JP2011211132A - Led driving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED driving circuit with a simple circuit structure, capable of maintaining a suitable minimum holding current of a light control circuit, according to an ON phase angle of AC voltage phase-controlled by the light control circuit.SOLUTION: A holding current control circuit 7 is connected between a waveform shaping circuit 4 and a constant current control circuit 6. The holding current control circuit 7 generates a control signal E for controlling a holding current of the light control circuit 2 according to the ON phase angle controlled by the light control circuit 2 when a pulse signal D formed in the waveform shaping circuit 4 is inputted. The holding current of the light control circuit 2 is controlled by allowing a pulse current superimposed on a light control current outputted from the light control circuit 2 to flow according to the control signal E.

Description

The present invention relates to a light emitting diode (LED: Light-Emitting).
Diode; hereinafter abbreviated as LED. Specifically, the present invention relates to an LED drive circuit that drives a LED at a constant current using a phase control type dimming circuit.

  2. Description of the Related Art Conventionally, in a lighting device using an incandescent lamp as a light source for illumination, a phase control type dimming circuit that performs dimming using a triac (bidirectional thyristor) has been widely used. The dimming circuit typically has a power supplied to the light source by changing the duty ratio of the commercial AC power supply voltage supplied to the dimming circuit by controlling the conduction angle of the triac by the control unit. Dimming is performed by changing the amount.

  2. Description of the Related Art In recent years, a dimming device that enables dimming with such a phase control type dimming circuit has also been proposed in an illuminating device that uses an LED as a light source for illumination (see, for example, Patent Document 1).

Such a phase control type dimming circuit is conventionally widely used as a dimming circuit for an incandescent lamp. However, when applied to an illumination light source having a small load current such as an LED, the following is used. It is known that problems will occur. That is, the thyristor needs to have a current greater than a predetermined minimum holding current flowing between the main terminals in order to maintain the ON state after the trigger is input and the ON state. Therefore, when this dimming circuit is applied to an illumination device having a small load current such as an LED, it is difficult to stably maintain the thyristor on-state due to the load current of the light source, and the dimming circuit malfunctions. Occurs, causing problems such as flickering of lighting. In particular, when external noise or noise due to interference between dimming circuits is applied to the dimming circuit, a negative current due to the noise is superimposed on the dimming current of the dimming circuit, so that the holding current is particularly small. In such a case, the dimming current may be reduced, and malfunctions such as malfunction of the dimming circuit and lighting extinction may occur.

  In order to cope with such a problem, conventionally, a lighting device has been proposed in which the minimum holding current of a thyristor is maintained using a constant current circuit (see, for example, Patent Document 2).

  In Patent Document 2, the on phase angle is controlled by a phase control dimming circuit that controls the on phase angle by turning on and off the AC power supply voltage using a switching element that is turned off when the flowing current falls below a predetermined holding current. First and second power receiving terminals for receiving the adjusted AC power supply voltage, a capacitor connected between the first and second power receiving terminals, and a constant current circuit for supplying a preset constant current in parallel with the capacitor A power control unit that outputs power according to the duty ratio at the voltage across the capacitor, and first and second output terminals for supplying the power output from the power control unit to an externally connected light emitting unit An illumination power supply circuit comprising: is disclosed.

JP 2004-327152 A JP 2007-227155 A

However, in the configuration using the constant current circuit as described in Patent Document 2, even when the minimum holding current of the thyristor is maintained by the load current, the current always flows through the constant current circuit. There are problems such as increased power consumption or increased heat generation of components.

  The present invention has been made in view of the above problems, and has an appropriate minimum holding current of the dimming circuit according to the on-phase angle of the AC voltage phase-controlled by the dimming circuit, while having a simple circuit configuration. An object of the present invention is to provide an LED drive circuit capable of maintaining the above.

  In order to achieve the above object, an LED drive circuit according to a first aspect of the present invention controls the phase of a current supplied to a light emitting diode (LED) by controlling a conduction angle of an AC voltage supplied from a commercial AC power supply. An optical circuit, a bridge circuit that rectifies the AC voltage output from the dimming circuit, a waveform shaping circuit that shapes a waveform of the AC voltage output from the bridge circuit to generate a pulse signal, and the LED flows In an LED drive circuit comprising a constant current control circuit for controlling the current to be kept constant, a holding current control circuit is connected between the waveform shaping circuit and the constant current control circuit, and the holding current control circuit is A control signal for controlling a holding current of the dimming circuit according to an ON phase angle controlled by the dimming circuit by inputting the pulse signal generated by the waveform shaping circuit Produced, and controlling the holding current by passing a pulse current to be superimposed on the dimming current outputted from the light control circuit in response to the control signal.

  According to a second aspect of the present invention, in the LED drive circuit according to the first aspect, the holding current control circuit receives the pulse signal and performs the holding according to an on phase angle controlled by the dimming circuit. A holding current control signal generation circuit that generates a control signal that enables adjustment of a current flow time, and a first switching element that performs an on / off operation by inputting the control signal.

  According to a third aspect of the present invention, in the LED drive circuit according to the first or second aspect, the holding current control circuit has a voltage of 0 V when the AC voltage supplied from the commercial AC power source shifts from a positive voltage to a negative voltage. When the phase angle is 0 °, the holding is performed when the ON phase angle controlled by the dimming circuit is in the range of −90 ° to 0 ° and 90 ° to 180 ° with reference to the phase angle. Control is performed so as to arbitrarily set the time during which the current flows.

  According to a fourth aspect of the present invention, in the LED drive circuit according to the third aspect, the holding current control circuit has an arbitrary phase angle ˜0 ° delayed from the on phase angle in the negative region of the on phase angle. And the holding current is controlled to flow during a period between an arbitrary phase angle and a range of 180 ° that is delayed from the ON phase angle in the positive region of the ON phase angle.

  According to a fifth aspect of the present invention, in the LED drive circuit according to the third aspect, the holding current control circuit has a range of an on phase angle to 0 ° in the negative region of the on phase angle and the on phase angle. The holding current is controlled to flow during a period in the range of the ON phase angle to 180 ° in the positive region.

  According to a sixth aspect of the present invention, in the LED drive circuit according to any one of the second to fifth aspects, the control signal output from the holding current control signal generation circuit to the first switching element is a pulse signal. It is characterized by being.

According to a seventh aspect of the present invention, in the LED drive circuit according to any one of the second to fifth aspects, the control signal output from the holding current control signal generation circuit to the first switching element is a DC signal. It is characterized by being.

  According to an eighth aspect of the present invention, in the LED drive circuit according to the seventh aspect, the holding current control signal generation circuit is a second switching element that inverts the signal level of the pulse signal input from the waveform shaping circuit. And an integration circuit for converting to a DC signal corresponding to the pulse width of the inverted pulse signal, and adjusting the magnitude of the DC signal output from the integration circuit to turn on the first switching element. And a control phase angle adjustment circuit for adjusting a range of the phase angle for controlling the holding current.

  According to the present invention configured as described above, an appropriate minimum holding current of the dimming circuit is maintained according to the on-phase angle of the AC voltage phase-controlled by the dimming circuit, while having a simple circuit configuration. It is possible to provide an LED drive circuit that can do this.

It is a circuit diagram which shows the structure of the LED drive circuit which concerns on 1st Embodiment of this invention. FIG. 2 is a signal waveform diagram showing an example of the operation of the holding current control circuit in the LED drive circuit shown in FIG. 1. FIG. 6 is a signal waveform diagram showing another example of the operation of the holding current control circuit in the LED drive circuit shown in FIG. 1. It is a circuit diagram which shows the structure of the LED drive circuit which concerns on 2nd Embodiment of this invention. FIG. 5 is a signal waveform diagram showing an example of the operation of the holding current control circuit in the LED drive circuit shown in FIG. 4. FIG. 5 is a diagram showing a relationship between a pulse width of a pulse signal generated by a waveform shaping circuit in the LED drive circuit shown in FIG. 4 and a DC signal generated by a holding current control circuit.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
(First embodiment)
FIG. 1 is a circuit diagram showing a configuration of an LED drive circuit according to the first embodiment of the present invention.

  As shown in FIG. 1, the LED drive circuit 1 includes a dimming circuit 2 that controls the phase of the current supplied to the LED module 5 by controlling the AC conduction angle supplied from the commercial AC power supply Vac. The light source for illumination includes a bridge circuit 3 that rectifies an AC voltage output from the optical circuit 2 and a waveform shaping circuit 4 that shapes a waveform of the AC voltage output from the bridge circuit 3 to generate a pulse signal. The LED module 5 is driven and illuminated. In addition, the LED drive circuit 1 includes a constant current control circuit 6 that controls the current flowing through the LED module 5 to flow constantly. In the present embodiment, the LED module 5 is formed by connecting a plurality of individual LED elements in series. However, the configuration of the LED module 5 in the LED drive circuit 1 according to the present invention is limited to this mode. It is not intended to include any illumination light source comprised of one or more LED elements. The output capacitor C1 connected in parallel to the LED module 5 is for reducing current ripple.

  Here, the dimming circuit 2 includes a triac Q0, and typically supplies a trigger to the triac Q0 at a predetermined conduction angle of the commercial AC power supply Vac to turn on the triac Q0. A control unit (not shown) and a variable resistor for changing the degree of dimming of the LED module 5 by setting the predetermined conduction angle in various ways are included.

The bridge circuit 3 is a full bridge circuit configured as a known diode bridge including four diodes D1 to D4.

The waveform shaping circuit 4 is a MOSFET (Metal-Oxide-Semiconductor).
A switching element Q2 including a field effect transistor, a Zener diode D6, and resistance elements R2 and R3 are provided. One end of the resistance element R2 is connected to the gate terminal of the switching element Q2 together with the cathode terminal of the Zener diode D6, and the other end of the resistance element R2 is connected to the drain terminal of the switching element Q2. The resistor element R3 has one end connected to the source terminal of the switching element Q2 and the other end connected to the anode terminal of the Zener diode D6.

  Between the LED module 5 and the ground (GND), an inductor L1, a switching element Q1 composed of a MOSFET, and a current detection resistor R1 are connected in series. When the switching element Q1 is on, the pulse current shaped by the waveform shaping circuit 4 passes through the LED module 5, the inductor L1, the switching element Q1, and flows to GND via the current detection resistor R1. The current flowing through the LED module 5 is detected by the current detection resistor R1, converted into a voltage signal, and fed back to the constant current control circuit 6. The constant current control circuit 6 outputs an off operation signal to the base terminal of the switching element Q1 when the value of the fed back voltage signal exceeds a predetermined reference voltage. While the switching element Q1 is off, the current charged in the inductor L1 flows to the LED module 5 via the diode D5 connected in parallel to the series circuit of the LED module 5 and the inductor L1. Thereafter, the constant current control circuit 6 fixes the OFF time of the switching element Q1, and therefore outputs an ON operation signal to the base terminal of the switching element Q1 after a predetermined OFF time has elapsed. By repeating the above operation, the constant current control circuit 6 controls the LED module 5 so that a constant current flows.

The LED drive circuit 1 according to this embodiment includes a holding current control circuit 7 connected between the waveform shaping circuit 4 and the constant current control circuit 6.

The holding current control circuit 7 receives the pulse signal generated by the waveform shaping circuit 4 and generates a control signal that can set an arbitrary holding current according to the ON phase angle controlled by the dimming circuit 2. A current control signal generation circuit 8 and a switching element (first switching element) Q3 made of a bipolar transistor are provided. The switching element Q3 has a base terminal connected to the output terminal of the holding current control signal generation circuit 8, a collector terminal connected to the output terminal of the waveform shaping circuit 4 via the resistance element R4, and an emitter terminal connected to GND. Has been. In the present invention, the on phase angle refers to a phase angle at which the triac Q0 of the dimming circuit 2 is turned on.

The operation of the holding current control circuit 7 will be specifically described with reference to FIGS. FIG. 2 is a signal waveform diagram showing an embodiment of the operation of the holding current control circuit 7 in the LED drive circuit 1, and FIG. 3 is a signal showing another embodiment of the operation of the holding current control circuit 7 in the LED drive circuit 1. It is a waveform diagram.

First, an example of the operation of the holding current control circuit 7 shown in FIG. 2 will be described.
As shown in FIG. 2, an AC voltage A having a sinusoidal voltage waveform is supplied from the commercial AC power supply Vac to the dimming circuit 2. The AC voltage A is converted into an AC voltage having a conduction angle set by the dimming circuit 2. In the present embodiment, when the phase angle that becomes 0 V when the AC voltage A shifts from the positive voltage to the negative voltage is set to 0 °, the AC voltage A is controlled by the dimming circuit 2 so that −45 ° to 0 ° and It is converted into a dimming signal (AC voltage) B having a conduction angle of 135 ° to 180 °. The dimming signal B input from the dimming circuit 2 to the bridge circuit 3 is rectified by the bridge circuit 3 and converted to a positive voltage only rectified signal (AC voltage) C having the same conduction angle as the dimming signal B. Is done. The rectified signal C is input from the bridge circuit 3 to the waveform shaping circuit 4, and is shaped by the waveform shaping circuit 4, and the phase angles are −45 ° to 0 ° and 135 ° to 180 ° according to the conduction angle. A pulse signal D having a high level is generated. That is, the pulse width of the pulse signal D is determined by the conduction angle of the AC voltage set by the dimming circuit 2.

The pulse signal D generated by the waveform shaping circuit 4 is input to the holding current control signal generation circuit 8 provided in the holding current control circuit 7. The holding current control signal generation circuit 8 generates and switches a pulse signal (control signal) E (E1 in FIG. 2) that becomes a high level during the ON period of the pulse signal D (t1 to t2 and t3 to t4 in FIG. 2). Output to the base terminal of the element Q3. The holding current control signal generation circuit 8 is not particularly limited in circuit configuration, but can be configured by, for example, a microcomputer.

When the control signal E1 from the holding current control signal generation circuit 8 is input to the base terminal, the switching element Q3 has a high level period of the control signal E1 (phase angles are −45 ° to 0 ° and 135 ° to 180 °). During a period of time), a pulse current of a predetermined magnitude flows from the switching element Q3 to the GND via the resistance element R4.

As a result, the pulse current is included in the dimming current output from the dimming circuit 2 in the period in which the phase angle through which the pulse current of a predetermined magnitude flows in the switching element Q3 is −45 ° to 0 ° and 135 ° to 180 °. Superimposed.

  In the LED drive circuit 1 according to the present embodiment, the dimming circuit 2 sets the on-phase angle of the AC voltage controlled by the dimming circuit 2 in the range of −90 ° to 0 ° and 90 ° to 180. In accordance with the conduction angle of the AC voltage to be applied, the holding current control signal generation circuit 8 has the on-phase angle in the negative region of the on-phase angle to the range of 0 ° and the on-phase angle in the positive region of the on-phase angle to 180. A control signal E that becomes a high level in the range of ° is generated, and the switching element Q3 is turned on during the high level period of the control signal E, and a pulse current is added to the dimming current output from the dimming circuit 2. It works to be superimposed.

If the holding current control circuit 7 is not provided in the LED drive circuit, when external noise or noise due to interference between the dimming circuits 2 is applied to the dimming circuit 2, a negative current due to the noise is generated. By being superimposed on the dimming current of the dimming circuit 2, it is output from the dimming circuit 2 in a period in which the dimming current flowing through the LED module 5 is small, particularly in a period from t1 to t2 and a period from t3 to t4. There is a possibility that a malfunction such as malfunction of the dimming circuit 2 or lighting extinction may occur due to a decrease in the dimming current.

On the other hand, in the LED drive circuit 1 according to the present embodiment, even if external noise or noise due to interference between the dimming circuits 2 is applied to the dimming circuit 2, the period from t1 to t2 and the period from t3 to t4. In FIG. 2, since a pulse current having a predetermined magnitude flowing in the holding current control circuit 7 is superimposed on the dimming current of the dimming circuit 2 in the plus direction, a decrease in the dimming current output from the dimming circuit 2 can be suppressed. Thus, it is possible to avoid problems such as malfunction of the dimming circuit 2 and lighting extinction.

As shown in FIG. 2, the control signal E generated by the holding current control signal generation circuit 8 is in the range of the ON phase angle to 0 ° in the negative region of the ON phase angle and the positive region of the ON phase angle. The on-phase angle is not limited to a control signal that is at a high level in the range from 180 ° to 180 °, and the on-phase angles controlled by the dimming circuit 2 are in the range of −90 ° to 0 ° and 90 ° to 180 °. In this case, the holding current of the dimming circuit 2 can be arbitrarily set by adjusting the high level period of the control signal E.

For example, as a specific example in which the control signal E is different from the above E1, another example of the operation of the holding current control circuit 7 will be described with reference to FIG.
As shown in FIG. 3, an AC voltage A having a sinusoidal voltage waveform is supplied from the commercial AC power supply Vac to the dimming circuit 2. The AC voltage A is converted into an AC voltage having a conduction angle set by the dimming circuit 2. In the present embodiment, when the phase angle that becomes 0 V when the AC voltage A shifts from the positive voltage to the negative voltage is set to 0 °, the AC voltage A is controlled by the dimming circuit 2 so that −90 ° to 0 ° and It is converted into a dimming signal (AC voltage) B having a conduction angle of 90 ° to 180 °. The dimming signal B input from the dimming circuit 2 to the bridge circuit 3 is rectified by the bridge circuit 3 and converted to a positive voltage only rectified signal (AC voltage) C having the same conduction angle as the dimming signal B. Is done. The rectified signal C is input from the bridge circuit 3 to the waveform shaping circuit 4, and is shaped by the waveform shaping circuit 4. The phase angles are −90 ° to 0 ° and 90 ° to 180 ° according to the conduction angle. A pulse signal D having a high level is generated. Up to this point, the same operation as in the embodiment shown in FIG. 2 is performed.

The pulse signal D generated by the waveform shaping circuit 4 is input to the holding current control signal generation circuit 8 provided in the holding current control circuit 7. The holding current control signal generation circuit 8 receives the pulse signal D that is at a high level during the phase angles of −90 ° to 0 ° and 90 ° to 180 °, so that the phase angle is greater than the on-phase angle of −90 °. In the range of the arbitrary phase angle ˜0 ° delayed and the arbitrary phase angle ˜180 ° delayed from the ON phase angle 90 ° (period t1a to t2 and period t3a to t4 shown in FIG. 3) A control signal E (E2 in FIG. 3) is generated and output to the base terminal of the switching element Q3.

  In the present embodiment, the on phase of the alternating voltage controlled by the dimming circuit 2 is within the range of the on phase angle of the alternating voltage controlled by the dimming circuit 2 in the range of −90 ° to 0 ° and 90 ° to 180 °. With respect to the angle, the holding current control signal generation circuit 8 has an arbitrary phase angle ˜0 ° delayed from the on phase angle in the negative region and the on phase angle in the positive region. A control signal E2 that becomes a high level in the range of the delayed arbitrary phase angle to 180 ° is generated, and the switching element Q3 is turned on during the high level period of the control signal E2 and is output from the dimming circuit 2 The pulse current is superimposed on the dimming current.

  As described above, the LED drive circuit 1 according to the present embodiment connects the holding current control circuit 7 between the waveform shaping circuit 4 and the constant current control circuit 6, and the holding current control circuit 7 includes the waveform shaping circuit 4. The control signal E for controlling the holding current of the dimming circuit 2 is generated according to the on-phase angle controlled by the dimming circuit 2 by inputting the pulse signal D generated in step 1, and the dimming according to the control signal E Since the holding current of the dimming circuit 2 is controlled by flowing a pulse current that is superimposed on the dimming current output from the circuit 2, the alternating current that is phase-controlled by the dimming circuit 2 while having a simple circuit configuration. It is possible to provide an LED driving circuit capable of maintaining an appropriate minimum holding current of the dimming circuit 2 in accordance with the on-phase angle of the voltage.

(Second Embodiment)
Next, the LED drive circuit 1a according to the second embodiment of the present invention will be described. In the following, the same reference numerals are used for the components corresponding to the components of the LED drive circuit 1 according to the first embodiment described above. The description of the parts common to the LED drive circuit 1 according to the first embodiment will be omitted as appropriate, and differences will be mainly described.

FIG. 4 is a circuit diagram showing a configuration of an LED drive circuit 1a according to the second embodiment of the present invention.
As shown in FIG. 4, in the LED drive device 1a according to the present embodiment, the holding current control circuit 7a receives the pulse signal D generated by the waveform shaping circuit 4, and inputs the pulse signal D to the switching element Q3. A holding current control signal generation circuit 8a that outputs a direct current F having a value inversely proportional to the pulse width is provided. The holding current control signal generation circuit 8a has a switching element (second switching element) Q4 for inverting the signal level of the pulse signal D input from the waveform shaping circuit 4 and a pulse width of the pulse signal whose signal level is inverted. An integration circuit 9 for converting to a proportional DC signal F and a control signal G in which the magnitude of the DC signal F output from the integration circuit 9 is adjusted are output to the switching element Q3 to control the holding current of the dimming circuit 2 And a control phase angle adjustment circuit 10 that can adjust the range of the phase angle to be adjusted. The configuration other than the above is the same circuit configuration as the LED drive circuit 1 according to the first embodiment.

  In the holding current control signal generation circuit 8a, the switching element Q4 is composed of a bipolar transistor, the collector terminal is connected to the secondary power supply (DC power supply) Vcc via the resistance element R5, and the emitter terminal is connected to GND. Has been. The integrating circuit 9 includes a resistor element R6 and a capacitor C2, and one end of each is connected to serve as an output end, and the other end of the resistor element R6 is connected to the collector terminal of the switching element Q4. The end is connected to GND. The control phase angle adjustment circuit 10 includes a resistance element R7 and a variable resistance VR1, and one end of each is connected as an output end, and the other end of the resistance element R7 is connected to an output end of the integration circuit 9. The other end of the variable resistor VR1 is connected to GND.

Next, the operation of the holding current control circuit 7a will be specifically described with reference to FIGS. FIG. 5 is a signal waveform diagram showing an embodiment of the operation of the holding current control circuit 7a in the LED drive circuit 1a. FIG. 6 is a pulse width d of the pulse signal D generated by the waveform shaping circuit 4 in the LED drive circuit 1a. It is a figure which shows the relationship between DC signal F produced | generated by the holding current control circuit 7a.

In FIG. 5, symbol A indicates an AC voltage that is a sinusoidal voltage waveform supplied from the commercial AC power supply Vac to the dimming circuit 2. Also in this embodiment, the phase angle that becomes 0 V when the AC voltage A shifts from the positive voltage to the negative voltage is set to 0 °. The pulse width d of the pulse signal D generated by the waveform shaping circuit 4 and output to the holding current control circuit 7a is determined by the conduction angle of the AC voltage controlled by the dimming circuit 2. Specifically, as shown in FIG. 5 (the waveforms of the dimming signal and the rectification signal are not shown), the conduction angle of the AC voltage controlled by the dimming circuit 2 is −135 ° to 0 ° and 45 ° to 180 °. When the angle is in the range of °, the pulse signal D becomes a pulse signal D1 having a pulse width d1 that is at a high level during the phase angles of −135 ° to 0 ° and 45 ° to 180 °, and is controlled by the dimming circuit 2. When the AC voltage conduction angle is in the range of -90 ° to 0 ° and 90 ° to 180 °, the pulse signal D is at a high level during the phase angles of -90 ° to 0 ° and 90 ° to 180 °. When the conduction angle of the AC voltage controlled by the dimming circuit 2 is in the range of −45 ° to 0 ° and 135 ° to 180 °, the pulse signal D has the phase angle Is at a high level in the period of −45 ° to 0 ° and 135 ° to 180 °. A pulse signal D3 of that pulse width d3.

The pulse signal D generated by the waveform shaping circuit 4 is input to the holding current control circuit 7a and applied to the base terminal of the switching element Q4 constituting the holding current control signal generation circuit 8a. Then, a pulse signal obtained by inverting the signal level of the pulse signal D is output from the collector terminal of the switching element Q4 to the integrating circuit 9.

The pulse signal input to the integration circuit 9 is converted into a DC signal F proportional to the pulse width of the pulse signal and output to the control phase angle adjustment circuit 10. As a result, the pulse width of the pulse signal D generated by the waveform shaping circuit 4 and the magnitude of the DC signal F generated by the integration circuit 9 are inversely proportional, and the pulse signals D1, Assuming that the DC signals F corresponding to D2 and D3 are F1, F2 and F3, respectively, the relationship between the pulse widths d1, d2 and d3 of the pulse signal D and the DC signals F1, F2 and F3 is as shown in FIG. As the pulse width of the pulse signal D increases (d3> d2> d1), the value of the DC signal F decreases (F3 <F2 <F1).

The DC signal F output from the integration circuit 9 is input to the control phase angle adjustment circuit 10. The DC signal F is divided by the control phase angle adjustment circuit 10 and a DC voltage (control signal) G having a predetermined magnitude is output to the base terminal of the switching element Q3.

The switching element Q3 is turned on when a control signal G equal to or higher than a threshold value at which the base terminal can be turned on, and acts so that a direct current is superimposed on the dimming current output from the dimming circuit 2. The control phase angle adjustment circuit 10 can change the magnitude of the control signal G to be output with respect to the input DC signal F by adjusting the resistance value of the variable resistor VR1, for example, the DC signal F2 is input. When the control signal G that is sometimes output is set to be a threshold value for turning on the base terminal of the switching element Q3, when the value of the DC signal F is F2 or more, that is, when the pulse width of the pulse signal D is d2 or less. When the switching element Q3 is turned on and the value of the DC signal F is lower than F2, that is, when the pulse width of the pulse signal D is larger than d2, the switching element Q3 is turned off. In other words, when the on phase angle of the AC voltage controlled by the dimming circuit 2 is in the range of −90 ° to 0 ° and 90 ° to 180 °, the switching element Q3 is turned on, and the on phase angle is In a range other than the above, the switching element Q3 is turned off. During the period in which the switching element Q3 is on, a pulse current is superimposed on the dimming current output from the dimming circuit 2.

  The period during which the switching element 3 is turned on is not limited to the range of the ON phase angle of the AC voltage controlled by the dimming circuit 2 described above, but the variable resistor VR1 of the control phase angle adjustment circuit 10. By appropriately adjusting the magnitude of the control signal G by varying the resistance value, the period during which the switching element 3 is turned on, that is, the period during which the holding current is passed, is appropriately set according to various design specifications of the LED drive circuit. be able to.

As described above, in the LED drive circuit 1a according to the present embodiment, the waveform shaping circuit 4 generates the pulse signal D corresponding to the conduction angle of the AC voltage phase-controlled by the dimming circuit 2, and the holding current control is performed. The circuit 7a generates a DC voltage that is inversely proportional to the pulse width d of the pulse signal D and outputs a control signal G that is a DC voltage of a predetermined magnitude to control the on / off operation of the switching element Q3. When the ON phase angle of the AC voltage controlled by the dimming circuit 2 is within a predetermined range, the DC current is superimposed on the dimming current output from the dimming circuit 2 to allow the holding current to flow. It can be set arbitrarily.

The LED drive circuit 1a according to the present embodiment has a simple circuit configuration as in the LED drive circuit 1 according to the first embodiment described above, but the on-phase angle of the AC voltage phase-controlled by the dimming circuit 2 Accordingly, it is possible to provide an LED driving circuit capable of maintaining an appropriate minimum holding current of the dimming circuit 2. In the present embodiment, in the actual usage environment, by adjusting the resistance value of the variable resistor VR1 included in the control phase angle adjustment circuit 10, an appropriate setting time for flowing the holding current according to the line impedance of the power supply line is set. Is possible.

  The representative embodiment of the present invention has been described above, but the present invention is not limited to the circuit configuration of the above embodiment, and various modifications can be made without departing from the spirit of the present invention. .

  For example, the switching elements Q1 and Q3 in the LED driving circuits 1 and 1a according to the first and second embodiments described above and the switching element Q4 in the LED driving circuit 1a according to the second embodiment are bipolar transistors. For example, a MOSFET may be used. The switching element Q2 is not limited to the MOSFET shown in the above embodiment, and may be a bipolar transistor.

  The rectifier circuit 3 is a full-wave rectifier circuit configured as a diode bridge, but is not limited to this, and may be another rectifier circuit.

Further, the conduction angle set in the dimming circuit 2 is not limited to that shown in the first and second embodiments described above, and the present invention provides a dimming circuit in which an arbitrary conduction angle is set. Is applicable.

1, 1a: LED drive circuit, 2: dimming circuit, 3: bridge circuit, 4: waveform shaping circuit, 5: LED module, 6: constant current control circuit, 7, 7a: holding current control circuit, 8, 8a: Holding current control signal generation circuit, 9: integration circuit, 10: control phase angle adjustment circuit, D1 to D5: diode, D6: Zener diode, L1: inductor, C1: output capacitor, C2: capacitor, R1: current detection resistor, R2 to R7: Resistance element, VR1: Variable resistance, Q0: Triac, Q1: Switching element, Q2: Switching element (MOSFET), Q3: Switching element (first switching element), Q4: Switching element (second switching) Element), Vac: commercial AC power supply, Vcc: secondary power supply (DC power supply)

Claims (8)

A dimming circuit that controls the phase of the current supplied to the light emitting diode (LED) by controlling the conduction angle of the AC voltage supplied from the commercial AC power supply, and a bridge that rectifies the AC voltage output from the dimming circuit An LED comprising: a circuit; a waveform shaping circuit for shaping a waveform of an alternating voltage output from the bridge circuit to generate a pulse signal; and a constant current control circuit for controlling the current flowing in the LED to be constant In the drive circuit,
A holding current control circuit is connected between the waveform shaping circuit and the constant current control circuit, and the holding current control circuit is controlled by the dimming circuit by inputting a pulse signal generated by the waveform shaping circuit. Generating a control signal for controlling the holding current of the dimming circuit according to the ON phase angle, and passing a pulse current superimposed on the dimming current output from the dimming circuit according to the control signal. An LED driving circuit that controls a holding current. The holding current control circuit is a holding current control signal generation circuit that generates a control signal that allows the holding current to flow in accordance with an ON phase angle controlled by the dimming circuit by inputting the pulse signal. The LED drive circuit according to claim 1, further comprising: a first switching element that performs an on / off operation by inputting the control signal. The holding current control circuit is configured to adjust the dimming circuit based on the phase angle when the phase angle that becomes 0 V when the AC voltage supplied from the commercial AC power supply shifts from a positive voltage to a negative voltage is set to 0 °. 2. The control is performed so as to arbitrarily set a time during which the holding current flows when the on-phase angle controlled by is in a range of −90 ° to 0 ° and 90 ° to 180 °. 2. The LED driving circuit according to 2. The holding current control circuit has a range of any phase angle to 0 ° delayed from the on phase angle in the negative region of the on phase angle, and an arbitrary phase delayed from the on phase angle in the positive region of the on phase angle. The LED driving circuit according to claim 3, wherein the holding current is controlled to flow during a period in a range of a phase angle of −180 °. The first holding current control circuit supplies the holding current during a period between an on phase angle in a negative region of the on phase angle and a range of 0 ° and an on phase angle in a positive region of the on phase angle. 4. The LED driving circuit according to claim 3, wherein the LED driving circuit is controlled to flow. 6. The LED driving circuit according to claim 2, wherein the control signal output from the holding current control signal generation circuit to the first switching element is a pulse signal.   6. The LED drive circuit according to claim 2, wherein the control signal output from the holding current control signal generation circuit to the first switching element is a DC signal.   The holding current control signal generation circuit includes a second switching element that inverts the signal level of the pulse signal input from the waveform shaping circuit, and an integration that converts the signal to a DC signal corresponding to the pulse width of the inverted pulse signal. A circuit and a control phase angle adjustment circuit that adjusts the magnitude of the DC signal output from the integration circuit and adjusts the range of the phase angle for controlling the holding current by turning on the first switching element. The LED drive circuit according to claim 7.

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