JP4741942B2 - LED lighting device - Google Patents

Description

  The present invention relates to an LED (Light Emitting Diode) lighting device.

  An LED lighting device in which an LED and a current limiting circuit are mounted on a small substrate is known. This type of LED lighting device has a structure that can be easily divided into an arbitrary size, and can be used as partial lighting or decoration by being incorporated into a part of a fixture or furniture. Therefore, from the viewpoint of convenience, it is desirable that the device substrate be as small as possible and have a small loss in order to suppress heat generation. In addition, it is desirable that the emission intensity is also constant. Furthermore, it is desired that the cost be as low as possible.

  The LED is a current control type element, and in general, the light emission intensity can be controlled by controlling the current flowing through the LED. That is, a constant light emission intensity can be obtained by making the current flowing through the LED constant. As a typical current limiting circuit for keeping the current flowing through the LED constant, there is a current limiting circuit as shown in FIGS.

The current limiting circuit shown in FIG. 5A is a circuit in which an LED 100 and a resistor RL are connected in series. The current I _LED flowing through the _LED 100 is

で与えられる。ここで、ＶＦは、直列に配置されたＬＥＤ１００の順方向降下電圧の総和である。

Given in. Here, VF is the total sum of forward drop voltages of the LEDs 100 arranged in series.

The current limiting circuit shown in FIG. 5B includes a circuit in which an LED 100, a transistor Q1, and a resistor R6 are connected in series, and an IC 101 that is an operational amplifier that controls the current I _LED that flows through the _LED 100, which is also the collector current of the transistor Q1. A voltage V4 obtained by dividing the power supply voltage Vin by the resistors R5 and R6 is supplied to the “+” side input of the IC 101, and a voltage V3 generated by the resistor R6 is supplied to the “−” side input. Yes. The IC circuit 101 operates so that the voltage V3 is always equal to the comparison voltage V4. In this case, the current I _LED is

で与えられる値に正確に維持され、ＬＥＤ１００の順方向降下電圧のばらつきの影響を受けない。

Is accurately maintained and is not affected by variations in the forward voltage drop of the LED 100.

  5C includes a circuit in which a transistor Q1, a choke coil L1, an LED 100, and a resistor R6 are connected in series, and a switching power supply control IC 102 that controls on / off of the transistor Q1. The emitter of the transistor Q1 is connected to the collector of the transistor Q1 through the resistor R2. The collector of the transistor Q1 is connected to the negative electrode side line of the power supply via the diode D1. The line connecting the choke coil L1 and the LED 100 is connected to the negative line of the power source via the capacitor C1.

  The switching power supply control IC 102 includes a comparative triangular wave oscillator (OSC) 103, an error amplifier A1, a PWM (Pulse Width Modulation) voltage comparator A2, and an output amplifier A3. The reference voltage Vref (comparison voltage V4) is supplied to the “+” side input of the error amplifier A1, and the line connecting the LED 100 and the resistor R6 is connected to the “−” side input via the resistor R7. ing. The “−” side input of the error amplifier A1 is connected to the output of the error amplifier A1 through a circuit in which a capacitor C2 and a resistor R8 are connected in parallel. The output of the error amplifier A1 is supplied to the “+” side input of the PWM voltage comparator A2, and the output of the oscillator (OSC) 103 is supplied to the “−” side input. The output of the PWM voltage comparator A2 is supplied to the input of the output amplifier A3, and the output of the output amplifier A3 is the output of the switching power supply control IC 102.

  FIG. 6 shows waveforms at various parts of the current limiting circuit shown in FIG. 5C. 6, (a) shows the waveform of the power supply voltage Vin, (b) shows the waveform of the voltage V1 at the point where the diode D1 is connected on the line connecting the transistor Q1 and the choke coil L1, and (c). Shows the waveform of the current ILED flowing through the LED 100 and the waveform of the voltage V2 at the point where the capacitor C1 is connected to the line connecting the choke coil L1 and the LED 100, and (d) shows the voltage V3 generated in the resistor 6 and the comparison Each waveform of the voltage V4 is shown.

In the current limiting circuit shown in FIG. 5C, the current I _LED flowing through the _LED 100 is converted to the voltage V3 by the resistor R6. The error amplifier A1 compares the voltage V3 and the reference voltage Vref, and amplifies the voltage difference. Then, the PWM voltage comparator A2 compares the voltage difference amplified by the error amplifier A1 with the triangular wave that is the reference signal supplied from the oscillator (OSC) 103, and outputs a PWM signal based on the comparison result. The Through such a series of operations, the current limiting circuit always operates so that the voltage V3 becomes the comparison voltage V4. As a result, the current I _LED is maintained at the value given by Equation 2 above.

  In addition to the typical current limiting circuit described above, there is also an LED power supply device as described in Patent Document 1. FIG. 7 shows the configuration of the main circuit portion of the LED power supply device.

  The main circuit unit 30 shown in FIG. 7 includes two connectors 31 and 32. The connector 31 is connected to a power source, and the connector 32 is connected to the LED 21. The input voltage Vi is input to the LED 21 via the transistor Tr1 as a switching circuit and is applied to the collector of the transistor Tr3. When the transistor Tr3 is on, the comparator drive voltage Vc is applied to the transistors Tr4 and Tr5, and the reference voltage Vr is applied to the base of the transistor Tr5. In this case, the transistor Tr3 functions as a reference voltage generation circuit.

  On the other hand, the feedback voltage Vf of the LED 21 is applied to the base of the transistor Tr4. When the reference voltage Vr is higher than the feedback voltage Vf, the transistor Tr4 is turned on and the transistor Tr5 is turned off. When the reference voltage Vr is smaller than the feedback voltage Vf, the transistor Tr4 is turned off and the transistor Tr5 is turned on. Therefore, when the reference voltage Vr is higher than the feedback voltage Vf (when the LED output is less than the reference value), the transistor Tr4 is turned on, the base potential of the transistor Tr2 is high, and the transistor Tr2 is turned on. As a result, the base potential of the transistor Tr1 becomes low and the transistor Tr1 is turned on. Thereby, the power from the power source is applied to the LED 21.

  At this time, since the transistor Tr5 is turned off, the transistor Tr3 transitions to an off state and does not function as a reference voltage generation circuit. Instead, the voltage that has passed through the transistor Tr1 passes through the capacitor 34 and the resistor 35. Thus, the reference voltage Vr is applied to the base of the transistor Tr5. In this case, the capacitor 34, the resistor 35, and the Zener diode 36 constitute a second reference voltage generation circuit. As a result, the transistor Tr5 is turned off and the transistor Tr4 is turned on.

When the transistor Tr1 is turned on and the output of the LED 21 is increased, the feedback voltage Vf is also increased. When the feedback voltage Vf becomes higher than the reference voltage Vr, the transistor Tr4 is turned off and the transistor Tr5 is turned on at the same time, then the transistor Tr2 is turned off, and then the transistor Tr1 is turned off, and the power supply to the LED 21 is stopped. Since the transistor Tr1 is turned off, the reference voltage cannot be generated via the capacitor 34 and the resistor 35, and the first reference voltage is restored. Thus, the entire circuit oscillates, and the current applied to the LED 21 is kept substantially constant.
Japanese Patent Laying-Open No. 2005-80353 (see FIG. 3)

  However, the above-described conventional apparatus has the following problems.

In the current limiting circuit shown in FIG. 5A, the drop voltage VF has a large manufacturing variation and also changes depending on the temperature. Therefore, the current I _LED calculated by Equation 1 fluctuates, and the emission intensity also fluctuates. Become. In order to suppress the fluctuation of the current I _LED , it is necessary to set the power supply voltage Vin larger than the drop voltage VF. In this case, the power loss generated in the resistor RL becomes large. The power loss P _RL generated in the resistor RL is

で与えられられる。このように、図５Ａに示す電流制限回路には、ＬＥＤに流れる電流のバラツキが大きいことや、抵抗で損失が発生して発熱するなどの問題がある。

Is given in As described above, the current limiting circuit shown in FIG. 5A has problems such as large variation in the current flowing through the LED and generation of heat due to loss in resistance.

In the current limiting circuit shown in FIG. 5B, the current I _LED is accurately maintained at the value given by Equation 2 above, and the LED is not affected by variations in the drop voltage VF. However, in the transistor Q1, there is a problem that power loss [(Vin−VF−V3) × I _LED )] is generated and heat is generated. Note that power loss can be reduced by making the power supply voltage Vin close to the value of the voltage (VF + V3). However, since the power supply voltage Vin is determined in consideration of variations in the drop voltage VF and temperature changes, a certain amount of power loss is inevitably generated. In addition to the problem of power loss, in order to reduce power loss as much as possible, it is necessary to specially prepare a power supply controlled to generate a power supply voltage Vin close to the value of voltage (VF + V3). There is also a problem that the cost becomes high.

Since the current limiting circuit shown in FIG. 5C has a switching circuit in the input stage of the LED 100, power loss can be kept low, and the current I _LED is also accurately determined. However, since the price of the IC 102 itself is expensive and the number of parts is large, there is a problem that the circuit scale is increased and the cost is increased.

  In the LED power supply device shown in FIG. 7, the transistor Tr3, the resistor R3, and the Zener diode ZD1 form a reference voltage source that is a constant voltage circuit. The comparator drive voltage Vc, which is a value obtained by subtracting the voltage value of, is supplied to the comparator composed of the transistors Tr4 and Tr5. As described above, since the reference voltage source (constant voltage circuit) is necessary, there is a problem that the circuit scale is increased correspondingly and the cost is increased.

  An object of the present invention is to solve the above problems and provide an LED lighting device with a simple circuit configuration and low loss.

In order to achieve the above object, the LED lighting device of the present invention has one electrode connected to the positive electrode of the power source, the other electrode connected to the negative electrode of the power source via a flywheel diode, and the LED via a choke coil. A switching element connected to the positive line,
A current detection resistor connected in series to the negative electrode side line of the LED;
The first and second resistors are connected in series, one end of the series circuit is connected to the positive electrode of the power source, and the other end is connected to the negative electrode of the power source. A comparison voltage generating circuit in which a connection point of the first and second resistors is connected to the other electrode of the switching element via the third resistor;
One input is connected to the line connecting the LED and the current detection resistor, and the other input is connected to the connection point of the first and second resistors, for comparison of the voltage supplied to these inputs. And a comparator for controlling on / off of the switching element.

  According to said structure, since the main circuit which restrict | limits the electric current which flows into LED was comprised by the switching element and choke coil provided in the input stage of LED, it is possible to suppress power loss.

  Further, since the switching element is controlled to be turned on / off by the self-excited oscillation action, a circuit such as a triangular wave oscillation circuit, an error amplifier, and a PWM voltage comparator is unnecessary.

  Further, the comparison voltage generation circuit has a simple configuration including only the first to third resistors. Therefore, not only a band gap reference element but also a reference voltage source (constant voltage circuit) using a transistor or a low voltage diode is not required.

  According to the present invention, since a circuit such as a triangular wave oscillation circuit, an error amplifier, a PWM voltage comparator, and a reference voltage source (constant voltage circuit) is unnecessary, the circuit can be simplified and downsized, and the price can be reduced. Can be kept low.

Next, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a circuit diagram showing a main part of the LED lighting device according to the first embodiment of the present invention.

Referring to FIG. 1, the LED lighting device lights a plurality of LEDs 100 connected in series, and includes a power source 10, a switching circuit composed of a switching element Q1 and a flywheel diode D1, a choke coil L1, and a smoothing circuit. A filter circuit composed of a capacitor C1, a resistor R6 for detecting a current I _LED flowing through the _LED 100, a voltage comparator IC1, and a resistor R3 for generating a comparison voltage V4 and giving the IC1 hysteresis characteristics. ~ R5. A control circuit for controlling on / off switching of the switching element Q1 is configured by the IC1 and the resistors R3 to R5. Here, a PNP-type bipolar transistor is used as the switching element Q1.

  The power source 10 is a DC power source for supplying a power source voltage Vin, and a circuit in which the positive line is connected to the emitter of the switching element Q1 and one terminal of the resistor R2, and the resistors R4 and R5 are connected in series. To the negative electrode side line. The base of the switching element Q1 is connected to the other terminal of the resistor R2, and is connected to the output of the IC1 through the resistor R1.

  The collector of the switching element Q1 is connected to one terminal of the choke coil L1, and is connected to the negative electrode side line of the power source 10 via the flywheel diode D1. A line connecting the switching element Q1 and the choke coil L1 is connected to a line connecting the resistor R4 and the resistor R5 via the resistor R3. A line connecting the resistors R4 and R5 is connected to the “−” side input of the IC1.

  The other terminal of the choke coil L1 is connected to one electrode terminal of the LED 100, and is connected to the negative electrode side line of the power source 10 through the smoothing capacitor C1. The other electrode terminal of the LED 100 is connected to the negative electrode side line of the power source 10 through the resistor R6. A line connecting the LED 100 and the resistor R6 is connected to the “+” side input of the IC1.

  FIG. 2 shows an output waveform of each part of the LED lighting device shown in FIG. FIG. 2A shows the waveform of the power supply voltage Vi supplied from the power supply 10. FIG. 2B shows the waveform of the voltage V1 generated at the connection point of the flywheel diode D1 on the line connecting the switching element Q1 and the choke coil L1. FIG. 2C shows the waveform of the current ILED and the waveform of the voltage V2 generated at the contact point with the capacitor C1 on the line connecting the choke coil L1 and the LED 100, respectively. FIG. 2D shows waveforms of the voltage V3 (voltage supplied to the “+” side input of IC1) and the comparison voltage V4 (voltage supplied to the “−” side input of IC1) generated in the resistor 6. Indicates. FIG. 2E shows the waveform of the output voltage V5 of IC1.

  Hereinafter, with reference to FIG. 1 and FIG. 2, operation | movement of the LED lighting device of this embodiment is demonstrated concretely.

When the switching element Q1 is turned on, the current I _LED flowing through the _LED 100 gradually increases due to the action of the inductance of the choke coil L1 and the capacitance of the smoothing capacitor C1. The current I _LED is converted to a voltage V3 (= I _LED × R6) by the current detection resistor R6 and supplied to the “+” side input of the IC1.

  The comparison voltage V4 generated in the circuit composed of the resistors R3 to R5 is supplied to the “−” side input of the IC1. At this time, since the switching element Q1 is in the ON state, the voltage V1 substantially equal to the power supply voltage Vin is supplied to one terminal of the resistor R3. For this reason, the comparison voltage V4 synthesized by the resistors R3, R4, and R5 has a maximum voltage value V4max. When the voltage value V3 becomes larger than the maximum voltage value V4max, the output voltage V5 of the IC1 is inverted, and as a result, the switching element Q1 changes from the ON state to the OFF state.

When the switching element Q1 is turned off, the voltage V1 drops to almost 0V due to the action of the choke coil L1 and the flywheel diode D1. In addition, the current I _LED gradually decreases as the current flowing through the choke coil L1 decreases and due to the action of the inductance of the choke coil L1 and the capacitance of the smoothing capacitor C1. As the current I _LED decreases, the voltage value V3 also decreases. At this time, as described above, since the voltage value V1 is substantially 0 V, the voltage value V4 synthesized by the resistors R3, R4, and R5 is the minimum voltage value V4min. When the voltage value V3 becomes smaller than the minimum voltage value V4min, the output voltage V5 of the IC1 is inverted, and as a result, the switching element Q1 changes from the OFF state to the ON state.

By repeating the above operation, self-excited oscillation occurs, and the voltage value V3 rises and falls between the maximum voltage value V4max and the minimum voltage value V4min. This is because the current I _LED has a maximum current value given by V4max / R6 (the value of the maximum voltage value V4max divided by the resistance value of R6) and V4min / R6 (the minimum voltage value V4min is the resistance value of R6). This means that the current value is repeatedly raised and lowered between the minimum current values given by In this case, the average current of the current I _LED is given by (V4max + V4min) / (2 × R6), and is kept at a substantially constant value.

  According to the LED lighting device of the present embodiment described above, the circuit that limits the LED current is based on the ON / OFF of the switching element and the filter action by the choke coil and the capacitor, and therefore a portion that actively generates power loss. There is no effect and the loss is reduced.

  Further, since the self-excited oscillation action is used for ON / OFF control of the switching element, a circuit such as a triangular wave oscillation circuit, an error amplifier, and a PWM voltage comparator for switching control is unnecessary. Therefore, the circuit is simplified and the number of parts is reduced.

  Further, the IC 1 can be configured with an inexpensive general-purpose voltage comparator (comparator), and a current limiting circuit for self-oscillation operation is formed instead of a constant current circuit, so that the number of parts is reduced, and the cost is low. Can be realized with loss.

  Further, in the conventional LED power supply apparatus shown in FIG. 7, a reference voltage source that is a constant voltage circuit is configured by the transistor Tr3, the resistor R3, and the Zener diode ZD1, whereas in the present embodiment, a comparison is made. A circuit for obtaining a voltage (comparison voltage generation circuit) is configured by a simple circuit including three resistors R3 to R5. As described above, in this embodiment, a reference voltage source (constant voltage circuit) using not only a band gap reference element but also a transistor or a constant voltage diode is not necessary, so that the circuit can be made simpler and smaller. Can do.

(Second Embodiment)
FIG. 3 is a circuit diagram showing a main part of the LED lighting device according to the second embodiment of the present invention. The LED lighting device of this embodiment is obtained by adding a function of changing the light emission intensity of the LED to the LED lighting device of the first embodiment described above.

  In the LED lighting device of this embodiment, as shown in FIG. 3, the PWM modulation circuit 11 is inserted in the positive line of the power supply 10. The other configuration is the same as the circuit configuration shown in FIG. The PWM modulation circuit 11 is an existing circuit, and PWM modulates the output of the power supply 10 based on a dimming signal supplied from an external device. By this PWM modulation, the current of the LED 100 limited to a constant current value is intermittent, and the light emission intensity of the LED 100 can be changed according to the ratio of the lighting time and the light-off time.

  Since the configuration and operation other than the PWM modulation circuit 11 are the same as those of the first embodiment, description thereof is omitted.

(Third embodiment)
FIG. 4 is a circuit diagram showing the main part of the LED lighting device according to the third embodiment of the present invention. The LED lighting device according to the present embodiment is obtained by adding an LED color changing function to the LED lighting device according to the first embodiment described above.

  In the LED lighting device of the present embodiment, as shown in FIG. 4, three primary color LEDs formed by connecting LED-R, LED-G, and LED-R in series are used as the LED 100, and the emission intensity is variable for each LED. A circuit is provided. The other configuration is the same as the circuit configuration shown in FIG.

  A light emission intensity variable circuit comprising a transistor QR is connected in parallel to the LED-R, a light emission intensity variable circuit comprising a transistor QG is connected in parallel to the LED-R, and a light emission intensity variable circuit comprising a transistor QB is parallel to the LED-R. It is connected to the. A red PWM signal, a green PWM signal, and a blue PWM signal are respectively supplied from the external device to the bases of the transistors QR, QG, and QB.

  In each LED, when a switching element connected in parallel is in an OFF state, a current flows through the LED and lights up. On the other hand, when the switching element is in the ON state, the voltage applied between the terminals of the LED is set so as to be smaller than the forward voltage drop VF of the LED. Will flow to the switching element. For this reason, the LED is turned off. The ratio of ON and OFF of the switching element is changed for each R, G, B LED by an external PWM signal, thereby changing the brightness and hue.

  As described above, according to the present embodiment, the current value flowing through each LED is controlled to be constant, and the ON / OFF of the switching element arranged in parallel to each LED is controlled by the PWM signal given from the outside. Change the color of the LED.

  According to the present embodiment, for example, a lighting device capable of dimming and toning control in which two three primary color LEDs are mounted on a small substrate of 15 mm × 30 mm can be realized at low cost.

  The LED lighting devices of the first to third embodiments described above are examples of the present invention, and the configuration thereof can be changed as appropriate. For example, in the circuit configuration shown in FIG. 1, the capacitor C1 is arranged so as to slow the temporal change of the current flowing through the LED and not to raise the self-excited oscillation frequency more than necessary, but for the circuit operation itself. This capacitor C1 may be omitted if it is only a secondary effect and it is allowed to increase the self-excited oscillation frequency.

  The switching element (transistor) may be any element that can achieve the purpose of turning on / off the current. As the switching element, a bipolar transistor or a switching element such as a MOS FET can be used.

  Further, the circuit composed of the resistors R3, R4, and R5 is configured to generate the comparison voltage of the IC1 from the power supply voltage. However, since a substantially constant comparison voltage can be obtained and the IC1 can have hysteresis characteristics. If so, another circuit such as a circuit using a Zener diode or a voltage standard element may be used.

  The current limiting circuit in the LED lighting device of the present invention described above can be applied as a current limiting circuit in a circuit that uses a load other than the LED, for example, a circuit that drives a heater, an incandescent bulb, an organic EL, or the like.

It is a circuit diagram which shows the principal part of the LED lighting device which is the 1st Embodiment of this invention. It is an output waveform figure of each part of the LED lighting device shown in FIG. It is a circuit diagram which shows the principal part of the LED lighting device which is the 2nd Embodiment of this invention. It is a circuit diagram which shows the principal part of the LED lighting device which is the 3rd Embodiment of this invention. It is a circuit diagram which shows a typical current limiting circuit. It is a circuit diagram which shows another typical current limiting circuit. It is a circuit diagram which shows another typical current limiting circuit. It is an output waveform diagram of each part of the current limiting circuit shown in FIG. 5C. It is a circuit diagram which shows the structure of the main circuit part of the conventional LED power supply device.

Explanation of symbols

1 IC
10 Power supply Q1 Switching element D1 Flywheel diode 100 LED
L1 Choke coil C1 Smoothing capacitor R1-R6 Resistance

Claims (3)

A switching element in which one electrode is connected to the positive electrode of the power supply, the other electrode is connected to the negative electrode of the power supply via a flywheel diode and connected to the positive electrode side line of the LED via a choke coil;
A current detection resistor connected in series to the negative electrode side line of the LED;
The first and second resistors are connected in series, one end of the series circuit is connected to the positive electrode of the power source, and the other end is connected to the negative electrode of the power source. A comparison voltage generating circuit in which a connection point of the first and second resistors is connected to the other electrode of the switching element via the third resistor;
One input is connected to the line connecting the LED and the current detection resistor, and the other input is connected to the connection point of the first and second resistors, for comparison of the voltage supplied to these inputs. And a comparison circuit that controls on / off switching of the switching element.   The LED lighting device according to claim 1, further comprising a modulation circuit that performs pulse width modulation on an output of the power source. The LED has a configuration in which three LEDs, a red LED that outputs red light, a green LED that outputs green light, and a blue LED that outputs blue light, are connected in series.
The LED lighting device according to claim 1, further comprising a second switching element provided in each of the three LEDs for adjusting a current flowing period in the LED.

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