Lighting circuit, and lighting device for vehicle

Abstract

To provide a lighting circuit capable of restricting heat generation and power consumption of a diode for reverse connection protection.SOLUTION: A lighting circuit includes: a drive circuit for driving a light source; a first diode having an anode connected to a first line to which a first power supply voltage is applied and a cathode connected to the drive circuit; a first switch connected to the first diode in parallel; a second diode having an anode connected to a second line to which a second power supply voltage is applied and a cathode connected to the drive circuit; a first switch control circuit for turning on the first switch if the second power supply voltage is not applied to the second line, and for turning off the first switch if the second power supply voltage is applied to the second line; and a control circuit for causing the drive circuit to supply first drive current to the light source if the first power supply voltage is applied to the first line and for causing the drive circuit to supply second drive current to the light source if the second power supply voltage is applied to the second line.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a lighting circuit and a vehicle lamp.

Background Art

[0002] For example, some lighting circuits for lighting a light source include a reverse connection protection circuit that protects the lighting circuit when the battery power supply is reversely connected (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, when a diode is used as a reverse connection protection circuit in such a lighting circuit, a current with a large current value flows through the diode, and heat generation and power consumption by the diode may become problems.

[0005] An object of the present invention is to provide a lighting circuit capable of suppressing heat generation and power consumption of a diode for reverse connection protection.

Means for Solving the Problems

[0006] The main invention for achieving the above object is a lighting circuit comprising: a drive circuit for driving a light source; a first diode having an anode connected to a first line to which a first power supply voltage is applied and a cathode connected to the drive circuit; a first switch connected in parallel with the first diode; a second diode having an anode connected to a second line to which a second power supply voltage is applied and a cathode connected to the drive circuit; a first switch control circuit for turning on the first switch when the second power supply voltage is not applied to the second line and turning off the first switch when the second power supply voltage is applied to the second line; and a control circuit for causing the drive circuit to supply a first drive current to the light source when the first power supply voltage is applied to the first line and causing the drive circuit to supply a second drive current to the light source when the second power supply voltage is applied to the second line.

Advantages of the Invention

[0007] According to the present invention, it is possible to provide a lighting circuit capable of suppressing heat generation and power consumption of a diode for reverse connection protection.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Embodiments for Carrying Out the Invention

[0009] From the descriptions in this specification and the accompanying drawings, at least the following matters become clear.

[0010] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Note that the same or equivalent components, members, etc. shown in each drawing are denoted by the same reference numerals, and duplicate explanations are appropriately omitted.

[0011] In addition, in this embodiment, "connection" means a state of being electrically connected unless otherwise specified. Therefore, "connection" includes cases where two components are connected not only by wiring but also, for example, via a resistor.

[0012] =====This Embodiment (First Embodiment)===== <<Configuration of Vehicle Lamp 1>> FIG. 1 is a diagram showing an example of the configuration of the vehicle lamp 1 of this embodiment. The vehicle lamp 1 includes a light source 10 and a lighting circuit 20a.

[0013] The light source 10 is lit by the driving current Iout supplied from the lighting circuit 20a. In the present embodiment, the light source 10 is used for a daytime running lamp (daytime running light, hereinafter referred to as DRL) and a clearance lamp (hereinafter referred to as CLL). Note that the DRL is a lamp that lights up to notify pedestrians, drivers of oncoming vehicles, etc. of the presence of a moving vehicle during the day, and is also called a daylight. The CLL is a lamp for indicating the size and presence of a vehicle in the width direction of the vehicle, and is also called a side marker lamp or a small lamp. As will be described later, the DRL lights up brighter than the CLL.

[0014] The light source 10 includes a plurality of light-emitting elements (for example, light-emitting diodes (LEDs)). However, the light-emitting elements are not limited to LEDs, and may be other semiconductor light-emitting elements such as laser diodes (LDs) and organic EL elements.

[0015] Also, although details will be described later, when the light source 10 lights up as a DRL, the lighting circuit 20a supplies the driving current Iout having a predetermined current value Id (for example, several hundred mA) to the light source 10. On the other hand, when the light source 10 lights up as a CLL, the lighting circuit 20a supplies the driving current Iout having a current value Ic (for example, several tens of mA) that is (on average) smaller than the predetermined current value Id to the light source 10. In this way, the DRL lights up brighter than the CLL.

[0016] The lighting circuit 20a is a circuit that controls the lighting and extinguishing of the light source 10 of the vehicle lamp 1. A power supply voltage Vbat (hereinafter also simply referred to as voltage Vbat) from a vehicle battery 30 is applied to each of the terminals Ta and Tb of the lighting circuit 20a via switches SW0 and SW1, respectively. Note that the voltage applied to the terminal Ta via the switch SW0 is defined as voltage Vd, and the voltage applied to the terminal Tb via the switch SW1 is defined as voltage Vc.

[0017] Also, for convenience, although different notations are used for voltages Vd and Vc, since the on-resistances of switches SW1 and SW2 are sufficiently small, the voltage levels of voltages Vd and Vc when each of switches SW1 and SW2 is on are the same as the voltage level of voltage Vbat. Note that voltage Vd corresponds to the "first power supply voltage", and voltage Vc corresponds to the "second power supply voltage".

[0018] And the lighting circuit 20a supplies a drive current Iout based on the on / off states of switches SW0 and SW1, and lights or turns off the light source 10 provided between terminals Td and Te as DRL or CLL. Note that terminal Tc is grounded. Also, hereinafter, the case where switch SW0 is on may be expressed as "voltage Vd is applied", and the case where switch SW0 is off may be expressed as "voltage Vd is not applied". Also, the case where switch SW1 is on may be expressed as "voltage Vc is applied", and the case where switch SW1 is off may be expressed as "voltage Vc is not applied".

[0019] <<Configuration of Lighting Circuit 20a>> FIG. 2 is a diagram showing an example of the configuration of the lighting circuit 20a. The lighting circuit 20a includes diodes 100, 104 to 106, a PMOS transistor 101, a Zener diode 102, a capacitor 103, a switch control circuit 107, a control circuit 108a, and a drive circuit 109.

[0020] Diode 100 is a reverse protection diode. Diode 100 prevents current from flowing in the direction opposite to the original direction through parasitic elements of the lighting circuit 20a, for example, when voltage Vbat is applied to terminal Tc and terminal Ta is grounded (i.e., the battery 30 is reversely connected).

[0021] Diode 100 has an anode connected to line L1 to which voltage Vd is applied via terminal Ta, and a cathode connected to the drive circuit 109 (described later).

[0022] When there is no PMOS transistor 101 described later, when the voltage Vbat is applied only to terminal Ta, a current corresponding to the drive current Iout of the predetermined current value Id when the light source 10 is lit as DRL flows through the diode 100. Note that since the predetermined current value Id is, for example, several hundred mA, when a current flows through the diode 100 in this way, heat generation or power consumption of the diode 100 becomes a problem. Note that the diode 100 corresponds to the "first diode", and the line L1 corresponds to the "first line".

[0023] The PMOS transistor 101 is an element connected in parallel with the diode 100. Although details will be described later, the PMOS transistor 101 is turned on when only the voltage Vd is applied to terminal Ta, and suppresses the flow of current through the diode 100. On the other hand, the PMOS transistor 101 is turned off when the voltage Vc is applied to terminal Tb. Thereby, the PMOS transistor 101 prevents the voltage Vc from being applied to terminal Ta.

[0024] Also, when the PMOS transistor 101 is turned on, since the on-resistance of the PMOS transistor 101 is small, the current flowing through the diode 100 is suppressed. Thereby, heat generation and power consumption of the diode 100 are suppressed. Note that the PMOS transistor 101 corresponds to the "first switch".

[0025] The Zener diode 102 is an element for protecting the PMOS transistor 101, with its anode connected to the gate terminal of the PMOS transistor 101 and its cathode connected to the source terminal of the PMOS transistor 101. The Zener diode 102 suppresses the application of a voltage equal to or higher than the breakdown voltage between the gate and source of the PMOS transistor 101 when a positive surge voltage is applied to terminal Ta.

[0026] The capacitor 103 is an element for protecting the PMOS transistor 101 from a negative surge voltage applied to the terminal Ta, and is connected between the gate terminal and the source terminal of the PMOS transistor 101. Specifically, the capacitor 103, together with other circuit elements, constitutes an integrating circuit having a predetermined time constant, and thus keeps the PMOS transistor 101 on for a period corresponding to a predetermined constant.

[0027] The diode 104 is a diode for reverse connection protection. For example, when a voltage Vbat is applied to the terminal Tc and the terminal Tb is grounded (i.e., the battery 30 is reversely connected), the diode 104 prevents a current from flowing in a direction opposite to the original direction through parasitic elements of the lighting circuit 20a or the like.

[0028] The diode 104 has an anode connected to a line L2 to which a voltage Vc is applied via the terminal Tb, and a cathode connected to a drive circuit 109 (described later).

[0029] When only the voltage Vc is applied to the terminal Tb, the lighting circuit 20a lights the light source 10 as a CLL, and a current corresponding to the drive current Iout of the current value Ic flows through the diode 104. Note that the current value Ic is, for example, several tens of mA. Also, the diode 104 corresponds to the "second diode", and the line L2 corresponds to the "second line".

[0030] The diode 105 is a diode for reverse connection protection, similar to the diode 104. Its anode is connected to the line L2, and its cathode is connected to the control circuit 108a. Also, the diode 106 is a diode for reverse connection protection, similar to the diode 100. Its anode is connected to the line L1, and its cathode is connected to the control circuit 108a.

[0031] The switch control circuit 107 is a circuit that outputs a voltage Vq for turning on and off the PMOS transistor 101 based on the voltage Vp from the diode 105. Specifically, when the voltage Vc is not applied to the terminal Tb and the voltage Vp becomes the ground voltage, the switch control circuit 107 turns on the PMOS transistor 101. On the other hand, when the voltage Vc is applied to the terminal Tb and the voltage Vp becomes a voltage corresponding to the voltage Vbat, the switch control circuit 107 turns off the PMOS transistor 101.

[0032] <<Configuration and Operation of Switch Control Circuit 107>> FIG. 3 is a diagram showing an example of the configuration of the switch control circuit 107. The switch control circuit 107 includes resistors 200 to 202, 204, 207, NPN transistors 203, 206, and a capacitor 205.

[0033] The resistors 200 and 201 are resistors for dividing the voltage Vp, and generate a voltage for turning on and off the NPN transistor 203 from the connection point via the resistor 202. The resistor 202 is a resistor for determining or adjusting the current flowing through the base terminal of the NPN transistor 203.

[0034] The NPN transistor 203 has its collector terminal connected to the voltage Vcc via the resistor 204, and its emitter terminal grounded. Thereby, the collector voltage of the NPN transistor 203 becomes the ground voltage when the NPN transistor 203 is on, and becomes the voltage Vcc when the NPN transistor 203 is off. The voltage Vcc is a constant voltage generated in the lighting circuit 20a based on the voltage Vd or the voltage Vc.

[0035] The capacitor 205 is an element for stabilizing the collector voltage of the NPN transistor 203. One end of the capacitor 205 is connected to the collector terminal of the NPN transistor 203, and the other end is grounded.

[0036] The NPN transistor 206 has the collector voltage of the NPN transistor 203 applied to its base terminal, its collector terminal connected to the gate terminal of the PMOS transistor 101 in FIG. 1 via the resistor 207, and its emitter terminal grounded.

[0037] Therefore, when the voltage Vc is not applied to the terminal Tb and the voltage Vp becomes the ground voltage, the NPN transistor 203 turns off and the NPN transistor 206 turns on. In this case, the switch control circuit 107 outputs the voltage Vq that turns on the PMOS transistor 101.

[0038] On the other hand, when the voltage Vc is applied to the terminal Tb and the voltage Vp becomes a voltage corresponding to the voltage Vbat, the NPN transistor 203 turns on and the NPN transistor 206 turns off. In this case, the collector terminal of the NPN transistor 206 becomes an open state, and the PMOS transistor 101 does not turn on due to the Zener diode 102 in FIG. 1. Therefore, the switch control circuit 107 turns off the PMOS transistor 101. Note that the switch control circuit 107 corresponds to the "first switch control circuit".

[0039] <<Configuration and Operation of Control Circuit 108a>> FIG. 4 is a diagram showing an example of the configuration of the control circuit 108a. The control circuit 108a is a circuit for lighting the light source 10 as the DRL when both SW0 and SW1 in FIG. 1 are on and the voltages Vd and Vc are applied to the terminals Ta and Tb, respectively. Therefore, the lighting circuit 20a operates in the "DRL mode".

[0040] The control circuit 108a includes resistors 300, 304 to 306, a Zener diode 301, capacitors 302, 307, an NPN transistor 303, an oscillation circuit (OSC) 308, and terminals Tx1 to Tx4, Ty1 to Ty7.

[0041] Note that terminals Tx1 to Tx4 are the terminals to which elements are connected in the case of the lighting circuit 20a. Although details will be described later, terminals Ty1 to Ty7 are the terminals to which elements are connected in the case of the lighting circuit 20b.

[0042] Resistor 300 is provided between terminals Tx1 and Tx2. One end has a voltage Vr (i.e., the voltage Vd via diode 106) applied thereto, and the other end is connected to the cathode of zener diode 301.

[0043] Zener diode 301 is an element that causes a voltage drop in the voltage Vr applied via resistor 300. Its anode is connected to one end of capacitor 302 and the base terminal of NPN transistor 303, and its cathode is connected to terminals Tx2 and Ty2. Note that the other end of capacitor 302 is grounded.

[0044] For NPN transistor 303, the collector terminal is connected to one end of resistor 304, and the emitter terminal is grounded.

[0045] Resistor 304 is provided between terminals Tx3 and Tx4 and, together with resistors 305 and 306, constitutes a voltage dividing circuit. When NPN transistor 303 is turned on, a voltage Vdiv obtained by dividing the voltage Vcc is generated at the connection point of resistors 305 and 306. On the other hand, when NPN transistor 303 is turned off, although details will be described later, the voltage level of the voltage Vdiv generated at the connection point of resistors 305 and 306 changes in a sawtooth waveform.

[0046] Capacitor 307 is an element that, together with resistor 306, constitutes an integrating circuit. Therefore, when NPN transistor 303 is turned off, the integrating circuit will be connected to the oscillation circuit 308 (described later).

[0047] The oscillation circuit (OSC) 308 is a circuit that controls the drive circuit 109 according to the voltage Vdiv. Specifically, when the NPN transistor 303 is on, the oscillation circuit 308 outputs a high-level (hereinafter referred to as "H" level) signal Sosc for lighting the light source 10 as DRL. On the other hand, when the NPN transistor 303 is off, an integrating circuit composed of a resistor 306 and a capacitor 307 is connected to the oscillation circuit 308, and the oscillation circuit 308 changes the voltage level of the voltage Vdiv in a sawtooth waveform according to the constant of the integrating circuit. Then, the oscillation circuit 308 compares the voltage level of the voltage Vdiv with a predetermined level and outputs a PWM-modulated signal Sosc for lighting the light source 10 as CLL. Note that the predetermined level is lower than the voltage level of the voltage Vdiv when the NPN transistor 303 is on.

[0048] That is, when the voltage Vr is a voltage corresponding to the voltage Vbat, the control circuit 108a outputs an "H" level signal Sosc for lighting the light source 10 as DRL. On the other hand, when the voltage Vr is the ground voltage, the control circuit 108a outputs a PWM-modulated signal Sosc for lighting the light source 10 as CLL.

[0049] Note that the duty of the PWM-modulated signal Sosc (that is, the ratio of the period of the signal Sosc during which the signal Sosc is at the "H" level to the period of the signal Sosc) is determined based on how much light intensity the light source 10 is lit as CLL.

[0050] The drive circuit 109 in FIG. 2 is a circuit that supplies a drive current Iout for lighting the light source 10 to the light source 10 based on the signal Sosc when at least one of the voltages Vd and Vc is applied to each of the terminals Ta and Tb.

[0051] Specifically, when at least one of the voltages Vd and Vc is applied to each of the terminals Ta and Tb, the drive circuit 109 supplies the drive current Iout to the light source 10 based on the "H" level signal Sosc. Therefore, the light source 10 emits light.

[0052] On the other hand, when at least one of the voltages Vd and Vc is applied to each of the terminals Ta and Tb, the drive circuit 109 stops supplying the drive current Iout to the light source 10 based on a signal Sosc at a low level (hereinafter referred to as the "L" level). Therefore, the light source 10 does not emit light. When the light source 10 is lit as a CLL (i.e., when the signal Sosc is PWM - modulated), the signal Sosc becomes the "L" level.

[0053] In addition, when neither of the voltages Vd and Vc is applied to each of the terminals Ta and Tb, the drive circuit 109 stops supplying the drive current Iout to the light source 10. Therefore, the light source 10 does not emit light (i.e., turns off).

[0054] Also, when only the voltage Vd is applied, the lighting circuit 20a causes the drive circuit 109 to supply a drive current Iout with a predetermined current value Id to the light source 10, and when only the voltage Vc is applied, the lighting circuit 20a causes the drive circuit 109 to supply a drive current Iout with a current value Ic to the light source 10. Further, when both the voltages Vd and Vc are applied, the lighting circuit 20a causes the drive circuit 109 to supply a drive current Iout with a predetermined current value Id to the light source 10.

[0055] Moreover, the drive circuit 109 supplies a drive current Iout with a predetermined current value Id to the light source 10 to light the light source 10 as a daytime running lamp, and supplies a drive current Iout with a current value Ic to the light source 10 to light the light source 10 as a clearance lamp. The drive current Iout with the predetermined current value Id corresponds to the "first drive current", and the drive current Iout with a current value Ic smaller than the predetermined current value Id corresponds to the "second drive current".

[0056] FIG. 5 is a diagram showing the lighting pattern of the light source 10. In FIG. 5, “H” of the power supplies Vd and Vc indicates the case where the power supplies Vd and Vc are respectively applied, and “L” of the power supplies Vd and Vc indicates the case where the power supplies Vd and Vc are not respectively applied. Also, “101” refers to the PMOS transistor 101. “ON” and “OFF” indicate the on / off of the PMOS transistor 101. Further, “DRL” and “CLL” in the column of “DRL mode” indicate whether the light source 10 lights up as DRL or as CLL.

[0057] First, when SW0 and SW1 in FIG. 1 are turned off and neither voltage Vd nor Vc is applied, since a voltage corresponding to Vbat is not applied to the drive circuit 109, the light source 10 is turned off. Note that since neither voltage Vd nor Vc is applied, the switch control circuit 107 does not operate and the PMOS transistor 101 is turned off.

[0058] Next, when SW0 is turned on, SW1 is turned off, and only voltage Vd is applied, a voltage corresponding to Vbat is applied to the drive circuit 109, and a signal Sosc of “H” level is input to the drive circuit 109. Therefore, the light source 10 lights up as DRL. Note that since voltage Vc is not applied to the terminal Tb, the switch control circuit 107 turns on the PMOS transistor 101. As a result, a current corresponding to the drive current Iout of a predetermined current value Id does not flow through the diode 100.

[0059] Furthermore, when SW0 is turned off, SW1 is turned on, and only voltage Vc is applied, a voltage corresponding to Vbat is applied to the drive circuit 109, and a PWM-modulated signal Sosc is input to the drive circuit 109. Therefore, the light source 10 lights up as CLL. Note that since voltage Vc is applied to the terminal Tb, the switch control circuit 107 turns off the PMOS transistor 101. As a result, the voltage Vc applied to the terminal Tb is not applied to the terminal Ta.

[0060] Finally, when SW0 and SW1 are turned on and both voltages Vd and Vc are applied, a voltage corresponding to the voltage Vbat is applied to the drive circuit 109, and a signal Sosc at the "H" level is input to the drive circuit 109. Therefore, the light source 10 lights up as a DRL.

[0061] In this way, when both voltages Vd and Vc are applied, the lighting circuit 20a lights up the light source 10 as a DRL. In this case, since the voltage Vc is applied to the terminal Tb, the switch control circuit 107 turns off the PMOS transistor 101.

[0062] Also, when both voltages Vd and Vc are applied, even if the PMOS transistor 101 is turned off, a voltage corresponding to the voltage Vbat is applied to the drive circuit 109 due to the voltages Vd and Vc. Therefore, a current corresponding to the drive current Iout with a predetermined current value Id does not flow only through the diode 100. As a result, heat generation and power consumption by the diode 100 are suppressed.

[0063] <<Operation of the lighting circuit 20a>> FIG. 6 is a diagram showing an example of the operation of the lighting circuit 20a. Before time t0, the voltages Vd and Vc are not applied, and the light source 10 is turned off. Also, since the voltage Vcc becomes the ground voltage, the voltage Vdiv also becomes the ground voltage, and the oscillation circuit 308 outputs a signal Sosc at the "L" level.

[0064] At time t0, when only the voltage Vd is applied, the voltage Vp to which the voltage Vc is applied via the diode 105 remains at the ground voltage. Therefore, the switch control circuit 107 outputs a voltage Vq that turns on the PMOS transistor 101. Then, the PMOS transistor 101 is turned on.

[0065] Also, the voltage Vr applied through the diode 106 to the voltage Vd becomes a voltage corresponding to the voltage Vbat. As a result, the voltage Vdiv in FIG. 4 becomes a voltage obtained by dividing the voltage Vcc. Therefore, the oscillation circuit 308 outputs a signal Sosc at the "H" level. Then, the light source 10 lights up as a DRL.

[0066] At time t1, when only the voltage Vc is applied, the voltage Vp applied through the diode 105 to the voltage Vc becomes a voltage corresponding to the voltage Vbat. Therefore, the switch control circuit 107 turns off the PMOS transistor 101. As a result, the application of the voltage Vc to the terminal Ta through the PMOS transistor 101 and the line L1 is suppressed.

[0067] Also, the voltage Vr applied through the diode 106 to the voltage Vd becomes the ground voltage. As a result, the voltage level of the voltage Vdiv in FIG. 4 changes in a sawtooth waveform. Therefore, the oscillation circuit 308 outputs a PWM-modulated signal Sosc. Then, the light source 10 lights up as a CLL.

[0068] At time t2, when both the voltages Vd and Vc are applied, the voltage Vp applied through the diode 105 to the voltage Vc becomes a voltage corresponding to the voltage Vbat. Therefore, the switch control circuit 107 turns off the PMOS transistor 101.

[0069] Also, the voltage Vr applied through the diode 106 to the voltage Vd becomes a voltage corresponding to the voltage Vbat. As a result, the voltage Vdiv in FIG. 4 becomes a voltage obtained by dividing the voltage Vcc. Therefore, the oscillation circuit 308 outputs a signal Sosc at the "H" level. Then, the light source 10 lights up as a DRL.

[0070] Therefore, when both the voltages Vd and Vc are applied to the lighting circuit 20a, the light source 10 lights up as a DRL. Also, in this case, although the PMOS transistor 101 is off, as described above, a large current does not flow through the diode 100, and the heat generation and power consumption of the diode 100 are suppressed.

[0071] ===Second Embodiment=== <<Configuration of Lighting Circuit 20b>> As shown in FIG. 2, the lighting circuit 20b includes diodes 100, 104 to 106, a PMOS transistor 101, a Zener diode 102, a capacitor 103, a switch control circuit 107, a control circuit 108b, and a drive circuit 109.

[0072] <<Configuration and Operation of Control Circuit 108b>> FIG. 7 is a diagram showing an example of the configuration of the control circuit 108b. The control circuit 108b is a circuit for lighting the light source 10 as CLL when both SW0 and SW1 in FIG. 1 are turned on and both voltages Vd and Vc are applied. Therefore, the lighting circuit 20b operates in the "CLL mode".

[0073] The control circuit 108b includes resistors 310, 305, 306, a Zener diode 301, capacitors 302, 307, NPN transistors 303, 312, an oscillation circuit (OSC) 308, and terminals Tx1 to Tx4, Ty1 to Ty7.

[0074] The resistor 310 is provided between the terminals Ty1 and Ty2, and a voltage Vp (that is, the voltage Vc via the diode 105) is applied to one end, and the other end is connected to the cathode of the Zener diode 301.

[0075] The resistor 311 is provided between the terminals Ty3 and Ty4, and a voltage Vcc is applied to one end, and the collector terminal of the NPN transistor 303 is connected to the other end. Therefore, when the NPN transistor 303 is turned on, the collector voltage of the NPN transistor 303 becomes the ground voltage, and when the NPN transistor 303 is turned off, the collector voltage of the NPN transistor 303 becomes the voltage Vcc.

[0076] The NPN transistor 312 has the collector voltage of the NPN transistor 303 applied to the base terminal connected to the terminal Ty5. The collector terminal connected to the terminal Ty6 is connected to the resistor 305, and the emitter terminal connected to the terminal Ty7 is grounded. Therefore, when the NPN transistor 303 is on, the ground voltage is applied to the terminal Ty5, and the NPN transistor 312 is off. When the NPN transistor 303 is off, the voltage Vcc is applied to the terminal Ty5, and the NPN transistor 312 is on.

[0077] Also, when the NPN transistor 312 is on, a voltage Vdiv obtained by dividing the voltage Vcc is generated at the connection point of the resistors 305 and 306. On the other hand, when the NPN transistor 312 is off, the voltage level of the voltage Vdiv changes in a sawtooth waveform. Note that the operation of the oscillation circuit 308 is the same as that in the case of the control circuit 108a.

[0078] That is, when the voltage Vp is a voltage corresponding to the voltage Vbat, the control circuit 108b outputs a PWM-modulated signal Sosc for lighting the light source 10 as CLL. On the other hand, when the voltage Vp is the ground voltage, the control circuit 108b outputs an “H” level signal Sosc for lighting the light source 10 as DRL.

[0079] That is, when only the voltage Vd is applied, the lighting circuit 20b causes the drive circuit 109 to supply a drive current Iout with a predetermined current value Id to the light source 10. When only the voltage Vc is applied, the lighting circuit 20b causes the drive circuit 109 to supply a drive current Iout with a current value Ic to the light source 10. When both the voltages Vd and Vc are applied, the lighting circuit 20b causes the drive circuit 109 to supply a drive current Iout with a current value Ic to the light source 10.

[0080] Therefore, when both the voltages Vd and Vc are applied, the lighting circuits 20a and 20b cause the drive circuit 109 to supply a predetermined drive current Iout to the light source 10.

[0081] FIG. 8 is a diagram showing the lighting pattern of the light source 10. In FIG. 8, “H” of the power supplies Vd and Vc indicates the case where the power supplies Vd and Vc are respectively applied, and “L” of the power supplies Vd and Vc indicates the case where the power supplies Vd and Vc are not respectively applied. Also, “101” refers to the PMOS transistor 101. “ON” and “OFF” indicate the on / off state of the PMOS transistor 101. Also, “DRL” and “CLL” in the column of “CLL mode” indicate whether the light source 10 lights up as DRL or as CLL. Note that since it is the same as FIG. 5 except when both of the voltages Vd and Vc are applied, the description is omitted.

[0082] When SW0 and SW1 are turned on and both of the voltages Vd and Vc are applied, a voltage corresponding to Vbat is applied to the drive circuit 109, and a PWM-modulated signal Sosc is input to the drive circuit 109. Therefore, the light source 10 lights up as CLL.

[0083] In this way, the lighting circuit 20b lights up the light source 10 as CLL when both of the voltages Vd and Vc are applied. Note that in this case, since the voltage Vc is applied to the terminal Tb, the switch control circuit 107 turns off the PMOS transistor 101.

[0084] Also, when both of the voltages Vd and Vc are applied, since the light source 10 lights up as CLL, no current corresponding to the drive current Iout of a predetermined current value Id flows through the diodes 100 and 104. Thereby, heat generation and power consumption by the diodes 100 and 104 are suppressed.

[0085] <<Operation of the Lighting Circuit 20b>> FIG. 9 is a diagram showing the operation of the lighting circuit 20b. Note that before the time t10, the voltages Vd and Vc are not applied and the light source 10 is turned off.

[0086] At time t10, when only the voltage Vd is applied, the voltage Vc and the voltage Vp applied through the diode 105 remain at the ground voltage. Therefore, the switch control circuit 107 outputs a voltage Vq that turns on the PMOS transistor 101. Then, the PMOS transistor 101 is turned on.

[0087] Also, since the voltage Vp is the ground voltage, as a result, the voltage Vdiv in FIG. 5 becomes a voltage obtained by dividing the voltage Vcc. Therefore, the oscillation circuit 308 outputs a signal Sosc at the "H" level. Then, the light source 10 lights up as a DRL.

[0088] At time t11, when only the voltage Vc is applied, the voltage Vc and the voltage Vp applied through the diode 105 become a voltage corresponding to the voltage Vbat. Therefore, the switch control circuit 107 turns off the PMOS transistor 101. As a result, the application of the voltage Vc to the terminal Ta through the PMOS transistor 101 and the line L1 is suppressed.

[0089] Also, since the voltage Vp is a voltage corresponding to the voltage Vbat, as a result, the voltage level of the voltage Vdiv in FIG. 5 changes in a sawtooth wave shape. Therefore, the oscillation circuit 308 outputs a PWM-modulated signal Sosc. Then, the light source 10 lights up as a CLL.

[0090] At time t12, when both the voltages Vd and Vc are applied, the voltage Vc and the voltage Vp applied through the diode 105 become a voltage corresponding to the voltage Vbat. Therefore, the switch control circuit 107 turns off the PMOS transistor 101.

[0091] Also, since the voltage Vp is a voltage corresponding to the voltage Vbat, as a result, the voltage level of the voltage Vdiv in FIG. 5 continues to change in a sawtooth wave shape. Therefore, the oscillation circuit 308 outputs a PWM-modulated signal Sosc. Then, the light source 10 lights up as a CLL.

[0092] Therefore, when both voltages Vd and Vc are applied to the lighting circuit 20b, the light source 10 lights up as a CLL, so no current corresponding to the drive current Iout of a predetermined current value Id flows through the diodes 100 and 104. As a result, heat generation and power consumption by the diodes 100 and 104 are suppressed.

[0093] ===Third Embodiment=== FIG. 10 is a diagram showing an example of the configuration of the lighting circuit 20c. The lighting circuit 20c includes diodes 100, 104 to 106, PMOS transistors 101, 110, Zener diodes 102, 111, capacitors 103, 112, switch control circuits 107, 113, a control circuit 108a, and a drive circuit 109.

[0094] The PMOS transistor 110 is connected in parallel to the diode 104 and is turned on when only the voltage Vc is applied, so that no current flows through the diode 104. On the other hand, the PMOS transistor 110 is turned off when the voltage Vd is applied to the terminal Ta. Thereby, the PMOS transistor 110 prevents the voltage Vd from being applied to the terminal Tb. Also, when the PMOS transistor 110 is turned on, since the on-resistance of the PMOS transistor 110 is small, the current flowing through the diode 104 is suppressed. As a result, heat generation and power consumption of the diode 104 are suppressed. Note that the PMOS transistor 110 corresponds to the "second switch".

[0095] Similar to the Zener diode 102, the Zener diode 111 is an element for protecting the PMOS transistor 110, with its anode connected to the gate terminal of the PMOS transistor 110 and its cathode connected to the source terminal of the PMOS transistor 110. The Zener diode 111 suppresses the application of a voltage equal to or higher than the breakdown voltage between the gate and source of the PMOS transistor 110 when a positive surge voltage is applied to the terminal Tb.

[0096] The capacitor 112 is an element for protecting the PMOS transistor 110 from the negative surge voltage applied to the terminal Tb, and is connected between the gate terminal and the source terminal of the PMOS transistor 110. Specifically, the capacitor 112, together with other circuit elements, constitutes an integrating circuit having a predetermined time constant, and keeps the PMOS transistor 110 on for a period corresponding to the predetermined time constant.

[0097] The switch control circuit 113 has the same circuit configuration as the switch control circuit 107 in FIG. 3, and is a circuit that outputs a voltage Vs for turning the PMOS transistor 110 on and off based on the voltage Vr from the diode 106. Specifically, the switch control circuit 113 turns on the PMOS transistor 110 when the voltage Vd is not applied to the terminal Ta and the voltage Vr becomes the ground voltage. On the other hand, the switch control circuit 113 turns off the PMOS transistor 110 when the voltage Vd is applied to the terminal Ta and the voltage Vr becomes a voltage corresponding to the voltage Vbat. Note that the switch control circuit 113 corresponds to the "second switch control circuit".

[0098] FIG. 11 is a diagram showing the lighting pattern of the light source 10. In FIG. 11, "H" of the power supplies Vd and Vc indicates the case where the power supplies Vd and Vc are applied respectively, and "L" of the power supplies Vd and Vc indicates the case where the power supplies Vd and Vc are not applied respectively. Also, "101" refers to the PMOS transistor 101, and "110" refers to the PMOS transistor 110. "ON" and "OFF" indicate the on and off states of the PMOS transistors 101 and 110. Also, "DRL" and "CLL" in the column of "DRL mode" indicate whether the light source 10 lights up as DRL or CLL. Note that the description is omitted because it is the same as FIG. 5 except that the PMOS transistor 110 is off when the voltage Vd is applied to the terminal Ta.

[0099] In this way, when both voltages Vd and Vc are applied, the lighting circuit 20c lights the light source 10 as DRL. In this case, since both voltages Vc and Vd are applied, the switch control circuit 107 turns off the PMOS transistor 101, and the switch control circuit 113 turns off the PMOS transistor 110.

[0100] Also, when both voltages Vd and Vc are applied, even if the PMOS transistor 101 is turned off, a voltage corresponding to Vbat is applied to the drive circuit 109 due to voltages Vd and Vc. Therefore, a current corresponding to the drive current Iout of a predetermined current value does not flow only through the diode 100. As a result, heat generation and power consumption by the diode 100 are suppressed. Similarly, a large current does not flow through the diode 104.

[0101] <<Operation of Lighting Circuit 20c>> FIG. 12 is a diagram showing the operation of the lighting circuit 20c. Also, times t20 to t22 in FIG. 12 correspond to times t0 to t2 in FIG. 6. Also, the main difference in the operations of the lighting circuits 20a and 20c is that when the voltage Vd is applied to the terminal Ta, the switch control circuit 113 turns off the PMOS transistor 110. Therefore, the description of FIG. 12 is omitted.

[0102] ===Fourth Embodiment=== As shown in FIG. 10, the lighting circuit 20d includes diodes 100, 104 to 106, PMOS transistors 101, 110, Zener diodes 102, 111, capacitors 103, 112, switch control circuits 107, 113, a control circuit 108b, and a drive circuit 109.

[0103] FIG. 13 is a diagram showing the lighting pattern of the light source 10. In FIG. 13, “H” of the power supplies Vd and Vc indicates the case where the power supplies Vd and Vc are respectively applied, and “L” of the power supplies Vd and Vc indicates the case where the power supplies Vd and Vc are not respectively applied. Also, “101” refers to the PMOS transistor 101, and “110” refers to the PMOS transistor 110. “ON” and “OFF” indicate the on / off states of the PMOS transistors 101 and 110. Also, “DRL” and “CLL” in the column of “CLL mode” indicate whether the light source 10 lights up as DRL or CLL. Note that since it is the same as FIG. 8 except that the PMOS transistor 110 is turned off when the voltage Vd is applied to the terminal Ta, the description is omitted.

[0104] As described above, when both the voltages Vd and Vc are applied, the lighting circuit 20d lights up the light source 10 as CLL. In this case, since the voltage Vc is applied to the terminal Tb, the switch control circuit 107 turns off the PMOS transistor 101, and since the voltage Vd is applied to the terminal Ta, the switch control circuit 113 turns off the PMOS transistor 110.

[0105] Also, when both the voltages Vd and Vc are applied, since the light source 10 lights up as CLL, no current corresponding to the drive current Iout of the predetermined current value Id flows through the diodes 100 and 104. Thereby, the heat generation and power consumption by the diodes 100 and 104 are suppressed.

[0106] <<Operation of the Lighting Circuit 20d>> FIG. 14 is a diagram showing the operation of the lighting circuit 20d. Also, the times t30 to t32 in FIG. 14 correspond to the times t10 to t12 in FIG. 9. Also, the main difference in the operation of the lighting circuits 20b and 20d is only that when the voltage Vd is applied to the terminal Ta, the switch control circuit 113 turns off the PMOS transistor 110, so the description of FIG. 14 is omitted.

[0107] ===Other Embodiments=== In the above-described embodiment, a plurality of light-emitting elements (LEDs) were connected in series to the light source 10, but this is not restrictive. For example, a plurality of light-emitting elements may be connected in parallel. Also, the number of light-emitting elements may be one.

[0108] In the above-described embodiment, the diode 100 and the PMOS transistor 101 were described as separate elements, but the diode 100 may be the parasitic diode of the PMOS transistor 101. Similarly, although the diode 104 and the PMOS transistor 110 were described as separate elements, the diode 104 may be the parasitic diode of the PMOS transistor 110.

[0109] ===Summary=== The lighting circuit 20a of the present embodiment has been described above. The lighting circuit 20a includes diodes 100, 104, a PMOS transistor 101, a switch control circuit 107, and a control circuit 108a. The PMOS transistor 101 provided in parallel with the diode 100 suppresses the current flowing through the diode 100. Thereby, it is possible to provide a lighting circuit that can suppress the heat generation and power consumption of the reverse protection diode.

[0110] Also, the drive current Iout of the predetermined current value Id is larger than the drive current Iout of the current value Ic that is smaller than the predetermined current value Id. Also, by providing a PMOS transistor 101 with a small on-resistance in parallel with the diode 100 through which a current corresponding to the drive current Iout of the predetermined current value Id flows, the heat generation and power consumption of the diode 100 can be efficiently suppressed.

[0111] Also, the lighting circuit 20c (20d) includes a PMOS transistor 110 and a switch control circuit 113. Thereby, the heat generation and power consumption in the diode 104 can also be suppressed.

[0112] Further, when both voltages Vd and Vc are applied, the control circuit 108a (108b) causes the drive circuit 109 to supply a predetermined current to the light source 10 from among the drive currents Iout of a predetermined current value Id and the drive current Iout of a current value Ic. Thereby, the circuit configuration can be changed as the control circuit 108a or 108b, and the required settings can be realized.

[0113] Also, the diodes 100 and 104 are parasitic diodes of the PMOS transistors 101 and 110, respectively. Thereby, a reverse connection protection diode can be realized without providing another diode in addition to the PMOS transistors 101 and 110.

[0114] The vehicle lamp 1 includes a lighting circuit 20a (20b, 20c, 20d) and a light source 10. Thereby, the light source 10 can be lit as a daytime running lamp or a clearance lamp.

[0115] The above embodiments are for facilitating the understanding of the present invention and are not for limiting the interpretation of the present invention. Further, the present invention can be changed and improved without departing from its gist, and it goes without saying that equivalents of the present invention are included therein.

Description of Reference Numerals

[0116] 1 Vehicle lamp 10 Light source 20a, 20b Lighting circuit 30 Battery 100, 104 to 106 Diode 101, 110 PMOS transistor 102, 111, 301 Zener diode 103, 112, 205, 302, 307 Capacitor 107, 113 Switch control circuit 108a, 108b Control circuit 109 Drive circuit 200 to 202, 204, 207, 300, 304 to 306, 310, 311 Resistor 203,206,303,312 NPN transistors 308 Oscillation circuit

Claims

1. A drive circuit for driving a light source, a first diode having an anode connected to a first line to which a first power supply voltage is applied and a cathode connected to the drive circuit, a first switch connected in parallel with the first diode, a second diode having an anode connected to a second line to which a second power supply voltage is applied and a cathode connected to the drive circuit, a first switch control circuit that turns on the first switch when the second power supply voltage is not applied to the second line and turns off the first switch when the second power supply voltage is applied to the second line, a control circuit that causes the drive circuit to supply a first drive current to the light source when the first power supply voltage is applied to the first line and causes the drive circuit to supply a second drive current to the light source when the second power supply voltage is applied to the second line, A lighting circuit comprising the above.

2. The lighting circuit according to Claim 1, wherein the first drive current is greater than the second drive current, A lighting circuit.

3. The lighting circuit according to Claim 2, a second switch connected in parallel with the second diode, a second switch control circuit that turns on the second switch when the first power supply voltage is not applied to the first line and turns off the second switch when the first power supply voltage is applied to the first line, A lighting circuit comprising the above.

4. The lighting circuit according to Claim 3, wherein the control circuit causes the drive circuit to supply a predetermined current among the first drive current and the second drive current to the light source when the first and second power supply voltages are applied to the first and second lines respectively, A lighting circuit.

5. The lighting circuit according to Claim 4, wherein each of the first and second switches is a MOS transistor, and each of the first and second diodes is a parasitic diode of the MOS transistor, A lighting circuit.

6. The lighting circuit according to any one of Claims 1 to 5, the light source, comprising wherein the drive circuit lights the light source as a daytime running lamp based on the first drive current and lights the light source as a clearance lamp based on the second drive current, A vehicle lamp.

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