JP2015125959A - LED lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED lighting device capable of obtaining an optical output equivalent to the case when the LED is turned on by DC smooth voltage while reducing a harmonic component of input current.SOLUTION: An LED lighting device comprises: a full-wave rectifier which carries out full-wave rectification of a commercial AC power supply; a first capacitor connected in parallel to an output terminal of the full-wave rectifier; a switching power supply circuit unit whose input terminal is connected in parallel to the first capacitor; an LED light-emitting unit connected to an output terminal of the switching power supply circuit unit; and a second capacitor connected in parallel to the LED light-emitting unit. The switching power supply circuit unit operates in discontinuous mode. The capacity of the first capacitor is not more than 0.5 μF. The capacity of the second capacitor is set so that a ripple factor of current flowing in the LED light-emitting unit becomes less than 1.

Description

  The present invention relates to an LED lighting device that lights a light emitting diode (hereinafter referred to as an LED (Light Emitting Diode) as appropriate) using, for example, a commercial AC power supply.

  In recent years, the optical performance of LEDs has increased, and lighting fixtures using LEDs have been replaced with conventional light sources for reasons such as long life. If the performance of LEDs further improves in the future, it will be adopted in the field of general-purpose lighting equipment. Moreover, in order to raise the efficiency as a lighting fixture, the lighting device of LED is also going to improve efficiency. For this reason, a switching power supply type constant current type using a switching element is employed as the lighting device.

  FIG. 4 shows a circuit diagram of a conventional LED lighting device disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2007-189819). In the figure, Vs is a commercial AC power supply, DB is a full-wave rectifier, C2 is a capacitor, T1 is a transformer, and the LED lighting device includes a primary winding n1 and a secondary winding n2. Q1 is a switching element, D1 is a rectifier diode, 13 is a control circuit for the switching element Q1, 2 is an LED light emitting unit, and 14 is a constant current element.

Next, the operation of the circuit shown in FIG. 4 will be described. AC voltage of commercial AC power supply Vs is rectified by full-wave rectifier DB, smoothed by capacitor C2, converted to high-frequency rectangular wave AC voltage by switching element Q1 such as transformer T1, MOSFET, and rectified by rectifier diode D1. A series circuit of the constant current element 14 and the LED light emitting unit 2 is connected to the pulse voltage. The switching element Q1 is ON / OFF controlled by the control circuit 13.

FIG. 5 shows a waveform of the secondary voltage Vn2 of the transformer T1 and the pulse voltage Vp obtained by rectification using the rectifier diode D1. Only when there is a pulse voltage Vp, the constant current Ic defined by the constant current element 14 flows to the LED light emitting unit 2 and the LED is lit.

A characteristic example of the constant current element 14 is shown in FIG. The horizontal axis is the applied voltage, and the vertical axis is the current. When a voltage equal to or higher than the voltage Vc existing in the constant current element 14 is applied, a constant current Ic flows regardless of the applied voltage. The fluctuation of the power supply voltage and the fluctuation of the forward voltage of the LED change so that the voltage applied to the constant current element 14 absorbs the fluctuation of the voltage and the fluctuation of the forward voltage, and the flowing current is kept constant as Ic. Therefore, the power consumption increases or decreases by the fluctuation of the power supply voltage, but the brightness of the LED does not change.

In the circuit shown in FIG. 4, the LED light emitting unit 2 is turned off when there is no pulse voltage Vp. However, if the pulse voltage Vp is a high frequency of several kHz (kilohertz) or more, it cannot be recognized by human eyes. Therefore, it seems that the LED light emission part 2 continues lighting.

When the ratio (t / T) of the pulse voltage Vp with respect to one cycle T of the pulse voltage Vp shown in FIG. 5 is decreased, the luminance of the LED light emitting unit 2 is decreased and the ratio (t / T) of the pulse voltage Vp is increased. And the brightness seems to rise. The ratio (t / T) of the pulse voltage Vp can be adjusted by the control circuit 13.

JP 2007-189819 A

However, in a constant current power source using a constant current element as in Patent Document 1, if the output voltage is not smoothed, a voltage equal to or higher than the voltage Vc in the constant current element 14 cannot be maintained. That is, since the constant current element 14 has a voltage equal to or higher than the voltage Vc as in a diode, the flowing current is kept constant as Ic. In this conventional circuit, the primary side of the transformer T1 Smoothing is performed by a capacitor C2 provided at the subsequent stage of the full-wave rectifier DB. Without this capacitor C2, the output voltage of the full-wave rectifier DB becomes a full-wave pulsating voltage, and therefore a 50/60 Hz AC power supply causes a low-frequency flicker of 100 Hz or 120 Hz. However, since this capacitor C2 exists for smoothing, the harmonic component of the input current becomes large, and there arises a problem that it deviates from the standard value of the harmonic regulation guideline defined in the lighting equipment.

In addition, the secondary side of the transformer T1 is turned on with the pulse voltage Vp. However, the efficiency decreases in terms of the efficiency of the appliance obtained by dividing the light output (luminous flux) of the luminaire by the input power including the appliance. That is, as with the diode, the LED characteristics exceed the forward voltage Vf, so that a forward current If corresponding thereto flows. In terms of LED specifications, the output light efficiency (the output luminous flux divided by the output power consumption) is the best when the DC current Idc is passed with a DC smoothing voltage with a ripple rate of approximately zero. Therefore, when pulse lighting is performed with the pulse voltage Vp, there is a problem that the current is averaged and smaller than the previous DC current Idc, and the output luminous flux is accordingly reduced. Further, if the pulse voltage Vp is increased to make the average value of the current passed by the pulse equal to the direct current Idc, the peak of the pulse voltage Vp must be increased, and the rating of the constant current element 14 also increases. However, there is a problem in that it causes an increase in cost and further exceeds the absolute maximum rating of the peak current of the LED.

This invention is made in view of such a point, and provides the LED lighting device which can obtain the light output equivalent to the case where it is made to light by DC smoothing voltage, reducing the harmonic component of input current. Is an issue.

The LED lighting device of the present invention includes a full-wave rectifier for full-wave rectification of a commercial AC power supply having a voltage of 200 V, a first capacitor connected in parallel to the output terminal of the full-wave rectifier, and an input to the first capacitor. A switching power supply circuit unit having an end connected in parallel; an LED light emitting unit connected to an output end of the switching power supply circuit unit; and a second capacitor connected in parallel to the LED light emitting unit, Section operates in a discontinuous mode, the capacity of the first capacitor is 0.5 μF or less, and the second capacitor is set to a capacity at which the ripple rate of the current flowing through the LED light emitting section is less than 1. The

  In the LED lighting device of the present invention, for example, since the capacitance of the first capacitor is 0.5 μF or less, the voltage waveform from the full-wave rectifier to the switching power supply circuit section is almost full-wave pulsating. As described above, since the capacity of the first capacitor is small, the waveform of the input current from the commercial AC power supply is not a capacitor input type current waveform as in the conventional example, but in almost the whole area except for the valley portion of the full wave. Since the current flows in a waveform, it falls within the standard value of the harmonic regulation guidelines established for lighting equipment. If the voltage waveform of the output becomes a pulsating voltage as it is, current does not flow in the voltage range below the forward voltage Vf of the LED, so a capacitor having a capacity of, for example, 100 times the capacity of the first capacitor is set to the LED. By connecting in parallel at both ends of the light emitting unit and making the ripple ratio obtained by dividing the fluctuation range of the current flowing through the LED by the effective current less than 1, there is an effect that it is possible to prevent a decrease in light output.

It is a block circuit diagram which shows the basic composition of this invention. It is a circuit diagram which shows the structure of embodiment of this invention. It is an operation | movement waveform diagram of embodiment of this invention. It is a circuit diagram of a conventional example. It is an operation | movement waveform diagram of a prior art example. It is a characteristic view of the constant current element used for a prior art example.

  The details of the present invention will be described below with reference to the illustrated embodiments.

A basic configuration of the present invention is shown in FIG. Vs is a commercial AC power supply, DB is a full-wave rectifier for full-wave rectification of the commercial AC power supply, C1 and C2 are capacitors, 1 is a switching power supply circuit unit including a switching element, 2 is an LED light emitting unit, and 3 is a filter circuit unit. Each is shown. The power consumption of the LED light emitting unit 2 is, for example, 20 W (watts) or less. A capacitor C1 is connected in parallel to the output terminal of the full-wave rectifier DB. The input terminal of the switching power supply circuit unit 1 is connected in parallel to the capacitor C1. The LED light emitting unit 2 is connected in parallel to the output terminal of the switching power supply circuit unit 1, and the capacitor C <b> 2 is connected in parallel to the LED light emitting unit 2.

In the circuit of FIG. 1, a capacitor C1 (first capacitor) is a capacitor having a capacity of, for example, 0.5 μF (microfarad) or less as a first capacity. In the following description, it is assumed that the capacitance of the capacitor C1 is 0.47 μF. Since the capacity of the capacitor C1 is small enough to smooth the output voltage of the full-wave rectifier DB, a pulsating voltage having a substantially full-wave waveform is applied to the switching power supply circuit unit 1 and is switched at a high frequency by an internal switching element. And a pulse voltage is output. The output of the switching power supply circuit unit 1 is connected in parallel with a capacitor C2 (second capacitor) having a larger capacity (second capacity) that satisfies the conditions described later than the capacity of the capacitor C1. Voltage smoothing is performed. A smoothing voltage is applied to the LED light emitting unit 2 connected in parallel to the capacitor C2.

At this time, even if the current flowing through the LEDs 2a to 2d is smoothed, the ripple does not completely disappear. In the embodiment of the present invention, the ripple ratio (Ipp / Iav) obtained by dividing the fluctuation range Ipp (= Imax−Imin) of the current defined by the maximum value Imax and the minimum value Imin by the average value Iav of the current flowing through the LED. ) Is set so that the capacitance of the output capacitor C2 is less than 1. As a result, the optical output obtained by the circuit of FIG. 1 is almost the same as the optical output obtained by a current flowing from a flat DC voltage.

A circuit diagram of an embodiment of the present invention is shown in FIG. In this embodiment, the switching power supply circuit unit 1 of FIG. 1 is a flyback type DC-DC converter circuit, and the DC-DC converter circuit includes a primary side control circuit 11 and a secondary side control circuit. 12. A DC power supply unit 4 including these circuits and the filter circuit unit 3 is formed.

The LED light emitting unit 2 includes four LEDs 2a to 2d, and the LED 2a to LED 2d are connected in series from the anode to the cathode. When a positive voltage is applied to the anode side of the LED 2a and a negative voltage is applied to the cathode side of the LED 2d, each of the LEDs 2a to 2d emits light. When a voltage equal to or higher than the total of the forward voltages Vf of the LEDs 2a to 2d is applied, a light beam can be obtained from the LEDs according to the value of the flowing current. Since the forward voltage Vf is generally about 3.5 V, the LEDs 2 a to 2 d can be lit at a DC voltage of 4 × 3.5 V or more if four are connected in series.

The output connector CN <b> 2 of the DC power supply unit 4 and the LED light emitting unit 2 are connected by a pair of lead wires 5. The input connector CN1 of the DC power supply unit 4 is connected to an AC power supply voltage (for example, AC (Alternating Current) 200 V (volt), 50/60 Hz) from the commercial AC power supply Vs.

The filter circuit unit 3 of the DC power supply unit 4 is connected to the commercial AC power supply Vs. The filter circuit unit 3 includes a fuse F, a capacitor C3, and a line filter LF. The fuse F is connected in series to one end of the commercial AC power supply Vs, and the capacitor C3 is connected to the other end of the commercial AC power supply Vs and the output terminal of the fuse F. And a line filter LF are connected in parallel.

A full-wave rectifier DB and a capacitor C1 are connected in parallel to the output of the filter circuit unit 3, respectively. A circuit in which the transformer T1 and the switching element Q1 are connected in series is connected in parallel to the capacitor C1. A resonance capacitor C4 is connected in parallel to both ends of the switching element Q1. A diode D1 is connected to the high potential side of the secondary winding side of the transformer T1, and a capacitor C2 and an output connector CN2 are connected in parallel via the diode D1. An input terminal (IN terminal) of the control circuit 12 is connected via a resistor R1 to a line between the low potential side of the output connector CN2 and the negative electrode of the capacitor C2. The output current Io is converted into a voltage value by the resistor R1.

The first control circuit 11 is provided on the primary side of the transformer T1, and outputs a switching signal of the switching element Q1 according to an input value from the feedback terminal FB. The second control circuit 12 is provided on the secondary side of the transformer T1, and receives a value obtained by converting the output current Io into a voltage by the resistor R1, and generates a feedback signal. The feedback input terminal FB of the first control circuit 11 is connected to the output of the second control circuit 12.

The circuit operation will be described below. This DC-DC converter circuit is, for example, a so-called flyback type DC power supply device that operates in a discontinuous mode, and is a partial resonance type having a capacitor C4 connected in parallel to the switching element Q1. The voltage input from the commercial AC power source Vs is full-wave rectified by the full-wave rectifier DB through the filter circuit unit 3 via the input connector CN1. The full-wave rectified voltage is applied to a series circuit of the transformer T1 and the switching element Q1 via the capacitor C1. The applied voltage waveform at this time is a full-wave rectified pulsating voltage because the capacitance of the capacitor C1 is set to 1.2 μF. That is, the full-wave rectified voltage is not smoothed by the capacitor C1, and a full-wave waveform pulsating voltage is applied to the series circuit of the transformer T1 and the switching element Q1. When the switching element Q1 is closed, a current flows through the transformer T1 so that it is charged as magnetic energy. When the switching element Q1 is opened, the magnetic energy is output to the output side via the secondary winding and the diode D1. To be released.

The output voltage is smoothed by the capacitor C2 until the ripple rate becomes less than 1, and is output via the output connector CN2. The voltage output from the DC power supply unit 4 is supplied to the LED light emitting unit 2, and the LEDs 2a to 2d are turned on when the voltage is equal to or greater than the total of the forward voltages Vf of the LEDs 2a to 2d.

Here, since the capacitance of the capacitor C1 is 0.47 μF, the output voltage of the transformer T1 also has a pulsating waveform. If this is applied to the LED light emitting unit 2 as it is, light is emitted only when the voltage is equal to or higher than the sum of the forward voltages Vf of the LEDs 2a to 2d in the LED light emitting unit 2, so that the light output becomes smaller than when there is no ripple. . Therefore, the capacity of the capacitor C2 is set larger than the capacity of the capacitor C1. For example, the capacitance of the capacitor C2 is set to 100 times or more (specifically, 470 μF) of the capacitor C1. At this time, the ripple ratio of the output current (current fluctuation range Ipp, that is, the maximum current value Imax−the minimum current value Imin divided by the average current value Ia) is less than 1.

FIG. 3 shows operation waveforms of the present embodiment, CH1 is a voltage waveform across the capacitor C1, CH2 is an output current waveform, and CH4 is an input current waveform. CH2 is measured in the range of 100 mA (milliampere) / 10 mV (millivolt), and the current fluctuation width Ipp is 10 mApp. Since the average current value is 340 mA, the ripple rate is 0.03 and less than 1.

The current flowing through each LED 2a to 2d flows to the resistor R1 via the output connector CN2, and the resistor R1 generates a voltage corresponding to the current. This voltage is monitored at the IN terminal of the control integrated circuit IC2 in the second control circuit 12, and compared with the reference voltage of the reference voltage terminal REF, whereby the second control circuit according to the current flowing through the LEDs 2a to 2d. 12 is determined, and the control voltage is fed back to the feedback terminal FB of the control integrated circuit IC1 of the first control circuit 11. At this time, the ON width of the switching element Q1 is determined according to the control voltage input to the feedback terminal FB. By operating in this way, control is performed to keep the current flowing through the LEDs 2a to 2d constant.

In other respects, the power supply Vcc of the first control circuit 11 is supplied from the voltage line after full-wave rectification. The first control circuit 11 is a quasi-resonant mode power factor correction circuit, the OCP terminal is a quasi-resonant signal input terminal, detects the bottom of energy emission of the transformer T1, and the switching element Q1 operates in the current critical mode. Like to do.

By operating in this way, it is cheaper than conventional circuits and can satisfy harmonic regulations, and it does not exceed the absolute maximum rated current of the LED, reducing the light output compared to lighting with a DC smoothed voltage. Can be suppressed.

In this embodiment, the flyback type DC power source has been described. However, the same effect can be obtained as long as the DC power source outputs a DC voltage regardless of the type. In addition, the LED light emitting unit 2 has been described with respect to the four LED connection in series, but may be connected in parallel as long as the directions of the anode and the cathode are the same regardless of the number.

Vs ... Commercial AC power supply DB ... Full wave rectifier C1 ... First capacitor C2 ... Second capacitor 1 ... Switching power supply circuit unit 2 ... LED light emitting unit 3 ... Filter Circuit part

Claims (2)

A full-wave rectifier for full-wave rectification of a commercial AC power supply having a voltage of 200 V, a first capacitor connected in parallel to the output terminal of the full-wave rectifier, and a switching power supply whose input terminal is connected in parallel to the first capacitor A circuit unit; an LED light emitting unit connected to an output terminal of the switching power supply circuit unit; and a second capacitor connected in parallel to the LED light emitting unit, wherein the switching power supply circuit unit operates in a discontinuous mode. The LED lighting is characterized in that the capacitance of the first capacitor is 0.5 μF or less, and the second capacitor is set to a capacitance at which a ripple rate of a current flowing through the LED light emitting unit is less than 1. apparatus. The LED lighting device according to claim 1, wherein the second capacity is set to a capacity that is 100 times or more of the first capacity.