JP6102293B2 - LED drive circuit - Google Patents

Description

  The present invention relates to an LED drive circuit for driving an LED.

  FIG. 9 is a circuit diagram showing Example 1 of a conventional LED driving circuit. This LED drive circuit rectifies an AC voltage from an AC power supply AC by a rectifier circuit BD via a reactor L1, and switches the rectified voltage by a switching element Q1 comprising a MOSFET via a primary winding P of a transformer T. Then, a DC output voltage obtained by rectifying and smoothing the AC voltage generated in the secondary winding S of the transformer T with the diode D1 and the capacitor C2 can be applied to the LED 1 to light the LED 1.

  Further, the difference voltage between the current flowing through the LED 1 and the voltage generated by the resistor R2 and the reference voltage Vref is amplified, and the amplified difference voltage is applied to one end of the resistor R1. The amplified differential voltage controls the current flowing through the photodiode of the photocoupler PC and the resistor R1, and the feedback signal is fed back to the control circuit IC1 formed of an integrated circuit via the phototransistor of the photocoupler PC. The control circuit IC1 controls on / off of the switching element Q1 so that the DC output voltage becomes the reference voltage.

  However, in the LED drive circuit shown in FIG. 9, a commercial ripple voltage of the AC power supply AC is applied to the LED 1, the ripple is expanded by the voltage-current characteristics of the LED, and uneven brightness occurs in the LED.

  Thus, for example, LED driving circuit example 2 as shown in FIG. 10 is used as a circuit for improving unevenness in brightness. In the LED driving circuit of Example 2, a constant current circuit including resistors R2 to R6, a transistor Q2, and a comparator IC3 including an integrated circuit is further provided in the LED driving circuit shown in FIG. Since this constant current circuit causes a constant current to flow through the LED 1, unevenness in brightness at commercial frequencies can be improved.

  However, a loss of the current Io flowing through (LED V1 across the capacitor C2−forward voltage Vf of LED1) × LED1 occurs.

  Further, as a circuit for improving unevenness in brightness, for example, an LED drive circuit example 3 as shown in FIG. 11 is used. The LED drive circuit of Example 3 is the LED drive circuit shown in FIG. 10 and includes a constant current step-down switching circuit having a diode D2, a reactor L2, and a capacitor C3 in front of LED1.

  According to this drive circuit, unevenness in brightness can be improved, and loss can be reduced, that is, efficiency can be improved. This efficiency is obtained by power supply efficiency × constant current switching efficiency. The efficiency is improved over the circuit shown in FIG. 10, but is less than 80%. Here, the power supply efficiency is 87%, the constant current switching efficiency is 92%, and the total efficiency is 80%.

JP 2011-62043 A

  However, the LED drive circuit shown in FIG. 11 has a problem that the number of parts increases.

  It is an object of the present invention to provide an LED drive circuit that can improve unevenness in brightness and efficiency of LEDs and can reduce the number of components.

In order to solve the above problems, an LED drive circuit according to the present invention is an LED drive circuit that converts an alternating current input voltage into a predetermined direct current output voltage and supplies the converted direct current output voltage to the LED. A ripple detection circuit to detect; a ripple control unit that reduces a ripple contained in the DC output voltage by the ripple detected by the ripple detection circuit; a phase of the ripple voltage detected by the ripple detection circuit; and the DC output voltage A phase matching unit that makes the phase of the ripple voltage included in the same phase, and the ripple control unit includes reducing a ripple included in the DC output voltage by an output signal from the phase matching unit. Features.

According to the present invention, when the ripple detection circuit detects a ripple included in the DC output voltage, the phase matching unit calculates the phase of the ripple voltage detected by the ripple detection circuit and the phase of the ripple voltage included in the DC output voltage. Since the ripple control unit reduces the ripple included in the DC output voltage by the output signal from the phase matching unit , the brightness unevenness and efficiency of the LED can be improved, and the number of components can be reduced. .

It is a circuit diagram which shows the structure of the LED drive circuit of Example 1 of this invention. It is a figure which shows the voltage V1 of the voltage ripple of the commercial frequency in a smoothing capacitor. It is a figure which shows the detailed structure of a voltage ripple reduction circuit. It is a figure which shows the addition voltage V4 which added the voltage V3 detected by the ripple detection circuit, the reference voltage V2, and the reference voltage V2 and the voltage V3. It is a figure which shows DC output voltage V1, the addition voltage V4 from an adder, and the phase matching voltage V5 of a phase matching circuit. It is a figure which shows the both-ends voltage V6 of LED1. It is a figure which shows the LED drive circuit carrying the concrete voltage ripple reduction circuit. It is a circuit diagram which shows the structure of the ripple reduction circuit provided in the LED drive circuit of Example 2 of this invention. It is a circuit diagram which shows Example 1 of the conventional LED drive circuit. It is a circuit diagram which shows Example 2 of the conventional LED drive circuit. It is a circuit diagram which shows Example 3 of the conventional LED drive circuit.

  Hereinafter, embodiments of an LED drive circuit of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a circuit diagram showing a configuration of an LED drive circuit according to Embodiment 1 of the present invention. The LED driving circuit according to the first embodiment shown in FIG. 1 is similar to the conventional LED driving circuit shown in FIG. 9 and further includes a ripple detection circuit 11, a reference power supply V2, an adder 12, a phase matching circuit 13, a differential amplifier 14, and a transistor. 15 (corresponding to a variable impedance element) is provided.

  FIG. 2 is a diagram illustrating the voltage V1 of the commercial frequency voltage ripple in the smoothing capacitor. The voltage V1 of the voltage ripple shown in FIG. 2 is a DC output voltage of the capacitor C2, and this DC output voltage includes a DC component and an AC component (ripple component). FIG. 3 is a diagram showing a detailed configuration of the voltage ripple reduction circuit.

  The ripple detection circuit 11 detects a ripple that is an AC component included in the DC output voltage of the capacitor C2. FIG. 4A shows a ripple voltage V3 detected by the ripple detection circuit 11 shown in FIG.

  The adder 12 adds the ripple voltage V3 included in the DC output voltage detected by the ripple detector 11 and the reference voltage V2 of the reference power source shown in FIG. 4B, as shown in FIG. 4C. To obtain an additional voltage V4. For example, the reference voltage V2 is set to a voltage that is about 0.5V to 1V higher than the ripple voltage (Vp-p) / 2.

  (Vp−p) is a difference voltage between the maximum value and the minimum value of the ripple voltage. 0.5V to 1V is a voltage margin for not being affected by the offset voltage of the adder 12 made of an integrated circuit.

  As shown in FIG. 5, the phase matching circuit 13 makes the phase of the ripple added voltage V4 from the adder 12 in-phase with the phase of the ripple voltage V1AC included in the DC output voltage V1 of the capacitor C2. The matching voltage V5 is output to the inverting input terminal of the differential amplifier 14.

  The inverting input terminal of the differential amplifier 14 is connected to the output terminal of the phase matching circuit 13, the non-inverting input terminal of the differential amplifier 14 is connected to the collector of the NPN bipolar transistor 15, and the output terminal of the differential amplifier 14 is It is connected to the base of the bipolar transistor 15. The emitter of the transistor 15 is connected to the negative electrode of the reference power source V2 and one end of the resistor R2. The collector of the transistor 15 is connected to one end of the capacitor C2 via the LED1.

  The differential amplifier 14 controls the transistor 15 so that the collector-emitter voltage V7 of the bipolar transistor 15 becomes equal to the phase matching voltage V5 from the phase matching circuit 13. The differential amplifier 14 and the transistor 15 constitute a ripple control unit that is controlled by negative feedback and reduces the ripple included in the voltage applied to the LED 1 by the ripple detected by the ripple detection circuit 11.

  As shown in FIG. 6, the both-ends voltage V6 of LED1 becomes (DC output voltage V1-voltage V7 between the collector and the emitter of the bipolar transistor 15), which is a DC voltage without commercial ripple.

  FIG. 7 is a diagram showing an LED drive circuit equipped with a specific voltage ripple reduction circuit. In FIG. 7, the ripple detection circuit 11 includes a series circuit including a capacitor C11 and a resistor R11. The ripple detection circuit 11 detects a ripple included in the DC output voltage V1 using a differentiation circuit including the capacitor C11 and the resistor R11. Output to the inverting input terminal.

  The differential amplifier 18 corresponds to the adder 12, a resistor R12 is connected to the inverting input terminal and the output terminal, and the ripple voltage V3 detected by the capacitor C11 and the resistor R11 is added to the reference voltage V2. The added voltage V4 is output to the phase matching circuit 13.

  The phase matching circuit 13 includes an integrating circuit including a resistor R13 and a capacitor C12, a differential amplifier 19, and resistors R14 and R15. One end of the resistor R13 and one end of the resistor R14 are connected to the output terminal of the differential amplifier 18, and the other end of the resistor R13 is connected to the non-inverting input terminal of the differential amplifier 19 and one end of the capacitor C12.

  The other end of the resistor R14 is connected to one end of the resistor R15 and the inverting input terminal of the differential amplifier 19, and the other end of the resistor R15 is connected to the output terminal of the differential amplifier 19 and the inverting input terminal of the differential amplifier 14. Yes.

  In the phase matching circuit 13, the phase of the addition voltage V4 obtained by adding the ripple voltage V3 and the reference voltage V2 is made in phase with the phase of the ripple of the DC output voltage V1 by the integration circuit using the resistor R13 and the capacitor C12. It is output to the inverting input terminal of the dynamic amplifier 14. That is, the phase of the addition voltage V4 is shifted by the integration circuit consisting of the resistor R13 and the capacitor C12 by the amount that the phase of the DC output voltage V1 is shifted by the differentiation circuit including the capacitor C11 and the resistor R11. The phase of the ripple of the DC output voltage V1 can be made in phase.

  The LED drive circuit 17 includes a differential amplifier 14, resistors R16 to R20, capacitors C13 and C14, and a MOSFET 15a (corresponding to a variable impedance element).

  LEDs 1 to LED7 are connected in series between the positive electrode of the DC output voltage V1 and the drain of the MOSFET 15a. The non-inverting input terminal of the differential amplifier 14 is connected to the cathode of the LED 7 and the drain of the MOSFET 15a via a resistor R20.

  The output terminal of the differential amplifier 14 is connected to one end of the capacitor C13 and one end of the resistor R16, and the other end of the capacitor C13 is connected to the non-inverting input terminal of the differential amplifier 14 via the resistor R19.

  The other end of the resistor R16 is connected to one end of the capacitor C14, one end of the resistor R17, and one end of the resistor R18, and the other end of the resistor R18 is connected to the gate of the MOSFET 15a. The source of the MOSFET 15a is connected to the other end of the resistor R17 and the other end of the capacitor C14.

  As described above, according to the LED drive circuit of the first embodiment, when the ripple detection circuit 11 detects a ripple included in the DC output voltage, the differential amplifier 14 and the transistor 15 which are ripple control units are detected by the ripple detection circuit 11. Since the ripples included in the voltages applied to the LEDs 1 to 7 are reduced by the generated ripple, it is possible to improve the brightness unevenness and the efficiency of the LED and reduce the number of components.

  FIG. 8 is a circuit diagram illustrating a configuration of a ripple reduction circuit provided in the LED drive circuit according to the second embodiment of the present invention. The ripple reduction circuit according to the second embodiment illustrated in FIG. 8 includes A / D 21, D / A 22, a differential amplifier 14, a resistor R 7, and a transistor 15.

  The output terminal of the D / A 22 is connected to the inverting input terminal of the differential amplifier 14, and the non-inverting input terminal of the differential amplifier 14 is connected to the collector of the transistor 15 via the resistor R7. The output terminal of the differential amplifier 14 is connected to the base of the transistor 15.

  The A / D 21 converts the DC output voltage V1 into a digital signal, obtains a difference Vp-p value between the maximum value and the minimum value of the DC output voltage V1, that is, a peak value, and outputs the DC output from the time of the Vp-p value. The frequency of the voltage V1 is obtained. Thereby, the ripple of the DC output voltage V1 can be detected.

  Next, the D / A 22 converts the digital signal composed of the ripple from the A / D 21 into an analog signal, and outputs the analog signal composed of the ripple to the inverting input terminal of the differential amplifier 14.

  The differential amplifier 14 controls the transistor 15 so that the collector-emitter voltage V7 of the bipolar transistor 15 is equal to the analog voltage V5 from the D / A 22. The differential amplifier 14 and the transistor 15 constitute a ripple control unit that is controlled by negative feedback and reduces the ripple included in the voltage applied to the LED 1 by the ripple detected by the ripple detection circuit 11.

  At this time, the voltage V7 between the collector and the emitter of the bipolar transistor 15 changes according to the ripple of the DC output voltage V1, but the voltage V6 across the LED 1 is (DC output voltage V1−bipolar as shown in FIG. The voltage V7) between the collector and the emitter of the transistor 15 becomes a DC voltage with no commercial ripple.

  As described above, according to the LED drive circuit of the second embodiment, the ripple control unit D / A 22, the differential amplifier 14, and the transistor 15 reduce the ripple included in the DC output voltage due to the ripple detected by the A / D 21. Therefore, the brightness unevenness and efficiency of the LED can be improved, and the number of components can be reduced.

  The LED drive circuit according to the present invention can be used for an LED lighting circuit.

11 Ripple detection circuit 12 Adder 13 Phase matching circuit 14 Differential amplifier 15 Transistor AC AC power supply L1, L2 Reactor BD Rectifier circuit T Transformer P Primary winding S Secondary winding IC1 Control circuit PC Photocoupler C1, C2 Capacitor IC2 Comparator R1-R6 Resistor Vref Reference power supply

Claims (4)

An LED drive circuit that converts an AC input voltage into a predetermined DC output voltage and supplies the converted voltage to an LED,
A ripple detection circuit for detecting ripples included in the DC output voltage;
A ripple control unit that reduces a ripple included in the DC output voltage due to a ripple detected by the ripple detection circuit;
A phase matching unit that makes the phase of the ripple voltage detected by the ripple detection circuit and the phase of the ripple voltage included in the DC output voltage in phase;
The LED drive circuit , wherein the ripple control unit reduces a ripple included in the DC output voltage by an output signal from the phase matching unit .   The ripple control unit inputs an output signal from the ripple detection circuit as a reference voltage to one input terminal, and an output signal of the ripple control unit is input to the other input terminal of the ripple control unit by negative feedback. The LED driving circuit according to claim 1. The ripple control unit includes a variable impedance element connected in series with the LED,
The variable impedance element is controlled based on a value of a ripple voltage detected by the ripple detection circuit and a voltage value at a connection point between the LED and the variable impedance element. Item 3. The LED drive circuit according to Item 2. The LED driving circuit according to claim 1, wherein the phase matching unit includes an integrating circuit having a second capacitor and a second resistor.

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