Abstract:
A light emitting diode system allows for high current end user LED matrix applications while mitigating internal damage to control circuitry that may be caused by excess current flow. In one example, multiple switches operate in parallel across an LED. When an overvoltage condition is detected in a first switch, a logic circuit determines those switches programmed to operate in parallel and causes them to conduct current. This reduces the amount of current flowing through any one switch and mitigates harm to the device. The parallel configuration of switches may be driven by a single pulse width modulated current. This allows the drive current to be divided between parallel transistors, limiting the damaging effects that can be caused by high currents flowing through the transistors.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional application No. 62/332,933, filed May 6, 2016, which is incorporated by reference in its entirety herein. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates generally to light emitting diode lighting applications and more specifically to control arrangements for light emitting diode lighting applications. 
       BACKGROUND 
       [0003]    Light emitting diode (LED) lighting solutions are replacing incandescent lighting and other less efficient solutions in a number of areas such as automotive headlamps. LEDs are more energy efficient, convert less energy to heat, and last much longer than incandescent bulbs. However, LED lighting solutions use more individual lighting elements than their incandescent counterparts. 
         [0004]    LED lighting solutions typically arrange LED lighting elements into a matrix. Depending on the application, an LED matrix can be controlled using an integrated circuit that drives individual LED lighting elements. LED control is often achieved by commutating LED current through a parallel/bypass switch, a process commonly known as shunt or parallel switch dimming. Depending upon the required power/lumen output there can be multiple LEDs in series or parallel, fed by a current source or sink. In many cases, to achieve control of individual LEDs, each LED is bypassed by a switch and controlled using standard pulse width modulation (PWM) dimming techniques. When an overvoltage condition exists across a control switch, the control switch is closed to shunt the current that otherwise flowed through the LED. Large amounts of current flowing through the switch, however, can cause damage to and limit the longevity of a control device. 
       SUMMARY 
       [0005]    Generally speaking, pursuant to the following embodiments, light emitting diode systems according to the following description allow for high current end user LED matrix applications while mitigating internal damage to control circuitry that may be caused by excess current flow. In one example, multiple switches operate in parallel across an LED. When an overvoltage condition is detected in a first switch, a logic circuit determines those switches programmed to operate in parallel and causes them to conduct current. This reduces the amount of current flowing through any one switch and mitigates harm to the device. 
         [0006]    In one example, the parallel configuration of switches allows those switches to be driven by a single pulse width modulated current. This allows the drive current to be divided between parallel transistors, limiting the damaging effects that can be caused by high currents flowing through the switches. 
         [0007]    These and other benefits may be clearer upon making a thorough review and study of the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  illustrates a functional block diagram of an example integrated circuit for controlling LEDs as configured in accordance with various embodiments of the invention. 
           [0009]      FIG. 2  illustrates a circuit diagram of an example switch and LED configuration as configured in accordance with various embodiments of the invention. 
           [0010]      FIG. 3  illustrates a circuit diagram of an example paralleled switch configuration across an LED as configured in accordance with various embodiments of the invention. 
           [0011]      FIG. 4  illustrates a circuit diagram of parts of an example control circuit as configured in accordance with various embodiments of the invention. 
           [0012]      FIG. 5  illustrates a circuit diagram of an example approach to individual parallel switch dimming across a single string of LEDs as configured in accordance with various embodiments of the invention. 
           [0013]      FIG. 6  illustrates a circuit diagram of an example approach to individual parallel switch dimming across multiple strings of LEDs as configured in accordance with various embodiments of the invention. 
           [0014]      FIG. 7  illustrates a block diagram of parts of a logic and registers circuit as configured in accordance with various embodiments of the invention. 
           [0015]      FIG. 8  illustrates example logic signals for controlling parallel switches as configured in accordance with various embodiments of the invention. 
           [0016]      FIG. 9  illustrates a flow chart of an example method of operation as configured in accordance with various embodiments of the invention. 
       
    
    
       [0017]    Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted to facilitate a less obstructed view of these various embodiments. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein. 
       DETAILED DESCRIPTION 
       [0018]    Referring now to the figures,  FIG. 1  is a functional block diagram illustrating components of an integrated circuit  100 , in this case, an example apparatus for light emitting diode systems. The integrated circuit has voltage inputs VIN  180 , a 5V input  181 , and a 3.3V input  182 . Inputs  181  and  182  are connected to linear regulators and references circuit  117 , which is connected to ground line  183 . The input  180  is connected to both the charge pumps  115  and the linear regulators and references circuit  117 . The analog to digital converter (ADC)  188  may be driven by an external voltage AREF  184 . Inputs  185  and  186  are general purpose inputs which can be used, for example, for temperature compensation, binning, or coding. These inputs are fed into the AMUX  187 , the output which is fed into the ADC  188 , which provides input to the logic and registers  105 . Additionally, an address pin (not illustrated) of the integrated circuit  100  is connected to the ADC to extend the addressability of the integrated circuit  100  from eight to thirty-one devices. 
         [0019]    Inputs SDA  189  and SCL  190  are I2C data and clock inputs, respectively, for this example implementation. SDA  189  and SCL  190  are connected to the UART to I2C circuit  110 . The UART to I2C circuit  110  receives data corresponding to the desired PWM information for internal switches, for example,  122 ,  124  and  126 . In addition, the UART to I2C circuit  110  can send back fault and other diagnostic data to the host, not illustrated. SYNC input  192  receives a synchronization signal so multiple of the integrated circuits  100  can be synchronized across a network. SYNC functionality can be programmed through a serial interface. Input RX  193  and output TX  194  are used to communicated between networked ones of the integrated circuit  100 . 
         [0020]    In this example, input CLK  195  serves as the primary clock for the integrated circuit  100 . Input XTALI  197  is an input to a Pierce oscillator inverter and can be connected to an external crystal circuit. The output XTALO  196  is an output of a Pierce oscillator invertor and can be connected to an external crystal circuit. The XTAL detect circuit  198  connects the XTALO  196  to the system clock only if there have been at least sixteen rising edges on XTALO  196 . 
         [0021]    The integrated circuit  100  contains a plurality of configurable switch banks, each switch bank having one or more switches configured to electrically connect to at least one light emitting diode to drive the at least one light emitting diode. A switch bank may, for example, comprise three switches; however, a switch bank may contain any number of switches. The integrated circuit  100  may contain any number of switch banks configured as described. In one example, the integrated circuit  100  contains four switch banks each containing three switches. In the illustrated exemplary integrated circuit  100 , switches  122 ,  124 , and  126  form one switch bank  120 , switches  132 ,  134 , and  136  form one switch bank  130 , switches  142 ,  144 , and  146  form one switch bank  140 , and switches  152 ,  154 , and  156  form another switch bank  150 . 
         [0022]      FIG. 2  illustrates exemplary individual switch banks  120 ,  130 ,  140 , and  150 . As illustrated, each switch bank may contain three series switches. For example, switch bank  120  contains switches  122 ,  124 , and  126 . The switch banks  120 ,  130 ,  140 , and  150  may be arranged in other ways, for example, as a series combination of twelve switches; a parallel combination of two, three, or four banks of three switches each; or four individual ground referenced three-switch banks. The switch banks  120 ,  130 ,  140 , and  150  can be configured in any other intermediate series-parallel switch combination. For instance,  FIG. 3  illustrates an exemplary series of LEDs, each LED having two switches arranged in parallel across an LED. In this example arrangement, the switches  122 ,  124 , and  126  of switch bank  120  have bank placed in parallel with the switch  132 ,  134 , and  136  of switch bank  130  respectively. 
         [0023]    Referring again to  FIG. 1 , the integrated circuit  100  further contains a control circuit  101  configured to selectively control at least a first switch  122  of a first switch bank  120  and at least a first switch  132  of a second switch bank  130 , in parallel. Control circuit  101  receives input from the UART to I2C circuit  110  and drives the switches of the integrated circuit  100  accordingly. The switches may be controlled, for example, by standard pulse width modulation dimming techniques. The control circuit  101  is configured to detect a voltage condition of one of the first switch  122  of the first bank  120  or the first switch  132  of the second bank  130 . In one example, illustrated in  FIG. 3 , a first switch  122  of a first switch bank  120  may be arranged in parallel with a first switch  132  of a second switch bank  130  by programming the logic and registers  105 . So arranged, the control circuit  101  is configured to cause the first switch of the second switch bank,  132 , to conduct current based at least in part on the voltage condition in the first switch of the first switch bank,  122 . For example, when the voltage condition in switch  122  is detected to be outside some threshold, the control circuit  101  will cause the switch  132  to conduct current. In a more specific example, the control circuit  101  is configured to cause the first switch of the second switch bank,  132 , to conduct current in response detecting that the voltage condition is above a threshold voltage for the first switch of the first switch bank  122 . 
         [0024]    In one example, the control circuit  101  is configured to determine when the first switch bank  120  and the second switch bank  130  are configured to be controlled in parallel and, in response, apply a driving signal synchronously to both the first switch bank  120  and the second switch bank  130 . For example,  FIG. 5  illustrates a single pulse width modulated signal being applied to a single series of a LEDs. A similar signal may be applied to multiple series strings of LEDs as illustrated in  FIG. 6 . In high power applications, it is advantageous to place multiple banks of switches in parallel with a single series string of LEDs as illustrated in  FIG. 3 . In the arrangement of  FIG. 3 , the control circuit  101  will recognize that the switch banks,  120  and  130 , are programmed to operate in parallel and drive the switch banks with the same pulse width modulated signal. Such an arrangement is advantageous because the drive current does not need to flow through a single switch. 
         [0025]    The control circuit  101  includes a plurality of driver circuits  400 - 411  and a register, wherein individual ones of the plurality of driver circuits are connected to drive individual ones of the first switch bank&#39;s  120  one or more switches  122 ,  124 , and  126  and the second switch bank&#39;s  130  one or more switches  132 ,  134 , and  136 . In one example, the driver circuits  400 - 411  communicate with the logic and registers  105  via level shifters  300 - 311 . In the exemplary illustration of  FIG. 4  the driver  400  is coupled to level shifters  330  and  370 . The driver circuits  400 - 411  are substantially similar, and for ease of description the drivers  400 - 411  will be described by example in view of the driver circuit  400  as illustrated in  FIG. 4 . As illustrated in  FIG. 7  the register may be, for example, a fault register  701  and be contained within the logic and registers  105 . The fault register  701  stores the fault status of LEDs arranged in parallel with the switches of the integrated circuit  100 . As can be seen from  FIG. 4 , the driver circuit  400  has the internal ability to cause its own switch  122  to conduct current when the driver circuit detects an overvoltage condition without needing to signal the logic circuit in the logic and registers  105 . To further protect the switch  122  from damage, the driver  400  employs switch  405 . For example, in response to the comparator&#39;s  440  detecting an overvoltage condition, the switch  405  will drive the gate of switch  122  HIGH via the inverter  425  in approximately 50-100 nano-seconds whereas it takes approximately 20 micro-seconds for the gate driver to respond. The driver  400  communicates the fault status of an LED corresponding to a switch  122  to logic and registers  105  via latch  420  where it is received by the fault register  701 . The OR gate  415  takes input from the latch  420  and the gate driver level shift circuit  330 . If the input from either latch  420  or level shift circuit  330  is logic HIGH, the OR logic will cause the gate driver  410  to power the gate of the switch  122  causing it to conduct current and bypassing the corresponding LED. Input from the gate driver level shift circuit  330  can cause the latch  420  to reset. 
         [0026]    As illustrated in  FIG. 4 , individual ones of the plurality of driver circuits  400  include an overvoltage detection circuit  440  configured to compare a voltage  445  across a switch  122  to an overvoltage threshold voltage  450  and, in response to detecting that the voltage  445  across the switch  122  exceeds the overvoltage threshold voltage  450 , sending a fault detection signal to the fault register  701 . In this approach, the driver circuit  300  also includes a short condition detection circuit  435  configured to compare the voltage  445  across the switch  122  to a short circuit condition voltage  455  threshold and, in response to detecting that the voltage  445  across the switch  122  is below the short circuit condition voltage  455 , send a fault detection signal to the register. For example, an internal comparator  440  monitors the drain-to-source voltage of the internal switch  122 . If the voltage exceeds a threshold, for instance in the event of an open LED failure or overvoltage condition, the device overrides the switch-off signal and turns on the switch  122  thereby maintaining current flow to the rest of the LED string in the presence of a faulty or damaged LED and protects the switch  122 . The driver circuit  400  causes the corresponding bit of the fault register  701  in the logic and registers  105  to be set. In a similar example, the driver circuit  400  can detect an LED open detection or under voltage condition of an LED by monitoring the drain-to-source voltage  445  of the internal switch  122 . In another example, the voltage condition indicates one of an effectively open circuit condition or an effectively short circuit condition for the one or more light emitting diodes. The driver circuit  400  then causes the logic and registers  105  to set the fault register and send signals to close the switches that are arranged in parallel based on the effectively short circuit condition or the effectively open circuit condition. The logic and registers  105  contain an over voltage limit register. The overvoltage limit register  460  can be set via the UART to I2C circuit  110  to control the effectively open voltage condition. The effectively open voltage condition is a voltage greater than the voltage set in the overvoltage limit register  460 . The effectively short voltage is any voltage less than the ref short voltage  455 . 
         [0027]    In one example, the control circuit  101  further comprises a parallel configuration register  703  configured, at least in part, to specify an association between individual ones of the first switch bank&#39;s  120  one or more switches  122 ,  124 , and  126  and the second switch bank&#39;s  130  one or more switches  132 ,  134 , and  136 . The parallel configuration register  703  is contained in the logic and registers  105  and may be programmed to configure the available switch banks as a series combination of switches; a parallel combination switches; or individual ground referenced three-switch banks. The switch banks can be configured in any other intermediate series-parallel switch combination. The parallel configuration register of integrated circuit  100  is to programmed to set the applied paralleling configuration and is contained in the logic and registers  105 . The parallel configuration register may be set, for example, by an external MCU communicating with the logic and registers  105  through UART to I2C circuit  110 . 
         [0028]    As illustrated in  FIG. 7 , the logic and registers  105  of the control circuit  101  includes a logic circuit  702 , the logic circuit operable to control individual ones of the first switch bank&#39;s  120  one or more switches  122 ,  124 , and  126  based at least in part on the voltage condition of the second switch bank&#39;s  130  one or more switches  132 ,  134 , and  136  and the association between individual ones of the first switch bank&#39;s  120  one or more switches  122 ,  124 , and  126  and the second switch bank&#39;s  130  one or more switches  132 ,  134 ,  136 . The logic circuit  702  may be coupled a fault register  701 . The fault register  701  configured to store a fault status of one or more light emitting diodes arranged electrically in parallel with one or more of the plurality of switches of the integrated circuit  100 . The logic circuit  702  may be coupled to, for example, the parallel configuration register  703 , the fault register  702 , and each driver circuit  400 - 411 . In one example, upon receiving a fault status signal from the driver  400 , the logic circuit  702  determines which switches are programmed to operate in parallel with the switch for which the driver  400  reported a fault status based on the content of the parallel configuration register  703  and causes those switches to close by signaling their respective driver  400 . In another example, after a driver circuit  400  communicates a fault status corresponding to an LED arranged in parallel with a switch  122 , to the fault register  701 , the fault register  701  and the parallel configuration register  703  will be polled. If other switches are programmed to operate in parallel with the switch  122  for which the driver  400  communicated a fault status signal to the logic circuit  702 , the logic circuit  702  will cause those switches programmed to operate in parallel with switch  122  to close (i.e., conduct current). 
         [0029]      FIG. 8  is a logic signal diagram. Signals ov[m]  803  and fault[m]  804  are output from the driver circuit  400  through sync &amp; level shift to fault register circuit  370  to the logic and registers  105  and are synchronized to the system clock. The signals ov[m]  803  and fault[m]  804  separately, together, or in combination may be considered a fault status signal. The sys_c signal  805  represents the frequency of the system clock. The arrow  811  represents the point in time in which the logic and registers  105  can read the signals from the driver  400  and cause switches programmed to operate in parallel to be closed. There is a delay of a number of clock cycles between when the driver  400  detects an overvoltage condition and when the logic and registers  105  can close the switches  122  programmed to be in parallel. The actual gate drive[m]  801  and actual gate drive[n]  809  signals illustrate this delay. The delay is much shorter in the driver  400  that detected the overvoltage condition because the driver  400  internally closed its own switch in response to detecting the overvoltage condition. The signal gate drv[m]  802  and the signal gate drv[n]  810  are inputs to the driver  400 . In the case of an overvoltage or under voltage condition being detected in a first switch  122 , the logic and registers  105  will determine the switches of the integrates circuit  100  programmed to be in parallel with the first switch and cause those switches to close by transmitting a gate drv[n] signal  810  to a gate driver level shift block  330  of a driver  400 . Once received, the signal will cause the OR gate  415  to transmit logic HIGH to the gate driver and close the switch. 
         [0030]    The fault[m]  804  signal is synchronized to the system clock and represented by s_fault[m]  807 . The logic and registers  105  uses the signal s_fault[m]  807  to determine an under voltage condition. For example, the logic and registers  105  will close the switch of the driver  400  and any other driver  400  that were programmed to be in parallel when an under voltage condition is determined. 
         [0031]    The output signal from the comparator  435  may be combined using OR logic at sync and level shift to fault register circuit  370  with an output of the latch  420 . In such a case the logic and registers  105  will not be able to distinguish whether an under voltage condition or an over voltage condition has occurred; however, if one of those conditions did occur, the logic and registers will determine which switches to close based on the contents of the parallel configuration register  703 . 
         [0032]    As illustrated in  FIG. 8  by arrow  812  the synchronized fault inputs are latched into the FAULT registers on the falling edge of the requested LED ON time to allow the controller to poll which LEDs had an open or short fault at the end of the LED ON pulse. The s_fault[m] signal  807  is sampled a number of clock cycles prior to the falling edge of the requested LED PWM[m] signal  800 , and bits in the fault register  701  in the logic and circuits  105  corresponding to the switch  122  corresponding to the s_fault[m]  807  signal are set in response to the s_fault_lat[m] signal  808 . 
         [0033]      FIG. 9  is a flow chart illustrating an example operation of an integrated circuit device controlling programmed parallel switches as described above. At step  900  the integrated circuit is programmed by an external device to create a series/parallel relationship between switches of the switch banks  120 ,  130 ,  140 , and  150 . For example, the integrated circuit  100  may associate a first configurable switch bank  120  and a second configurable switch bank  130  by programming the first configurable switch bank  120  to operate in parallel to the second configurable switch bank  130 . The association may be in response to input from an external MCU. At step  901 , the control circuit  101  determines which switches are programmed to be in parallel by using a parallel configuration register  703  in the logic and registers  105 . For example, the integrated circuit  100  may determine whether individual ones of the switches of the first configurable switch bank  120  and the second configurable switch bank  130  are programmed to operate in parallel based on the association. 
         [0034]    Optionally, at step  902  the integrated circuit  100  can drive switch banks arranged in parallel with a synchronous pulse width modulated signal. For example, the integrated circuit  100  may perform the step of applying a driving signal synchronously to both the first configurable switch bank  120  and the second configurable switch bank  130  when the first configurable switch bank  120  and the second configurable switch bank  130  are configured to operate in parallel. 
         [0035]    At step  903  the control circuit  101  controls, for example, a switch  132  because it is programmed to be parallel to switch  122 . The control circuit  101  may cause switch  132  to conduct current because of a voltage condition detected in the switch  122 . For example, the integrated circuit  100  may control the individual ones of the switches of the second switch bank  130  based on voltage conditions in individual ones of the switches in the first configurable switch bank  120  and the association between individual ones of the first switch bank&#39;s  120  one or more switches  122 ,  124 , and  126  and the second switch bank&#39;s  130  one or more switches  132 ,  134 , and  136 . The voltage condition may be, for example, an effectively open circuit condition or an effectively short circuit condition. For example, the integrated circuit  100  may cause a first switch of the second switch bank to conduct current based on the voltage condition in a first switch of the first switch bank when the voltage condition is one of an effectively open circuit condition or an effectively short circuit condition. 
         [0036]    Optionally, at step  904  the control circuit  101  stores a fault status of one more LEDs corresponding to the switches of the integrated circuit  100 . For example, the integrated circuit  100  stores a fault status of one or more light emitting diodes arranged in parallel with one or more of the plurality of switches of the first and the second configurable switch banks,  120  and  130 . In response to the driver circuit&#39;s  400  detecting an overvoltage or under voltage condition of a corresponding switch  122 , the driver circuit  400  communicates a fault status to the logic and registers  105 . For example, the integrated circuit  100  stores a fault status of one or more light emitting diodes arranged in parallel with one or more of the plurality of switches of the first and the second configurable switch banks,  120  and  130 . The logic and registers  105  uses the parallel configuration register  703  to determine those switches programmed to be in parallel with the switch  122  whose driver  300  reported a fault and causes those switches to conduct current. 
         [0037]    Certain terms are used throughout the description and the claims to refer to particular system components. As one skilled in the art will appreciate, components in digital systems may be referred to by different names and/or may be combined in ways not shown herein without departing from the described functionality. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” and derivatives thereof are intended to mean an indirect, direct, optical, and/or wireless electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, through an indirect electrical connection via other devices and connections, through an optical electrical connection, and/or through a wireless electrical connection. 
         [0038]    Although method steps may be presented and described herein in a sequential fashion, one or more of the steps shown and described may be omitted, repeated, performed concurrently, and/or performed in a different order than the order shown in the figures and/or described herein. Those skilled in the art will recognize that a wide variety of modifications, alterations, and combinations can be made with respect to the above described examples without departing from the scope of the invention, and that such modifications, alterations, and combinations are to be viewed as being within the ambit of the inventive concept.