JP6436226B2 - Light emitting load driving device and light emitting device - Google Patents

Description

  The present invention relates to a light emitting load driving device for driving, for example, an LED (light emitting diode) and a light emitting device including the driving device.

  Patent Document 1 discloses a conventional light-emitting load driving device and light-emitting device that does not turn off other LEDs even if any one of a plurality of LEDs connected in series is disconnected. The conventional driving device includes a disconnection detection circuit and a bypass switch connected in parallel to the LED. When the LED is disconnected, an alternative path for the LED current is secured by turning on the bypass switch. Further, the disconnection of the LED is output to the outside of the driving device via a wired OR circuit.

JP2003-209933A

  When the LED is disconnected in the conventional driving device, the LED current flows through the bypass switch and the disconnection detection circuit. Therefore, a power loss corresponding to the magnitude of the LED current occurs in the disconnection detection circuit. If the LED is a small-signal LED, the power loss in the disconnection detection circuit is small and can be ignored, but if the LED is a power LED for general lighting or a vehicle headlamp, the power loss becomes very large. Further, in the case of a power LED, the disconnection detection circuit must be configured with large individual components in consideration of heat dissipation, and there are problems of mounting area and cost.

  The present invention provides a light-emitting load driving device and a light-emitting device including an abnormality detecting unit configured to reduce power loss, reduce the mounting area, and be configured at low cost.

According to the present invention, a light emitting load driving device drives a light emitting load in which a first light emitting element and a second light emitting element are connected in series and a first potential difference is applied to both ends thereof. A load driving device, connected in parallel to each of the first light emitting element and the second light emitting element, and dimming the light emitting load by bypassing a current flowing through the light emitting element. A switching element, a drive signal output unit for switching the switching element, and an abnormality detection unit connected to the first light emitting element and driven by a second potential difference smaller than the first potential difference. And the abnormality detection unit outputs an abnormality detection signal synchronized with the switching drive based on a voltage between both ends of the first light emitting element .

According to the present invention, the abnormality detection unit driven by the second potential difference smaller than the first potential difference applied to the light emitting load is provided , and the abnormality detection unit performs switching driving based on the both-ends voltage of the first light emitting element. Since an abnormality detection signal synchronized with the output is output , power loss is reduced, and a light emitting load driving device and a light emitting device including an abnormality detecting unit configured to reduce the mounting area and cost can be provided. In addition, the disconnection state of the light emitting element can be detected.

It is a circuit diagram which shows the structure of the drive device of the light emission load which concerns on embodiment of this invention, and a light-emitting device. It is a circuit diagram which shows the structure of the abnormality detection part which concerns on 1st Example of this invention. It is a circuit diagram which shows the structure of the abnormality detection part which concerns on 2nd Example of this invention. It is a circuit diagram which shows the structure of the drive device of the light emission load which concerns on 3rd Example of this invention. It is a circuit diagram which shows the structure of the drive device of the light emission load which concerns on the 4th Example of this invention. It is a circuit diagram which shows the structure of the drive device and light-emitting device of the light emission load which concerns on the modification of this invention.

  Next, an embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic. Further, the embodiments described below exemplify apparatuses and methods for embodying the technical idea of the present invention, and the embodiments of the present invention have the following structure and arrangement of components. It is not something specific. The embodiment of the present invention can be variously modified within the scope of the claims.

  FIG. 1 is a circuit diagram showing a configuration of a light emitting load driving device and a light emitting device according to an embodiment of the present invention. The light-emitting device according to the embodiment of the present invention includes a light-emitting load 2 that includes a plurality of light-emitting elements D and is applied with a first potential difference V1 from a first power supply Vdc1 at both ends thereof, and a drive device that drives the light-emitting load 2. 1. The driving device 1 is connected to the switching element M for dimming the light emitting load 2, the drive signal output unit 12 for switching the switching element M, and the light emitting element D, and is applied from the second power source Vdc2. And an abnormality detection unit 13 driven by a second potential difference V2 smaller than one potential difference V1.

The light emitting load 2 includes a plurality of light emitting elements D1, D2,. The light emitting device is connected to the light emission control unit 3. The light emitting elements D1, D2,..., Dn are, for example, LEDs. The light emitting elements D1, D2,..., Dn are connected in series with each other between the positive terminal and the negative terminal of the first power supply Vdc1. The light emitting load 2 is applied with the first voltage V1 from the first power supply Vdc1. Light-emitting device, the control signals _{S C1, S} C2 ··· output from the light emission control unit _3, based on the _{S Cn,} the first power supply Vdc1 emitting element a DC power supplied from the D1, D2 · · ·, Dn To supply.

The driving device 1 includes a plurality of switching elements M1, M2,..., Mn and a gate driving unit 10. The drive device 1 is configured as a single semiconductor integrated circuit, for example. The drive device 1 is connected to the light emission load 2, the light emission control unit 3, and the first power supply Vdc1. Driving device 1, the control signals _{S C1, S} C2 ··· output from the light emission control unit _3, based on the _{S Cn,} adjusts the light emitting device D1, D2 · · ·, the brightness of Dn individually. The light emission control unit 3 is configured by a digital circuit using an ASIC, FPGA, or the like, a microcomputer, or the like. The light emission control unit 3 outputs pulse-like control signals S _C1 , S _C2 ..., S _Cn in order to individually determine the light emission luminances of the light emitting elements D1, D2 _,.

The plurality of switching elements M1, M2,..., Mn are, for example, MOSFETs. The switching elements M1, M2,..., Mn are connected in series between the positive terminal and the negative terminal of the first power supply Vdc1. The switching elements M1, M2,..., Mn are connected in parallel to the light emitting elements D1, D2,. When the switching elements M1, M2,..., Mn are in the off state, the direct current supplied from the first power supply Vdc1 flows through the light emitting elements D1, D2,. Each of the switching elements M1, M2,..., Mn bypasses the current I _LED flowing through each of the plurality of light emitting elements D1, D2,..., Dn based on the first potential difference V1 when in the on state. The light emitting load 2 is dimmed.

The gate drive unit 10 according to the present embodiment includes a signal processing unit 11, a plurality of drive signal output units 12-1, 12-2, ... 12-n, and a plurality of abnormality detection units 13-1, 13-2, ... 13-n. The gate driving unit 10 repeats high and low levels based on the control signals S _C1 , S _C2 , S _Cn output from the light emission control unit 3, and pulsed driving signals S ₁ , S _2. , _Sn are generated. Driving signals _{S 1,} S 2 · · ·, the ratio of high level and a low level of _{S n} (Duty), the control signals _{S C1,} S C2 · · _·, are modulated on the basis of the _{S Cn.} Driving signals _{S 1, S 2 ···, S} n , the drive signal output units 12-1 and 12-2, via the · · · 12-n, the switching element M1, M2 · · ·, the gate terminal of the Mn Is output. The gate driver 10 individually drives the switching elements M1, M2,..., Mn by PWM (Pulse Width Modulation). For example, a first driving signal S ₁ is at a high level, the first switching element M1 is turned on, the light emission load is turned off. When the first driving signal S ₁ is at the low level, the first switching element M1 is turned off, the light emission load is light. The gate driving unit 10 controls the on-state time and the off-state time of each switching element according to the control signals S _C1 , S _C2 , S _Cn , so that the light-emitting elements D1, D2,. The brightness of Dn is adjusted individually.

The signal processing unit 11 is connected to the light emission control unit 3, the signal output units 12-1, 12-2,..., 12-n, and the abnormality detection units 13-1, 13-2,. The The signal processing unit 11, a control signal _{S C1,} S C2, _..., driving signal _{S Cn S 1, S 2 ···} , is converted to _{S n} signal output unit 12-1, 12-2 ... Output to 12-n. In addition, the signal processing unit 11 outputs an abnormality signal output from the abnormality detection units 13-1, 13-2,..., 13-n to the light emission control unit 3.

The drive signal output units 12-1, 12-2,..., 12-n are connected to the signal processing unit 11 and the switching elements M1, M2,. Driving signal output unit 12-1 and 12-2 · · ·, 12-n, the drive signals _{S 1,} S 2 · · ·, when _{S n} is high, the switching elements M1, M2 · · ·, the Mn Control to ON state. Driving signal output unit 12-1 and 12-2 · · ·, 12-n, the drive signals _{S 1,} S 2 · · ·, when _{S n} is low, the switching elements M1, M2 · · ·, the Mn Control to off state.

  FIG. 2 is a circuit diagram showing the configuration of the abnormality detection unit according to the first embodiment of the present invention. Here, the first abnormality detection unit 13-1 connected to the first light emitting element D1 will be described, and description of the second abnormality detection unit and the nth abnormality detection unit having the same configuration will be omitted. . The first abnormality detection unit 13-1 is connected to both ends of the first light emitting element D1 through the input terminals T1a and T1b, is connected to the second power supply Vdc2 through the power supply terminal Tvcc, and is connected to the second power supply. It is driven by the second potential difference V2 applied from Vdc2. The second potential difference Vdc2 is set smaller than the first potential difference V1. The first abnormality detector 13-1 includes the first converter R1, the second converter R2, the first current mirror circuits Q1 and Q2, the second current mirror circuits Q3 to Q5, and the starting resistor R3. Prepare.

  The first conversion unit R1 converts the voltage across the first light emitting element D1 into a current signal and outputs the current signal. One end of the first conversion unit R1 is connected to the cathode of the first light emitting element D1 via the input terminal T1b, and the other end is connected to the emitter of the second transistor Q2. The second conversion unit R2 converts the current signal output from the first conversion unit R1 into a voltage signal and outputs the voltage signal. One end of the second conversion unit R2 is grounded, and the other end is connected to the collector of the third transistor Q3. The first conversion unit R1 and the second conversion unit R2 are preferably resistance elements having the same temperature characteristics such as a well-known polysilicon resistance and diffusion resistance.

  The first transistor Q1 and the second transistor Q2 are NPN transistors, respectively, and constitute a first current mirror circuit connected to the first conversion unit R1. The emitter of the first transistor Q1 is connected to the anode of the first light emitting element D1 via the input terminal T1a, and the collector is connected to the collector of the fifth transistor Q5. The base of the first transistor Q1 is connected to the base of the second transistor Q2 and to its own collector. The collector of the second transistor Q2 is connected to the collector of the fourth transistor Q4.

  The third transistor Q3, the fourth transistor Q4, and the fifth transistor Q5 are PNP transistors, respectively, and constitute a second current mirror circuit connected to the second conversion unit R2. The emitter of the third transistor Q3 is connected to the second power supply Vdc2 through the power supply terminal Tvcc together with the emitters of the fourth and fifth transistors Q4 and Q5. The base of the third transistor Q3 is connected to the bases of the fourth and fifth transistors Q4 and Q5. The collector of the fourth transistor Q4 is connected to its base. The collector and emitter of the fifth transistor Q5 are connected to both ends of the starting resistor R3. The connection point between the collector of the third transistor Q3 and the second conversion unit R2 is connected to the non-inverting input terminal of the disconnection detection comparator Comp_open via the output terminal To1.

  If the base-emitter voltage of the first and second transistors Q1, Q2 is the same VF, the emitter voltage of the second transistor Q2 becomes equal to the terminal voltage of the input terminal T1a. Therefore, the voltage VR1 across the first converter R1 is equal to the potential difference between the input terminals T1a and T1b, that is, the voltage across the first light emitting element D1 is equal to VD1. The magnitude of the first current I1 flowing through the first converter R1 changes according to the voltage VD1. That is, the first converter R1 converts the voltage VD1 across the first light emitting element D1 into a current signal I1 and outputs it. The second current mirror circuit returns the first current I1 as the second current I2 and supplies it to the second conversion unit R2. The voltage VR2 across the second converter R2 changes according to the magnitude of the second current I2. That is, the second conversion unit R2 converts the current signal I2 into the voltage signal VR2 and outputs it.

  With the above configuration, when the second potential difference V2 is applied to the first abnormality detector 13-1, the reference current I3 corresponding to the resistance value of the starting resistor R3 flows to the first and second current mirror circuits. . The first current I1 is a current corresponding to the reference current I3, and changes according to the voltage VD1 across the first light emitting element D1. Further, the voltage signal VR2 changes according to the change of the first current I1, that is, the change of the voltage VD1 across the first light emitting element D1. The disconnection detection comparator Comp_open compares the first reference voltage Vref1 connected to the inverting input terminal with the voltage signal VR2, and outputs the disconnection detection signal Vcomp_open. In this way, the drive device 1 detects the disconnection of the first light emitting element D1 by the first abnormality detection unit 13-1 detecting the voltage VD1 and converting it to the voltage signal VR2 with the ground potential as a reference. can do.

  Therefore, since the driving apparatus 1 according to the present embodiment includes the abnormality detection unit to which the second potential difference V2 smaller than the first potential difference V1 is applied from the second power supply Vdc2, the power loss is reduced and the mounting area is reduced. It is configured at low cost. Further, if the first and second conversion units R1 and R2 are resistance elements having the same temperature characteristics, the temperature characteristics and variations in the abnormality detection unit 13 are canceled out, so that the accuracy of the disconnection detection voltage of the light emitting load 2 is improved. Can be increased.

  FIG. 3 is a circuit diagram showing the configuration of the abnormality detection unit according to the second embodiment of the present invention. The difference of the second embodiment from the first embodiment is that a short circuit detection comparator Comp_short connected to the output terminal To1 is provided. The short circuit detection comparator Comp_short compares the second reference voltage Vref2 connected to the inverting input terminal with the voltage signal VR2, and outputs a short circuit detection signal Vcomp_short. In this way, the driving device 1 can detect a short circuit of the first light emitting element D1 by the first abnormality detector 13-1 detecting the voltage VD1 and converting it to the voltage signal VR2.

  Incidentally, in the light emitting device of FIG. 1, the connection between the driving device 1 and the first power supply Vdc1 and the light emitting load 2 may become unstable. In that case, the drive device 1 is required to provide a function of detecting the disconnection state of the light emitting elements D1, D2,..., Dn and notifying the light emission control unit 3 of the disconnection state. FIGS. 4 and 5 are circuit diagrams showing the configuration of the drive device for the light emitting load according to the third and fourth embodiments of the present invention, which satisfies such a requirement. Here, the configuration provided in the gate driving unit 10 corresponding to the nth light emitting element Dn will be described, and the description of the same configuration will be omitted.

  The signal processing unit 11a constituting the light emitting load driving device according to the third embodiment includes a holding unit 14a that holds the logic level of the abnormality detection signal over a plurality of switching drive cycles. The holding unit 14a is connected to the light emission control unit 3 and the abnormality detection unit 13-n. The holding unit 14 a includes a NOT circuit, an AND circuit, and a flip-flop 15. The input terminal of the NOT circuit is connected to the output terminal of the disconnection detection comparator Comp_open constituting the abnormality detection unit 13-n and the SET terminal of the flip-flop 15. One input terminal of the AND circuit is connected to the output terminal of the NOT circuit, and the other input terminal of the AND circuit is connected to the light emission control unit 3. The output terminal of the AND circuit is connected to the RESET terminal of the flip-flop 15. The OUT terminal of the flip-flop 15 is connected to the light emission control unit 3.

The abnormality detection unit 13-n outputs an abnormality detection signal synchronized with the switching drive of the switching element based on the voltage across the light emitting element. Holding section 14a, the period the light-emitting element is the disconnection state of the n, on the basis of a disconnection detection signal Vcomp_open, holds the diagnostic signal _{S Dn} to the H level. When the light emitting element returns from the disconnected state, the holding unit 14a inverts the diagnostic signal _SDn to L level simultaneously with the rise of the control signal _SCn . With the above configuration, the driving device 1 can detect the disconnection state of the light emitting elements D1, D2,..., Dn and notify the light emission control unit 3 of the disconnection state.

  The signal processing unit 11b configuring the light emitting load driving device according to the fourth embodiment is different from the signal processing unit 11a in that it includes a holding unit 14b that holds the logic level of the abnormality detection signal over a plurality of periods of switching driving. The holding unit 14 b includes a flip-flop 15 and a counter 16. The SET terminal of the flip-flop 15 is connected to the output terminal of the disconnection detection comparator Comp_open constituting the abnormality detection unit 13-n. The RESET terminal of the flip-flop 15 is connected to the output terminal of the counter 16. The CLK terminal of the counter 16 is connected to the output terminal of the short circuit detection comparator Comp_short that constitutes the abnormality detection unit 13-n. The RES terminal of the counter 16 is connected to the output terminal of the disconnection detection comparator Comp_open.

Holding section 14a, the period the light-emitting element is the disconnection state of the n, on the basis of a disconnection detection signal Vcomp_open, holds the diagnostic signal _{S Dn} to the H level, and resets the counter 16. When the light emitting element returns from the disconnected state, the counter 16 starts counting based on the short circuit detection signal Vcomp_short. The counter 16 resets the flip-flop 15 when the internal bits reach a predetermined number of bits. With the above configuration, the driving device 1 can detect the disconnection state of the light emitting elements D1, D2,..., Dn and notify the light emission control unit 3 of the disconnection state. In addition, since the diagnostic signal _SDn is held using a signal with a small time difference, the reliability of the diagnostic signal _SDn is improved.

  As mentioned above, although this invention was described by embodiment, it should not be understood that the description and drawing which form a part of this indication limit this invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art. That is, it goes without saying that the present invention includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

  For example, as shown in FIG. 6A, in the driving device 1, the switching element M may be connected between the first power supply Vdc1 and the light emitting load 2. In this case, the switching element M dimmes the light emitting load 2 by applying the first potential difference V1 to the light emitting load 2 when in the ON state. Further, as shown in FIG. 6B, the gate driving unit 10 may include a reactor L, a capacitor C, and a diode D, and the driving device 1 is a switching regulator including a switching element M and the gate driving unit 10. Also good. In this case, the gate drive unit 10 drives the switching element M by PWM to control the first potential difference V1 generated at both ends of the capacitor C to a desired magnitude and applies the light to the light emitting load 2 to emit light. Dimming load 2

  The driving device 1 may be composed of a plurality of switching elements M1, M2,..., Mn made up of individual devices and a gate drive unit 10 made up of a semiconductor integrated circuit. Further, the first and second current mirror circuits may be constituted by MOSFETs instead of bipolar transistors. The driving device 1 may include at least one of the light emission control unit 3 and the first power supply Vdc1. Moreover, each of the plurality of light emitting elements D1, D2,..., Dn may be configured by a plurality of LEDs. Further, the drive signal output units 12-1, 12-2,..., 12-n may be connected to the light emission control unit 3 without passing through the signal processing unit 11.

DESCRIPTION OF SYMBOLS 1 Drive apparatus 2 Light emission load 3 Light emission control part 10 Gate drive part 12 Drive signal output part 13 Abnormality detection part D1 1st light emitting element D2 2nd light emitting element Dn nth light emitting element M1 1st switching element M2 2nd Switching element Mn nth switching element V1 first potential difference V2 second potential difference Vdc1 first power supply Vdc2 second power supply R1 first converter R2 second converter Q1 first transistor Q2 second transistor Transistor Q3 Third transistor Q4 Fourth transistor Q5 Fifth transistor

Claims (2)

A light emitting load driving device for driving a light emitting load in which a first potential difference is applied to both ends of a first light emitting element and a second light emitting element connected in series,
A switching element connected in parallel to each of the first light-emitting element and the second light-emitting element, and dimming the light-emitting load by bypassing a current flowing through the light-emitting element ;
A drive signal output section for switching and driving the switching element;
An abnormality detection unit connected to the first light emitting element and driven by a second potential difference smaller than the first potential difference , and
The abnormality detection unit outputs an abnormality detection signal synchronized with the switching drive based on a voltage between both ends of the first light emitting element . A light-emitting device comprising: a light-emitting load in which the first light-emitting element and the second light-emitting element are connected in series; and the light-emitting load driving device according to claim 1.

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