Controller for controlling a light source module

Abstract

A controller for controlling a light source module is provided. The light source module includes a first string of light emitting diodes and a second string of light emitting diodes. The controller includes a power input terminal for receiving power from a boost converter, a power output terminal for providing power to the light source module via a buck converter, a first input terminal for receiving a first pulse width modulated signal, a second input terminal for receiving a second pulse width modulated signal, and a width monitor terminal for receiving a width monitor signal. The width monitor signal is indicative of a duration of a first state of the first pulse width modulated signal and a duration of a first state of the second pulse width modulated signal. The controller turns off the light source module if the width monitor signal is greater than a width threshold signal.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of controller, and in particular, to a controller for controlling a light source module. BACKGROUND

[0002] A driver monitoring system (DMS) is a vehicle safety system that monitors a driver's alertness to help prevent traffic accidents. The DMS uses a camera installed inside the driver's cabin of a vehicle to monitor the driver's distraction or improper driving behavior and issues an alert when a problem is detected. To help the camera generate 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. Typically, each LED string is controlled by one controller. To control two LED strings, two controllers are needed, which increases the cost. When the system is running, the current of the light source module needs to be adjusted within an appropriate range to produce sufficient illumination without causing harm 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 uncommon resistance values or the use of multiple shunt resistors to obtain the desired current, thus it has limited flexibility and increases the cost. When adjusting the current of the light source module, the traditional controller will generate electromagnetic interference (EMI) due to the rapidly changing current, which can cause malfunction of other electronic devices in the vehicle. In addition, to ensure the safe operation of the system, it is necessary to monitor the potential short circuit condition of the light source module, prevent large inrush current at the power terminals of the controller, and monitor and control the power consumption of the light source module and the controller. SUMMARY

[0003] A controller for controlling a light source module is provided. The light source module includes a first string of light emitting diodes and a second string of light emitting diodes. The controller includes a power input terminal, a power output terminal, a first input terminal, a second input terminal, and a width monitor terminal. The power input terminal is for receiving power from a boost converter. The power output terminal is coupled with the light source module for providing power to the light source module via a buck converter. The first input terminal is for receiving a first pulse width modulation signal for controlling a first switch coupled in series with the first string of light emitting diodes, the first switch being on if the first pulse width modulation signal is in a first state and the first switch being off if the first pulse width modulation signal is in a second state. The second input terminal is for receiving a second pulse width modulation signal for controlling a second switch coupled in series with the second string of light emitting diodes, the second switch being on if the second pulse width modulation signal is in the first state and the second switch being off if the second pulse width modulation signal is in the second state. The width monitor terminal is for receiving a width monitor signal indicative of a duration of the first state of the first pulse width modulation signal and a duration of the first state of the second pulse width modulation signal. The controller turns off the light source module if the width monitor signal is greater than a width threshold signal.

[0004] A controller for controlling a light source module is provided. The light source module includes a first string of light emitting diodes and a second string of light emitting diodes. The controller includes a power input terminal, a power output terminal, a first input terminal, a second input terminal, and a width monitor terminal. The power input terminal is for receiving power from a boost converter. The power output terminal is coupled with the light source module for providing power to the light source module via a buck converter. The first input terminal is for receiving a first pulse width modulation signal for controlling a first switch coupled in series with the first string of light emitting diodes, the first switch being on if the first pulse width modulation signal is in a first state and the first switch being off if the first pulse width modulation signal is in a second state. The second input terminal is for receiving a second pulse width modulation signal for controlling a second switch coupled in series with the second string of light emitting diodes, the second switch being on if the second pulse width modulation signal is in the first state and the second switch being off if the second pulse width modulation signal is in the second state. The width monitor terminal is for receiving a width monitor signal indicative of a duration of the first state of the first pulse width modulation signal and a duration of the first state of the second pulse width modulation signal. The controller turns off the light source module if the width monitor signal is greater than a width threshold signal. BRIEF DESCRIPTION OF DRAWINGS

[0005] The objectives, specific features and advantages of the present application can be further understood from the following description of some embodiments of the present application and the accompanying drawings.

[0006] Figure 1A light source driving circuit for controlling a light source module according to an embodiment of the present application is shown.

[0007] Figure 2 A signal waveform diagram of the light source driving circuit according to an embodiment of the present application is shown.

[0008] Figure 3 A block diagram of a controller for controlling a light source module according to an embodiment of the present application is shown.

[0009] Figure 4 A circuit diagram of a brightness limiting unit of the controller according to an embodiment of the present application is shown.

[0010] Figure 5 A circuit diagram of a protection unit of the controller according to an embodiment of the present application is shown.

[0011] Figure 6A A circuit diagram of a dimming unit of the controller according to an embodiment of the present application is shown.

[0012] Figure 6B A circuit diagram of a dimming unit of the controller according to an embodiment of the present application is shown.

[0013] Figure 7 A circuit diagram of a gradual start unit of the controller according to an embodiment of the present application is shown.

[0014] Figure 8 A circuit diagram of a surge current control unit of the controller according to an embodiment of the present application is shown.

[0015] Figure 9 A light source driving circuit for controlling a light source module according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0016] The embodiments of the present application will now be described in detail. Although the present application is illustrated and described with reference to these embodiments, it is not intended to be limited to the embodiments. Rather, the present application is intended to encompass all alternatives, modifications, and equivalents falling within the spirit and scope of the present application as defined by the appended claims.

[0017] In addition, numerous specific details are given in the following description. One skilled in the art will understand, however, that the application can be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the application.

[0018] Figure 1A light source drive circuit 100 for controlling a light source module is shown in accordance with one embodiment of the present application. The light source drive circuit 100 includes a controller 180.

[0019] In Figure 1 one example, the light source module includes two LED strings 101 and 102, where each LED string includes a plurality (e.g., two) of LEDs. In one embodiment, the LEDs in the LED strings 101 and 102 are infrared LEDs. This example is used as a basis for the discussion below; however, the present application is not limited to two LED strings and / or two LEDs per string.

[0020] 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 for receiving power from a boost converter. The power output terminal LX is coupled with the light source module for providing power to the light source module via a buck converter. In Figure 1 one example, the boost converter includes an inductor LI, a diode DI, an output capacitor COI, and a transistor 301 (shown in Figure 3 ). The buck converter includes an inductor L2, an output capacitor CO2, and transistors 302 and 303 (shown in Figure 3 ). The first input terminal DPWMA is for receiving a first pulse width modulated (PWM) signal PWMA. The second input terminal DPWMB is for receiving a second pulse width modulated signal PWMB. In one embodiment, the first and second pulse width modulated signals PWMA and PWMB are provided by an electronic control unit (ECU) of a vehicle. The first pulse width modulated signal PWMA is for controlling a first switch Ql coupled in series with the first LED string 101. If PWMA is a first state (e.g., logic high), the first switch Ql is on; if PWMA is a second state (e.g., logic low), the first switch Ql is off. The second pulse width modulated signal PWMB is for controlling a second switch Q2 coupled in series with the second LED string 102. If PWMB is a first state (e.g., logic high), the second switch Q2 is on; if PWMB is a second state (e.g., logic low), the second switch Q2 is off. PWMA and PWMB are configured such that the first and second switches Ql and Q2 are not on at the same time. As Figure 2As shown, during a time period Tona, the PWMA is in the first state and the switch Ql is turned on. During a time period Tonb, the PWMB is in the first state and the switch Q2 is turned on. By so configuring, the on period Tona of the switch Ql and the on period Tonb of the switch Q2 do not overlap. In one embodiment, the PWMA and the PWMB have the same duty cycle and different phases. In other words, in such an embodiment, Tona is equal to Tonb and the waveform of the PWMB is obtained by time delaying the waveform of the PWMA.

[0021] The controller 180 further includes a width monitoring terminal DPWMLIM, a current monitoring terminal ISEN, a first voltage monitoring terminal VS, a second voltage monitoring terminal VSEN BK, a dimming terminal APWM, a gradual start terminal SST BK, a power supply terminal PFETOUT, a third voltage monitoring terminal FB BST, monitoring terminals ISP and ISN, and a reference voltage terminal VREF.

[0022] The width monitoring terminal DPWMLIM is configured to receive a width monitoring signal WID, which indicates the first state duration Tona of the first pulse width modulation signal PWMA and the first state duration Tonb of the second pulse width modulation signal PWMB. If the width monitoring signal WID is greater than a width threshold signal, the controller 180 turns off the light source module. The width monitoring terminal DPWMLIM is coupled to the capacitor CP.

[0023] The current monitoring terminal ISEN is coupled to a monitoring resistor IRSEN. The monitoring resistor IRSEN is coupled to the cathode of the first LED string 101 through the switch Ql and to the cathode of the second LED string 102 through the switch Q2. The monitoring terminal ISEN is configured to receive a current monitoring signal ISEN1 from the monitoring resistor IRSEN. The current monitoring signal ISEN1 is a voltage across the monitoring resistor IRSEN, which can indicate the magnitude of the current of the first LED string 101 and the magnitude of the current of the second LED string 102. If the switch Ql is turned on, the current of the first LED string 101 flows from the buck converter, through the first LED string 101, the switch Ql and the monitoring resistor IRSEN to ground. If the switch Q2 is turned 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 monitoring resistor IRSEN to ground. Advantageously, the controller 180 can monitor the magnitude of the current of the LED strings 101 and 102 with a single current monitoring terminal ISEN and adjust the current accordingly. In contrast to conventional controllers that can only monitor and control one LED string, the controller 180 of the present application can monitor and control multiple (e.g., two) LED strings. These LED strings can be placed at different locations within the vehicle cab to provide illumination at different angles, so that the driver monitoring system can better monitor the condition of the driver.

[0024] The first voltage monitoring terminal VS is coupled to the anode of the light source module (e.g., the anode of the first LED string 101 and the second LED string 102) through the voltage divider 103 to receive a first voltage monitoring signal VS1 indicative of the voltage level at the anode of the light source module. The current monitoring signal ISEN1 can be indicative of the voltage level at the cathode of the light source module. The second voltage monitoring terminal VSEN BK is coupled to the anode of the light source module to receive a second voltage monitoring signal VSBK1 indicative of the voltage level across the light source module. The controller 180 detects a short circuit condition from the first voltage monitoring signal VS1, the second voltage monitoring signal VSBK1, and the current monitoring signal ISEN1, which will be discussed in connection with Figure 5 Further discussion.

[0025] The dimming terminal APWM is used to receive a third pulse width modulation signal APWM1. The controller 180 generates an analog signal ADJ from the duty cycle of the third pulse width modulation signal APWM1 and can 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 monitoring signal ISEN1. As shown in Figure 3 The controller 180 includes an amplifier 307 for comparing the analog signal ADJ with the current monitoring signal ISEN1 to generate an error signal EA1. The buck control unit 320 can control the buck converter to adjust the current of the first LED string 101 and the current of the second LED string 102 from the level of the error signal EA1.

[0026] Referring again to Figure 1 The gradual start terminal SST BK is coupled to the capacitor CS for generating a gradual start signal SST1 by charging and discharging the capacitor CS. When the switch Q1 is on, the controller 180 adjusts the current of the first LED string 101 from the voltage of the gradual start signal SST1 if the voltage of the gradual start signal SST1 is less than the error signal EA1. When the switch Q1 is off, the controller 180 adjusts the current of the first LED string 101 from the voltage of the gradual start signal SST1.

[0027] The power terminal PFETOUT is coupled to the output capacitor CO1 of the boost converter and provides a charging current to the output capacitor CO1, which is adjusted from the voltage at the power input terminal VBUCKIN.

[0028] The third voltage monitoring terminal FB_BST is coupled to the output of the boost converter via voltage divider 104 to monitor the level of the boost converter's output voltage VBSO. Specifically, the third voltage monitoring terminal FB_BST receives a voltage monitoring signal BST1 indicating the level of the output voltage VBSO. Monitoring terminals ISP and ISN are coupled across the monitoring resistor RS to monitor the input current IPWR provided by power supply 150, received by controller 180 via power supply terminal VIN. Monitoring resistor RS is coupled between power supply 150 and controller 180. Controller 180 controls the boost converter to regulate the output voltage VBSO below a voltage threshold and controls the boost converter to regulate the input current IPWR below a current threshold. Alternatively, in... Figure 9 In another embodiment shown, a monitoring resistor RS is coupled between diode D1 of the boost converter and output capacitor CO1 of the boost converter. Monitoring terminals ISP and ISN, coupled to both ends of the monitoring resistor RS, are used to monitor the magnitude of the output current IBSO of the boost converter. Controller 180 controls the boost converter to regulate the output voltage VBSO below a voltage threshold and controls the boost converter to regulate the output current IBSO below a current threshold.

[0029] Figure 3 The diagram shows a control module for a light source (e.g., according to an embodiment of the present invention) Figure 1 The block diagram shows a controller 180 for LED strings 101 and 102. 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 progressive start unit 360, a surge current control unit 370, and a power limiting unit 380. The boost control unit 310 controls the boost converter by controlling transistor 301. The buck control unit 320 controls the buck converter by controlling transistors 302 and 303. More specifically, the boost control unit 310 adjusts the output current IBSO and output voltage VBSO of the boost converter by adjusting the duty cycle of transistor 301. The buck control unit 320 adjusts the output current and output voltage of the buck converter by controlling the duty cycles of transistors 302 and 303.

[0030] Figure 4A circuit diagram of the brightness limiting unit 330 according to an embodiment of the present application is shown. The brightness limiting unit 330 comprises an NOR gate 401, a switch 402, a comparator 403 and a flip-flop 404. The NOR gate 401 receives the PWMA and the PWMB and generates an output signal to control the switch 402. The switch 402 is coupled in parallel with the capacitor CP. If either of the PWMA or the PWMB is in the first state (e.g. logic high), the switch 402 is open and the capacitor CP is charged by the current provided by the reference voltage terminal VREF. If both the PWMA and the PWMB are in the second state (e.g. logic low), the switch 402 is on and the capacitor CP is discharged. The voltage across the capacitor CP is the width monitoring signal WID, which indicates the duration Tona of the first state of the first pulse width modulated signal PWMA and the duration Tonb of the first state of the second pulse width modulated signal PWMB. The comparator 403 compares the width monitoring signal WID with the width threshold signal VTH WID, which indicates a width (i.e. duration) threshold, and outputs the comparison result to the flip-flop 404. The flip-flop 404 generates the alarm signal based on the output of the comparator 403. If the width monitoring signal WID is greater than the width threshold signal VTH WID, the flip-flop 404 outputs the alarm signal PWM LIM with the first state (e.g. logic high) and the controller 180 accordingly turns off the light source module. Since the PWMA and the 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 is safe for the human eye.

[0031] Figure 5 A circuit diagram of the protection unit 340 according to an embodiment of the present application is shown. The protection unit 340 detects the light source module (e.g. the light source module 100) according to the first voltage monitoring signal VS1, the second voltage monitoring signal VSBK1 and the current monitoring signal ISEN1. Figure 1The first voltage monitor signal VS1 is indicative of the level of the voltage at the anode of the light source module, the second voltage monitor signal VSBK1 is indicative of the level of the voltage drop across the light source module, and the current monitor signal ISEN1 is indicative of the level of the voltage at the cathode of the light source module. The protection unit 340 comprises a difference 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 difference unit 501 is configured to generate a difference signal DIF indicative of the difference between the first voltage monitor signal VS1 and the current monitor signal ISEN1. The first comparator COMP1 is configured to compare the difference signal DIF with a first protection threshold VTH1. The second comparator COMP2 is configured to compare the current monitor signal ISEN1 with a second protection threshold VTH2. The third comparator COMP3 is configured to compare the second voltage monitor signal VSBK1 with a third protection threshold VTH3. The OR gate 502 is configured to perform a logical OR operation on the output of the first comparator COMP1 and the output of the third comparator COMP3. The AND gate 503 is configured to perform a logical AND operation on the output of the OR gate 502 and the output of the second comparator COMP2. The timing unit 504 is configured to generate an alarm signal LEDSHORT in dependence on the output of the AND gate 503, the first pulse width modulated signal PWMA, the second pulse width modulated signal PWMB, and a predetermined time duration TP. During operation, the protection unit 340 monitors whether the current monitor signal ISEN1 is greater than the second protection threshold VTH2. If the current monitor signal ISEN1 is greater than the second protection threshold VTH2, the protection unit 340 further monitors whether the difference signal DIF is less than the first protection threshold VTH1 or the second voltage monitor signal VSBK1 is less than the third protection threshold VTH3. If the difference signal DIF is less than the first protection threshold VTH1 or the second voltage monitor signal VSBK1 is less than the third protection threshold VTH3, the protection unit 340 monitors the time duration of this condition using the timing unit 504. If the time duration of this condition is greater than the predetermined time duration TP, the timing unit 504 generates the alarm signal LEDSHORT indicative of the occurrence of a short circuit condition, and the controller 180 can accordingly shut down the light source module.

[0032] Figure 6AThe diagram shows a circuit of a dimming unit 350 according to an embodiment of the present invention. The dimming unit 350 includes a capacitor C1 that generates an analog signal ADJ based on the duty cycle of a third pulse width modulation signal APWM1. If APWM1 is in a first state, capacitor C1 is charged; if APWM1 is in a second state, capacitor C1 is discharged. More specifically, an inverter 602 generates an inverted pulse width modulation signal APWM2 based on the third pulse width modulation signal APWM1. The third pulse width modulation signal APWM1 controls a switch SW1 coupled between a current source 601 and capacitor C1. The inverted pulse width modulation signal APWM2 controls a switch SW2 coupled in parallel with capacitor C1. If APWM1 is in the first state (e.g., logic high), switch SW1 is turned on, switch SW2 is turned off, and capacitor C1 is charged by current from the current source 601. If APWM1 is in the second state (e.g., logic low), switch SW2 is turned on, switch SW1 is turned off, and capacitor C1 is discharged. The voltage across capacitor C1 is the analog signal ADJ. The level of the analog signal ADJ is proportional to the duty cycle of the third pulse width modulation signal APWM1. The controller 180 can adjust the current of the first LED string 101 and the second LED string 102 by comparing the analog signal ADJ and the current monitoring signal ISEN1.

[0033] like Figure 3 As shown, controller 180 includes amplifier 307 for comparing analog signal ADJ with current monitoring signal ISEN1 to generate error signal EA1. Error signal EA1 is transmitted to buck control unit 320 via multiplexer 390. Buck control unit 320 can adjust the duty cycle of transistors 302 and 303 according to the voltage of error signal EA1 to regulate the current of first LED string 101 and second LED string 102. Advantageously, the brightness of the light source module can be adjusted by a third pulse width modulation signal APWM1, so the resistance value of monitoring resistor IRSEN coupled to current sensing terminal ISEN can be set to a fixed value or selected from several standard resistance values, thereby reducing manufacturing costs.

[0034] Figure 6B Another embodiment of the dimming unit 350 is shown. In this embodiment, the controller 180 further includes a current setting terminal ISET (shown in the figure) for receiving a setting signal ISET1. Figure 1). The setting signal ISET1 is generated by a voltage divider 603 from a 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 to the capacitor CI according to the voltage of the setting signal ISET1. This embodiment can further adjust the analog signal ADJ by changing the resistance ratio of the voltage divider 603. Therefore, the brightness of the light source module can be further adjusted by configuring the voltage divider 603. Advantageously, the controller 180 according to the present application can satisfy different application requirements (e.g., applicable to light source modules with different types or different numbers of LEDs).

[0035] Figure 7 A circuit diagram of a progressive start unit 360 according to an embodiment of the present application is shown. The progressive start unit 360 generates a progressive start signal SST1 by charging and discharging a second capacitor CS, where the progressive start signal SST1 is a voltage across the second capacitor CS. The progressive start unit 360 includes a discharging unit 702, a comparator COMP4, a flip-flop 706, and an OR gate 703. The discharging unit 702 generates a discharging control signal DSC according to a first pulse width modulation signal PWMA and a second pulse width modulation signal PWMB. In one embodiment, the discharging unit 702 includes an OR gate 704 for performing a logical OR operation on PWMA and PWMB to generate a signal PWMAB, and an inverter 705 for generating the discharging control signal DSC according to the signal PWMAB. The discharging control signal DSC is used to turn on a switch 714 coupled in parallel with the capacitor CS to discharge the capacitor CS. The comparator COMP4 compares an error signal EA1 and the progressive start signal SST1. The R terminal of the flip-flop 706 receives an output of the comparator COMP4, and generates a charging control signal CHG at the Q terminal according to the output of the comparator COMP4. The charging control signal CHG is used to turn on a switch 713 coupled between the capacitor CS and a power source 701 to charge the capacitor CS. In one embodiment, the power source 701 is provided by a reference voltage terminal VREF (see FIG. 6A). Figure 1 、 4 The OR gate 703 generates a selection signal SEL according to the charging control signal CHG and the discharging control signal DSC.

[0036] As Figure 3As shown, the controller 180 further includes a multiplexer 390 for selectively transmitting the error signal EA1 and the gradual start signal SST1 to the buck control unit 320 according to a selection signal SEL. During operation, when the first switch Q1 is on, if the voltage of the gradual start signal SST1 is less than the error signal EA1, the multiplexer 390 selectively transmits the gradual start signal SST1 to the buck control unit 320 according to the selection signal SEL, and the buck control unit 320 adjusts the current of the first LED string 101 according to the voltage of the gradual start signal SST1. When the first switch Q1 is off, the multiplexer 390 selectively transmits the gradual start signal SST1 to the buck control unit 320 according to the selection signal SEL, and the buck control unit 320 adjusts the current of the first LED string 101 according to the voltage of the gradual start signal SST1. As a result, the current of the first LED string 101 is gradually changed when the first switch Q1 is on or off. Similarly, for the second LED string 102, the current of the second LED string 102 is also gradually changed when the second switch Q2 is on or off. In this way, electromagnetic interference (EMI) caused by the rapid change of the current of the LED strings 101 and 102 can be reduced.

[0037] Figure 8A circuit diagram of the inrush current control unit 370 according to one embodiment of the present application is shown. The inrush current control unit 370 includes a comparator COMP5, a comparator COMP6, a selection unit 820, a current monitoring unit 810, and an error amplifier EA_CHG. During the start-up phase of the boost converter, the power terminal PFETOUT provides a current ICH for charging the output capacitor COl of the boost converter, and the inrush current control unit 370 adjusts the current ICH according to the voltage value of the output voltage VBSO of the boost converter. During the running phase, the comparator COMP5 compares the output voltage VBSO of the boost converter with a first threshold VTHl, and the comparator COMP6 compares the output voltage VBSO of the boost converter with a second threshold VTH2. In one embodiment, the first threshold VTHl and the second threshold VTH2 are proportional to the voltage VINl at the power terminal VIN, and VTHl is less than VTH2. In one embodiment, VTHl equals 0.8*VINl, and VTH2 equals 0.4*VINl. The selection unit 820 selects one reference signal from a plurality of reference signals REF1, REF2, and REF3 according to 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 VTHl, the selection unit 802 selects REF1; if VBSO is greater than VTHl 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 monitoring unit 810 generates a monitoring signal SENSE indicative of the amplitude of the current ICH. The error amplifier EA_CHG controls a transistor 803 coupled in series with the output capacitor COl according to the monitoring signal SENSE and the reference signal selected by the selection unit 820 to adjust the amplitude of the current ICH. As described above, during the start-up phase, the inrush current control unit 370 adjusts the current ICH to different values according to the output voltage VBSO of the boost converter. Advantageously, the output capacitor COl can be charged relatively quickly while also not receiving too much inrush current from the power terminal VIN, and thus, over-consumption of power or excessive temperature is not likely to occur.

[0038] Reference Figure 1 and Figure 3, the controller 180 includes a power limiting unit 380. The power limiting unit 380 controls the boost converter to regulate the output voltage VBSO of the boost converter to be lower than a voltage threshold, and controls 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 compares a voltage monitor signal BST1 indicative of the level of the output voltage VBSO of the boost converter with a first threshold signal V1 indicative of the voltage threshold (e.g., 2V). The second error amplifier EA_I compares a current monitor signal ISEN2 indicative of the magnitude of the input current IPWR with a second threshold signal V2 indicative of the current threshold. The current monitor signal ISEN2 is generated by an amplifier 382 from monitor signals ISP1 and ISN1 received by monitor terminals ISP and ISN.

[0039] With reference to Figure 1 , the monitor terminals ISP and ISN are coupled to two ends of a monitor resistor RS. In Figure 1 the example, the monitor resistor RS is coupled between the power source 150 and the controller 180, and the current monitor signal ISEN2 is indicative of the magnitude of the input current IPWR flowing from the power source 150 to the controller 180. The selection unit 381 selectively passes 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. During operation, if the output voltage VBSO of the boost converter is greater than the voltage threshold (e.g., 2V), the selection unit 381 selectively passes the output of the first error amplifier EA_V to the boost control unit 310. In response, the boost control unit 310 regulates the output voltage VBSO to be lower than the voltage threshold. If the output voltage VBSO of the boost converter is less than the voltage threshold, the selection unit 381 selectively passes the output of the second error amplifier EA_I to the boost control unit 310. In response, the boost control unit 310 regulates 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, thereby protecting the power source 150 (e.g., a battery) from being over-discharged.

[0040] In another embodiment, the power limiting unit 380 controls the boost converter to regulate the output voltage VBSO of the boost converter to be lower than a voltage threshold, and controls the boost converter to regulate the output current IBSO of the boost converter to be less than a current threshold. In this embodiment, as Figure 9As shown, a monitoring resistor RS is coupled between a diode D1 of the boost converter and an output capacitor CO1 of the boost converter to monitor the magnitude of an output current IBSO of the boost converter. In this configuration, the current monitoring signal ISEN2 is indicative of the magnitude of the output current IBSO. During operation, if the output voltage VBSO of the boost converter is greater than a voltage threshold (e.g., 2V), the selection unit 381 selectively transmits 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 lower than the voltage threshold. If the output voltage VBSO of the boost converter is less than the voltage threshold, the selection unit 381 selectively transmits 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 lower than the current threshold. Figure 3

[0041] The above detailed description and annexed drawings only constitute common embodiments of the present application. Obviously, various additions, modifications and substitutions can be made without departing from the spirit and scope of the present application as defined in the following claims. It should be understood by those skilled in the art that the present application can be varied in form, structure, layout, proportion, material, element, component and other aspects in practical application without departing from the inventive principles, according to specific environment and working requirements. Therefore, the embodiments disclosed herein are only for illustration and not for limitation, and the scope of the present application is defined by the following claims and their legal equivalents, and not limited to the foregoing description.​

Claims

1. A controller for controlling a light source module, the light source module comprising a first string of light emitting diodes and a second string of light emitting diodes, characterized in that, The controller comprises: a power input terminal for receiving power from a boost converter; a power output terminal coupled to the light source module for providing the power to the light source module via a buck converter; a first input terminal for receiving a first pulse width modulation signal, wherein the first pulse width modulation signal is for controlling a first switch coupled in series with the first string of light emitting diodes, the first switch being on if the first pulse width modulation signal is in a first state and the first switch being off if the first pulse width modulation signal is in a second state; a second input terminal for receiving a second pulse width modulation signal, wherein the second pulse width modulation signal is for controlling a second switch coupled in series with the second string of light emitting diodes, the second switch being on if the second pulse width modulation signal is in a first state and the second switch being off if the second pulse width modulation signal is in a second state; and a width monitor terminal for receiving a width monitor signal indicative of a duration of the first state of the first pulse width modulation signal and a duration of the first state of the second pulse width modulation signal, wherein the controller turns off the light source module if the width monitor signal is greater than a width threshold signal.

2. The controller of claim 1, wherein, The controller further comprises: a current monitor terminal coupled to a monitor resistor, wherein the monitor resistor is coupled to a cathode of the first string of light emitting diodes through the first switch and to a cathode of the second string of light emitting diodes through the second switch, the current monitor terminal for receiving a current monitor signal from the monitor resistor, the current monitor signal being indicative of a current of the first string of light emitting diodes and a current of the second string of light emitting diodes, wherein the current of the first string of light emitting diodes flows from the buck converter, through the first string of light emitting diodes, the first switch and the monitor resistor to ground if the first switch is on, and the current of the second string of light emitting diodes flows from the buck converter, through the second string of light emitting diodes, the second switch and the monitor resistor to ground if the second switch is on.

3. The controller of claim 2, wherein, The controller further comprises: a first voltage monitor terminal coupled to an anode of the light source module through a voltage divider for receiving a first voltage monitor signal indicative of a voltage at the anode of the light source module; and a second voltage monitor terminal coupled to the anode of the light source module for receiving a second voltage monitor signal indicative of a voltage drop across the light source module, wherein the controller detects a short circuit condition based on the first voltage monitor signal, the second voltage monitor signal and the current monitor signal.

4. The controller of claim 2, wherein, The controller further comprises: a dimming terminal for receiving a third pulse width modulation signal, wherein the controller generates an analog signal based on the third pulse width modulation signal and adjusts the current of the first string of light emitting diodes and the current of the second string of light emitting diodes by comparing the analog signal and the current monitor signal.

5. The controller of claim 4, wherein, The controller further comprises: an amplifier for comparing the analog signal and the current monitor signal to generate an error signal; a gradual start terminal, coupled to a capacitor, for generating a gradual start signal by charging and discharging the capacitor, wherein, when the first switch is on, the controller adjusts a current of the first string of light emitting diodes according to the gradual start signal if a voltage of the gradual start signal is less than the error signal, wherein, when the first switch is off, the controller adjusts the current of the first string of light emitting diodes according to the gradual start signal.

6. The controller of claim 1, wherein, the controller further comprises: a power terminal, coupled to an output capacitor of the boost converter, for providing a current to charge the output capacitor, wherein the current is adjusted according to a voltage at the power input terminal.

7. The controller of claim 1, wherein, the controller further comprises: a voltage monitor terminal, coupled to an output of the boost converter through a voltage divider, for monitoring an output voltage of the boost converter; a first monitor terminal and a second monitor terminal, coupled to a monitor resistor, for monitoring an input current received by the controller from a power supply, wherein the monitor resistor is coupled between the power supply and the controller, the controller controls the boost converter to adjust the output voltage to be lower than a voltage threshold, and controls the boost converter to adjust the input current to be lower than a current threshold.

8. The controller of claim 1, wherein, the controller further comprises: a voltage monitor terminal, coupled to an output of the boost converter through a voltage divider, for monitoring an output voltage of the boost converter; a first monitor terminal and a second monitor terminal, coupled to a monitor resistor, for monitoring an output current of the boost converter, wherein the monitor resistor is coupled between a diode of the boost converter and an output capacitor of the boost converter, the controller controls the boost converter to adjust the output voltage to be lower than a voltage threshold, and controls the boost converter to adjust the output current to be lower than a current threshold.

9. A controller for controlling a light source module, the light source module comprising a first string of light emitting diodes and a second string of light emitting diodes, characterized in that, the controller comprises: a boost control unit for controlling a boost converter; a buck control unit for controlling a buck converter; and a brightness limiting unit for receiving a first pulse width modulation signal and a second pulse width modulation signal, wherein, the first pulse width modulation signal is for controlling a first switch coupled in series with the first string of light emitting diodes, the first switch is on if the first pulse width modulation signal is in a first state, and the first switch is off if the first pulse width modulation signal is in a second state, the second pulse width modulation signal is for controlling a second switch coupled in series with the second string of light emitting diodes, the second switch is on if the second pulse width modulation signal is in a first state, and the second switch is off if the second pulse width modulation signal is in a second state, the brightness limiting unit turns off the light source module if a width monitoring signal indicating a duration of the first state of the first pulse width modulation signal and a duration of the first state of the second pulse width modulation signal is greater than a width threshold signal indicating a width threshold.

10. The controller of claim 9, wherein, the brightness limiting unit comprises: a switch coupled in parallel to the capacitor, wherein the switch is open to charge the capacitor if the first pulse width modulated signal is in a first state or the second pulse width modulated signal is in a first state, and the switch is closed to discharge the capacitor if both the first pulse width modulated signal and the second pulse width modulated signal are in a second state, wherein the width monitor signal is a voltage across the capacitor; a comparator for comparing the width monitor signal to the width threshold signal; and a flip-flop for generating an alarm signal in dependence on an output of the comparator.

11. The controller of claim 9, wherein, The controller further comprises: a current monitor terminal coupled to a monitor resistor for receiving a current monitor signal indicative of a current of the first string of light emitting diodes and a current of the second string of light emitting diodes, wherein the monitor resistor is coupled to a cathode of the first string of light emitting diodes and a cathode of the second string of light emitting diodes, wherein the current of the first string of light emitting diodes flows from the step-down converter through the first string of light emitting diodes, the first switch and the monitor resistor to ground, and the current of the second string of light emitting diodes flows from the step-down converter through the second string of light emitting diodes, the second switch and the monitor resistor to ground.

12. The controller of claim 11, wherein, The controller further comprises: a protection unit for detecting a short circuit condition in dependence on a first voltage monitor signal, a second voltage monitor signal and the current monitor signal, wherein the first voltage monitor signal is indicative of a voltage at an anode of the light source module, the second voltage monitor signal is indicative of a voltage drop across the light source module, and the current monitor signal is further indicative of a voltage at a cathode of the light source module, wherein the protection unit comprises: a difference unit for generating a difference signal indicative of a difference between the first voltage monitor signal and the current monitor signal; a first comparator for comparing the difference signal to a first protection threshold; a second comparator for comparing the current monitor signal to a second protection threshold; a third comparator for comparing the second voltage monitor signal to a third protection threshold; an OR gate for performing a logical OR operation on an output of the first comparator and an output of the third comparator; an AND gate for performing a logical AND operation on an output of the OR gate and an output of the second comparator; and a timing unit for generating an alarm signal in dependence on an output of the AND gate, the first pulse width modulated signal, the second pulse width modulated signal and a predetermined time duration.

13. The controller of claim 11, wherein, The controller further comprises: a dimming unit, the dimming unit comprising: a first capacitor for generating an analog signal in dependence on a third pulse width modulated signal, wherein the first capacitor is charged if the third pulse width modulated signal is in a first state and discharged if the third pulse width modulated signal is in a second state, wherein a level of the analog signal is proportional to a duty cycle of the third pulse width modulated signal, wherein the controller adjusts the current of the first string of light emitting diodes and the current of the second string of light emitting diodes by comparing the analog signal to the current monitor signal.

14. The controller of claim 13, wherein, The dimming unit further comprises: an amplifier for generating a current charging the first capacitor according to a setting signal, wherein the setting signal is generated by a voltage divider according to a reference voltage signal provided by a reference voltage terminal of the controller.

15. The controller of claim 13, wherein, The controller further comprises: an amplifier for comparing the analog signal and the current monitoring signal to generate an error signal; a gradual start-up unit for generating a gradual start-up signal by charging and discharging a second capacitor, wherein the gradual start-up signal is a voltage on the second capacitor, the gradual start-up unit comprising: a discharging unit for generating a discharging control signal according to the first pulse width modulation signal and the second pulse width modulation signal; a comparator for comparing the error signal and the gradual start-up signal; a flip-flop for generating a charging control signal according to an output of the comparator; and an OR gate for generating a selection signal according to the charging control signal and the discharging control signal, wherein the charging control signal is for turning on a third switch to charge the second capacitor, and the discharging control signal is for turning on a fourth switch to discharge the second capacitor, wherein the controller further comprises a multiplexer for selectively transmitting the error signal and the gradual start-up signal to the step-down control unit according to the selection signal, wherein when the first switch is turned on, if a voltage of the gradual start-up signal is less than the error signal, the step-down control unit adjusts the current of the first LED string according to the gradual start-up signal, wherein when the first switch is turned off, the step-down control unit adjusts the current of the first LED string according to the gradual start-up signal.

16. The controller of claim 9, wherein, The controller further comprises: a power terminal coupled with an output capacitor of the step-up converter for providing a current charging the output capacitor; a surge current control unit for adjusting the current according to an output voltage of the step-up converter, wherein the surge current control unit comprises: a first comparator for comparing the output voltage of the step-up converter with a first threshold value; a second comparator for comparing the output voltage of the step-up converter with a second threshold value; a selection unit for selecting one reference signal from a plurality of reference signals according to an output of the first comparator and an output of the second comparator; a current monitoring unit for generating a monitoring signal indicative of the current; and an error amplifier for controlling a transistor coupled in series with the output capacitor to adjust the current according to the monitoring signal and the reference signal selected by the selection unit.

17. The controller of claim 9, wherein, The controller further comprises: a power limiting unit for controlling the step-up converter to adjust the output voltage of the step-up converter to be lower than a voltage threshold value, and for controlling the step-up converter to adjust an input current received by the controller from a power source to be lower than a current threshold value, wherein the power limiting unit comprises: a first error amplifier for comparing a voltage monitoring signal indicative of the output voltage of the step-up converter with a first threshold signal indicative of the voltage threshold value; a second error amplifier configured to compare a current monitor signal indicative of the input current to a second threshold signal indicative of the current threshold; and a selection unit configured to selectively pass an output of the first error amplifier and an output of the second error amplifier to the boost control unit.

18. The controller of claim 9, wherein, The controller further comprises: a power limiting unit configured to control the boost converter to regulate an output voltage of the boost converter to be lower than a voltage threshold and to control the boost converter to regulate an output current of the boost converter to be lower than a current threshold, wherein the power limiting unit comprises: a first error amplifier configured to compare a voltage monitor signal indicative of the output voltage to a first threshold signal indicative of the voltage threshold; a second error amplifier configured to compare a current monitor signal indicative of the output current to a second threshold signal indicative of the current threshold; and a selection unit configured to selectively pass an output of the first error amplifier and an output of the second error amplifier to the boost control unit.

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