JP2012195999A - Power circuit and lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power circuit and a lighting device that suppress ripples without using a high capacity capacitor.SOLUTION: A power circuit 100 for converting an AC input to output a DC voltage includes: a rectification circuit 110 for rectifying the AC input to generate a pulsating voltage; a control circuit 130 for improving the power factor of the AC input by switching control; and a voltage dividing circuit 120 for generating a trapezoidal voltage cut at a predetermined voltage or higher from the pulsating voltage. The control circuit 130 switching-controls the pulsating voltage in accordance with the magnitude of the trapezoidal voltage.

Description

  The present invention relates to a power supply circuit and a lighting device.

  In order to supply power from a household power supply to a DC driving load such as an LED, it is necessary to convert an AC voltage into a DC voltage. Patent Document 1 discloses a discharge lamp lighting device that converts a commercial AC power source into a DC voltage and supplies the converted voltage to a discharge lamp.

International Publication No. 2001/060129

  When an AC voltage is converted to a DC voltage, voltage fluctuations called ripple remain due to its characteristics. If you want to suppress ripple and obtain a smoother DC voltage, it is necessary to use a capacitor with a larger capacity, that is, a capacitor with a larger volume, but a capacitor with a larger volume is an adverse effect of circuit miniaturization. .

  The present invention has been made in view of such a problem, and an object thereof is to provide a power supply circuit and an illumination device that can suppress ripples without using a large-capacitance capacitor.

In order to achieve the above object, a power supply circuit according to a first aspect of the present invention includes:
A power supply circuit that converts an AC input into a DC voltage and outputs it,
A rectifier circuit that rectifies an AC input to generate a pulsating voltage;
A power factor improving circuit which has a control means and improves the power factor of the AC input by switching control of the control means;
A trapezoidal voltage generation circuit that generates a trapezoidal voltage in which a predetermined voltage or more is cut based on the pulsating voltage; and
The control means performs switching control of the pulsating voltage based on the magnitude of the trapezoidal voltage;
It is characterized by that.

In order to achieve the above object, a lighting device according to a second aspect of the present invention includes:
A power supply circuit according to a first aspect;
An illumination light source to which power is supplied by the power supply circuit,
It is characterized by that.

  A power supply circuit and a lighting device that can suppress ripples without using a large-capacitance capacitor can be provided.

It is a block diagram for demonstrating the power supply circuit concerning embodiment of this invention. It is a figure for demonstrating the internal structure of the control circuit shown in FIG. It is a wave form chart for explaining operation of the power supply circuit of this embodiment, (a) is a waveform of a power supply voltage outputted from an alternating current power supply, (b) is a rectified voltage generated by a rectifier circuit, and a voltage dividing circuit FIG. 5C is a diagram illustrating a waveform of a trapezoidal voltage generated, FIG. 5C is a diagram illustrating a waveform of a multiplication voltage and a sawtooth voltage generated in the control circuit, and FIG. . It is a figure which shows a mode that the power factor was improved by the power supply circuit of this embodiment, (a) is a waveform of the power supply voltage output from AC power supply, (b) is the current which flows through the coil | winding L1, and output from AC power supply. It is a figure which shows the average of the power supply currents each performed. It is a figure which shows the voltage dividing circuit comprised by removing a Zener diode from the voltage dividing circuit of the control circuit shown in FIG. FIG. 6 is a waveform diagram for explaining the operation of a power supply circuit configured using the voltage dividing circuit shown in FIG. 5, where (a) is a waveform of a power supply voltage output from an AC power supply, and (b) is a rectifier circuit. Waveform of trapezoidal voltage generated by the rectified voltage and voltage dividing circuit generated, (c) is a waveform of the multiplication voltage and sawtooth voltage generated in the control circuit, and (d) is generated by the rectifying and smoothing circuit. It is a figure which shows the waveform of LED voltage, respectively.

  Hereinafter, the power supply circuit of the present embodiment will be described with reference to the drawings. The power supply circuit 100 is a one-stone flyback converter having a power factor improvement function and a current control function. As shown in FIG. 1, a rectifier circuit 110, a voltage dividing circuit 120, a switching element Q1, , Control circuit 130, transformer T1, rectifying and smoothing circuit 140, LED 150, and feedback circuit 160.

  The rectifier circuit 110 is a diode bridge circuit in which four diodes (diodes D1 to D4) are arranged in a bridge shape between the positive electrode terminal and the negative electrode terminal of the AC power supply 200. The rectifier circuit 110 performs full-wave rectification on the AC voltage VAC supplied from the AC power supply 200 to generate a pulsating voltage V1 as shown in FIG.

  The voltage dividing circuit 120 is a circuit that generates a trapezoidal voltage V2 to be input to the FB1 terminal of the control circuit 130, and includes voltage dividing resistors R1 and R2 and a Zener diode D5.

  The voltage dividing resistors R1 and R2 are resistors for dividing the pulsating voltage V1, one end of the voltage dividing resistors R1 and R2 connected in series is the cathode of the diodes D1 and D3, and the other end is the diodes D2 and D4. Are respectively connected to the anodes.

  The Zener diode D5 is a constant voltage diode having a Zener voltage Vz. The Zener diode D5 has an anode connected to the anodes of the diodes D2 and D4 and a cathode connected to one end of the voltage dividing resistors R1 and R2. The upper limit of the divided voltage divided by the voltage dividing resistors R1 and R2 is cut by the Zener diode D5, and is output to the control circuit 130 as a trapezoidal voltage V2 as shown in FIG.

  The switching element Q1 is an N-channel MOSFET (Metal Oxide Field Effect Transistor) for controlling the current flowing in the winding L1 of the transformer T1, the drain terminal is one end of the winding L1, and the source terminal is a resistor R3. The gate terminal is connected to the DRV terminal of the control circuit 130, respectively. When a voltage is applied from the DRV end to the gate terminal, the switching element Q1 connects the drain and the source and causes a current to flow through the winding L1. Further, when the application of the voltage to the gate terminal is stopped, the switching element Q1 cuts off the current flowing through the winding L1 by cutting between the drain and the source.

  The control circuit 130 performs switching control including a power factor control function that improves the power factor of the power supply circuit 100 by choppering the pulsating voltage V1 in a sawtooth shape, and a current control function that keeps the current flowing through the LED 150 constant. Circuit. The control circuit 130 is, for example, an analog processor having a function of processing a signal, and includes an FB1 terminal, an FB2 terminal, an FB3 terminal, a DRV terminal, and a REF terminal as input / output terminals. The FB1 terminal is one end of the voltage dividing resistors R1 and R2 of the voltage dividing circuit 120, the FB2 terminal is one end of the switching element Q1 and the resistor R3, the FB3 terminal is one end of the resistor R5 of the feedback circuit 160, and the FB4 terminal is the one of the transformer T1. The DRV terminal is connected to one end of the winding L3, the gate terminal of the switching element Q1, and the REF terminal is connected to the photocoupler 162 of the feedback circuit 160.

  Further, as shown in FIG. 2, the control circuit 130 includes a multiplier 131, a comparator 132, a flip-flop 133, a driver 134, a reference power supply 135, a voltage divider 136, an error amplifier 137, and a zero current. A detector 138 is provided inside.

  The multiplier 131 is an analog multiplier that multiplies and outputs voltages input from two input terminals. One input terminal of the multiplier 131 is the FB1 terminal of the control circuit 130, and the other input terminal is an error amplifier. The output terminal 137 is connected to one input terminal of the comparator 132.

  The comparator 132 is an element that compares the magnitudes of voltages input from two input terminals and outputs a voltage corresponding to a logic level “0” or “1” according to the comparison result. The output terminal of the multiplier 131, the other input terminal is connected to the FB2 terminal, and the output terminal is connected to the reset terminal of the flip-flop 133. When the FB2 terminal voltage V5 exceeds the output voltage V4 of the multiplier 131, the comparator 132 outputs a logic level “1” voltage.

  The flip-flop 133 is an RS flip-flop, the reset terminal is connected to the output terminal of the comparator 132, the set terminal is connected to the output of the zero current detector 138, and the output terminal is connected to the input terminal of the driver 134. ing.

  The driver 134 is an element for driving the switching element Q1, and the input terminal is connected to the output terminal of the flip-flop 133, and the output terminal is connected to the DRV terminal. When the driver 134 receives a predetermined voltage from the flip-flop 133, the driver 134 applies a voltage to the DRV terminal.

  The reference power supply 135 is a power supply for generating a reference voltage for detecting whether or not the current flowing through the LED 150 is constant. Two output terminals of the reference power source 135 are connected to the voltage divider 136 and the REF terminal, respectively. The voltage output from the REF terminal is converted by the photocoupler 162 to a voltage level proportional to the magnitude of the current flowing through the LED 150 and fed back to the FB3 terminal.

  The voltage divider 136 is a circuit for stepping down the reference voltage output from the reference power supply 135 to a predetermined level so that the error amplifier 137 can detect an error. The voltage divider 136 appropriately reduces the reference voltage based on the resistance value of the resistor R5 (FIG. 1).

  The error amplifier 137 is an element for amplifying and outputting an error of a voltage input from two input terminals. One input terminal of the error amplifier 137 is an output terminal of the voltage divider 136 from the voltage divider 136. The other input terminal is connected to the FB3 terminal, and the output terminal is connected to one input terminal of the multiplier 131.

  The zero current detector 138 is a circuit for detecting whether or not current is flowing through the FB4 terminal (that is, whether or not current is flowing through the transformer T1). The input terminal is connected to the FB4 terminal and the output is a flip-flop. 133 set terminals are connected to each other. When the zero current detector 138 detects that no current flows through the FB4 terminal, the zero current detector 138 outputs a predetermined voltage to the set terminal of the flip-flop 133.

  The transformer T1 is a transformer for transforming and transmitting a voltage from a primary circuit to a secondary circuit, and includes an iron core and three windings (windings L1, L2, and L3). The windings L1 and L2 are connected to the primary circuit and the secondary circuit, respectively, and when the current flowing through the winding L1 varies due to on / off of the switching element Q1, the winding L2 is generated by the action of mutual inductance. The back electromotive force is transmitted to the secondary circuit. The winding L3 is connected to the FB4 terminal of the control circuit 130, and detects whether or not a magnetic field is generated in the iron core, that is, whether or not a current flows through the windings L1 and L2. Is transmitted to the circuit 130.

  The rectifying / smoothing circuit 140 is a circuit for rectifying and smoothing the back electromotive voltage generated in the winding L2, and includes a diode D6 and an electrolytic capacitor C1. One end of the diode D6 is connected to one terminal of the winding L2, the other end is connected to one end of the LED 150, one end of the electrolytic capacitor C1 is connected to the other terminal of the winding L2, and the other end is connected to one end of the LED 150. It is connected. The voltage transmitted to the secondary circuit by the transformer T1 is rectified and smoothed by the diode D6 and the electrolytic capacitor C1, and is supplied to the LED 150 as the DC voltage VLED.

  The LED 150 is a portion that becomes a light source of the power supply circuit 100, and includes a plurality of light emitting diodes. The anode of LED 150 is connected to one end of diode D6 and electrolytic capacitor C1 of rectifying and smoothing circuit 140, and the other end is connected to one end of current detection resistor R4.

  The feedback circuit 160 is a circuit for feeding back the current ILED flowing through the LED 150 to the control circuit 130. As shown in FIG. 1, the current detection resistor R4, the VI conversion circuit 161, the photocoupler 162, and the resistor And R5. The VI conversion circuit 161 is a circuit that outputs a current proportional to the magnitude of the voltage, and two input terminals are respectively connected to both ends of the current detection resistor R4. The voltage applied to both ends of the current detection resistor R4 is measured by the VI conversion circuit 161 and fed back to the FB3 terminal of the control circuit 130 via the photocoupler 162 and the resistor R5.

  The configuration of the power supply circuit 100 has been described above. Next, the operation of the power supply circuit 100 will be described.

  When the AC power source 200 is turned on, the AC power source 200 supplies the AC voltage VAC (FIG. 3A) to the rectifier circuit 110. The rectifier circuit generates a pulsating voltage V1 as shown in FIG. 3B by full-wave rectifying the AC voltage VAC.

  The voltage dividing circuit 120 divides the pulsating voltage V1 by the voltage dividing resistors R1 and R2, and further cuts the upper limit of the voltage by the Zener diode D5. Thereby, the voltage dividing circuit 120 generates the trapezoidal voltage V2 as shown in FIG. 3B in which the zener voltage Vz or higher is cut off. The generated trapezoidal voltage V2 is input to the FB1 terminal of the control circuit 130.

  The multiplier 131 multiplies the input trapezoidal voltage V2 by the output V7 of the error amplifier 137, converts it into a multiplied voltage V4 as shown in FIG. 3C, and outputs it to the comparator 132. At this point, the switching element Q1 is turned off. Therefore, since the GND voltage is applied from the FB4 terminal to the other input terminal of the comparator 132, the comparator 132 outputs a voltage (GND voltage) having a logic level “0” to the reset terminal of the flip-flop 133. At this time, since no current flows through the transformer T1, a voltage corresponding to the logic level “1” is applied to the set terminal of the flip-flop 133 by the zero current detector 138. Then, since the voltage corresponding to the logic level “1” is applied to the driver 134 by the flip-flop 133, the driver 134 applies a predetermined voltage to the DRV terminal and turns on the switching element Q1.

  When the switching element Q1 is turned on, a current that increases with time flows through the winding L1 of the transformer T1. The voltage V5 between the source of the switching element Q1 and the resistor R3 is converted into a sawtooth voltage V5 as shown in FIG. 3C by the current flowing through the winding L1, and is compared via the FB2 terminal. 132 is input.

  The comparator 132 outputs a voltage corresponding to the logic level “1” to the reset terminal of the flip-flop 133 when the sawtooth voltage V5 reaches the multiplication voltage V4. Then, the flip-flop 133 is reset, and a voltage of logic level “0” (GND voltage) is applied to the driver 134. Then, the driver 134 turns off the switching element Q1 via the DRV terminal.

  When the switching element Q1 is turned off, the current flowing through the winding L1 rapidly decreases. Then, a counter electromotive voltage is generated in the winding L2 by the action of the mutual inductance. The generated back electromotive voltage is converted into the LED voltage VLED as shown in FIG. 3D by the rectifying and smoothing circuit 140 and supplied to the LED 150.

  The current flowing through the winding L2 decreases with time, and when the current becomes zero, it is detected by the zero current detector 138 in the control circuit 130. The zero current detector 138 applies a voltage of logic level “1” to the set terminal of the flip-flop 133 when the zero current is detected. Then, a voltage corresponding to the logic level “1” is applied to the driver 134 by the flip-flop 133, and in response to this, the driver 134 turns on the switching element Q1 again via the DRV terminal.

  Since the on / off of the switching element Q1 is repeated at high speed, the current IL1 flowing through the winding L1 has a chopper waveform as shown in FIG. Therefore, the average value of the power supply current IAC has a substantially sinusoidal waveform (the broken line portion in FIG. 4B), and as a result, the phase of the power supply voltage VAC and the phase of the power supply current IAC match. Thereby, the power factor of the power supply circuit 100 is improved.

  The average value of the current flowing through the LED 150 is detected by the VI conversion circuit 161 and fed back to the FB3 terminal of the control circuit 130 via the photocoupler 162. The feedback voltage V3 is compared with the reference voltage V6 by the error amplifier 137 in the control circuit 130, and the error is amplified. The multiplier 131 multiplies the amplified voltage V7 and the trapezoidal voltage V2 and inputs the multiplication result to the comparator 132. The comparator 132 outputs the voltage corresponding to the logic level “1” or “0” to the reset terminal of the flip-flop 133 as described above while comparing the multiplication voltage V4 and the sawtooth voltage V5. The driver 134 performs switching control of the switching element Q1 based on the output from the flip-flop 133. Thus, the LED current ILED is reflected in the switching control of the control circuit 130, and the LED current ILED is maintained at a constant value.

  Note that the control circuit 130 compares the sawtooth voltage V5 and the trapezoidal multiplication voltage V4 to control the switching element Q1. Therefore, the length of the ON period Ton of the switching element Q1 is suppressed in the upper side (flat) portion of the trapezoid as shown in FIG. As a result, the amplitude of the back electromotive voltage generated in the winding L2 is also suppressed, and the LED voltage VLED has a waveform in which the ripple Vrp is suppressed as shown in FIG.

  On the other hand, when the voltage dividing circuit 120 is configured as shown in FIG. 5 without using the Zener diode D5, the divided voltage V2 has a mountain-like waveform as shown in FIG. 6B. . Therefore, the multiplication voltage V4 also has a mountain-like waveform as shown in FIG. 6C, and the length of the ON period Ton of the switching element Q1 is near the top of the multiplication voltage V4 as shown in FIG. 6C. In this case, it becomes longer than that of the present embodiment. As a result, the back electromotive voltage generated by the winding L2 has a large amplitude, and the LED voltage VLED also has a large ripple Vrp as shown in FIG.

  According to the present embodiment, since the amplitude of the back electromotive voltage transmitted to the secondary circuit can be suppressed by inserting the Zener diode D5 into the voltage dividing circuit 120, a large capacity capacitor can be used. The ripple of the LED voltage VLED can be suppressed. As a result, the capacity of the electrolytic capacitor C1 can be reduced, and the circuit can be easily downsized.

  Note that the LED 150 is not limited to a light emitting diode composed of an inorganic crystal. It may be an organic EL composed of organic molecules, or another light source such as a light bulb or a fluorescent lamp. The load connected to the power supply circuit 100 is not limited to a light source such as an LED, but may be a device or a semiconductor for obtaining heat, sound, or the like.

  In this embodiment, the “current” flowing through the LED 150 is fed back to the control circuit 130, but the “voltage” applied to the load instead of the current is divided by, for example, a voltage divider and fed back to the control circuit 130. May be. As a result, the power supply circuit 100 can be used as a constant voltage drive power supply.

  In the present embodiment, instead of comparing the multiplication voltage V4 and the sawtooth voltage V5, the trapezoidal voltage V2 and the sawtooth voltage V5 may be directly compared. The present invention can also be applied to a power supply circuit that does not require feedback of the current flowing through the LED 150.

  A part or all of the above-described embodiment can be described as in the following supplementary notes, but is not limited thereto.

(Appendix 1) A power supply circuit that converts an AC input into a DC voltage and outputs the DC voltage,
A rectifier circuit that rectifies an AC input to generate a pulsating voltage;
A power factor improving circuit which has a control means and improves the power factor of the AC input by switching control of the control means;
A trapezoidal voltage generation circuit that generates a trapezoidal voltage in which a predetermined voltage or more is cut based on the pulsating voltage; and
The control means performs switching control of the pulsating voltage based on the magnitude of the trapezoidal voltage;
A power supply circuit characterized by that.

(Supplementary Note 2) The control means performs switching control of the pulsating voltage based on a comparison output obtained by comparing the trapezoidal voltage and a sawtooth voltage generated by switching control of the pulsating voltage.
The power supply circuit according to appendix 1, wherein:

(Supplementary Note 3) A feedback circuit that further feeds back the magnitude of the output current of the power supply circuit to the control means as a feedback voltage,
The control means includes the pulsating voltage based on a comparison output obtained by comparing a multiplication voltage obtained by multiplying the trapezoidal voltage and the feedback voltage with a sawtooth voltage generated by switching control of the pulsating voltage. The switching control,
The power supply circuit according to appendix 1, wherein:

(Supplementary Note 4) The trapezoidal voltage generation circuit generates the trapezoidal voltage by suppressing the pulsating voltage or a predetermined voltage or more of the divided pulsating voltage with a Zener diode.
4. The power supply circuit according to any one of appendices 1 to 3, wherein

(Supplementary note 5) The power supply circuit according to any one of supplementary notes 1 to 4,
An illumination light source to which power is supplied by the power supply circuit,
A lighting device characterized by that.

(Appendix 6) The illumination light source is a light emitting diode.
The illumination device according to appendix 5, characterized in that:

DESCRIPTION OF SYMBOLS 100 Power supply circuit 110 Rectifier circuit 120 Voltage divider circuit 130 Control circuit 131 Multiplier 132 Comparator 133 Flip-flop 134 Driver 135 Reference power supply 136 Voltage divider 137 Error amplifier 138 Zero current detector 140 Rectifier smoothing circuit 150 LED
160 Feedback circuit 161 VI converter circuit 162 Photocoupler 200 AC power supply C1 Electrolytic capacitor D1 to D4 Diode D5 Zener diode D6 Diode L1 to L3 Winding Q1 Switching element R1, R2 Voltage dividing resistor R3, R5 resistor R4 Current detection resistor T1 Trance

Claims (6)

A power supply circuit that converts an AC input into a DC voltage and outputs it,
A rectifier circuit that rectifies an AC input to generate a pulsating voltage;
A power factor improving circuit which has a control means and improves the power factor of the AC input by switching control of the control means;
A trapezoidal voltage generation circuit that generates a trapezoidal voltage in which a predetermined voltage or more is cut based on the pulsating voltage; and
The control means performs switching control of the pulsating voltage based on the magnitude of the trapezoidal voltage;
A power supply circuit characterized by that. The control means performs switching control of the pulsating voltage based on a comparison output comparing the trapezoidal voltage and a sawtooth voltage generated by switching control of the pulsating voltage.
The power supply circuit according to claim 1. A feedback circuit that feeds back the magnitude of the output current of the power supply circuit to the control means as a feedback voltage;
The control means is configured to output the pulsating voltage based on a comparison output obtained by comparing a multiplication voltage obtained by multiplying the trapezoidal voltage and the feedback voltage with a sawtooth voltage generated by switching control of the pulsating voltage. The switching control,
The power supply circuit according to claim 1. The trapezoidal voltage generation circuit generates the trapezoidal voltage by suppressing the pulsating voltage or a predetermined voltage or more of the divided pulsating voltage with a Zener diode.
The power supply circuit according to any one of claims 1 to 3. The power supply circuit according to any one of claims 1 to 4,
An illumination light source to which power is supplied by the power supply circuit,
A lighting device characterized by that. The illumination light source is a light emitting diode,
The lighting device according to claim 5.

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