JP4698560B2 - Variable load lighting circuit - Google Patents

Description

  The present invention relates to a lighting circuit used when lighting is required by changing brightness and light distribution shape, such as a tail / stoplight for an automobile, or a headlight for traveling / a headlight for passing, for example. Specifically, the present invention relates to a lighting circuit configured to prevent accidents such as disconnection due to an overcurrent temporarily flowing in the LED when the brightness is changed.

  FIG. 4 shows an example in which this type of lighting circuit 90 of the related art is adopted for automobiles. The output of the lighting circuit 90 includes, for example, a low beam light 91 configured as a light source block by a plurality of LEDs. Are connected in series, and each light source block, that is, the low beam light 91 and the high beam light 92 is composed of one or more LED lamps.

  The lighting circuit 90 is connected to a battery 80 of an automobile via a high beam switch 81 and a low beam switch 82, and a light source selector 70 is connected to the high beam switch 81 and the low beam switch 82. Here, when the high beam switch 81 is off, the PNP transistor 93a of the light source selector 93 is on.

  Accordingly, the FET 94 connected to the PNP transistor 93a is turned on, the high beam light 92 is turned off when the anode and the cathode are short-circuited, and only the low beam light 91 is turned on.

  On the other hand, when the high beam switch 81 is turned on, the PNP transistor 93a is turned off, and accordingly, the FET 94 is also turned off. Therefore, the short circuit between the anode and the cathode of the high beam light 92 is opened, and both the low beam light 91 and the high beam light 92 are lit.

The lighting circuit 90 is provided with a switching regulator 95 and an output control unit 96. For example, the current when both the low beam light 91 and the high beam light 92 are lit, and the low beam When only the light 91 is turned on, the current value applied to each LED is adjusted to be appropriate.
JP 2002-300962 A

  However, in the circuit having the conventional configuration described above, for example, when switching from the state where both the low beam light 91 and the high beam light 92 are lit to the state where only the low beam light 91 is lit, the FET 94 is suddenly changed. For example, a voltage of several tens of volts previously applied to the low beam light 91 and the high beam light 92 is applied only to the low beam light 91 for a moment, resulting in an overvoltage state. , The burden on the LED increases.

  In particular, when this lighting circuit 90 is used for switching between passing light distribution / running light distribution of LED headlights of automobiles and two-wheeled vehicles, as described above, since LEDs with high output are used, the above-described LED is used. Thus, a high voltage of several tens of volts tends to cause an overvoltage state applied only to the low beam light 91 for a moment, and the possibility of breakage is increased.

  Further, even if it is a moment, if an overvoltage is applied and an overcurrent flows, a protection circuit such as a short-circuit protection circuit provided along with the lighting circuit 90 may be erroneously detected. For this reason, the protection circuit is activated during use of the automobile, and it becomes easier to create a more dangerous state, for example, the power supply is stopped.Therefore, the operating current of the short-circuit detection circuit must be set to a larger value. But it creates a disadvantage.

In the present invention, as specific means for solving the above-described conventional problems, a plurality of light source blocks composed of at least one LED are connected in series to a power source, and a plurality of the light source blocks can be connected as necessary. In the lighting circuit that is adjusted according to the number of light source blocks in which one part is short-circuited by a short-circuit and at the same time the power supplied from the power source remains, an integrating circuit is incorporated on the input side of the short-circuit. When a control signal is input to the short circuit, the voltage applied to the light source block to be short-circuited is gradually short-circuited with a slope in a gradual decrease direction from a predetermined value according to the output voltage from the integration circuit. The problem is solved by providing a variable load type lighting circuit characterized by reaching a state.

  According to the present invention, when a short circuit is performed, the voltage applied to the light source block is made to reach a short circuit state with a slope in a slightly decreasing direction from a predetermined value by using an integration circuit. The voltage applied to the light source block also rises for a while, so that it does not rise instantly, prevents malfunction of the protection circuit, and the like, which is effective for improving safety.

  Below, this invention is demonstrated in detail based on embodiment shown in a figure. 1 is a first embodiment of a variable load type lighting circuit according to the present invention. In this first embodiment, when the power source is a switching regulator 2 as shown in the conventional example. This is shown in the example.

  This variable load type lighting circuit 1 is provided with a switching regulator 2 that is a power source. Each output of the switching regulator 2 is formed by connecting one or more LEDs 3 in series or in parallel. The light source block 31 and the second light source block 32 are connected in series. For example, when it is necessary to change the brightness and the light distribution shape, such as switching between a tail lamp and a stop lamp, or a traveling beam and a passing beam, the second light source block 32 side is short-circuited.

  In actual implementation, the number of the first light source blocks 31 and the second light source blocks 32 connected to the output of the switching regulator 2 is not limited to two, and the light source is short-circuited. Although the number of blocks is not limited to one, here, an example in which there are two light source blocks will be described, and a light source block that is short-circuited by the short circuit 4 as necessary, such as switching of illuminance, The description will be made assuming that the block 32 is located.

  In the variable load type lighting circuit 1 of the present invention, for example, a voltage from a battery (not shown) mounted on an automobile is connected to the primary winding 21a of the transformer 21 of the switching regulator 2 and the primary winding. 21a is connected in series with a switch 22 made of a semiconductor element, such as an FET, which is intermittently connected at an appropriate frequency by an external signal.

  Accordingly, the DC voltage from the battery 20 is boosted in accordance with the winding ratio of the primary winding 21a and the secondary winding 21b of the transformer 21, and is rectified by the diode 23 and then smoothed by the capacitor 24. The light source block 31 and the light source block 32 connected in series are supplied.

  Next, the short circuit 4 according to the present invention will be described. The short circuit 4 is basically supplied with power from the vehicle battery 20 as in the conventional example, but finally the FET 4a attached to short the light source block 32. Is not shown in the figure, but the voltage may be adjusted by an appropriate means such as resistance division.

  Here, the configuration of the short circuit 4 will be described. First, a first resistor 4b is provided at the input of the short circuit 4, and one end of the resistor 4b is connected to the ground near the FET 4a. The connected capacitor 4c is connected. In addition, in the present invention, a second resistor 4d is connected in parallel with the capacitor 4c.

  The ungrounded side of the capacitor 4c and the second resistor 4d is connected to the gate of the FET 4a. The open side of the first resistor 4b is an input terminal for inputting a control signal for conducting the FET 4a indicated by CS in the figure on the power supply side.

  By doing so, when the control signal CS is input, the capacitor 4c is charged through the first resistor 4b, whereby the FET 4a becomes conductive and the second light source block 32 is short-circuited and turned off. In the present invention, the capacitor 4c is charged through the first resistor 4b.

  Accordingly, the voltage charged at both ends of the capacitor 4c is a curve shown in FIG. 2 depending on the resistance value of the first resistor 4b, the capacitance value of the capacitor 4c, the time constant depending on the resistance value of the second resistor 4e, and the like. As indicated by CF, a current is applied to the gate of the FET 4a with an inclination in the direction in which the potential gradually rises.

  Accordingly, the FET 4a also gradually increases the conduction current according to the current flowing through the gate, and eventually the second light source block 32 is short-circuited, and the light is completely turned off by the short-circuit. It becomes. Therefore, as shown in FIG. 1, if a constant current control unit 4 f that detects and controls the current flowing through the first light source block 31 and the second light source block 32 is provided, the first power supply block 31 can be The current applied to the power supply block 32 is not added and applied, no overvoltage is applied to the LED 3, and accidents in which various protection circuits such as a short circuit detection circuit malfunction can be prevented.

  FIG. 3 shows another embodiment of the variable load type lighting circuit according to the present invention. As this type of variable load type lighting circuit 10, as shown in FIG. 3, for example, the output from a DC-DC inverter is positive. The positive potential power supply 10a is formed by rectifying by a rectifier circuit (not shown) in the direction, and the negative potential power supply 10b is rectified by rectifying the output from the same DC-DC inverter in the negative potential direction by a charge pump type rectifier circuit. There is also a method of connecting the first light source block 31 and the second light source block 32 between the positive potential power source 10a and the negative potential power source 10b.

  The present invention can also be used for the variable load type lighting circuit 10 having such a configuration. First, the control signal CS having a phase opposite to that of the first embodiment is employed, and the short circuit 11 is first configured. An input is given to the base of the NPN transistor 11a, so that the NPN transistor 11a becomes conductive, and the capacitor 11b connected between the emitter and collector of the NPN transistor 11a is in a discharged state, and the first resistor 11c and The connection point with the second resistor 11d is also at ground potential. Accordingly, the FET 11e becomes non-conductive, and both the first light source block 31 and the second light source block 32 are turned on.

  Here, if the potential applied to the base of the NPN transistor 11a is lost, the NPN transistor 11a becomes non-conductive, and the capacitor 11b is charged with the voltage from the positive potential power supply 10a, and the voltage is applied to the gate of the FET 11e. The FET 11e is turned on, and the first light source block 31 is short-circuited and turned off.

  Here, considering the process in which the capacitor 11b is charged, since the first resistor 11c is connected to the capacitor 11b, the capacitor 11b is charged via the first resistor 11c. Thus, the charging time is delayed by the time constant generated by the resistance value of the first resistor 11c and the capacitance of the capacitor 11b, and gradually short-circuiting the first light source block 31 as shown in FIG. Will do.

  Accordingly, as in the first embodiment, a current is applied to the gate of the FET 11e with a slope in a gradually increasing direction, and overcurrent applied to the LED 3 is prevented (constant current) as in the first embodiment. It is possible to prevent malfunctions of various protection circuits such as the control unit 10c) and the short circuit detection circuit.

  As described above, in a vehicular lamp using an LED as a light source, for example, switching between a running light distribution and a passing light distribution, etc. When the system is configured to switch the light quantity or lighting state by short-circuiting the part, the current turned off by the short-circuit rapidly flows to the side of the LED that continues to light, and the lighting continues. An electric shock is applied to the LED to easily cause a disconnection and the like, and a possibility of causing a malfunction in a protective device such as a short-circuit detection device is high.

  Therefore, when switching the lighting state as in the present invention, the shock applied to the LED that continues to light is increased by increasing the current applied to the LED that continues to light with a slight slope. And the occurrence of the above-mentioned various problems is avoided.

  In the present invention, the embodiment has been described as an example of a lighting circuit for a vehicular lamp such as a headlamp, a rear combination lamp, a fog lamp, and a DRL (driving lamp). However, the present invention is not limited thereto. The application is not limited, and it can be used as various lighting circuits such as a lighting circuit for LED street lamps and a lighting circuit for LED lighting fixtures.

1 is a schematic wiring diagram showing a first embodiment of a variable load lighting circuit according to the present invention. It is a graph which shows the example of the current waveform at the time of switching of the variable load type lighting circuit concerning the present invention. FIG. 6 is a schematic wiring diagram showing a second embodiment of a variable load lighting circuit according to the present invention. It is a schematic wiring diagram which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 10 ... Variable load type lighting circuit 2 ... Switching regulator 21 ... Transformer 21a ... Primary winding 21b ... Secondary winding 22 ... Switch 3 ... LED
31 ... First light source block 32 ... Second light source block 4 ... Short circuit 4a ... FET
4b ... 1st resistor 4c ... Capacitor 4d ... 2nd resistor 4e ... Switch 10a ... Positive potential power supply 10b ... Negative potential power supply 10c ... Constant current control part 11 ... Short circuit 11a ... NPN transistor 11b ... Capacitor 11c ... 1st One resistor 11d ... Second resistor 11e ... FET
20 ... Battery

Claims (2)

A plurality of light source blocks composed of at least one LED are connected in series to a power source, and if necessary, one part of the plurality of light source blocks is short-circuited by a short circuit and at the same time the power supplied from the power source is also In the lighting circuit adjusted according to the number of remaining light source blocks, an integration circuit is incorporated on the input side of the short circuit, and when a control signal is input to the short circuit, the output voltage from the integration circuit Accordingly, the voltage applied to the light source block to be short-circuited gradually reaches a short-circuit state with a slope in a direction of decreasing from a predetermined value.   The variable load type lighting circuit according to claim 1, wherein the supply power from the power source is also adjusted in accordance with an output voltage from the integration circuit.

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