JP2016149309A - Light source driving device and lighting fixture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light source driving device that can prevent an overcurrent from flowing to a light source when a light source is attached and detached and also has simple constitution.SOLUTION: A light source driving device 1 comprises: a DC/DC converter 2; a current control circuit 4 connected in series to an output end of the DC/DC converter 2 through a light source 10; an output voltage detection circuit 3 which generates a first voltage Va using a DC voltage output from the DC/DC converter 2; and a feedback circuit 5 having an operational amplifier 1. A first voltage Va is input to an inverting input terminal of the operational amplifier U1 through a diode D3, and a second voltage Vb at a point, connected to the light source 10, of the current control circuit 4 is input through a diode D4. A non-inverting input terminal is connected to a reference voltage Vref1. The feedback circuit 5 controls the DC/DC converter 2 in such a way that a voltage which is higher between the first voltage Va and second voltage Vb becomes equal to the reference voltage Vref1.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a light source driving device and a lighting fixture, and more particularly to a light source driving device and a lighting fixture capable of driving a light source such as an LED (light emitting diode).

  2. Description of the Related Art A light source driving device that lights a light source such as an LED module composed of a plurality of LEDs by dimming and controlling the light source is known.

  As such a light source driving device, for example, as described in Patent Document 1 below, an LED power supply device configured to prevent an excessive current from flowing through the LED lamp when the LED lamp is disconnected and reconnected. There is.

  The LED power supply device described in Patent Document 1 has the following configuration. That is, a current limiting circuit is connected in series with the LED module. At the timing of reconnecting the LED module, the LED current flowing through the LED module is limited to a predetermined threshold value. Further, the LED current that normally flows is controlled to be constant at a predetermined value by the current control circuit. When the LED power supply device and the LED module are disconnected, the constant current control by the current control circuit is switched to the constant voltage control by the voltage control circuit. As a result, the output voltage is controlled to be constant. Thereafter, when the LED module is reconnected, the current control circuit operates again, and the LED current flowing through the LED module is controlled to be constant. That is, an overcurrent does not flow through the LED module without interrupting the commercial power supply, and the LED module can be removed.

JP2012-129129A

  Incidentally, the configuration described in Patent Document 1 has the following problems.

  That is, it is necessary to provide a current limiting circuit in order to limit overcurrent. Further, in order to control each of the LED current and the output voltage, it is necessary to provide a current control circuit and a voltage control circuit each including an operational amplifier. As a result, the circuit becomes complicated, the number of parts increases, and there is a problem that the apparatus becomes large and the manufacturing cost increases.

  The present invention has been made to solve such problems, and provides a light source driving device and a lighting fixture having a simple configuration that can prevent an overcurrent from flowing to the light source when the light source is attached or detached. It is an object.

  In order to achieve the above object, according to one aspect of the present invention, there is provided a light source driving apparatus that drives a light source using an input DC voltage, and the input DC voltage is smaller in magnitude than the input DC voltage. A DC / DC converter for converting to a different DC voltage, a current control circuit connected to the output terminal of the DC / DC converter in series with the DC / DC converter via a light source, and an output from the DC / DC converter An output voltage detection circuit for generating a first voltage from the DC voltage, an operational amplifier, a feedback circuit having a first rectifier element, and a second rectifier element. 1 is input via the first rectifier element, and a second voltage, which is a voltage at a point connected to the light source of the current control circuit, is input via the second rectifier element. The non-inverting input terminal of the amplifier is connected to the reference voltage, and the feedback circuit receives the larger one of the first voltage and the second voltage, which is input to the inverting input terminal of the operational amplifier. The DC / DC converter is controlled so that is equal to the reference voltage.

  Preferably, in the feedback circuit, when the light source is connected to the light source driving device and the second voltage becomes larger than the first voltage, the second voltage is input to the inverting input terminal of the operational amplifier, and the input voltage is When the DC / DC converter is controlled to be equal to the reference voltage and the light source is not connected to the light source driving device, the first voltage is input to the inverting input terminal of the operational amplifier, and the input voltage becomes equal to the reference voltage. Thus, the DC / DC converter is controlled.

  Preferably, a dimming instruction signal is input to the light source driving device, and the current control circuit controls a current supplied to the light source in accordance with the dimming instruction signal.

  When the other situation of this invention is followed, a lighting fixture is provided with the light source drive device in any one of the above-mentioned, and the light source driven by a light source drive device.

  According to these inventions, the DC / DC converter is controlled by the feedback circuit so that the larger one of the second voltage and the first voltage is equal to the reference voltage. Therefore, an overcurrent can be prevented from flowing to the light source when the light source is attached or detached, and a light source driving device and a lighting fixture having a simple configuration can be provided.

It is a block diagram which shows the structure of the lighting fixture using the light source drive device in one of embodiment of this invention. It is a circuit diagram which shows the structure of a light source drive device.

  Hereinafter, the lighting fixture using the light source drive device in embodiment of this invention is demonstrated.

  [Embodiment]

  FIG. 1 is a block diagram showing a configuration of a lighting fixture using a light source driving device according to one embodiment of the present invention.

  As shown in FIG. 1, the lighting fixture 100 includes a light source driving device 1, a light source 10, and a dimming control device 80. The luminaire 100 illuminates when the light source 10 is driven and turned on.

  The light source driving device 1 is connected to the light source 10. The light source driving device 1 drives the light source 10.

  In the present embodiment, the light source 10 is an LED module having an LED unit formed by connecting a plurality of light emitting diodes (LEDs) in series. The light source 10 may have one LED, or may use another type of light source instead of the LED.

  The light source driving device 1 is connected to the dimming control device 80. The dimming control device 80 outputs a dimming instruction signal Vref <b> 2 to the light source driving device 1. The dimming instruction signal Vref2 is, for example, a voltage value corresponding to the brightness of illumination. The light source driving device 1 performs a dimming operation of the light source 10 based on the dimming instruction signal Vref2 output from the dimming control device 80. That is, in the lighting fixture 100, the brightness of illumination by the light source 10 can be changed.

  FIG. 2 is a circuit diagram showing a configuration of the light source driving device 1.

  As shown in FIG. 2, the light source driving device 1 includes a rectifier circuit BD1, a DC / DC converter 2, a current control circuit 4, an output voltage detection circuit 3, a feedback circuit 5, and a control power supply circuit 6. Have.

  The rectifier circuit BD1 is connected to, for example, an AC commercial power supply Vac. The rectifier circuit BD1 full-wave rectifies the AC voltage from the AC commercial power supply Vac and outputs a DC voltage.

  The DC / DC converter 2 converts the DC voltage output from the rectifier circuit BD1 into a DC voltage having a magnitude different from that of the DC voltage output from the rectifier circuit BD1.

  The DC / DC converter 2 includes, for example, a smoothing capacitor C1 that smoothes a DC voltage, a control circuit 2a, a transformer T1, a transistor Q1, a smoothing capacitor C2, and the like. The transformer T1 includes a primary winding n1 connected to the input end of the DC / DC converter 2, a secondary winding n2 connected to the output end of the DC / DC converter 2, and an auxiliary winding n3. Have.

  The smoothing capacitor C1 is connected in parallel to the primary winding n1. A diode D2 is connected to the high-voltage side output terminal of the secondary winding n2, and the low-voltage side output terminal is connected to the ground potential. The cathode of the diode D2 and the low-voltage side output end of the secondary winding n2 serve as the output end of the DC / DC converter 2 (hereinafter sometimes simply referred to as the output end). The smoothing capacitor C2 is connected to the output terminal in parallel with the light source 10 and the current control circuit 4 described later.

  The control circuit 2a is connected to the photocoupler PC1. A feedback signal is input to the control circuit 2a via the photocoupler PC1 and the resistor R1. The control circuit 2a drives the transistor Q1 based on the feedback signal and controls the output voltage of the DC / DC converter 2. The auxiliary winding n3 is connected to the control circuit 2a via the diode D1. The control circuit 2a monitors the timing when the current flowing through the secondary winding n2 becomes zero by the auxiliary winding n3 and the diode D1. The control circuit 2a turns on the transistor Q1 based on the timing when the current flowing through the secondary winding n2 becomes zero. Transistor Q1 controls whether or not current flows through primary winding n1. That is, the control circuit 2a drives the transistor Q1 in the critical mode so that the power conversion efficiency of the DC / DC converter 2 is increased. Note that the transistor Q1 may be driven in a discontinuous mode in which the auxiliary winding n3 and the diode D1 are unnecessary or in a continuous mode. In the present embodiment, the DC / DC converter 2 is a flyback converter, but may be a step-down chopper or a step-up / step-down chopper.

  A light source 10 and a current control circuit 4 are connected in series between output terminals of the DC / DC converter 2. That is, the current control circuit 4 is connected to the output terminal via the light source 10. The current control circuit 4 is connected between the end of the light source 10 opposite to the connection end with the DC / DC converter 2 and the ground potential.

  The current control circuit 4 receives the dimming instruction signal Vref2. The current control circuit 4 controls the magnitude of the current supplied to the light source 10 according to the dimming instruction signal Vref2.

  The current control circuit 4 includes, for example, a transistor Q3 that is an FET, a resistor R8, and an operational amplifier U2. The transistor Q3 is arranged with the gate connected to the output terminal of the operational amplifier U2 and the drain connected to the light source 10. The resistor R8 is disposed between the source of the transistor Q3 and the ground potential. The inverting input terminal of the operational amplifier U2 is connected to the source of the transistor Q3. The dimming instruction signal Vref2 is input to the non-inverting input terminal of the operational amplifier U2.

  The operational amplifier U2 uses the dimming instruction signal Vref2 as a reference voltage (second reference voltage), and drives the transistor Q3 so that the magnitude of the source voltage Vc of the transistor Q3 and the dimming instruction signal Vref2 are equal. The source voltage Vc corresponds to the current flowing through the resistor R8, that is, the current IL flowing through the light source 10. That is, the operational amplifier U2 controls the current IL flowing through the light source 10 based on the dimming instruction signal Vref2. Accordingly, the light source 10 is driven (lighted) by the output voltage supplied from the DC / DC converter 2, and the magnitude of the current IL at that time is controlled by the dimming instruction signal Vref 2 input to the current control circuit 4. Is done. That is, the current control circuit 4 operates as a constant current circuit that controls the current IL having a magnitude corresponding to the dimming instruction signal Vref2 to flow through the light source 10. As described above, the light source 10 can be dimmed and controlled by using the variable voltage signal input from the outside as the dimming instruction signal Vref2 as the reference voltage of the operational amplifier U2.

  The output voltage detection circuit 3 is connected to the output end of the DC / DC converter 2 in parallel to the light source 10 and the current control circuit 4. The output voltage detection circuit 3 has two resistors R5 and R6 arranged in series between the output terminals. The output voltage detection circuit 3 divides the DC voltage output from the DC / DC converter 2 by the resistor R5 and the resistor R6, and generates the first voltage Va. The first voltage Va is input to the feedback circuit 5.

  The control power supply circuit 6 is connected in parallel to the light source 10 and the current control circuit 4 at the output end. The limited power supply circuit 6 includes a transistor Q4, resistors R2, R3, and R4, and a Zener diode ZD1.

  The control power supply circuit 6 generates a control power supply voltage for driving the photocoupler PC1 of the feedback circuit 5 from the output voltage of the DC / DC converter 2. The control power supply voltage is a constant voltage. That is, the transistor Q4, the resistor R3, and the resistor R4 constitute an emitter follower circuit, and the Zener voltage Vzd generated by the Zener diode ZD1 is input to the base of the transistor Q4. An emitter voltage Vzd-0.7 V having a magnitude obtained by subtracting a base-emitter voltage (here, 0.7 V) is output from the emitter of the transistor Q4. That is, the control power supply circuit 6 converts the output voltage of the DC / DC converter 2 into a control power supply voltage that is an emitter voltage by an emitter follower circuit. At the same time, the control power supply voltage is supplied to the secondary side of the photocoupler PC1 (the portion connected to the secondary side circuit of the transformer T1) via the resistor R4.

  The transistor Q4 may be a MOSFET or the like.

  In addition to the photocoupler PC1, the feedback circuit 5 includes an operational amplifier U1, a diode (first rectifier element) D3, a diode (second rectifier element) D4, a transistor Q2, a resistor R7, a capacitor C3, and the like.

  The first voltage Va generated by the output voltage detection circuit 3 is input to the inverting input terminal of the operational amplifier U1 through the diode D3. The second voltage Vb, which is the voltage at the point connected to the light source of the current control circuit, is input to the inverting input terminal of the operational amplifier U1 through the diode D4. That is, the higher voltage of the first voltage and the second voltage is input to the inverting input terminal of the operational amplifier U1. On the other hand, the non-inverting input terminal of the operational amplifier U1 is connected to a reference voltage (first reference voltage) Vref1. The reference voltage Vref1 is, for example, a predetermined constant voltage.

  The output terminal of the operational amplifier U1 is connected to the base of the transistor Q2. The transistor Q2 is disposed between the secondary side of the photocoupler PC1 and the ground potential, and is configured such that the photocoupler PC1 is driven when the transistor Q2 is turned on. When the photocoupler PC1 is driven via the transistor Q2, a feedback signal is input from the photocoupler PC1 to the control circuit 2a.

  The capacitor C3 and the resistor R7 constitute a phase compensation circuit for feedback control. That is, one end of the capacitor C3 is connected between the photocoupler PC1 and the transistor Q2, and the other end of the capacitor C3 is connected to the inverting input terminal of the operational amplifier U1 via the resistor R7.

  The feedback circuit 5 controls the DC / DC converter 2 so that the larger one of the first voltage Va and the second voltage Vb input to the inverting input terminal of the operational amplifier U1 is equal to the reference voltage Vref1. Control. That is, the feedback circuit 5 uses the operational amplifier U1 to input a feedback signal to the control circuit 2a so that the larger one of the first voltage Va and the second voltage Vb is equal to the reference voltage Vref1. Let

  In the present embodiment, since the primary side and the secondary side are insulated, the photocoupler PC1 is used. In the case of non-insulation, this is not necessary, and the photocoupler PC1 and the control power supply circuit 6 may not be used.

  In the present embodiment, the light source driving device 1 operates as follows when the light source 10 is attached to and detached from the light source driving device 1.

  That is, when the light source 10 is not connected to the light source driving device 1, the feedback circuit 5 controls the DC / DC converter 2 so that the first voltage Va becomes equal to the reference voltage Vref1. When the light source 10 is connected to the light source driving device 1, the second voltage Vb becomes higher than the first voltage Va. In particular, when the voltage of the light source 10 is the maximum (VFmax), the second voltage Vb is larger than the first voltage Va. When the second voltage Vb becomes larger than the first voltage Va, the feedback circuit 5 controls the DC / DC converter 2 so that the second voltage Vb becomes equal to the reference voltage Vref1.

  Such an operation will be described below with a specific example.

  In the following, the reference voltage Vref1 and the dimming instruction signal (second reference voltage) Vref2 are both 0.5 V, the voltage dividing ratio between the resistors R5 and R6 of the output voltage detection circuit 3 is 0.02, and the light source 10 is connected. In the following description, the output voltage Vout of the DC / DC converter 2 is 36V, and the output voltage Vout when the light source 10 is not connected is 40V. When the light source 10 is an LED, the output voltage Vout of 36V is obtained by setting the drain voltage (second voltage Vb) of the transistor Q3 to the value at the maximum tolerance of the forward voltage of the LED (VFmax = 35.2V). This is the applied voltage.

  When the light source 10 is connected to the light source driving device 1, the current control circuit 4 performs control so that the source voltage Vc of the transistor Q3 is 0.5 V, which is the same as the dimming instruction signal Vref2. Therefore, the current IL of the light source 10 has a current value obtained by dividing 0.5 V of the source voltage Vc by the resistance value of the resistor R8.

  The transistor Q3 should be driven so that the drain-source voltage has a small value in order to suppress power loss. For example, when driven at 0.3 V where the power loss is sufficiently reduced, the drain voltage of the transistor Q3 is 0.8 V (the magnitude obtained by adding 0.5 V that is the source voltage Vc to 0.3 V). The second voltage Vb). The voltage drop of the diode D4 is about 0.3V. Therefore, the voltage at the inverting input terminal of the operational amplifier U1 is 0.5 V obtained by subtracting 0.3 V corresponding to the voltage drop from the second voltage Vb. That is, 0.5 V of the reference voltage Vref1 is input to the non-inverting input terminal of the operational amplifier U1, and feedback control is performed so that the voltage drop of the inverting input terminal becomes 0.5 V, whereby the second voltage Vb Is controlled to be 0.8V.

  When the light source 10 is connected, the output voltage Vout of the DC / DC converter 2 is 36V. Therefore, the output voltage detection circuit 3 generates the first voltage Va having a magnitude of 0.7V (= 36 × 0.02). Since the second voltage Vb is 0.8V, the first voltage Va is smaller than the second voltage Vb. Therefore, a so-called reverse bias is applied to the diode D3, and the first voltage Va is not input to the inverting input terminal of the operational amplifier U1. That is, since the second voltage Vb is set to be larger than the first voltage Va, it is input to the inverting input terminal of the operational amplifier U1 and fed back.

  When the light source 10 is not connected to the light source driving device 1 (when disconnected from the light source driving device 1), the output voltage Vout of the DC / DC converter 2 is 40V. Therefore, the output voltage detection circuit 3 generates the first voltage Va having a magnitude of 0.8 V (= 40 × 0.02). Since the voltage drop of the diode D3 is about 0.3V, the voltage at the inverting input terminal of the operational amplifier U1 is about 0.5V obtained by subtracting 0.3V from the first voltage Va (0.8V). That is, 0.5 V of the reference voltage Vref1 is input to the non-inverting input terminal of the operational amplifier U1, and the feedback circuit 5 performs the feedback control so that the voltage drop of the inverting input terminal becomes 0.5 V, whereby the output voltage Vout Is controlled to 40V.

  Here, since the light source 10 is disconnected, the second voltage Vb has no potential, and the second voltage Vb is not input to the inverting input terminal of the operational amplifier U1. Therefore, the first voltage Va is input to the inverting input terminal of the operational amplifier U1, and feedback control by the feedback circuit 5 is performed.

  When the light source 10 is connected to the light source driving device 1 from the state in which the light source 10 is disconnected, the light source 10 is steadily lit through a transition period from the moment of connection. In this transition period, the output voltage Vout changes from 40V to 36V, and the second voltage Vb changes from about 4.8V (= 40V-35.2V) to 0.8V. Since the source voltage Vc of the transistor Q3 is controlled to be constant at 0.5V, the voltage value between the drain and source of the transistor Q3 is 4.3V (= 4.8V-0.5V) to 0.3V ( = 0.8V-0.5V). That is, even during the transition period, a constant voltage of 35.2V is applied to the light source 10, and the current IL flowing through the light source 10 becomes a current value obtained by dividing 0.5V by the resistance value of the resistor R8. Since the transistor Q3 bears the difference 5V (= 41V−36V) in the output voltage Vout depending on the presence or absence of the light source 10, no overvoltage is applied to the light source 10. Further, since the source voltage Vc of the transistor Q3 is controlled to be constant, no overcurrent flows through the light source 10.

  [Effects of the embodiment]

  As described above, in the present embodiment, the feedback circuit 5 having the single operational amplifier U1 can be configured using the diode OR circuit configured using the diode D3 and the diode D4. That is, one operational amplifier U1 can be shared for controlling the output voltage Vout when the light source 10 is disconnected and for controlling the output voltage Vout when the light source 10 is connected. Therefore, the circuit configuration of the light source driving device 1 can be simplified.

  In addition, since the current control circuit 4 controls the current IL flowing through the light source 10, no inrush current flows through the light source 10 when the light source 10 is attached or detached. That is, the current control circuit 4 has a current limiting function for limiting the current IL. Thereby, failure of the light source 10 can be avoided. Further, since it is not necessary to provide a current limiting circuit separately from the current control circuit 4, the circuit configuration of the light source driving device 1 can be further simplified.

  The current IL flowing through the light source 10 is determined by the current control of the current control circuit 4. Therefore, no pulsating flow (ripple) occurs in the current IL flowing through the light source 10. Since the current IL becomes a current without a pulsating current, the quality of the light emitted from the light source 10 can be improved. Further, since the current control circuit 4 controls the current IL, the rate of change (regulation) of the current IL with respect to the drive voltage of the light source 10, the AC voltage of the AC commercial power supply Vac, and the environmental temperature can be reduced. Also by this, the quality of the light emitted from the light source 10 can be improved.

  [Others]

  Each circuit of the light source driving device may have a circuit configuration different from that of the above-described embodiment. As a circuit element constituting each circuit, a different element from the above-described embodiment that functions in the same manner may be used. In addition to the circuit as described above, another circuit may be provided in the light source driving device.

  The dimming control device may not be provided. In other words, the light source driving device only needs to be configured to turn on the light source with a predetermined brightness. In this case, a constant voltage reference voltage may be used in place of the dimming instruction signal in the current control circuit described above, or a constant current circuit having a configuration different from that of the current control circuit described above may be used. Also good.

  The rectifier circuit may half-wave rectify an AC voltage from an AC commercial power supply and output a DC voltage to the DC / DC converter. Further, a direct current voltage may be directly input to the dimming control device. In this case, the DC / DC converter may convert the input DC voltage into a DC voltage having a magnitude different from that of the input DC voltage.

  The light source driving device according to the present invention is not limited to that used in a lighting fixture that illuminates a space. For example, the light source driving device according to the present invention may be used in a lighting fixture used as a backlight of various devices. In addition, the present invention can be applied to various devices such as an instrument that irradiates a light beam for a specific purpose using an LED and an instrument that displays and transmits information by the light from the LED itself.

  The light source is not limited to the LED. Various light sources can be used as the light source driven by the light source driving device.

  The above embodiment should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Light source drive device 2 DC / DC converter 2a Control circuit 3 Output voltage detection circuit 4 Current control circuit 5 Feedback circuit 6 Control power supply circuit 10 Light source 80 Light control device 100 Lighting fixture BD1 Rectification circuit D3 Diode (1st rectification element)
D4 diode (second rectifier)
IL light source current U1 operational amplifier Va first voltage Vac AC power supply Vb second voltage Vout output voltage Vref1 reference voltage Vref2 dimming instruction signal

Claims (4)

A light source driving device that drives a light source using an input DC voltage,
A DC / DC converter that converts the input DC voltage into a DC voltage having a magnitude different from that of the input DC voltage;
A current control circuit connected to the output end of the DC / DC converter in series with the DC / DC converter via the light source;
An output voltage detection circuit that generates a first voltage from a DC voltage output from the DC / DC converter;
A feedback circuit having an operational amplifier, a first rectifying element, and a second rectifying element;
The inverting input terminal of the operational amplifier has a second voltage that is a voltage at a point where the first voltage is input via the first rectifier element and is connected to the light source of the current control circuit. Input via the second rectifier element;
The non-inverting input terminal of the operational amplifier is connected to a reference voltage,
The feedback circuit is configured such that the larger one of the first voltage and the second voltage is input to the inverting input terminal of the operational amplifier, and the input voltage is equal to the reference voltage. A light source driving device that controls a DC converter. The feedback circuit includes:
When the light source is connected to the light source driving device and the second voltage becomes higher than the first voltage, the second voltage is input to the inverting input terminal of the operational amplifier, and the input voltage is Controlling the DC / DC converter to be equal to a reference voltage;
When the light source is not connected to the light source driving device, the first voltage is input to the inverting input terminal of the operational amplifier, and the DC / DC converter is controlled so that the input voltage becomes equal to the reference voltage. The light source driving device according to claim 1. A dimming instruction signal is input to the light source driving device,
The light source driving device according to claim 1, wherein the current control circuit controls a current supplied to the light source in accordance with the dimming instruction signal. A light source driving device according to any one of claims 1 to 3,
And a light source driven by the light source driving device.

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