JP5803004B2 - LED lighting device - Google Patents

Description

  The present invention relates to an LED lighting device for lighting an LED which is a light emitting diode.

  2. Description of the Related Art Conventionally, an LED lighting device is known in which an AC voltage from a commercial AC power supply is rectified to a DC voltage, and the DC voltage is DC-DC converted and then applied to an LED (see, for example, Patent Document 1). ).

  Further, in the LED lighting device, a constant voltage circuit that holds a DC voltage after DC-DC conversion at a constant voltage, and a DC voltage from the constant voltage circuit is applied to the LED, and a DC current flowing through the LED is set to a constant current. A device having a constant current circuit for holding has been proposed. For example, as shown in FIG. 4, an input filter circuit 2 that removes noise from an AC voltage applied to the input terminal unit 1 or prevents noise from entering the AC voltage, and an AC output from the input filter circuit 2. An input rectifying / smoothing circuit 3 that rectifies and smoothes the voltage into a DC voltage, a DC-DC converting circuit 4 that DC-DC converts the DC voltage output from the input rectifying / smoothing circuit 3, and a DC after DC-DC conversion An LED comprising a constant voltage circuit 5 that holds a voltage at a constant voltage, and a constant current circuit 6 that applies a DC voltage output from the constant voltage circuit 5 to the LED and holds a DC current flowing through the LED at a constant current. A lighting device has been proposed.

  The input filter circuit 2 includes a capacitor C1 and a line filter L1.

  The input rectifying / smoothing circuit 3 includes a rectifying circuit 7 for full-wave rectifying the pulsating voltage and a capacitor C2 for smoothing the full-wave rectified pulsating voltage.

  The DC-DC conversion circuit 4 includes a transformer T, a transistor Q1 connected in series to the primary winding T1 of the transformer T, and a drive circuit 8 that turns on and off the transistor Q1 at a predetermined period. The phototransistor 9a of the photocoupler 9 is connected to the input terminal 8a of the drive circuit 8, and the drive circuit 8 controls the on-time of the transistor Q1 according to the voltage of the input terminal 8a.

  The DC-DC conversion circuit 4 includes a diode D1 that half-wave rectifies the AC voltage output from the secondary winding T2 of the transformer T, and a capacitor C3 that smoothes the voltage half-wave rectified by the diode D1. Have.

  The constant voltage circuit 5 includes a light emitting diode 9b of the photocoupler 9 and a constant voltage IC 10 provided in series with the light emitting diode 9b.

  The constant current circuit 6 includes a comparator 11 and a transistor Q2 that is driven by an output signal of the comparator 11 and controls a direct current flowing through the LED. A reference voltage Ref that determines the direct current value flowing through the LED is input to the non-inverting input terminal of the comparator 11 via the resistor R7, and the voltage on the source side of the transistor Q2 is input to the inverting input terminal of the comparator 11. It has come to be.

  Since the LED has a large variation in the forward drop voltage (VF), the constant voltage circuit 5 must be set so that the voltage applied to the LED is equal to or greater than the maximum forward drop voltage (VF). . The constant current circuit 6 controls the transistor Q2 on and off with the comparator 11 so that the current value (= LED current value) flowing through the resistor R9 is equal to the reference voltage Ref.

JP 2011-3326 A

  However, in the above conventional technique, when the forward voltage drop (VF) of the LED greatly varies, a loss of several W to several tens W is generated in the constant current circuit. That is, in the constant current circuit, ((voltage value of the constant voltage circuit 5−forward voltage drop (VF)) × constant current value) is a loss in the transistor Q2, and this loss is several W to several tens W. .

  When such a loss occurs, the superiority of the LED, which should originally be highly efficient, is lost.

  The subject of this invention is providing the LED lighting device which can reduce the loss in a constant current circuit.

In order to solve the above-mentioned problem, the invention according to claim 1 is an input rectifying / smoothing circuit that rectifies and smoothes an AC voltage and outputs a DC voltage;
The DC voltage output from the input rectifying / smoothing circuit is turned on / off to be converted into an AC voltage, and the AC voltage is transformed into a predetermined AC voltage. A DC-DC conversion circuit that outputs
A constant voltage circuit that holds and outputs a DC voltage output from the DC-DC conversion circuit at a predetermined voltage value;
A constant current circuit having a switching element that applies a direct current voltage output from the constant voltage circuit to the LED and controls the direct current flowing through the LED to be a constant value ;
The constant current circuit compares the source-side voltage of the switching element with a reference voltage, and outputs a gate signal to the gate of the switching element so that the source-side voltage and the reference voltage are equal. An LED lighting device having a first comparator for making a current flowing in a switching element constant ,
A loss reduction circuit for detecting a loss in the switching element during lighting of the LED and reducing the magnitude of the predetermined voltage value in the constant voltage circuit when the loss exceeds a predetermined value is provided,
The loss reduction circuit includes a second comparator in which a drain voltage of the switching element is input to the non-inverting terminal only when the switching element is turned on, and a preset target voltage is input to the inverting terminal;
The second comparator compares the drain voltage input to the non-inverting terminal with the target voltage input to the inverting terminal, and when the drain voltage becomes equal to or higher than the target voltage, the second comparator The constant voltage circuit is controlled so as to reduce the magnitude of the voltage value .

  According to the above configuration, when the loss in the switching element becomes large, the magnitude of the predetermined voltage value in the constant voltage circuit is changed, whereby the voltage generated in the switch element can be lowered. As a result, loss in the constant current circuit can be reduced.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to reduce the loss in a constant current circuit, and can implement | achieve a highly efficient LED lighting device.

It is a circuit diagram of the LED lighting device which concerns on this invention. It is a circuit diagram for demonstrating the effect | action of this invention. It is a timing chart for demonstrating the effect | action of this invention. It is a circuit diagram of the LED lighting device by a prior art.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol shall be described about the same location as a prior art.

  FIG. 1 shows an LED lighting device according to the present invention. The LED lighting device 20 includes an input filter circuit 2 that removes noise from an AC voltage applied to the input terminal unit 1 or prevents noise from entering the AC voltage, and an AC output from the input filter circuit 2. An input rectifying / smoothing circuit 3 that rectifies and smoothes the voltage into a DC voltage, a DC-DC converting circuit 4 that DC-DC converts the DC voltage output from the input rectifying / smoothing circuit 3, and a DC after DC-DC conversion A constant voltage circuit 5 that holds the voltage at a constant voltage; and a constant current circuit 6 that applies a DC voltage output from the constant voltage circuit 5 to the LED and holds a DC current flowing through the LED at a constant current. Yes. Here, three LEDs are provided, and these LEDs are connected in series.

  In the LED lighting device 20 of the present embodiment, a loss reduction circuit 21 is connected to the constant voltage circuit 5 and the constant current circuit 6.

  An input terminal unit 1 is connected to the input filter circuit 2, and a fuse F <b> 1 is provided between the input terminal unit 1 and the input filter circuit 2. The input filter circuit 2 includes a capacitor C1 and a line filter L1. Z1 is a varistor.

  The input rectifying / smoothing circuit 3 includes a rectifying circuit 7 for full-wave rectifying the pulsating voltage and a capacitor C2 for smoothing the full-wave rectified pulsating voltage.

  The DC-DC conversion circuit 4 includes a transformer T, a transistor Q1 connected in series to the primary winding T1 of the transformer T, and a drive circuit 8 that turns on and off the transistor Q1 at a predetermined period. The phototransistor 9a of the photocoupler 9 is connected to the input terminal 8a of the drive circuit 8, and the drive circuit 8 controls the on-time of the transistor Q1 according to the voltage of the input terminal 8a. A resistor R1 is connected in series to the primary winding T1 of the transformer T.

  The DC-DC conversion circuit 4 includes a diode D1 that half-wave rectifies the AC voltage output from the secondary winding T2 of the transformer T, and a capacitor C3 that smoothes the voltage half-wave rectified by the diode D1. Have.

  The constant voltage circuit 5 is provided with a resistor R2, a light emitting diode 9b of the photocoupler 9, and a constant voltage IC10 connected in series between the positive and negative electrodes. A resistor R3 is connected in parallel to the light emitting diode 9b.

  The constant voltage circuit 5 is provided with a resistor R4 and a resistor R5 connected in series between the plus and minus poles. An intermediate point between the light emitting diode 9b and the constant voltage IC10 and an intermediate point between the resistors R4 and R5 are connected to each other via a capacitor C4 and a resistor R6.

  The constant current circuit 6 includes a comparator 11 and a transistor Q2 (switching element) that is driven by an output signal of the comparator 11 and controls a direct current flowing through the LED. A reference voltage Ref for determining the direct current value flowing through the LED is input to the non-inverting input terminal of the comparator 11 via the resistor R7, and a voltage on the source side of the transistor Q2 is input to the inverting input terminal of the comparator 11. The The output terminal of the comparator 11 is connected to the gate of the transistor Q2 via the resistor R8, and a resistor R9 is provided on the source side of the transistor Q2.

  The constant current circuit 6 controls the transistor Q2 on and off with the comparator 11 so that the current value (= LED current value) flowing through the resistor R9 is equal to the reference voltage Ref.

  The loss reduction circuit 21 is provided with a resistor R10 and a resistor R11 connected in series between both positive and negative electrodes, and a resistor R12 and a capacitor C5 connected in series. The loss reduction circuit 21 is provided with a comparator 22. The non-inverting input terminal of the comparator 22 is connected to the intermediate point between the resistor R12 and the capacitor C5 via the resistor R13, and the inverting input terminal of the comparator 22 is connected to the negative line via the resistor R14. Yes.

  The output terminal of the comparator 22 is connected to the constant voltage IC10 via a resistor R15 and a resistor R16, and an intermediate point between the resistors R4 and R5. The intermediate point between the resistors R15 and R16 is connected to the negative line via the capacitor C6.

  The inverting input terminal and the output terminal of the comparator 22 are connected to each other via a resistor R17 and a capacitor C7, and the both terminals are connected to each other by a capacitor C8 arranged in parallel with the resistor R17 and the capacitor C7. .

  In the loss reduction circuit 21, the intermediate point between the resistor R12 and the capacitor C5 and the drain side of the transistor Q2 in the constant current circuit 6 are connected to each other via the diode D2 and the resistor R18.

  Next, the operation of the LED lighting device having the above configuration will be described.

  The AC voltage applied to the input terminal unit 1 is input to the input rectifying / smoothing circuit 3 after noise removal (or prevention of noise from entering the AC voltage) in the input filter circuit 2.

  In the input rectifying / smoothing circuit 3, the AC voltage input from the input filter circuit 2 is rectified into a DC voltage by the rectifying circuit 7, and the DC voltage is smoothed by the capacitor C 2 and then input to the DC-DC conversion circuit 4. The

  The DC voltage input to the DC-DC conversion circuit 4 is applied to the primary winding T1 of the transformer T. Then, the drive circuit 8 turns on / off the transistor Q1 at a predetermined cycle. By this on / off operation, the DC voltage applied to the primary winding T1 of the transformer T is intermittent, and an AC voltage is induced in the secondary winding T2 of the transformer T by this interruption. The AC voltage of the secondary winding T2 is proportional to the voltage applied to the primary winding T1 of the transformer T.

  The AC voltage is half-wave rectified by the diode D1 and further smoothed by the capacitor C3 to become a DC voltage. This DC voltage is applied to the three LEDs via the loss reduction circuit 21, and a current flows through each LED to cause each LED to emit light.

  In the constant current circuit 6, the comparator 11 controls the transistor Q2 on / off so that the voltage on the source side of the transistor Q2 is equal to the reference voltage Ref. Thereby, the current flowing through the resistor R9 (that is, the current flowing through the LED) becomes a constant current.

  In the loss reduction circuit 21, the loss in the transistor Q2 is always detected while the LED is lit, and when the loss exceeds a predetermined value, the voltage value of the DC voltage output from the constant voltage circuit 5 is determined. The constant voltage circuit 5 is controlled to decrease.

  Here, when attention is paid only to the resistor R12, the capacitor C5, the diode D2, the resistor R18, the drain side voltage (drain voltage) of the transistor Q2, and the negative side line, a circuit as shown in FIG. 2 is obtained.

  The resistor R18 is for limiting the discharge current of the capacitor C5 when it flows to the drain side of the transistor Q2 when the transistor Q2 is turned on (this is a detection error, so the value of the resistor R18 should be small). . The diode D2 is used for protecting the loss reduction circuit 21 when the value of the constant voltage from the constant voltage circuit 5 (this is referred to as the constant voltage 4) is high and the transistor Q2 is off (because a detection error occurs). The forward drop voltage VF ′ of the diode D2 is preferably small.)

Since drain voltage (constant voltage value−VF value) × drain current (LED current value) = loss, we want to detect the drain voltage value of the transistor Q2. When the transistor Q2 is turned on, the voltage V _{C5 of the} capacitor C5 changes from the value of the constant voltage 4 as follows (see also FIG. 3).

Here, assuming that the resistance R18≈0Ω and VF′≈0V of the diode D2, “the voltage V _{C5 of the} capacitor C5≈the drain voltage” is obtained. Now that the drain voltage has been detected, the target loss value is determined by the resistors R10 and R11, and the two values are compared by the comparator 22 to determine the amount of loss. This determination is fed back to the constant voltage IC 10 that determines the value of the constant voltage circuit 5. If the loss is large, the value of the constant voltage circuit 5 is lowered. When the value of the constant voltage circuit 5 decreases, the drain voltage also decreases, and loss reduction can be realized.

  A target voltage signal that determines the loss is input to the inverting input terminal of the comparator 22. This target voltage is preset by a resistor R17, a capacitor C7, and a capacitor C8.

  The comparator 22 compares the voltage input to the non-inverting input terminal (this voltage is approximately equal to the voltage generated in the transistor Q2) with the target voltage input to the inverting input terminal, and compares the voltage to the non-inverting input. When the voltage input to the terminal (that is, the voltage generated in the transistor Q2) becomes equal to or higher than the target voltage, a control signal is output to the constant voltage IC 10 so that the voltage value of the constant voltage circuit 5 decreases. The circuit 5 is controlled.

  According to the present embodiment, when the voltage generated in the transistor Q2 becomes equal to or higher than the target voltage, the magnitude of the DC voltage of the constant voltage circuit 5 is reduced, thereby reducing the voltage generated in the transistor Q2. . As a result, loss in the constant current circuit 6 can be reduced.

  As mentioned above, although the Example of this invention has been explained in full detail with drawing, the said Example is only the illustration of this invention, and this invention is not limited only to the structure of the said Example. Needless to say, changes in design and the like within the scope of the present invention are included in the present invention.

2 Input Filter Circuit 3 Input Rectification Smoothing Circuit 4 DC-DC Conversion Circuit 5 Constant Voltage Circuit 6 Constant Current Circuit 11 Comparator 20 LED Lighting Circuit 21 Loss Reduction Circuit 22 Comparator Q2 Transistor (Switching Element)
LED light emitting diode

Claims (3)

An input rectifying / smoothing circuit for rectifying and smoothing an alternating voltage and outputting a direct current voltage;
The DC voltage output from the input rectifying / smoothing circuit is turned on / off to be converted into an AC voltage, and the AC voltage is transformed into a predetermined AC voltage. A DC-DC conversion circuit that outputs
A constant voltage circuit that holds and outputs a DC voltage output from the DC-DC conversion circuit at a predetermined voltage value;
A constant current circuit having a switching element that applies a direct current voltage output from the constant voltage circuit to the LED and controls the direct current flowing through the LED to be a constant value ;
The constant current circuit compares the source-side voltage of the switching element with a reference voltage, and outputs a gate signal to the gate of the switching element so that the source-side voltage and the reference voltage are equal. An LED lighting device having a first comparator for making a current flowing in a switching element constant ,
A loss reduction circuit for detecting a loss in the switching element during lighting of the LED and reducing the magnitude of the predetermined voltage value in the constant voltage circuit when the loss exceeds a predetermined value is provided,
The loss reduction circuit includes a second comparator in which a drain voltage of the switching element is input to the non-inverting terminal only when the switching element is turned on, and a preset target voltage is input to the inverting terminal;
The second comparator compares the drain voltage input to the non-inverting terminal with the target voltage input to the inverting terminal, and when the drain voltage becomes equal to or higher than the target voltage, the second comparator An LED lighting device characterized by controlling the constant voltage circuit so as to reduce the magnitude of a voltage value . The LED lighting device according to claim 1, wherein the loss reduction circuit is provided between the constant voltage circuit and a constant current circuit . 3. The LED lighting according to claim 1, wherein the drain voltage of the switching element is input to an inverting terminal of the second comparator via a resistor and a diode for protection of the loss reduction circuit. apparatus.