JP2010119008A - Driver circuit of light-emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress abnormal oscillation in a driver circuit of a light-emitting element. <P>SOLUTION: The driver circuit of the light-emitting element includes: a series connection unit of the light-emitting element 202 and a current limiting inductor 24 directly connected to the light-emitting element 202; a regenerative diode 28 connected to the series connection unit in parallel to regenerate energy stored in the current limiting inductor 24; a transistor 26 for controlling currents flowing into the light-emitting element 202 and the current limiting inductor 24; and a control unit 22 for controlling the operation of the transistor 26 wherein the control part 22 controls a switching element according to a voltage value of power applied to the light-emitting element 202. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a driver circuit for a light emitting element.

  With the development of light-emitting elements such as light-emitting diodes, driver circuits have been devised that drive light sources that emit light by connecting a plurality of light-emitting elements in series.

  As shown in FIG. 3, the conventional light emitting element driver circuit 100 includes a rectifier bridge 10, a control unit 12, a current limiting inductor 14, a transistor 16, and a regenerative diode 18.

  The current limiting inductor 14 is connected in series to a series connection body 102 of a plurality of light emitting elements to be driven. When the light emitting elements are light emitting diodes (LEDs), the respective light emitting diodes are connected in series so as to align the forward direction. The regenerative diode 18 is connected in parallel to the current limiting inductor 14 and the series connection body 102 of the light emitting elements. The transistor 16 is connected in series to the current limiting inductor 14 and the series connection body 102 of the light emitting elements so as to control the current flowing through the light emitting elements and the inductors included in the LED connection unit 102.

  A power supply voltage is applied from the rectifying bridge 10 to the series connection body 102 of light emitting elements and the current limiting inductor 14. When the control unit 12 sets the gate voltage of the transistor 16 to a high level, the transistor 16 is turned on. At this time, the drain-source voltage Vds of the transistor 16 decreases, and the current ID flowing through the series connection body 102 of the light emitting elements and the current limiting inductor 14 gradually increases due to the current limiting action of the current limiting inductor 14. The controller 12 switches the gate voltage of the transistor 16 to a low level before the current ID exceeds the rated value of each light emitting element. As a result, the transistor 16 is turned off, the drain-source voltage Vds of the transistor 16 becomes the power supply voltage Vdc, and the current ID decreases. Further, the energy accumulated in the current limiting inductor 14 in the on state is regenerated to the power source via the regenerative diode 18 by the regenerative current Ioff. Thus, by controlling the switching of the transistor 16 by the control unit 12, it is possible to emit light while maintaining below the rating of each light emitting element by the action of the current limiting inductor 14.

  By the way, in the conventional driver circuit 100, the full-wave rectified power supply voltage is supplied from the rectifier bridge 10. At this time, as shown in FIG. 4A, switching of the transistor 16 may oscillate abnormally in the region A where the power supply voltage is low.

  Therefore, as shown in FIG. 5, a capacitor C for smoothing the power supply voltage is connected to the output side of the rectifier bridge 10, and measures are taken to smooth the power supply voltage as shown in FIG. Can do. However, the provision of the capacitor C causes a new problem that the power factor of the driver circuit 100 is lowered.

  In view of the above problems, an object of the present invention is to provide a driver circuit for a light-emitting element in which abnormal switching oscillation is suppressed without reducing the power factor.

  One aspect of the present invention is a series connection portion of a light emitting element and a current limiting inductor directly connected to the light emitting element, and is connected in parallel to the series connection portion and stored in the current limiting inductor. A regenerative unit that regenerates the generated energy, a switch element that controls a current flowing through the light emitting element and the current limiting inductor, and a control unit that controls the operation of the switch element, It is a light emitting element driver circuit for controlling the switching element in accordance with a voltage value of a power source applied to the light emitting element.

  Here, it is preferable that the control unit stops switching of the switching element when the voltage value is equal to or lower than a predetermined threshold value.

  According to the present invention, abnormal oscillation of switching can be suppressed without reducing the power factor in the driver circuit of the light emitting element.

  Further, by adjusting the reference voltage Vref, the light emission time of the LED can be adjusted at a frequency twice as high as the commercial frequency.

  As shown in FIG. 1, the driver circuit 200 according to the first embodiment includes a rectifier bridge 20, a control unit 22, a current limiting inductor 24, a transistor 26, a regeneration diode 28, and an oscillation prevention circuit 30. The

  The rectifying bridge 20 is a circuit in which rectifying diodes are connected in a bridge shape, and full-wave rectifies the input AC power supply voltage Vac and outputs it as a DC power supply voltage Vdc.

  A light emitting element to be driven by the driver circuit 200 can be a light emitting diode (LED), a laser diode (LD), or the like. A series connection body 202 in which a plurality of light emitting elements are connected in series may be a driving target. In the case of a light emitting diode (LED), when the series connection body 202 of light emitting elements is formed, the light emitting diodes are connected in series so that their forward directions are aligned with each other. Furthermore, the serial connection body 202 may be connected in parallel.

  The current limiting inductor 24 is connected in series to a series connection body 202 of a plurality of light emitting elements to be driven. The regenerative diode 28 is connected in parallel to the current limiting inductor 24 and the series connection body 202 of the light emitting elements.

  The transistor 26 is a switching element whose on state and off state are controlled by the control unit 22. The transistor 26 is connected in series to the current limiting inductor 24 and the serial connection 202 of the light emitting elements. The power supply voltage Vdc is applied from the rectifier bridge 20 to the series connection body 202 of the light emitting elements and the current limiting inductor 24 via the drain-source of the transistor 26. The control unit 22 is connected to the gate of the transistor 26. The controller 22 intermittently supplies power to the light emitting element to emit light by performing on / off control of the transistor 26 at a predetermined timing.

  When the transistor 26 is controlled to be in an on state, a current flows through the current limiting inductor 24 and the series connection body 202 via the drain-source. At this time, the current flowing through the light emitting element is limited by the action of the current limiting inductor 24 so as to gradually increase. Further, when the transistor 26 is controlled to be turned off, the drain-source is cut off, and the electromagnetic energy accumulated in the current limiting inductor 24 is regenerated to the power supply via the regenerative diode 28.

  At this time, the control unit 22 controls the switching cycle or pulse width of the transistor 26 so that the operation of each light emitting element is limited to a rated value or less by the action of the current limiting inductor 24. Accordingly, the light emitting element can appropriately emit light.

  The driver circuit 200 in this embodiment is provided with an oscillation prevention circuit 30. The oscillation prevention circuit 30 always detects the rectified power supply voltage Vdc and controls the switching of the transistor 26 by the control unit 22 according to the power supply voltage Vdc. That is, when the power supply voltage Vdc is low, switching of the transistor 26 is stopped.

  As shown in FIG. 1, the oscillation prevention circuit 30 may be configured by resistors R1, R2, R3, capacitors C1, C2, and a comparator COMP. The resistors R1 and R2 are connected in series, and are connected in parallel between the output ends of the rectifier bridge 20. The connection point between the resistors R1 and R2 is connected to the inverting input terminal (−) of the comparator COMP. The connection point of the resistors R1 and R2 is grounded through the capacitor C1. The output terminal of the comparator COMP is grounded via a series connection of a resistor R3 and a capacitor C2. The reference voltage Vref is applied to the non-inverting input terminal (+) of the comparator COMP.

  The output of the rectifier bridge 20 is divided by resistors R1 and R2. When the power supply voltage Vdc output from the rectifier bridge 20 decreases, the voltage of the resistor R2 decreases. As shown in FIG. 2, when the voltage input to the inverting input terminal (−) of the comparator COMP becomes smaller than the reference voltage Vref, the voltage at the output terminal of the comparator COMP becomes low level. In response to the output of the comparator COMP, the control unit 22 stops the switching of the transistor 26.

  On the other hand, when the power supply voltage Vdc increases, the voltage of the resistor R2 also increases. As shown in FIG. 2, when the voltage input to the inverting input terminal (−) of the comparator COMP becomes equal to or higher than the reference voltage Vref, the voltage at the output terminal of the comparator COMP becomes high level. In response to the output of the comparator COMP, the control unit 22 resumes switching of the transistor 26.

  In this manner, abnormal oscillation can be suppressed by stopping the switching of the transistor 26 in the region where the power supply voltage Vdc is low. Further, it is not necessary to provide a large-capacitance capacitor for smoothing the power supply voltage Vdc, and it is possible to prevent the power factor of the entire driver circuit 200 from being lowered.

  In addition, by intentionally changing the reference voltage Vref, the time during which the LED is lit changes at a frequency synchronized with the commercial frequency, and as a result, the amount of light changes. If this is utilized, it will become possible to utilize for the light control of LED.

It is a figure which shows the structure of the driver circuit of the light emitting element in embodiment of this invention. 3 is a timing chart illustrating an operation of a driver circuit of a light emitting element in an embodiment of the present invention. It is a figure which shows the structure of the driver circuit of the conventional light emitting element. It is a figure which shows the time change of a power supply voltage. It is a figure which shows the structure of the driver circuit of the conventional light emitting element which suppressed abnormal oscillation.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Rectification bridge, 12 Control part, 14 Current limiting inductor, 16 transistor, 18 regeneration diode, 20 Rectification bridge, 22 Control part, 24 Current limitation inductor, 26 Transistor, 28 regeneration diode, 30 Oscillation prevention circuit, 100 , 200 Driver circuit, 102, 202 Series connection body.

Claims (2)

A series connection part of a light emitting element and a current limiting inductor directly connected to the light emitting element;
A regenerative unit that is connected in parallel to the series connection unit and regenerates energy stored in the current limiting inductor;
A switch element for controlling a current flowing through the light emitting element and the current limiting inductor;
A control unit for controlling the operation of the switch element,
The light emitting element driver circuit, wherein the control unit controls the switching element according to a voltage value of a power source applied to the light emitting element. The driver circuit according to claim 1,
The control unit stops the switching of the switching element when the voltage value is equal to or lower than a predetermined threshold value.

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