 . In other embodiments, the memory  315  may be internal to the microcontroller  155  but may be separate from the microprocessor. In still other embodiments, the memory may be external to the microcontroller  155 . The microprocessor  310  and memory  315  may be supplied with power from the primary side auxiliary power circuit  145 , for example from 5 volt output  215 . A ground signal may be provided by ground signal  225 . As mentioned above, the microcontroller  155  may be coupled to the control and communication circuit  150  by isolated control and communications signals  185 , such as, a receive data signal  320 , a transmit data signal  325 , and a dimming signal  330 . 
         [0039]    Referring again to  FIG. 2 , the control side auxiliary power circuit  140  of the isolated circuit  110  may convert AC power from secondary winding  130  to various DC outputs for the control and communication circuit  150  and associated support circuitry, for example, a 15 volt output  235 , a 5 volt output  245 , and a ground signal  250 . 
         [0040]      FIG. 4  shows a schematic diagram of an embodiment of the control and communication circuit  150  of the isolated circuit  110 . The control and communication circuit  150  may utilize the 15 volt output  235  and ground signal  250  to power communication circuitry  410  for converting between the receive data signal  320  and transmit data signal  325  of the microcontroller  155 , and the communication bus signal  170  of the communication port  160 . The control and communication circuit  150  may utilize the 5 volt output  245  and ground signal  250  to control circuitry  415  for converting between an externally provided dimming signal  175  and the dimming signal  330  of the microcontroller  155 . 
         [0041]    According to the disclosed embodiments, the auxiliary bias supply  100  includes a facility for providing power to components of the LED driver circuit  100  without supplying AC power to the primary circuit  105 . 
         [0042]    Returning to  FIG. 2 , in at least one embodiment, the isolated control side auxiliary power circuit  140  includes a conductor  260  connected to an end of winding  130  for connection to a winding driver signal  255 . A diode  265  may be provided in series with the conductor  260 . By applying an AC or oscillating signal between winding driver signal  255  and ground signal  250 , an AC voltage may be developed across winding  130  resulting in an AC voltage across winding  135 . The primary side auxiliary power circuit  145  may use the voltage developed across winding  135  in this manner to provide the 15 volt output  210 , 5 volt output  215 , and the regulated 15 volt output  220 . Thus, by driving winding driver signal  255  and winding  130  with an oscillating signal, power may be provided to components of the primary circuit  105  of the auxiliary bias supply  100 . Similarly, the control side auxiliary power circuit  140  of the isolated circuit  110  may use the voltage developed across winding  130  to provide the 15 volt output  235  and the 5 volt output  245 . The availability of the various power outputs  210 ,  215 ,  220 ,  235 ,  245  enables offline communication with the auxiliary bias supply  100  without providing an AC supply to the non-isolated primary circuit  105 . 
         [0043]    From at least one viewpoint, the disclosed embodiments provide structures and methods that use a switch mode power supply “backwards” in order to pass power by adding only a very low cost conductor and diode, and without adding additional rectifying circuitry, and without utilizing other power delivery techniques. 
         [0044]    As shown in  FIG. 1 , the winding driver signal  255  may be accessible from outside the auxiliary bias supply  100  through communication port  160 .  FIG. 5  shows an exemplary frequency generator  500  for producing the winding driver signal  255 . The frequency generator  500  may include a timer  505  having an output  510  for producing the winding driver signal  255  at a frequency and duty cycle determined by resistors  515 ,  520 ,  525 , and capacitor  530 . The frequency generator  500  may also include one or more power drivers  545 ,  550  for providing the winding driver signal  255  at a specified voltage and current. In some embodiments, one or more of the frequency, duty cycle, voltage and current may be determined by the characteristics of one or more of the transformer  115 , windings  130 ,  135  and an electrical load presented by one or more of the primary circuit and the electrically isolated circuit. 
         [0045]    When power is provided to the microcontroller  155  according to the disclosed embodiments, communication may be established with the microcontroller  155  in order to program the microcontroller  155 , store data in memory  315 , or read data from memory  315 .  FIG. 6  shows an exemplary external communication circuit  600  for exchanging data with the microcontroller  155 . A conductor  605  of the external communication circuit  600  may be connected to the bus signal  170  of the communication port  160 . Data received from the microcontroller  155  may be extracted from the bus signal  170  using circuit  610  and may be provided by signal  615 . Data to be transmitted to the microcontroller  155  may be provided as signal  620  and may be conditioned for injection onto the bus signal  170  by circuit  625 . The data to be transmitted may include commands to be executed by the microprocessor  310  and data to be stored in memory  315 , while the data received from the microcontroller may include test results, performance statistics, or data retrieved from memory  315 . 
         [0046]    It should be understood that frequency generator  500  and external communication circuit  600  may be incorporated as part of a test fixture for configuring, characterizing, or testing the auxiliary bias supply  100 . 
         [0047]    In some embodiments, the frequency generator  500  may be incorporated as part of the isolated circuit  110  of the auxiliary bias supply  100 . 
         [0048]      FIG. 7  shows an equivalent circuit used for simulating the performance of the disclosed embodiments where simulated circuit  705  represents the frequency generator  500  driving winding  130  and simulated circuit  710  represents a load provided by winding  135  and the circuitry of the primary circuit. 
         [0049]      FIG. 8  shows the results produced by the simulated circuit when sweeping winding driver signal  255  is over a range of periods or frequencies. 
         [0050]    Some of the technical and commercial advantages associated with the features of the disclosed embodiments include, but are not limited to being able to program the auxiliary bias supply  100  without connecting the AC line, as well as safer LED driver circuit current programming at the factory. In addition, the solutions presented herein provide communication with the LED driver circuit without having to connect the AC line. This is useful to retrieve data that was logged within a memory of the microcontroller or to store data in the memory. In addition, the solutions of the present disclosure make it easier for customers, contractors, installers, and others to upload parameters or download firmware updates to the LED driver circuit during installation or servicing. The disclosed embodiments operate to pass power to LED driver circuit components by adding low cost components to the LED driver circuit. Other benefits and advantages over known systems and methods is that the disclosed embodiments do not require additional rectifying circuitry or antenna and rectifying circuitry. 
         [0051]    Various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. However, all such and similar modifications of the teachings of the disclosed embodiments will still fall within the scope of the disclosed embodiments. 
         [0052]    Furthermore, some of the features of the exemplary embodiments could be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles of the disclosed embodiments and not in limitation thereof.