WO2013172259A1

WO2013172259A1 - Switching power supply circuit and led lighting device

Info

Publication number: WO2013172259A1
Application number: PCT/JP2013/063135
Authority: WO
Inventors: 弘之小路; 金森　淳
Original assignee: シャープ株式会社
Priority date: 2012-05-17
Filing date: 2013-05-10
Publication date: 2013-11-21

Abstract

A flyback-type switching power supply circuit equipped with a rectification circuit capable of connecting to an alternating current power supply via a phase-control-type dimmer, a transformer having a primary winding to which voltage from the rectification circuit is supplied, and a secondary winding, a rectification/smoothing circuit connected between the secondary winding and a load, and a switching element connected to the first winding, said power supply circuit being constructed so as to be further equipped with: a voltage-dividing circuit that divides the output voltage from the rectification circuit; a reference voltage generation circuit that generates a reference voltage on the basis of the output voltage from the rectification circuit that has been divided by the voltage-dividing circuit; and a primary peak current control circuit that switches the switching element and controls the peak value of the primary current so as to match a current value corresponding to the reference voltage generated by the reference voltage generation circuit.

Description

Switching power supply circuit and LED lighting device

The present invention relates to a switching power supply circuit.

LEDs (Light Emitting Diodes) have features such as low current consumption and long life, and their use is spreading not only to display devices but also to lighting equipment.

Common lighting fixtures often use a commercial AC 100V power source. Considering the use of LED lighting fixtures instead of general lighting fixtures such as incandescent bulbs, LED lighting fixtures are similar to general lighting fixtures. It is desirable to use a commercial AC100V power source (for example, Patent Document 1). In order to make the illuminance and color constant, the LED needs to be driven with a constant current, and a switching power supply circuit that makes the output current constant is used.

As a general switching power supply circuit technology, for example, Patent Document 2 detects the time during which the secondary current of the transformer flows, and the ratio of this time in the switching cycle, that is, the on-duty ratio of the secondary current. A technique for making it constant is disclosed.

The switching power supply circuit disclosed in Patent Document 1 (FIG. 1 of Patent Document 1) includes a semiconductor device 100, a transformer 110, diodes 121 and 141, capacitors 122 and 142, and resistors 151 and 152. This is a flyback switching power supply circuit that generates a predetermined DC output voltage Vo from the AC input voltage VIN and supplies it to a load 130. Transformer 110 includes a primary winding 111, a secondary winding 112, and an auxiliary winding 113.

FIG. 3 of Patent Document 2 shows a timing chart showing voltage waveforms and current waveforms of each part of the switching power supply circuit. In this timing chart, the auxiliary winding voltage VTR obtained by dividing the voltage appearing at one end of the auxiliary winding 113, the primary current Ids flowing through the switching element 1, and the secondary current I2p flowing through the secondary winding 112 are shown. It is depicted.

Here, T1 is a first period in which the secondary current I2p flows, T2 is a second period in which the secondary current I2p does not flow, T3 is a third period in which the first period T1 and the second period T2 are combined, Ipk1 Is the peak value of the primary current Ids, and Ipk2 is the peak value of the secondary current I2p.

The output current Iout supplied from the switching power supply circuit to the load 130 is an average value of the secondary current I2p. The average value of the secondary current I2p in the first period T1 is ½ of the peak value Ipk2 of the secondary current I2p. The average value of the secondary current I2p in the third period T3 is a value obtained by multiplying the average value of the secondary current I2p in the first period T1 by the on-duty ratio of the secondary current. Accordingly, when the number of turns of the primary winding 111 is N1 and the number of turns of the secondary winding 112 is N2, the output current Iout is expressed by the following equation (1).
Iout = (1/2) × (N1 / N2) × (T1 / T3) × Ipk1 (1)

The conventional switching power supply circuit uses the secondary current on-duty ratio control circuit 8 in the above formula (1) to keep the peak current Ipk1 of the primary current Ids constant using the drain current limiting circuit 3 and the secondary current. By making the on-duty ratio (T1 / T3) constant, the output current Iout is controlled to be constant.

In addition, dimming control is performed on conventional incandescent bulbs. When dimming control is to be performed, switching elements (typically thyristor elements and triac elements) should be turned on at a phase angle with an AC power supply voltage. Therefore, a phase control dimmer (generally called an incandescent lycon) that can easily control the dimming of power to the incandescent bulb with a single volume element is used.

However, when an LED is connected to an existing dimmer, flickering occurs in which the amount of light changes regardless of the phase angle control of the dimmer. In particular, it is known that when an LED bulb with a small wattage is connected to a dimmer, flickering or blinking tends to occur, and dimming cannot be performed normally.

JP 2004-327152 A JP 2009-11073 A

FIG. 11 shows a conventional example of an LED illumination system capable of dimming control of an LED illumination lamp using an AC power source. The LED illumination system shown in FIG. 11 includes a phase control dimmer 2, an LED drive circuit 4, and an LED array 3 in which LEDs are connected in series. A phase control dimmer 2 is connected in series between the AC power source 1 and the LED drive circuit 4. The LED drive circuit 4 includes, for example, a full-wave rectifier circuit 41 configured by a diode bridge, a filter circuit 42, an input voltage detection means 43, a phase angle detection means 44, a current extraction means 45, and a current limiting means 46. I have.

In the phase control dimmer 2, the triac Tri1 is turned on at a power supply phase angle depending on the resistance value by varying the resistance value of the semi-fixed resistor Rvar1. Usually, the semi-fixed resistor Rvar1 is a rotary knob or a slide type, and the dimming control of the illumination lamp can be performed by changing the rotation angle of the knob or changing the slide position. Further, in the phase control dimmer 2, a noise suppression circuit including the capacitor C1 and the inductor L1 is configured to reduce noise returning from the phase control dimmer 2 to the AC power supply line.

FIG. 12 shows the output waveform of the dimmer and the output waveform of the full-wave rectifier circuit 41 when the phase angle of the phase control dimmer 2 is 0 °, 45 °, 90 °, and 135 °. As the phase angle increases, the average voltage value of the full-wave rectifier circuit output waveform decreases. As the phase angle of the dimmer increases, the brightness of the LED array 3 decreases.

When the phase angle of the phase control dimmer 2 is increased and the brightness of the LED array 3 is reduced, the output voltage of the full-wave rectifier circuit 41 becomes smaller than the forward voltage of the LED array 3. Sometimes the LED does not shine and the current flowing through the dimmer decreases rapidly. When the current flowing through the dimmer decreases rapidly, the current falls below the holding current of the internal triac Tri1, so the triac is turned off and the dimmer output stops and becomes unstable, causing flickering in the brightness of the LED. To do.

Also, when the dimmer output is phase-controlled and the triac Tri1 is turned on from off, the LED is turned on from off and the impedance of the LED changes abruptly. As a result, ringing occurs at the edge portion where the output voltage of the dimmer abruptly changes, so that the triac Tri1 becomes unstable and turns off, and the brightness of the LED may flicker.

In addition, as shown in FIG. 11, in order to improve the power factor and reduce the EMI noise, a filter circuit composed of a resistor, an inductor, a diode, and a capacitor is often disposed between the full-wave rectifier circuit and the current limiting means. When the phase angle of the dimmer becomes 90 ° or more, the current supplied to the LED drive circuit decreases due to the dimming operation of the LED drive circuit, and at the same time, the output voltage of the dimmer changes from rising to falling. The electric current stored in the capacitor in the circuit causes the current limiting means to operate, and the current supplied from the dimmer decreases rapidly. As a result, when the current flowing through the triac in the dimmer is lower than the holding current, the triac may be turned off, causing the dimmer to malfunction and causing flickering.

Also, here, when the AC power supply, the phase control dimmer, and the full-wave rectifier circuit are connected to the previous stage of the above-described switching power supply circuit of Patent Document 2 (FIG. 1 of Patent Document 2) as in FIG. think of. When a circuit including a full-wave rectifier circuit in the switching power supply circuit of Patent Document 2 is regarded as a switching power supply circuit, an average input current Iin flowing into the switching power supply circuit is expressed by the following equation.

Iin = (1/2) × Ipk1 × (T1 / T3) × (N1 / N2) ×
(Vout / Vin) (2)
Where Vout: output voltage, Vin: input voltage

Here, in the switching power supply circuit of Patent Document 2, the drain current limiting circuit 3 is used to make the peak Ipk1 of the primary current flowing through the switching element 1 constant, and the on-duty ratio (T1 / T3) of the secondary current is set. The output current Iout is controlled to be constant. Further, the winding number ratio (N1 / N2) is also constant. Further, since the output current Iout flowing through the load 130 is substantially constant, the output voltage Vout is also substantially constant.

Therefore, as shown in FIG. 13, when the input voltage Vin of the switching power supply circuit fluctuates, the average input current Iin of the switching power supply circuit fluctuates in inverse proportion to the input voltage Vin, and switching is performed when the input voltage Vin is high. The current flowing into the power supply circuit is reduced. Therefore, the current flowing through the triac in the phase control dimmer tends to be lower than the holding current, the triac is turned off, the dimmer malfunctions, and flicker may occur when the load 130 is an LED.

In view of the above problems, the present invention includes a switching power supply circuit capable of suppressing malfunction of the phase control dimmer by maintaining the average input current flowing into the switching power supply circuit substantially constant, and the same. An object of the present invention is to provide an LED lighting device.

In order to achieve the above object, the present invention provides:
A rectifier circuit connectable to an AC power supply via a phase control dimmer;
A transformer having a primary winding to which a voltage is supplied from the rectifier circuit and a secondary winding;
A rectifying / smoothing circuit connected between the secondary winding and a load;
A switching device connected to the primary winding, and a flyback switching power supply circuit comprising:
A voltage dividing circuit for dividing the output voltage of the rectifier circuit;
A reference voltage generating circuit that generates a reference voltage based on the output voltage of the rectifier circuit divided by the voltage dividing circuit;
A primary peak current control circuit that controls the peak value of the primary current by switching the switching element so as to match the current value corresponding to the reference voltage generated by the reference voltage generation circuit. .

In the above configuration, the reference voltage generation circuit includes:
A control reference voltage output circuit that outputs a control reference voltage corresponding to the output voltage of the rectifier circuit divided by the voltage divider circuit;
A primary average current detection circuit for detecting an average of primary currents;
A primary control reference voltage generation circuit that generates a primary control reference voltage by comparing the output of the control reference voltage output circuit with the detection output of the primary average current detection circuit;
A secondary current on-duty ratio detection circuit for detecting an on-duty ratio of the secondary current;
A first multiplication circuit that multiplies the output of the primary control reference voltage generation circuit by the output of the secondary current on-duty ratio detection circuit;
A reference voltage source;
An error amplifier for amplifying an error between a multiplication result of the first multiplication circuit and a reference voltage by the reference voltage source;
A second multiplier circuit that multiplies the output voltage of the rectifier circuit divided by the voltage divider circuit by the output of the error amplifier and outputs a multiplication result as the reference voltage;
You may make it provide.

In any of the above configurations,
A phase angle detection circuit for detecting a phase angle of a rise of the output voltage of the rectifier circuit;
A power supply for supplying a voltage from the rectifier circuit to the primary winding at the moment when the phase control dimmer is turned on with an amount of current corresponding to the phase angle detected by the phase angle detection circuit. A current drawing circuit for drawing current from the supply line.

Further, in any one of the above configurations, an input current control circuit that controls an input current by drawing a current from a power supply line for supplying a voltage from the rectifier circuit to the primary winding may be provided.

In any of the above configurations,
A phase angle detection circuit for detecting a phase angle of a rise of the output voltage of the rectifier circuit;
A power supply for supplying a voltage from the rectifier circuit to the primary winding at the moment when the phase control dimmer is turned on with an amount of current corresponding to the phase angle detected by the phase angle detection circuit. A current drawing control for drawing current from a supply line, and a current drawing and input current control circuit for controlling an input current by drawing current from the power supply line, and
The current drawing and input current control circuit may share a circuit for drawing current for controlling the current drawing and controlling the input current.

In any of the above-described configurations, the average input current may be controlled to increase from the phase angle of the output voltage of the rectifier circuit being 90 ° or more.

In the above configuration, the switching frequency of the switching element is variable according to the output voltage of the rectifier circuit,
The sampling time for averaging of the primary average current detection circuit may be variable according to the switching frequency.

The LED lighting device of the present invention includes a switching power supply circuit having any one of the above-described configurations and an LED load connected to the output side of the switching power supply circuit.

According to the present invention, it is possible to suppress malfunction of the phase control dimmer by maintaining the average input current flowing into the switching power supply circuit substantially constant.

1 is a configuration diagram of a switching power supply circuit according to a first embodiment of the present invention. It is a figure which shows the example of 1 structure of the primary current detection circuit which concerns on 1st Embodiment of this invention. It is a figure which shows one structural example of the primary average current detection circuit which concerns on 1st Embodiment of this invention. It is a figure which shows the example of 1 structure of the secondary current on-duty ratio detection circuit which concerns on 1st Embodiment of this invention. It is a figure which shows the example of 1 structure of the 1st multiplication circuit which concerns on 1st Embodiment of this invention. It is a figure which shows the example of a waveform of the average input current which concerns on embodiment of this invention. It is a figure which shows an example of the relationship between the phase angle and drawing current amount which concern on 1st Embodiment of this invention. It is a block diagram of the switching power supply circuit which concerns on 2nd Embodiment of this invention. It is a figure which shows one structural example of the input current control circuit which concerns on 2nd Embodiment of this invention. It is a block diagram of the switching power supply circuit which concerns on 3rd Embodiment of this invention. It is a block diagram which shows the prior art example of an LED lighting system. It is a figure which shows a dimmer output waveform and a full wave rectifier circuit output waveform at the time of changing the phase angle of a dimmer. It is a figure which shows the example of a waveform of the average input current which concerns on the past.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Here, an LED lighting device using an LED load as a load of the switching power supply circuit will be described as an example.

<First Embodiment>
The configuration of the switching power supply circuit according to the first embodiment of the present invention is shown in FIG. A switching power supply circuit 10 shown in FIG. 1 is a so-called flyback converter, and an AC power supply 1 is connected to a front stage side via a phase control dimmer 2. An LED lighting device is configured by the switching power supply circuit 10 and the LED array 15 in which a plurality of LEDs connected to the output side of the rectifying and smoothing circuit 120 are connected in series.

The switching power supply circuit 10 includes a full-wave rectifier circuit 101, a voltage dividing circuit 102, a phase angle detection circuit 103, a current extraction circuit 104, a resistor R11, a primary peak current control circuit 131, and a reference voltage generation circuit 132. And a switching element 109 for primary current control, a primary current detection circuit 110, a transformer 119, and a rectifying and smoothing circuit 120.

The primary peak current control circuit 131 includes an oscillation circuit 105, an RS flip-flop 106, a gate driver 107, and a voltage comparison circuit 108. The reference voltage generation circuit 132 includes a primary average current detection circuit 111, a primary control reference voltage generation circuit 112, a control reference voltage output circuit 113, a secondary current on-duty ratio detection circuit 114, and a first multiplication circuit 115. And an error amplifier 116, a reference voltage source 117, and a second multiplier circuit 118.

The transformer 119 includes a primary winding 119A, a secondary winding 119B, and an auxiliary winding 119C. The polarities of the primary winding 119A and the secondary winding 119B are reversed. The secondary winding 119B and the auxiliary winding 119C have the same polarity, and a voltage proportional to the voltage generated in the secondary winding 119B is generated in the auxiliary winding 119C.

A full-wave rectifier circuit 101 is connected to one end of the primary winding 119A. The other end of the primary winding 119A is connected to the drain of the switching element 109 formed of an N-channel MOS transistor. Both ends of the secondary winding 119B are connected to the input side of the rectifying and smoothing circuit 120.

One end of the auxiliary winding 119C is connected to the ground potential, and the other end is connected to the input end of the secondary current on-duty ratio detection circuit 114.

The phase control dimmer 2 has the same configuration as that shown in FIG. The AC voltage output from the AC power source 1 is phase-controlled by the phase control dimmer 2, and the AC voltage after phase control is full-wave rectified by the full-wave rectifier circuit 101 and applied to the primary winding 119A.

When the switching element 109 is turned on, the primary current flowing through the primary winding 119A gradually increases, and the core of the transformer 119 is magnetized by the generated magnetic flux, and energy is accumulated in the core. When the switching element 109 is turned off, the energy is released and the secondary current flowing in the secondary winding 119B rises and then gradually decreases.

The primary current detection circuit 110 is a circuit that detects a primary current flowing through the switching element 109, and outputs a detection voltage signal to the voltage comparison circuit 108 and also to the primary average current detection circuit 111.

A configuration example of the primary current detection circuit 110 is shown in FIG. The primary current detection circuit 110 shown in FIG. 2 is subjected to current / voltage conversion by a current detection resistor R110 having one end connected to the source of the switching element 109 and the other end connected to the ground potential, and the current detection resistor 110. The buffer circuit 110A outputs the detected voltage signal as a detected voltage signal.

The primary average current detection circuit 111 is a circuit that averages the primary current detected by the primary current detection circuit 110 every predetermined sampling time and outputs the average result as a detection voltage signal.

An example of the configuration of the primary average current detection circuit 111 is shown in FIG. The primary average current detection circuit 111 shown in FIG. 3 is configured as an integration circuit that integrates an input voltage, and includes resistors R111 and R112, a capacitor C111, and an operational amplifier OP111.

The control reference voltage output circuit 113 is a circuit that receives the output voltage of the full-wave rectifier circuit 101 divided by the voltage dividing circuit 102 and outputs a control reference voltage corresponding to the input voltage.

The primary control reference voltage generation circuit 112 compares the control reference voltage output from the control reference voltage output circuit 113 with the detection voltage output from the primary average current detection circuit 111 to obtain the primary control reference voltage. A circuit that generates and outputs.

The secondary current on-period detection circuit 114 is a circuit that detects a secondary current on-duty ratio that is a ratio of a period in which the secondary current flows (secondary current on period) to a switching cycle, and firstly multiplies the detection signal by the first multiplication. Output to the circuit 115.

An example of the configuration of the secondary current on period detection circuit 114 is shown in FIG. The secondary current on period detection circuit 114 shown in FIG. 4 includes a waveform shaping circuit 114A whose input end is connected to one end of the auxiliary winding 119C, and a reference voltage source 114B.

When the switching element 109 is turned on, the primary current gradually increases, and when the switching element 109 is turned off, the secondary current rises and gradually decreases. During the period when the secondary current is flowing, a voltage is generated in the auxiliary winding 119C. During the period when the secondary current flows and the voltage of the auxiliary winding 119C is generated, the auxiliary winding voltage becomes equal to or higher than the reference voltage by the reference voltage source 114B, and the waveform shaping circuit 114A is at the low level while detecting this. Output voltage V114. When the secondary current becomes zero, the auxiliary winding voltage starts to decrease and falls below the reference voltage. When the waveform shaping circuit 114A detects this, the waveform shaping circuit 114A outputs the output voltage V114 as a high level. That is, the on-duty ratio of the secondary current is detected as a pulse voltage signal.

The first multiplication circuit 115 multiplies the primary control reference voltage generated by the primary control reference voltage generation circuit 112 by the secondary current on duty ratio detected by the secondary current on duty ratio detection circuit 114. It is.

One configuration example of the first multiplication circuit 115 is shown in FIG. The first multiplication circuit 115 shown in FIG. 5 includes an inverting circuit 115A, switches 115B and 115C, and a smoothing circuit 115D. The

switches

115B and 115C are connected in series between the output terminal of the primary control reference voltage generation circuit 112 and the ground potential, and the connection point between the

switches

115B and 115C is connected to the input terminal of the smoothing circuit 115D.

The output of the secondary current on-duty ratio detection circuit 114 is inverted by the inversion circuit 115A, and the switch 115B is switched according to the inversion result. The switch 115C is switched by the output of the secondary current on-duty ratio detection circuit 114. By such switching, a voltage signal that is a result of multiplication of the primary control reference voltage and the secondary current on-duty ratio is output from the output terminal of the smoothing circuit 115D.

The error amplifier 116 is a circuit that amplifies an error between the output of the first multiplier circuit 115 and the first reference voltage caused by the reference voltage source 117.

The second multiplication circuit 118 multiplies the output voltage of the full-wave rectification circuit 101 divided by the voltage dividing circuit 102 by the output of the error amplifier 116, and outputs the multiplication result to the voltage comparison circuit 108 as a second reference voltage. Circuit.

As shown in FIG. 2, the detection voltage output from the primary current detection circuit 110 is input to the non-inverting input terminal of the voltage comparison circuit 108, and the second multiplication circuit 118 is input to the inverting input terminal of the voltage comparison circuit 108. The output second reference voltage is input. The set terminal of the RS flip-flop 106 is connected to the output terminal of the voltage comparison circuit 108.

The oscillation circuit 105 is a circuit that outputs an oscillation pulse to the reset terminal of the RS flip-flop 106, and outputs an oscillation pulse having a frequency that is variable according to the output voltage (that is, the input voltage Vin) of the full-wave rectification circuit 101. . Here, the higher the input voltage Vin, the higher the frequency. This is because if the frequency is constant, the primary current increases according to the voltage when the input voltage increases, and the ripple of the output current increases. In addition, noise radiated from the switching power supply increases, and many noise countermeasure components are required. In particular, in a power supply device with a rated output of 10 W or less, it is difficult to increase the number of noise countermeasure components because the product itself is small and inexpensive.

The Q bar output terminal of the RS flip-flop 106 is connected to the input terminal of the gate driver 107. The output terminal of the gate driver 107 is connected to the gate of the switching element 109.

When the output of the oscillation circuit 105 becomes a high level, the RS flip-flop 106 is reset, and the switching element 109 is turned on by the gate driver 107. After that, when the primary current increases and the primary current reaches the current value corresponding to the second reference voltage, the RS flip-flop is set by the output of the voltage comparison circuit 108, and the switching element 109 is controlled by the gate driver 107. It is turned off. Thereafter, the switching element 109 is turned on again by the high level output of the oscillation circuit 105. In this way, the peak value of the primary current is controlled.

As described above, in the present embodiment, the reference voltage generation circuit 132 generates the second reference voltage based on the output voltage of the full-wave rectification circuit 101 divided by the voltage dividing circuit 102, and the generated second reference voltage. The peak value of the primary current is controlled by the primary peak current control circuit 131 so as to match the current value corresponding to. As a result, when the input voltage Vin increases, the peak value of the primary current is increased, the average input current Iin flowing into the switching power supply circuit 10 is suppressed from decreasing, and the average input current Iin is held substantially constant. It becomes possible. Therefore, it is possible to suppress the current flowing in the triac Tri1 in the phase control dimmer 2 from being lower than the holding current, and to suppress malfunction of the dimmer due to the triac Tri1 being turned off. Thereby, generation | occurrence | production of the flicker of the LED array 15 can be suppressed. FIG. 6 shows a waveform example of the input voltage Vin (upper stage) and the average input current Iin (middle stage) according to the present embodiment, and the average input current Iin is held substantially constant.

Further, when the triac Tri1 in the phase control dimmer 2 is turned on by phase control, the capacitor C1 and the inductor L1 (FIG. 11) in the dimmer and the capacitance, inductor, resistance in the switching power supply circuit Therefore, the current flowing through the triac Tri1 is likely to be lower than the holding current due to vibration, and the malfunction of the dimmer is likely to occur.

Therefore, the switching power supply circuit according to the present embodiment is also provided with a phase angle detection circuit 103 and a current drawing circuit 104. The phase angle detection circuit 103 is a circuit that detects the phase angle at which the output voltage of the full-wave rectifier circuit 101 rises (that is, the phase angle of the rise by the phase control dimmer 2). The current extraction circuit 104 is an extraction current amount corresponding to the rising phase angle detected by the phase angle detection circuit 103, and a predetermined time (for example, several times) from the moment when the triac Tri1 in the phase control dimmer 2 is turned on. The current is drawn from the power supply line L1 provided between the full-wave rectifier circuit 101 and the primary winding 119A for only 100 μs). An example of the relationship between the rising phase angle and the amount of extraction current is shown in FIG.

As shown in FIG. 7, when the phase angle is 90 ° or more, the amount of extraction current is increased compared to the case where it is smaller than 90 ° (in the example of FIG. 7, 30 mA compared to 20 mA). This is because the triac Tri1 is easily turned off by ringing that occurs at the moment when the dimmer is turned on because the input voltage is lowered when the phase angle is 90 ° or more. Further, when the input voltage decreases, a current is supplied to the switching element 109 from the energy stored in a capacitor on a circuit (not shown) such as a filter, and the current from the dimmer 2 to the switching power supply circuit 10 is increased. This is because the input current decreases and the triac Tri1 is easily turned off.

With such a configuration, when the triac Tri1 in the phase control dimmer 2 is turned on, the energy stored in the capacitor C1 and the inductor L1 in the dimmer can be discharged by drawing current. Occurrence of the phenomenon can be suppressed.

As described above, the oscillation frequency of the oscillation circuit 105, that is, the switching frequency of the switching element 109 is variable according to the output voltage of the full-wave rectification circuit 101, that is, the input voltage Vin. Therefore, it is desirable that the averaging sampling time in the primary average current detection circuit 111 is variable according to the switching frequency. In particular, when the input voltage Vin is high, the switching frequency becomes high, so that the primary current peak can be controlled early by shortening the sampling time, and fluctuations in the average input current Iin due to control delay can be suppressed. . Therefore, the average input current Iin can be kept constant.

<Second Embodiment>
FIG. 8 shows the configuration of a switching power supply circuit according to the second embodiment of the present invention. The difference of the configuration of the switching power supply circuit 20 shown in FIG. 8 from the first embodiment (FIG. 1) is that an input current control circuit 201 is further provided.

The input current control circuit 201 is a circuit that controls the input current by drawing current from the power supply line L1 during the period from the moment when the dimmer 2 is turned on until it is turned off.

An example of the configuration of the input current control circuit 201 is shown in FIG. An input current control circuit 201 shown in FIG. 9 includes a switching element 201A for current extraction control from the power supply line L1, a current detection resistor 201B, a buffer circuit 201C, a reference voltage source 201D, a comparator 201E, An oscillator 201F, an RS flip-flop 201G, and a gate driver 201H are provided. The input current control circuit 201 repeatedly draws a current from the power supply line L1 with a current amount corresponding to the reference voltage by the reference voltage source 201D.

As a result, the peak value of the primary current controlled by the primary peak current control circuit 131 can be lowered. Therefore, even if the capacitance of the capacitor in the rectifying and smoothing circuit 120 is reduced, the peak value is output to the LED array 15. The ripple of the output current Iout can be reduced. Accordingly, the switching power supply circuit can be reduced in size and cost.

<Third Embodiment>
FIG. 10 shows a configuration of a switching power supply circuit according to the third embodiment of the present invention. A switching power supply circuit 30 shown in FIG. 10 includes a current extraction and input current control circuit 301.

As described in the first embodiment, the current extraction and input current control circuit 301 is configured so that the triac Tri1 in the phase control dimmer 2 has a current amount corresponding to the phase angle detected by the phase angle detection circuit 103. In addition to performing an operation of drawing current when turned on, as described in the second embodiment, the current is drawn and input from the power supply line L1 during the period from when the dimmer 2 is turned on until it is turned off. Control the current.

The current extraction and input current control circuit 301 shares, for example, a circuit for extracting current shown in FIG. 9 for current extraction and input current control in accordance with the phase angle. Cost can be reduced.

<Fourth embodiment>
Next, a fourth embodiment of the present invention will be described. In the first to third embodiments, when a voltage having a phase angle of 90 ° or more is output from the full-wave rectifier circuit 101, the peak value of the primary current flowing through the primary winding 119A is expected to decrease. The More specifically, when the switching power supply circuit is downsized, the transformer needs to be downsized. For this purpose, it is necessary to increase the switching frequency range of the switching element 109. When the phase angle is 90 ° or more and the input voltage is reduced, the switching frequency is lowered. However, since it cannot be lower than the lower limit of the switching frequency range, the peak value of the primary current is reduced.

Therefore, in this embodiment, by controlling so that the average input current is increased from the phase angle of 90 ° or more, the current flowing through the triac in the dimmer is lower than the holding current, and the dimmer malfunctions. Can be suppressed. More specifically, for example, the peak value of the primary current is increased by increasing the extraction current amount of the current extraction circuit 104 or increasing the primary control reference voltage obtained from the primary control reference voltage generation circuit 112. Increase it. A waveform example of the average input current Iin according to the present embodiment is shown in the lower part of FIG.

Although one embodiment of the present invention has been described above, specific examples of the LED lighting device according to the present invention include an LED bulb, a ceiling light, and a straight tube light.

DESCRIPTION OF SYMBOLS 1 AC power supply 2 Phase control type dimmer 10 Switching power supply circuit 15 LED array 101 Full wave rectifier circuit 102 Voltage divider circuit 103 Phase angle detection circuit 104 Current drawing circuit 105 Oscillation circuit 106 RS flip-flop 107 Gate driver 108 Voltage comparison circuit 109 Switching element 110 Primary current detection circuit 111 Primary average current detection circuit 112 Primary control reference voltage generation circuit 113 Control reference voltage output circuit 114 Secondary current on-duty ratio detection circuit 115 First multiplication circuit 116 Error amplifier 117 Reference voltage source 118 Second multiplying circuit 119 Transformer 119A Primary winding 119B Secondary winding 119C Auxiliary winding 120 Rectifier smoothing circuit 131 Primary peak current control circuit 132 Reference voltage generating circuit L1 Power supply Supply line R11 resistor 201 Input current control circuit 301 current sink and the input current control circuit

Claims

A rectifier circuit connectable to an AC power supply via a phase control dimmer;
A transformer having a primary winding to which a voltage is supplied from the rectifier circuit and a secondary winding;
A rectifying / smoothing circuit connected between the secondary winding and a load;
A switching device connected to the primary winding, and a flyback switching power supply circuit comprising:
A voltage dividing circuit for dividing the output voltage of the rectifier circuit;
A reference voltage generating circuit that generates a reference voltage based on the output voltage of the rectifier circuit divided by the voltage dividing circuit;
A primary peak current control circuit that controls the peak value of the primary current by switching the switching element so as to coincide with the current value corresponding to the reference voltage generated by the reference voltage generation circuit;
A switching power supply circuit comprising:
The reference voltage generation circuit includes:
A control reference voltage output circuit that outputs a control reference voltage corresponding to the output voltage of the rectifier circuit divided by the voltage divider circuit;
A primary average current detection circuit for detecting an average of primary currents;
A primary control reference voltage generation circuit that generates a primary control reference voltage by comparing the output of the control reference voltage output circuit with the detection output of the primary average current detection circuit;
A secondary current on-duty ratio detection circuit for detecting an on-duty ratio of the secondary current;
A first multiplication circuit that multiplies the output of the primary control reference voltage generation circuit by the output of the secondary current on-duty ratio detection circuit;
A reference voltage source;
An error amplifier for amplifying an error between a multiplication result of the first multiplication circuit and a reference voltage by the reference voltage source;
A second multiplier circuit that multiplies the output voltage of the rectifier circuit divided by the voltage divider circuit by the output of the error amplifier and outputs a multiplication result as the reference voltage;
The switching power supply circuit according to claim 1, further comprising:
A phase angle detection circuit for detecting a phase angle of a rise of the output voltage of the rectifier circuit;
A power supply for supplying voltage from the rectifier circuit to the primary winding at the moment when the phase control dimmer is turned on with an amount of current corresponding to the phase angle detected by the phase angle detection circuit. The switching power supply circuit according to claim 1, further comprising: a current drawing circuit that draws a current from the supply line.
4. An input current control circuit for controlling an input current by drawing a current from a power supply line for supplying a voltage from the rectifier circuit to the primary winding. The switching power supply circuit according to any one of the above.
A phase angle detection circuit for detecting a phase angle of a rise of the output voltage of the rectifier circuit;
A power supply for supplying a voltage from the rectifier circuit to the primary winding at the moment when the phase control dimmer is turned on with an amount of current corresponding to the phase angle detected by the phase angle detection circuit. A current drawing control for drawing current from a supply line, and a current drawing and input current control circuit for controlling an input current by drawing current from the power supply line, and
The current drawing / input current control circuit shares a circuit for drawing a current for controlling the current drawing and for controlling the input current, according to any one of claims 1 to 4. Switching power supply circuit.
The switching power supply circuit according to any one of claims 1 to 5, wherein the average input current is controlled to increase from a phase angle of an output voltage of the rectifier circuit of 90 ° or more.
The switching frequency of the switching element is variable according to the output voltage of the rectifier circuit,
The switching power supply circuit according to claim 2, wherein a sampling time for averaging of the primary average current detection circuit is variable in accordance with the switching frequency.
8. An LED illumination device comprising: the switching power supply circuit according to claim 1; and an LED load connected to an output side of the switching power supply circuit.