Controller for controlling light source module

Abstract

To provide a controller for controlling a light source module.SOLUTION: A controller for controlling a light source module including a first LED string and a second LED string includes: a power input terminal operable for receiving electric power from a boost converter; a power output terminal operable for providing electric power to the light source module through a buck converter; a first input terminal operable for receiving a first pulse width modulation (PWM) signal; a second input terminal operable for receiving a second PWM signal; and a width monitoring terminal operable for receiving a width monitoring signal indicating a duration of a first state of the first PWM signal and a duration of a first state of the second PWM signal. The controller is operable for turning off the light source module if the width monitoring signal is greater than a width threshold signal.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present application relates to a controller for controlling a light source module. [Background technology]

[0002] A driver monitoring system (DMS) is a vehicle safety system that measures driver alertness to help prevent accidents on the road. The DMS uses a camera installed in the vehicle's cabin to check for signs of inattentive or intoxicated driving behavior by the driver and issues a warning if it detects a problem. To help the camera produce better images, a light source module can be used for illumination. The light source module can include one or more infrared light emitting diode (IR LED) strings. Traditionally, each LED string is controlled by one controller. To control two LED strings, two controllers are needed, which increases costs. In operation, the current of the light source module needs to be adjusted within a suitable range to generate sufficient illumination without being harmful to the human eye. In the traditional method, the current of the light source module is adjusted by changing the resistance of one or more resistors. This traditional method requires the use of resistors with significant resistance values ​​or the use of multiple shunt resistors to achieve the desired current magnitude, which limits flexibility and increases costs. For a conventional controller, when adjusting the current of the light source module, the rapidly changing current will cause electromagnetic interference (EMI) that may cause other electronic devices in the vehicle to malfunction. In addition, to ensure the safe operation of the system, any potential short-circuit condition of the light source module needs to be monitored, large inrush current at the power terminals of the controller needs to be prevented, and the power consumption of the light source module and the controller needs to be monitored and controlled. Summary of the Invention [Means for solving the problem]

[0003] In an embodiment, a controller operable to control a light source module including a first light emitting diode (LED) array and a second LED array includes a power input terminal operable to receive power from a step-up converter, a power output terminal operable to provide power to the light source module through a step-down converter, a first input terminal operable to receive a first pulse width modulation (PWM) signal, a second input terminal operable to receive a second PWM signal, and a width monitor terminal operable to receive a width monitor signal indicative of a duration of a first state of the first PWM signal and a duration of a first state of the second PWM signal. The first PWM signal is operable to control a first switch coupled in series with the first LED string. The first switch is on if the first PWM signal is in a first state and is off if the first PWM signal is in a second state. The second PWM signal is operable to control a second switch coupled in series with the second LED string. The second switch is on when the second PWM signal is in a first state and is off when the second PWM signal is in a second state. The controller is operable to turn off the light source module when the width monitor signal is greater than the width threshold signal.

[0004] In another embodiment, a controller for controlling a light source module comprising a first LED string and a second LED string includes a boost control unit operable to control a boost converter, a buck control unit operable to control a buck converter, and a brightness limiting unit operable to receive a first PWM signal and a second PWM signal. The first PWM signal is operable to control a first switch coupled in series with the first LED string. The first switch is on if the first PWM signal is in a first state and is off if the first PWM signal is in a second state. The second PWM signal is operable to control a second switch coupled in series with the second LED string. The second switch is on if the second PWM signal is in a first state and is off if the second PWM signal is in a second state. The brightness limiting unit is operable to turn off the light source module if a width monitor signal indicative of a duration of the first state of the first PWM signal and a duration of the first state of the second PWM signal is greater than a width threshold signal indicative of a width threshold.

[0005] Features and advantages of embodiments of the claimed subject matter will become apparent as the following detailed description proceeds and upon reference to the drawings, in which like numerals represent like parts and in which: [Brief description of the drawings]

[0006] [Figure 1] 1 illustrates a light source driving circuit for controlling a light source module according to an embodiment of the present invention. [Diagram 2] 4 illustrates signal waveforms associated with a light source driving circuit according to an embodiment of the present invention. [Diagram 3] 2 shows a block diagram of a controller for controlling a light source module according to an embodiment of the present invention. [Figure 4] 1 shows a circuit diagram of a brightness limiting unit in a controller for controlling a light source driving circuit according to an embodiment of the present invention. [Diagram 5]4 shows a circuit diagram of a protection unit in a controller for controlling a light source driving circuit according to an embodiment of the present invention; [Figure 6A] 1 shows a circuit diagram of a dimming unit in a controller for controlling a light source module according to an embodiment of the present invention. [Figure 6B] 1 shows a circuit diagram of a dimming unit in a controller for controlling a light source module according to an embodiment of the present invention. [Figure 7] 1 shows a circuit diagram of a soft start unit in a controller for controlling a light source module according to an embodiment of the present invention. [Figure 8] 4 shows a circuit diagram of an inrush current control unit in a controller for controlling a light source module according to an embodiment of the present invention. [Figure 9] 1 illustrates a light source driving circuit for controlling a light source module according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Reference will now be made in detail to the embodiments of the invention. While the invention will be described in conjunction with these embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications, and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims.

[0008] Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be recognized by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention.

[0009] 1 illustrates a light source driving circuit 100 for controlling a light source module according to an embodiment of the present invention. The light source driving circuit 100 includes a controller 180.

[0010] 1, the light source module includes two LED strings 101 and 102, each of which includes multiple (e.g., two) LEDs. In one embodiment, the LEDs in LED strings 101 and 102 are infrared LEDs. This example is used as a reference for the following discussion, however, the invention is not limited to two LED strings and / or two LEDs per string.

[0011] The controller 180 includes a power input terminal VBUCKIN, a power output terminal LX, a first input terminal, and a second input terminal. The power input terminal VBUCKIN is operable to receive power from a boost converter. The output terminal LX is coupled to the light source module and operable to provide power to the light source module through a buck converter. In the example of FIG. 1, the boost converter includes an inductor L1, a diode D1, an output capacitor CO1, and a transistor 301 (illustrated in FIG. 3). The buck converter includes an inductor L2, an output capacitor CO2, and transistors 302 and 303 (illustrated in FIG. 3). The first input terminal DPWMA is operable to receive a first pulse width modulated (PWM) signal PWMA. The second input terminal DPWMB is operable to receive a second PWM signal PWMB. In one embodiment, the first and second PWM signals PWMA and PWMB are provided by an electronic control unit (ECU) of the vehicle. The first PWM signal PWMA is operable to control a first switch Q1 coupled in series with the first LED string 101. The first switch Q1 is on when PWMA is in a first state (e.g., logic high) and off when PWMA is in a second state (e.g., logic low). The second PWM signal PWMB is operable to control a second switch Q2 coupled in series with the second LED string 102. The second switch Q2 is on when PWMB is in a first state (e.g., logic high) and off when PWMB is in a second state (e.g., logic low). PWMA and PWMB are configured such that the first switch Q1 and the second switch Q2 are not on at the same time. As illustrated in FIG. 2, during a time period Tona, PWMA is in a first state and switch Q1 is on. During a time period Tonb, PWMB is in a first state and switch Q2 is on. With such a configuration, the time periods when switch Q1 is on (Tona) and the time periods when switch Q2 is on (Tonb) do not overlap. In one embodiment, PWMA and PWMB have the same duty cycle and different phases.In other words, in such an embodiment, Tona is equal to Tonb, and the PWMB waveform is a time delayed version of the PWMA waveform.

[0012] The controller 180 further includes a width monitoring terminal DPWMLIM, a current sensing terminal ISEN, a first voltage sensing terminal VS, a second voltage sensing terminal VSEN_BK, a dimming terminal APWM, a soft-start terminal SST_BK, a power terminal PFETOUT, a third voltage sensing terminal FB_BST, sensing terminals ISP and ISN, and a reference voltage terminal VREF.

[0013] The width monitor terminal DPWMLIM is operable to receive a width monitor signal WID indicative of a duration Tona of a first state of the first PWM signal PWMA and a duration Tonb of a first state of the second PWM signal PWMB. The controller 180 is operable to turn off the light source module if the width monitor signal WID is greater than a width threshold signal. The width monitor terminal DPWMLIM is coupled to a capacitor CP.

[0014] The current sense terminal ISEN is coupled to a sense resistor IRSEN. The sense resistor IRSEN is coupled to the cathode of the first LED string 101 through a switch Q1 and to the cathode of the second LED string 102 through a switch Q2. The sense terminal ISEN is operable to receive a current sense signal ISEN1 from the sense resistor IRSEN. The current sense signal ISEN1 is a voltage across the sense resistor IRSEN and can indicate the magnitude (level) of the current of the first LED string 101 and the magnitude of the current of the second LED string 102. If the switch Q1 is on, the current of the first LED string 101 flows from the buck converter through the first LED string 101, the switch Q1 and the sense resistor IRSEN to ground. If the switch Q2 is on, the current of the second LED string 102 flows from the buck converter through the second LED string 102, the switch Q2 and the sense resistor IRSEN to ground. Advantageously, the controller 180 is operable to sense the magnitude of the current in both LED strings 101 and 102 through a single current sensing terminal ISEN, and to adjust the current accordingly. Compared with conventional controllers that can only monitor and control one LED string, the controller 180 according to the present invention can monitor and control multiple (e.g., two) LED strings. These LED strings can be placed at different positions in the vehicle cabin to provide illumination from different angles, so that the driver condition can be better monitored by the driver monitoring system.

[0015] The first voltage sense terminal VS is coupled to the anode of the light source module (e.g., the anodes of the first and second LED strings 101 and 102) through a voltage divider 103 and is operable to receive a first voltage sense signal VS1 indicative of a level of the voltage at the anode of the light source module. The current sense signal ISEN1 can further indicate a level of the voltage at the cathode of the light source module. The second voltage sense terminal VSEN_BK is coupled to the anode of the light source module and is operable to receive a second voltage sense signal VSBK1 indicative of a level of a voltage drop across the light source module. The controller 180 is operable to detect a short circuit condition based on the first voltage sense signal VS1, the second voltage sense signal VSBK1 and the current sense signal ISEN1, which will be further described in conjunction with FIG. 5.

[0016] The dimming terminal APWM is operable to receive a third PWM signal APWM1. The controller 180 is operable to generate an analog signal ADJ based on a duty cycle of the third PWM signal APWM1, and to adjust the current of the first LED string 101 and the current of the second LED string 102 by comparing the analog signal ADJ with the current sense signal ISEN1. As illustrated in FIG. 3, the controller 180 includes an amplifier 307 for comparing the analog signal ADJ with the current sense signal ISEN1 to generate an error signal EA1. A step-down control unit 320 is operable to control the step-down converter to adjust the current of the first LED string 101 and the current of the second LED string 102 according to the level of the error signal EA1.

[0017] Referring again to FIG. 1, the soft-start terminal SST_BK is coupled to the capacitor CS and is operable to generate a soft-start signal SST1 by charging and discharging the capacitor CS. The controller 180 is operable to adjust the current of the first LED string 101 based on the voltage of the soft-start signal SST1 if the voltage of the soft-start signal SST1 is less than the error signal EA1 when the switch Q1 is turned on. The controller 180 is operable to adjust the current of the first LED string 101 based on the voltage of the soft-start signal SST1 when the switch Q1 is turned off.

[0018] The power terminal PFETOUT is coupled to an output capacitor CO1 of the boost converter and is operable to provide a current for charging the output capacitor CO1, the charging current being regulated according to the voltage at the power input terminal VBUCKIN.

[0019] The third voltage sensing terminal FB_BST is coupled to the output terminal of the boost converter through a voltage divider 104 and is operable to sense the level of the output voltage VBSO of the boost converter. Specifically, the third voltage sensing terminal FB_BST receives a voltage sensing signal BST1 indicative of the level of the output voltage VBSO. The sensing terminals ISP and ISN are coupled to two ends of a sensing resistor RS and are operable to sense an input current IPWR provided by the power source 150 and received by the controller 180 through a power terminal VIN. The sensing resistor RS is coupled between the power source 150 and the controller 180. The controller 180 is operable to control the boost converter to regulate the output voltage VBSO to be less than a voltage threshold and to control the boost converter to regulate the input current IPWR to be less than a current threshold. Alternatively, in another embodiment as illustrated in FIG. 9, the sensing resistor RS is coupled between the diode D1 of the boost converter and the output capacitor CO1 of the boost converter. The sense terminals ISP and ISN are coupled to two ends of a sense resistor RS and are operable to sense the magnitude of the output current IBSO of the boost converter. The controller 180 is operable to control the boost converter to regulate the output voltage VBSO to be less than a voltage threshold, and to control the boost converter to regulate the output current IBSO to be less than a current threshold.

[0020] FIG. 3 shows a block diagram of a controller 180 for controlling a light source module (e.g., LED strings 101 and 102 in FIG. 1) according to an embodiment of the present invention. The controller 180 includes a boost control unit 310, a buck control unit 320, a brightness limiting unit 330, a protection unit 340, a dimming unit 350, a soft start unit 360, an inrush current control unit 370, and a power limiting unit 380. The boost control unit 310 is operable to control the boost converter by controlling the transistor 301. The buck control unit 320 is operable to control the buck converter by controlling the transistors 302 and 303. More specifically, the boost control unit 310 is operable to adjust the output current IBSO and the output voltage VBSO of the boost converter by adjusting the duty cycle of the transistor 301. The buck control unit 320 is operable to adjust the output current and the output voltage of the buck converter by controlling the duty cycle of the transistors 302 and 303.

[0021] 4 shows a circuit diagram of the brightness limiting unit 330 according to an embodiment of the present invention. The brightness limiting unit 330 includes a NOR gate 401, a switch 402, a comparator 403 and a flip-flop 404. The NOR gate 401 receives PWMA and PWMB and provides an output signal to control the switch 402. The switch 402 is coupled in parallel with the capacitor CP. If either PWMA or PWMB is in a first state (e.g., logic high), the switch 402 is turned off and the capacitor CP is charged by a current provided by the reference voltage terminal VREF. If neither PWMA nor PWMB is in a second state (e.g., logic low), the switch 402 is turned on and the capacitor CP is discharged. The voltage across the capacitor CP is a width monitor signal WID, which indicates the duration Tona of the first state of the first PWM signal PWMA and the duration Tonb of the first state of the second PWM signal PWMB. The comparator 403 compares the width monitor signal WID with a width threshold signal VTH_WID indicative of a width (duration) threshold, and outputs the comparison result to the flip-flop 404. The flip-flop 404 is operable to generate a warning signal based on the output of the comparator 403. If the width monitor signal WID is greater than the width threshold signal VTH_WID, the flip-flop 404 outputs a warning signal PWM_LIM having a first state (e.g., logic high), and the controller 180 is operable to turn off the light source module accordingly. Since both PWMA and PWMB are used to control the switches Q1 and Q2, the overall brightness of the light source module is proportional to the durations Tona and Tonb. Advantageously, the brightness of the light source module can be limited within a range that would not be harmful to human eyes.

[0022] FIG. 5 shows a circuit diagram of a protection unit 340 according to an embodiment of the present invention. The protection unit 340 is operable to detect a short-circuit condition of a light source module (e.g., LED strings 101 and 102 in FIG. 1) based on a first voltage sensing signal VS1, a second voltage sensing signal VSBK1 and a current sensing signal ISEN1. The first voltage sensing signal VS1 indicates the level of the voltage at the anode of the light source module, the second voltage sensing signal VSBK1 indicates the level of the voltage drop across the light source module, and the current sensing signal ISEN1 further indicates the level of the voltage at the cathode of the light source module. The protection unit 340 includes a differential unit 501, a first comparator COMP1, a second comparator COMP2, a third comparator COMP3, an OR gate 502, an AND gate 503 and a timing unit 504. The differential unit 501 is operable to generate a differential signal DIF indicating a difference between the first voltage sensing signal VS1 and the current sensing signal ISEN1. The first comparator COMP1 is operable to compare the differential signal DIF to a first protection threshold VTH1. The second comparator COMP2 is operable to compare the current sense signal ISEN1 to a second protection threshold VTH2. The third comparator COMP3 is operable to compare the second voltage sense signal VSBK1 to a third protection threshold VTH3. The OR gate 502 is operable to OR an output of the first comparator COMP1 and an output of the third comparator COMP3. The AND gate 503 is operable to AND an output of the OR gate 502 and an output of the second comparator COMP2. The timing unit 504 is operable to generate a warning signal LEDSHORT based on the output of the AND gate 503, the first PWM signal PWMA, the second PWM signal PWMB, and a predetermined time duration TP. In operation, the protection unit 340 monitors whether the current sense signal ISEN1 is greater than the second protection threshold VTH2. If the current sensing signal ISEN1 is greater than the second protection threshold VTH2, the protection unit 340 further detects whether the differential signal DIF is less than the first protection threshold VTH1 or whether the second voltage sensing signal VSBK1 is less than the third protection threshold VTH3.If the differential signal DIF is less than the first protection threshold VTH1 or the second voltage sense signal VSBK1 is less than the third protection threshold VTH3, the protection unit 340 monitors the duration of such condition using the timing unit 504. If the time duration of such condition is greater than a predetermined time duration TP, the timing unit 504 generates a warning signal LEDSHORT indicating that a short circuit condition has occurred, and the controller 180 is operable to turn off the light source module accordingly.

[0023] FIG. 6A shows a circuit diagram of a dimming unit 350 according to an embodiment of the present invention. The dimming unit 350 includes a capacitor C1 for generating an analog signal ADJ based on a duty cycle of a third PWM signal APWM1. The capacitor C1 is charged when APWM1 is in a first state, and discharged when APWM1 is in a second state. More specifically, an inverter 602 generates an inverted PWM signal APWM2 based on the third PWM signal APWM1. The third PWM signal APWM1 controls a switch SW1 coupled between a current source 601 and the capacitor C1. The inverted PWM signal APWM2 controls a switch SW2 coupled in parallel with the capacitor C1. When APWM1 is in a first state (e.g., logic high), the switch SW1 is on, the switch SW2 is off, and the capacitor C1 is charged by a current from the current source 601. When APWM1 is in a second state (e.g., logic low), switch SW2 is on, switch SW1 is off, and capacitor C1 is discharged. The voltage across capacitor C1 is an analog signal ADJ, and the level of the analog signal ADJ is proportional to the duty cycle of the third PWM signal APWM1. The controller 180 is operable to adjust the current of the first LED string 101 and the current of the second LED string 102 by comparing the analog signal ADJ with the current sense signal ISEN1.

[0024] As shown in Fig. 3, the controller 180 includes an amplifier 307 for comparing the analog signal ADJ with the current sense signal ISEN1 to generate an error signal EA1. The error signal EA1 is sent to the step-down control unit 320 through a multiplexer 390. The step-down control unit 320 is operable to adjust the current of the first LED string 101 and the current of the second LED string 102 by controlling the duty cycle of the transistors 302 and 303 based on the voltage of the error signal EA1. Advantageously, the resistance of the sense resistor IRSEN coupled to the current sense terminal ISEN can be fixed or selected among several standard resistance values ​​to reduce manufacturing costs, while the brightness of the light source module can be adjusted by the third PWM signal APWM1.

[0025] FIG. 6B illustrates another embodiment of a circuit diagram of the dimming unit 350. In this embodiment, the controller 180 further includes a current setting terminal ISET (shown in FIG. 1) for receiving the setting signal ISET1. The setting signal ISET1 is generated by a voltage divider 603 based on the voltage of a reference voltage signal VREF1 provided by a reference voltage terminal VREF. The dimming unit 350 includes an amplifier 604 for generating a charging current for the capacitor C1 based on the voltage of the setting signal ISET1. Therefore, the analog signal ADJ can be further adjusted by changing the resistance ratio of the voltage divider 603. The brightness of the light source module can be further adjusted by configuring the voltage divider 603 accordingly. Advantageously, the controller 180 according to the present invention can meet different application requirements (e.g., light source modules with different types or numbers of LEDs).

[0026] FIG. 7 illustrates a circuit diagram of a soft start unit 360 according to an embodiment of the present invention. The soft start unit 360 is operable to generate a soft start signal SST1 by charging and discharging a second capacitor CS, where the soft start signal SST1 is a voltage across the second capacitor CS. The soft start unit 360 includes a discharge unit 702, a comparator COMP4, a flip-flop 706, and an OR gate 703. The discharge unit 702 is operable to generate a discharge control signal DSC based on a first PWM signal PWMA and a second PWM signal PWMB. In one embodiment, the discharge unit 702 includes an OR gate 704 for generating a signal PWMAB by performing an OR operation on PWMA and PWMB, and an inverter 705 for generating a discharge control signal DSC based on the signal PWMAB. The discharge control signal DSC is operable to turn on a switch 714 coupled in parallel with the capacitor CS to discharge the capacitor CS. The comparator COMP4 is operable to compare an error signal EA1 with the soft start signal SST1. Flip-flop 706 receives the output of comparator COMP4 at its R terminal and generates a charge control signal CHG based on the output of comparator COMP4 at its Q terminal. The charge control signal CHG is operable to turn on a switch 713 coupled between capacitor CS and a power supply 701 to charge capacitor CS. In one embodiment, power supply 701 is provided by a reference voltage terminal VREF (FIGS. 1, 4 and 6B). OR gate 703 is operable to generate a select signal SEL based on the charge control signal CHG and the discharge control signal DSC.

[0027] 3, the controller 180 further includes a multiplexer 390 operable to selectively send the error signal EA1 and the soft start signal SST1 to the buck control unit 320 based on the selection signal SEL. In operation, if the voltage of the soft start signal SST1 is less than the error signal EA1 when the first switch Q1 is turned on, the multiplexer 390 selectively sends the soft start signal SST1 to the buck control unit 320 based on the selection signal SEL, and the buck control unit 320 is operable to adjust the current of the first LED string 101 based on the voltage of the soft start signal SST1. When the first switch Q1 is turned off, the multiplexer 390 selectively sends the soft start signal SST1 to the buck control unit 320 based on the selection signal SEL, and the buck control unit 320 is operable to adjust the current of the first LED string 101 based on the voltage of the soft start signal SST1. As a result, when the first switch Q1 is turned on or off, the current of the first LED string 101 changes gradually. Similarly, for the second LED string 102, when the second switch Q2 is turned on or off, the current of the second LED string 102 changes gradually. Advantageously, electromagnetic interference (EMI) caused by the rapidly changing currents of the LED strings 101 and 102 can be reduced.

[0028] FIG. 8 shows a circuit diagram of an inrush current control unit 370 according to an embodiment of the present invention. The inrush current control unit 370 includes a comparator COMP5, a comparator COMP6, a selection unit 820, a current sensing unit 810, and an error amplifier EA_CHG. During the startup phase of the boost converter, the power terminal PFETOUT provides a current ICH for charging the output capacitor CO1 of the boost converter, and the inrush current control unit 370 is operable to adjust the current ICH based on the voltage of the output voltage VBSO of the boost converter. In operation, the comparator COMP5 is operable to compare the output voltage VBSO of the boost converter with a first threshold VTH1, and the comparator COMP6 is operable to compare the output voltage VBSO of the boost converter with a second threshold VTH2. In one embodiment, the first threshold VTH1 and the second threshold VTH2 are proportional to the voltage VIN1 at the power terminal VIN, and VTH1 is less than VTH2. In one embodiment, VTH1 is equal to 0.8*VIN1, and VTH2 is equal to 0.4*VIN1. The selection unit 820 is operable to select a reference signal from a plurality of reference signals REF1, REF2, and REF3 based on the output of the comparator COMP5 and the output of the comparator COMP6, where REF1 is less than REF2 and REF2 is less than REF3. In one embodiment, if VBSO is less than VTH1, the selection unit 820 selects REF1, if VBSO is greater than VTH1 and less than VTH2, the selection unit 820 selects REF2, and if VBSO is greater than VTH2, the selection unit 820 selects REF3. The current sense unit 810 is operable to generate a sense signal SENSE indicative of the magnitude of the current ICH. The error amplifier EA_CHG is operable to control a transistor 803 coupled in series with the output capacitor CO1 to adjust the magnitude of the current ICH based on the sense signal SENSE and the reference signal selected by the selection unit 820. As mentioned above, the current ICH can be adjusted to different levels during the start-up phase according to the voltage of the output voltage VBSO of the boost converter.Advantageously, the output capacitor CO1 can be charged relatively quickly without experiencing too large an inrush current from the power terminal VIN, and accordingly, excessive power consumption and over-temperature conditions can be avoided.

[0029] 1 and 3, the controller 180 includes a power limiting unit 380. The power limiting unit 380 is operable to control the boost converter to regulate the output voltage VBSO of the boost converter to be less than a voltage threshold, and to control the boost converter to regulate the input current IPWR received by the controller 180 from the power source 150 to be less than a current threshold. The power limiting unit 380 includes a first error amplifier EA_V, a second error amplifier EA_I, and a selection unit 381. The first error amplifier EA_V is operable to compare a voltage sense signal BST1 indicative of the level of the output voltage VBSO of the boost converter with a first threshold signal V1 indicative of a voltage threshold (e.g., 2V). The second error amplifier EA_I is operable to compare a current sense signal ISEN2 indicative of the magnitude of the input current IPWR with a second threshold signal V2 indicative of a current threshold. The current sense signal ISEN2 is generated by an amplifier 382 based on sense signals ISP1 and ISN1 received at sense terminals ISP and ISN.

[0030] Referring to FIG. 1, the sense terminals ISP and ISN are respectively coupled to two ends of a sense resistor RS. In the example of FIG. 1, the sense resistor RS is coupled between the power supply 150 and the controller 180, and the current sense signal ISEN2 indicates the magnitude of the input current IPWR flowing from the power supply 150 to the controller 180. The selection unit 381 is operable to selectively send the output of the first error amplifier EA_V and the output of the second error amplifier EA_I to the boost control unit 310. In operation, if the output voltage VBSO of the boost converter is greater than a voltage threshold (e.g., 2V), the selection unit 381 selectively sends the output of the first error amplifier EA_V to the boost control unit 310. In response, the boost control unit 310 adjusts the output voltage VBSO to be less than the voltage threshold. If the output voltage VBSO of the boost converter is less than the voltage threshold, the selection unit 381 selectively sends the output of the second error amplifier EA_I to the boost control unit 310. In response, the boost control unit 310 adjusts the input current IPWR to be less than the current threshold. Advantageously, the power consumption of the light source driving circuit 100, including the controller 180 and the light source module, can be monitored and controlled within a desired range, and the power source 150 (e.g., a battery) can be protected from over-discharge.

[0031] In another embodiment, the power limiting unit 380 is also operable to control the boost converter to adjust the output voltage VBSO of the boost converter to be less than a voltage threshold, and to control the boost converter to adjust the output current IBSO of the boost converter to be less than a current threshold. In this embodiment, as illustrated in FIG. 9, a sense resistor RS is coupled between the diode D1 of the boost converter and the output capacitor CO1 of the boost converter to sense the magnitude of the output current IBSO of the boost converter. With such a configuration, referring to FIG. 3, the current sense signal ISEN2 indicates the magnitude of the output current IBSO. In operation, if the output voltage VBSO of the boost converter is greater than a voltage threshold (e.g., 2V), the selection unit 381 selectively sends the output of the first error amplifier EA_V to the boost control unit 310. In response, the boost control unit 310 adjusts the output voltage VBSO to be less than the voltage threshold. If the output voltage VBSO of the boost converter is less than the voltage threshold, the selection unit 381 selectively sends the output of the second error amplifier EA_I to the boost control unit 310. In response, the boost control unit 310 adjusts the output current IBSO to be less than the current threshold.

[0032] While the above description and drawings represent embodiments of the present invention, it will be understood that various additions, modifications and substitutions may be made in the same without departing from the spirit and scope of the principles of the present invention as defined in the appended claims. Those skilled in the art will recognize that the present invention may be used with many modifications of the shape, structure, arrangement, size, materials, elements and parts used in the implementation of the present invention, particularly adapted to specific environmental and operating requirements, without departing from the principles of the present invention. The embodiments of the present disclosure are therefore to be considered in all respects as illustrative and not restrictive, and the scope of the present invention is indicated by the appended claims and their legal equivalents, and is not limited to the above description. [Explanation of symbols]

[0033] 100 Light source driving circuit 101 LED string 102 LED string 103 Voltage Divider 104 Voltage Divider 150 Power supply 180 Controller 301 Transistor 302 Transistor 303 Transistor 307 Amplifier 310 Boost control unit 320 Step-down control unit 330 Brightness Limit Unit 340 Protection Unit 350 Dimmer Unit 360 Soft Start Unit 370 Inrush Current Control Unit 380 Power Limiting Unit 381 Selection Units 382 Amplifier 390 Multiplexer 401 NOR Gate 402 Switch 403 Comparator 404 Flip-flop 501 Differential unit 502 OR Gate 503 AND Gate 504 Timing unit 601 Current source 602 Inverter 603 Voltage Divider 604 Amplifier 701 Power supply 702 Discharge unit 703 OR Gate 704 OR Gate 705 Inverter 706 Flip-flop 713 Switch 714 Switch 803 Transistor 810 Current Sensing Unit 820 Selection Units APWM dimming terminal COMP1 First comparator COMP2 Second comparator COMP3 Third comparator COMP4 Comparator COMP5 Comparator COMP6 Comparator CO1 Output Capacitor CO2 Output Capacitor CP Capacitor CS Capacitor C1 Capacitor DPWMA 1st input terminal DPWMB 2nd input terminal DPWMLIM Width monitoring terminal D1 Diode EA_CHG Error amplifier EA_I Second Error Amplifier EA_V First error amplifier FB_BST 3rd voltage sensing pin IRSEN Sensing Resistor ISEN Current sensing terminal ISN Second sensing terminal ISP 1st sensing terminal LX power output terminal L1 Inductor L2 inductor PFETOUT power terminal Q1 First switch Q2 Second Switch RS sense resistor SST_BK Soft start terminal SW1 Switch SW2 switch VBUCKIN Power input terminal VS First voltage sensing terminal VSEN_BK Second voltage sensing pin

Claims

1. A controller operable to control a light source module comprising a first light emitting diode (LED) string and a second LED string, a power input terminal operable to receive power from the boost converter; a power output terminal coupled to the light source module operable to provide the power to the light source module through a step-down converter; a first input terminal operable to receive a first pulse width modulated (PWM) signal, the first PWM signal operable to control a first switch coupled in series with the first LED string, the first switch being on when the first PWM signal is in a first state and off when the first PWM signal is in a second state; a second input terminal operable to receive a second PWM signal, the second PWM signal operable to control a second switch coupled in series with the second LED string, the second switch being on when the second PWM signal is in a first state and off when the second PWM signal is in a second state; a width monitor terminal operable to receive a width monitor signal indicative of a duration of the first state of the first PWM signal and a duration of the first state of the second PWM signal; The controller is operable to turn off the light source module if the width monitor signal is greater than a width threshold signal.

2. a current sense terminal coupled to a sense resistor, the sense resistor coupled to a cathode of the first LED string through the first switch and to a cathode of the second LED string through the second switch, the current sense terminal operable to receive a current sense signal from the sense resistor, the current sense signal indicative of a current in the first LED string and a current in the second LED string; When the first switch is on, the current of the first LED string flows from the buck converter through the first LED string, the first switch, and the sensing resistor to ground, and when the second switch is on, the current of the second LED string flows from the buck converter through the second LED string, the second switch, and the sensing resistor to ground.

2. The controller of claim 1.

3. a first voltage sense terminal coupled to the anode of the light source module through a voltage divider and operable to receive a first voltage sense signal indicative of a voltage at the anode of the light source module; a second voltage sense terminal coupled to the anode of the light source module and operable to receive a second voltage sense signal indicative of a voltage drop across the light source module; the controller is operable to detect a short circuit condition based on the first voltage sense signal, the second voltage sense signal, and the current sense signal.

3. The controller of claim 2.

4. a dimming terminal operable to receive a third PWM signal; the controller is operable to generate an analog signal based on the third PWM signal, and to adjust the current of the first LED string and the current of the second LED string by comparing the analog signal and the current sense signal.

3. The controller of claim 2.

5. an amplifier operable to compare the analog signal and the current sense signal to generate an error signal; a soft start terminal coupled to a capacitor and operable to generate a soft start signal by charging and discharging the capacitor; the controller is operable to adjust the current in the first LED string based on a soft start signal if a voltage of the soft start signal is less than the error signal when the first switch is turned on; the controller is operable to adjust the current in the first LED string based on the soft-start signal when the first switch is turned off. The controller of claim 4.

6. a power terminal coupled to an output capacitor of the boost converter and operable to provide a current to charge the output capacitor, the current being regulated according to a voltage at the power input terminal.

2. The controller of claim 1.

7. a voltage sense terminal coupled to an output of the boost converter through a voltage divider and operable to sense an output voltage of the boost converter; a first sense terminal and a second sense terminal coupled to the sense resistor and operable to sense an input current received by the controller from a power source; the sense resistor is coupled between the power source and the controller, and the controller is operable to control the boost converter to regulate the output voltage to be less than a voltage threshold and to control the boost converter to regulate the input current to be less than a current threshold.

2. The controller of claim 1.

8. a voltage sense terminal coupled to an output of the boost converter through a voltage divider and operable to sense an output voltage of the boost converter; a first sense terminal and a second sense terminal coupled to the sense resistor and operable to sense an output current of the boost converter; the sense resistor is coupled between a diode of the boost converter and an output capacitor of the boost converter, and the controller is operable to control the boost converter to regulate the output voltage to be less than a voltage threshold and to control the boost converter to regulate the output current to be less than a current threshold.

2. The controller of claim 1.

9. A controller operable to control a light source module comprising a first light emitting diode (LED) string and a second LED string, a boost control unit operable to control the boost converter; a buck control unit operable to control the buck converter; a brightness limiting unit operable to receive a first pulse width modulated (PWM) signal and a second PWM signal; the first PWM signal is operable to control a first switch coupled in series with the first LED string, the first switch being on when the first PWM signal is in a first state and off when the first PWM signal is in a second state; the second PWM signal is operable to control a second switch coupled in series with the second LED string, the second switch being on when the second PWM signal is in a first state and off when the second PWM signal is in a second state; a controller, the brightness limiting unit operable to turn off the light source module if a width monitoring signal indicative of a duration of the first state of the first PWM signal and a duration of the first state of the second PWM signal is greater than a width threshold signal indicative of a width threshold.

10. The brightness limiting unit is a switch coupled in parallel with a capacitor, the switch being turned off to charge the capacitor when either the first PWM signal or the second PWM signal is in the first state, the switch being turned on to discharge the capacitor when both the first PWM signal and the second PWM signal are in the second state, and the width monitor signal is a voltage across the capacitor; a comparator operable to compare said width monitor signal to said width threshold signal; and a flip-flop operable to generate a warning signal based on an output of the comparator.

11. a current sense terminal coupled to a sense resistor, the current sense terminal operable to receive a current sense signal indicative of a current in the first LED string and a current in the second LED string, the sense resistor coupled to a cathode of the first LED string and a cathode of the second LED string; the current of the first LED string flows from the buck converter through the first LED string, the first switch and the sensing resistor to ground, and the current of the second LED string flows from the buck converter through the second LED string, the second switch and the sensing resistor to ground; The controller of claim 9.

12. a protection unit operable to detect a short circuit condition based on the first voltage sensing signal, the second voltage sensing signal and the current sensing signal; the first voltage sense signal indicative of a voltage at an anode of the light source module, the second voltage sense signal indicative of a voltage drop across the light source module, and the current sense signal further indicative of a voltage at a cathode of the light source module; The protection unit comprises: a differential unit operable to generate a differential signal indicative of a difference between the first voltage sense signal and the current sense signal; a first comparator operable to compare the differential signal and a first protection threshold; a second comparator operable to compare the current sense signal and a second protection threshold; a third comparator operable to compare the second voltage sense signal and a third protection threshold; an OR gate operable to OR the output of the first comparator and the output of the third comparator; an AND gate operable to AND an output of the OR gate and an output of the second comparator; a timing unit operable to generate a warning signal based on an output of the AND gate, the first PWM signal, the second PWM signal, and a predetermined duration. The controller of claim 11.

13. The light control device further includes a dimming unit, a first capacitor operable to generate an analog signal based on a third PWM signal, the first capacitor being charged when the third PWM signal is in a first state and being discharged when the third PWM signal is in a second state, and a level of the analog signal being proportional to a duty cycle of the third PWM signal; the controller is operable to adjust the current in the first LED string and the current in the second LED string by comparing the analog signal and the current sense signal. The controller of claim 11.

14. The dimming unit is an amplifier operable to generate a current to charge the first capacitor based on a set signal; The controller of claim 13 , wherein the set signal is generated by a voltage divider based on a reference voltage signal provided by a reference voltage terminal of the controller.

15. an amplifier for comparing the analog signal and the current sense signal to generate an error signal; a soft start unit operable to generate a soft start signal by charging and discharging a second capacitor, the soft start signal being a voltage across the second capacitor, and the soft start unit comprising: a discharge unit operable to generate a discharge control signal based on the first PWM signal and the second PWM signal; a comparator operable to compare the error signal to the soft start signal; a flip-flop operable to generate a charge control signal based on an output of the comparator; a soft start unit comprising: an OR gate operable to generate a selection signal based on the charge control signal and the discharge control signal; the charge control signal is operable to turn on a third switch to charge the second capacitor, and the discharge control signal is operable to turn on a fourth switch to discharge the second capacitor; the controller further comprising a multiplexer operable to selectively send the error signal and the soft start signal to the step-down control unit based on the selection signal; the step-down control unit is operable to adjust the current in the first LED string based on a soft-start signal if a voltage of the soft-start signal is less than the error signal when the first switch is turned on; the buck control unit is operable to adjust the current in the first LED string based on the soft-start signal when the first switch is turned off; The controller of claim 13.

16. a power terminal coupled to an output capacitor of the boost converter operable to provide a current to charge the output capacitor; an inrush current control unit operable to regulate the current based on an output voltage of the boost converter, the inrush current control unit comprising: a first comparator operable to compare the output voltage of the boost converter to a first threshold; a second comparator operable to compare the output voltage of the boost converter to a second threshold; a selection unit operable to select a reference signal from a plurality of reference signals based on an output of the first comparator and an output of the second comparator; a current sensing unit operable to generate a sense signal indicative of said current; an inrush current control unit comprising: an error amplifier operable to control a transistor coupled in series with the output capacitor to regulate the current based on the sense signal and the reference signal selected by the selection unit. The controller of claim 9.

17. a power limiting unit operable to control the boost converter to regulate an output voltage of the boost converter to be below a voltage threshold and to control the boost converter to regulate an input current received by the controller from a power source to be below a current threshold, the power limiting unit comprising: a first error amplifier operable to compare a voltage sense signal indicative of the output voltage of the boost converter to a first threshold signal indicative of the voltage threshold; a second error amplifier operable to compare a current sense signal indicative of the input current to a second threshold signal indicative of the current threshold; a selection unit operable to selectively send an output of the first error amplifier and an output of the second error amplifier to the boost control unit; The controller of claim 9.

18. a power limiting unit operable to control the boost converter to regulate an output voltage of the boost converter below a voltage threshold and to control the boost converter to regulate an output current of the boost converter below a current threshold, the power limiting unit comprising: a first error amplifier operable to compare a voltage sense signal indicative of the output voltage to a first threshold signal indicative of the voltage threshold; a second error amplifier operable to compare a current sense signal indicative of the output current to a second threshold signal indicative of the current threshold; a selection unit operable to selectively send an output of the first error amplifier and an output of the second error amplifier to the boost control unit; The controller of claim 9.

Images