JP6210936B2 - Self-excited resonance type power factor correction circuit and light source driving device - Google Patents

Description

  The present invention relates to a self-excited resonance type power factor correction circuit that improves the power factor of an alternating voltage, and a light source driving device that drives a light source using the self-excited resonance type power factor correction circuit.

  In recent years, LED lighting fixtures using LEDs (Light Emitting Diodes) as light sources instead of conventional incandescent bulbs and fluorescent lamps have begun to spread. This is because the LED has a long life and low power consumption, does not use environmental pollutants such as mercury in fluorescent lamps, and has impact resistance and high-speed response. This LED lighting apparatus includes a plurality of LED light emitting elements, and emits light by applying a predetermined constant current to each LED light emitting element. As described above, the LED lighting apparatus needs an LED driving device that supplies a predetermined current to each LED light emitting element.

  There exists an LED lighting device of patent document 1 as this kind of LED drive device. The subject of the abstract of Patent Literature 1 is described as “providing a light-emitting diode lighting device that is flexible in adaptability to the number of light-emitting diodes connected in series to a load circuit while improving the power factor”. Paragraph 0021 of the specification of Patent Document 1 states, “According to the present invention, a plurality of series circuits composed of a plurality of series circuits are formed at the output terminal by boosting a rectified DC voltage with a boost chopper and further stepping down with a step-down chopper. By connecting light emitting diodes connected in parallel and equalizing the currents that flow through a plurality of series circuits by means of a constant current circuit, a large number of light emitting diodes can emit light uniformly and flexibility in compatibility with the number of light emitting diodes in series is flexible. A light-emitting diode lighting device can be provided. "

JP 2010-40878 A

  The step-up chopper of Patent Document 1 needs to control the DC voltage to be constant and to control the input power factor to be high. Therefore, the control circuit is provided with a dedicated IC (Integrated Circuit), which makes the circuit configuration complicated and expensive.

  Accordingly, the present invention provides a self-excited resonance type power factor correction circuit and a small light source driving device that reduce the reactive power while reducing the size and cost with a simple circuit configuration without providing a dedicated IC. Objective.

In order to solve the above-described problem, a self-excited resonance type power factor correction circuit according to the present invention includes a rectifier circuit that outputs a rectified voltage obtained by full-wave rectification of an AC voltage, a first coil and a second coil that are magnetically coupled. Including a first transformer excited by a current supplied from the rectifier circuit, and a gate-drain capacitance. The first coil is chopper-operated to switch whether or not a current flows to the first diode. A first switching element; a first smoothing capacitor that smoothes a PFC (Power Factor Correction) voltage output from the first diode; and a feedback voltage induced in the second coil as a gate terminal of the first switching element. as well as fed back to, when the current flowing in the first coil is zero, the first scan by outputting a voltage based on the rectified voltage to the gate terminal via the second coil A first feedback circuit for turning on the switching element, is connected between the gate terminal and the ground of the first switching element, the gate of the first switching element - a first zener diode for clamping the source voltage, the first A first current detection resistor connected between the source terminal of one switching element and the ground to detect a current flowing through the first switching element as a voltage value and a first reference voltage obtained by dividing the rectified voltage are generated. And a first switch circuit that sets the voltage of the gate terminal of the first switching element to L level if the voltage value detected by the first current detection resistor exceeds the first reference voltage. And comprising.

The light source driving device of the present invention includes the self-excited resonance type power factor correction circuit and a DC-DC conversion circuit that receives the PFC voltage and supplies a direct current to the light source.
Further, the light source driving device of the present invention includes the self-excited resonance type power factor correction circuit, and the PFC voltage is input to supply a direct current to the light source and is output from the self-excited resonance type power factor improvement circuit. And a DC-DC conversion circuit that controls the direct current supplied to the light source to be constant based on a voltage corresponding to the PFC voltage.
Other means will be described in the embodiment for carrying out the invention.

  According to the present invention, it is possible to provide a self-excited resonance type power factor correction circuit and a small light source driving device that reduce the reactive power while reducing the size and cost with a simple circuit configuration without providing a dedicated IC. it can.

It is a circuit diagram which shows the structure of the self-excited resonance type | mold power factor improvement circuit and light source drive device in 1st Embodiment. It is a wave form diagram showing each part signal of a self-excitation resonance type power factor improvement circuit in a 1st embodiment. It is a graph which shows the relationship between the alternating voltage supplied to a self-excited resonance type power factor improvement circuit, and the PFC voltage which a self-excitation resonance type power factor improvement circuit outputs. It is a circuit diagram which shows the structure of the self-excited resonance type | mold power factor improvement circuit and light source drive device in 2nd Embodiment. It is a graph which shows the power factor of the self-excitation resonance type power factor improvement circuit in 2nd Embodiment.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 is a circuit diagram showing a configuration of a self-excited resonance type power factor correction circuit and a light source driving device in the first embodiment.
A light source driving apparatus 100 shown in FIG. 1 performs lighting control of the light source 10 and includes a self-excited resonance type power factor correction circuit 1 and a DC-DC conversion circuit 2. The self-excited resonance type power factor correction circuit 1 converts the AC voltage Vac applied from the commercial power source Ps to generate a PFC (Power Factor Correction) voltage Vpfc. The DC-DC conversion circuit 2 receives the PFC voltage Vpfc and supplies a direct current to the light source 10. The light source 10 is, for example, an LED. However, the light source 10 may be another type of light source.

The self-excited resonance type power factor correction circuit 1 is a so-called step-up chopper, and includes a rectifier circuit BD1, a capacitor C1, a transformer T1, a feedback circuit 3, a reference voltage generation circuit 4, a switch circuit 5, and a switching element. Q1, Q2, a Zener diode ZD1, a current detection resistor Ra1, a diode D1, a PFC voltage detection circuit 6, and a smoothing capacitor Ca1.
The rectifier circuit BD1 is a diode bridge. A commercial power supply Ps is connected to the input side of the rectifier circuit BD1, and an AC voltage Vac is applied. The rectifier circuit BD1 outputs a rectified voltage obtained by full-wave rectifying the AC voltage Vac. The capacitor C1 is connected between the positive terminal and the negative terminal of the rectifier circuit BD1. The capacitor C1 functions as a filter that removes high-frequency component noise due to switching.

The transformer T1 (first transformer) is configured by magnetically coupling a primary side coil L1 (first coil) and a secondary side coil L2 (second coil). The first end of the coil L1 is connected to the positive terminal of the rectifier circuit BD1. The second end of the coil L1 is connected to the anode of the diode D1 and the drain of the switching element Q1. The coil L1 is excited by a current supplied from the rectifier circuit BD1.
The feedback circuit 3 (first feedback circuit) includes a coil L2, a resistor R1, and a capacitor C3. The feedback circuit 3 feeds back the voltage induced in the coil L2 to the gate (control terminal) of the switching element Q1. Further, when the current flowing through the coil L1 becomes zero, the feedback circuit 3 applies a voltage based on the rectified current to the gate (control terminal) of the switching element Q1 via the coil L2, and turns on the switching element Q1.
The first end of the coil L2 is connected to the positive terminal of the rectifier circuit BD1 via the resistor R1. The second end of the coil L2 is connected to the gate of the switching element Q1. The capacitor C3 is connected between a connection node between the resistor R1 and the coil L2 and the ground. The feedback circuit 3 feeds back the voltage induced in the coil L2 to the gate of the switching element Q1.
The switching element Q1 (first switching element) is an N-type FET (Field Effect Transistor), the drain is connected to the second end of the coil L1, and the source is connected to the ground via the current detection resistor Ra1. The switching element Q1 is turned on when the gate voltage Vgs exceeds the threshold voltage Vzcd. The switching element Q1 switches the coil L1 to perform a chopper operation to switch whether or not a current flows to the diode D1 (first diode).
The current detection resistor Ra1 (first current detection resistor) detects the current flowing through the switching element Q1 as the detection voltage Va1. The detection voltage Va1 is applied to the inverting input terminal of the comparator U1.

A Zener diode ZD1 is connected between the gate of the switching element Q1 and the ground. The Zener diode ZD1 clamps the voltage so that the gate voltage Vgs does not exceed the rated gate voltage Vgss. When the gate voltage Vgs is a low voltage that does not exceed the rated gate voltage Vgss, the Zener diode ZD1 is not necessary. Further, the emitter of the PNP transistor Q3 is connected to the gate of the switching element Q1.
The smoothing capacitor Ca1 (first smoothing capacitor) smoothes the PFC voltage Vpfc output from the diode D1.

  The reference voltage generation circuit 4 is a voltage dividing circuit in which resistors R2 and R3 are connected in series. The reference voltage generation circuit 4 is connected between the positive terminal of the rectifier circuit BD1 and the ground. The reference voltage generation circuit 4 divides the rectified voltage to generate a reference voltage Vb1 (first reference voltage). This reference voltage Vb1 is applied to the non-inverting input terminal of the comparator U1.

The switch circuit 5 (first switch circuit) includes a comparator U1 and a PNP transistor Q3. The non-inverting input terminal of the comparator U1 is connected to the connection node of the resistors R2 and R3, and the reference voltage Vb1 is applied. The inverting input terminal of the comparator U1 is connected to the source of the switching element Q1, and the detection voltage Va1 is applied thereto. The switch circuit 5 turns off the switching element Q1 when the detection voltage Va1 detected by the current detection resistor Ra1 exceeds the reference voltage Vb1.
A PNP transistor Q3 is connected to the output terminal of the comparator U1. By turning on the PNP transistor Q3, the voltage of the gate of the switching element Q1 can be quickly set to L level to turn off the switching element Q1.

The PFC voltage detection circuit 6 and the switching element Q2 function as a limiting circuit for the PFC voltage Vpfc.
The PFC voltage detection circuit 6 is a voltage dividing circuit in which resistors R5, R6, and R7 are connected in series between the cathode of the diode D1 and the ground. The PFC voltage detection circuit 6 divides the PFC voltage Vpfc by resistors R5, R6, and R7. The PFC voltage detection circuit 6 detects the detection voltage Va2 from the connection node of the resistors R6 and R7. The detection voltage Va2 is obtained by dividing the PFC voltage Vpfc by the ratio of the resistor R7 to the sum of the resistors R5, R6, and R7. This detection voltage Va2 is output to the base of the switching element Q2.
The PFC voltage detection circuit 6 detects the detection voltage Va3 from the connection node of the resistors R5 and R6. The detection voltage Va3 is obtained by dividing the PFC voltage Vpfc by the ratio of the sum of the resistors R6 and R7 to the sum of the resistors R5, R6, and R7. The detection voltage Va3 is output to the DC-DC conversion circuit 2.

  Switching element Q2 (second switching element) has an emitter grounded, a collector connected to the output terminal of comparator U1, and a base connected to a connection node of resistors R6 and R7. A detection voltage Va2 is applied to the base of the switching element Q2, and turns on when the detection voltage Va2 exceeds the threshold voltage Vbe. Since the detection voltage Va2 is proportional to the PFC voltage Vpfc, the switching element Q2 is turned on when the PFC voltage Vpfc exceeds a predetermined value. Thereby, the PNP transistor Q3 is turned on, the gate voltage Vgs of the switching element Q1 becomes L level regardless of the feedback voltage induced in the coil L2, and the self-excited resonance operation is stopped. Accordingly, the switching element Q2 can limit the PFC voltage Vpfc so as not to exceed a predetermined value (threshold value).

  Thus, the self-excited resonance type power factor correction circuit 1 of the first embodiment uses a passive element and an active element for the step-up chopper operation and the power factor correction operation without using an expensive dedicated IC. It is realized at low cost with a small and simple circuit configuration.

The DC-DC conversion circuit 2 supplies a constant current-controlled direct current to the light source 10 when a PFC voltage Vpfc in a predetermined range (160 V to 250 V) is applied. The DC-DC conversion circuit 2 only needs to supply a direct current to the light source 10, and may be a step-down chopper, a step-up / step-down chopper, a flyback converter, or the like.
Although the DC-DC conversion circuit 2 performs constant current control, when the input PFC voltage Vpfc fluctuates greatly, there is a tendency that the line regulation, which is the rate of fluctuation of the output current with respect to this, deteriorates. In order to improve this line regulation, the DC-DC conversion circuit 2 corrects the output current according to the input PFC voltage Vpfc. The DC-DC conversion circuit 2 feeds back the detection voltage Va3 output from the self-excited resonance type power factor correction circuit 1 and corrects and controls the output current. This detection voltage Va3 is detected by the PFC voltage detection circuit 6.
As described above, the DC-DC conversion circuit 2 has a constant DC current supplied to the light source 10 based on the detection voltage Va3 output from the self-excited resonance power factor correction circuit 1 and corresponding to the PFC voltage Vpfc. Correction control is performed so that Thereby, the light source 10 can be lighted stably and the lifetime reduction of the light source 10 can be prevented.

FIGS. 2A to 2C are waveform diagrams showing signals of the respective parts of the self-excited resonance type power factor correction circuit 1 in a half cycle of the AC power supply. The basic operation of the self-excited resonance type power factor correction circuit 1 will be described with reference to FIG.
FIG. 2A is a waveform diagram showing the gate voltage Vgs of the switching element Q1 (see FIG. 1) and the like. The solid line shows the waveform of the gate voltage Vgs. The broken line indicates the level of the threshold voltage Vzcd of the switching element Q1. Here, the gate voltage Vgs is a voltage between the gate and the source.
From time t0 to time t1, the gate voltage Vgs exceeds the threshold voltage Vzcd.
From time t1 to time t2, the gate voltage Vgs decreases to 0 V and then increases in a ramp shape.
Thereafter, until the time tn, the gate voltage Vgs has a waveform that periodically exceeds the threshold voltage Vzcd.

FIG. 2B is a waveform diagram showing the current IL1 flowing through the coil L1. The solid line indicates the current IL1 itself. The broken line indicates the average current IL1avg.
From time t0 to time t1, the current IL1 increases in a ramp shape.
From time t1 to time t2, the current IL1 decreases in a ramp shape.
Thereafter, the current IL1 has a waveform that increases in a ramp shape when the gate voltage Vgs exceeds the threshold voltage Vzcd, and decreases in a ramp shape at other times. The envelope of the current IL1 has a waveform similar to that of the reference voltage Vb1 (see FIG. 2C).
The average current IL1avg is a waveform obtained by filtering the current IL1 with the capacitor C1. The average current IL1avg has a waveform similar to that of the reference voltage Vb1 (see FIG. 2C).

A solid line in FIG. 2C indicates the detection voltage Va1. The broken line indicates the reference voltage Vb1.
From time t0 to time t1, the detection voltage Va1 increases in a ramp shape.
From time t1 to time t2, the detection voltage Va1 is 0V.
Thereafter, the detection voltage Va1 increases in a ramp shape when the gate voltage Vgs exceeds the threshold voltage Vzcd, and has a waveform of 0 V otherwise.
The reference voltage Vb1 is obtained by dividing the rectified voltage and is proportional to the rectified voltage. The reference voltage Vb1 is substantially equal to the envelope of the detection voltage Va1.

Hereinafter, the waveform will be described together with the operation of each part.
At time t0, the rectified voltage of the rectifier circuit BD1 is applied to the gate of the switching element Q1 via the resistor R1 and the coil L2, and the gate voltage Vgs exceeds the threshold voltage Vzcd. Therefore, the switching element Q1 is turned on.
As a result, the current IL1 flows from the positive terminal of the rectifier circuit BD1 to the ground via the path of the coil L1, the switching element Q1, and the current detection resistor Ra1. The negative terminal of the rectifier circuit BD1 is grounded to the ground.
Since the coil L1 and the coil L2 are magnetically coupled, an excitation voltage is generated in the coil L2 by the current IL1 flowing through the coil L1. That is, a positive voltage is fed back to the gate of the switching element Q1. The gate voltage Vgs continuously exceeds the threshold voltage Vzcd. Switching element Q1 continues to be on.
The current IL1 flowing through the coil L1 flows through the switching element Q1 and gradually increases in a ramp shape. As a result, the detection voltage Va1 increases in proportion to the current IL1. Thus, electromagnetic energy is accumulated in the coil L1 during the ON period of the switching element Q1.

When the detection voltage Va1 exceeds the reference voltage Vb1 at time t1, the switch circuit 5 turns off the switching element Q1. When the switching element Q1 is turned off, the current IL1 flows through the path of the coil L1, the diode D1, and the smoothing capacitor Ca1 due to the induced voltage of the coil L1, and gradually decreases in a ramp shape. As a result, the electromagnetic energy of the coil L1 is released, the smoothing capacitor Ca1 is charged, and the PFC voltage Vpfc is output.
From time t1 to time t2, a negative excitation voltage is generated in the coil L2 by the current IL1 flowing through the coil L1. That is, the negative voltage is fed back to the gate of the switching element Q1. The gate voltage Vgs of the switching element Q1 is obtained by superimposing a negative voltage on the rectified voltage. Therefore, from time t1 to time t2, the gate voltage Vgs has a ramp waveform that rises from 0 V toward the threshold voltage Vzcd. The threshold voltage Vzcd is a threshold voltage between the gate and the source for turning on the switching element Q1. At this time, the switching element Q1 continues in the off state.
When the current IL1 flowing through the coil L1 becomes zero at time t2, the excitation voltage of the coil L2 also becomes zero. The rectified voltage of the rectifier circuit BD1 is again applied to the gate of the switching element Q1 through the resistor R1 and the coil L2, and the gate voltage Vgs again exceeds the threshold voltage Vzcd. Therefore, the switching element Q1 is turned on again. In this way, the switching element Q1 operates the coil L1 as a chopper.
Hereinafter, the self-excited resonance type power factor correction circuit 1 repeats the self-excited resonance oscillation operation similar to the times t0 to t2.

By repeating the self-resonant oscillation operation as described above, the current IL1 flowing through the coil L1 becomes a continuous triangular wave whose peak value is controlled in a sine wave shape. When the continuous triangular wave current IL1 is filtered by the capacitor C1, an average current IL1avg corresponding to 1/2 of the envelope of the peak value of the current IL1 is obtained. Therefore, since the voltage waveform of the AC voltage Vac and the input current waveform of the rectifier circuit BD1 are substantially similar, a high power factor can be obtained.
Further, the switching element Q1 is turned on by detecting that the current IL1 flowing through the coil L1 has become zero. Thereby, switching loss is eliminated and high efficiency can be obtained.
Furthermore, since the self-excited resonance oscillation operation is realized by turning the FET on and off, the generation of switching noise can be reduced.
The switching element Q1 is an FET and has a gate-drain capacitance Cgd. The switching time for turning on and turning off the switching element Q1 is determined by the gate-drain capacitance Cgd and the reactance of the coil L2.

The switching-on switching time of the switching element Q1 is a transition time until the drain voltage is switched from the H level to the L level. The switching time for turning off the switching element Q1 is a transition time until the drain voltage is switched from the L level to the H level.
In the switching element Q1, the charge current started by the voltage applied to the gate is turned on in the time for charging the gate-drain capacitance Cdg (charging time), and the drain voltage is switched from the H level to the L level. This charging time is determined by the gate-drain capacitance Cgd and the reactance of the coil L2.
The switching element Q1 is turned off by the time (discharge time) for discharging the gate-drain capacitance Cgd, and the drain voltage is switched from the L level to the H level. This discharge time is also determined by the gate-drain capacitance Cgd and the reactance of the coil L2.
In the self-excited resonance oscillation operation, the switching element Q1 is gently turned on / off according to the discharge time / discharge time of the gate-drain capacitance Cgd, and no overshoot or undershoot occurs in the drain voltage. That is, the generation of switching noise can be suppressed.

FIG. 3 is a graph showing a specific example of the relationship between the PFC voltage Vpfc and the AC voltage Vac. The horizontal axis of the graph indicates the AC voltage Vac input to the self-excited resonance type power factor correction circuit. The vertical axis of the graph represents the PFC voltage Vpfc output from the self-excited resonance type power factor correction circuit.
A voltage K1 indicated by a broken line indicates a change in the PFC voltage Vpfc of the comparative example in which the PFC voltage detection circuit 6 and the switching element Q2 are removed from the self-excited resonance type power factor correction circuit 1. At this time, the voltage K1 increases linearly with respect to the AC voltage Vac.
The current IL1 flowing through the coil L1 is controlled by comparing the reference voltage Vb1 with the detection voltage Va2. That is, the PFC voltage Vpfc is determined by the AC voltage Vac and the current detection resistor Ra1. In the comparative example shown by the broken line in FIG. 3, when the AC voltage Vac is 90V to 120V, the current detection resistor Ra1 is set so that the PFC voltage Vpfc is 160V to 250V.
Since the PFC voltage Vpfc increases in proportion to the AC voltage Vac, a circuit for limiting the PFC voltage Vpfc is provided in consideration of the possibility that the AC voltage Vac may be larger than expected for some reason for safety. Is desirable. The self-excited resonance power factor correction circuit 1 of the first embodiment limits the PFC voltage Vpfc by the PFC voltage detection circuit 6 and the switching element Q2.

A voltage K2 indicated by a solid line in FIG. 3 indicates the PFC voltage Vpfc of the self-excited resonance power factor correction circuit 1 of the first embodiment. At this time, the voltage K2 increases linearly when the AC voltage Vac is about 105V or less, and is limited to 200V when the AC voltage Vac exceeds about 105V.
The detection voltage Va2 detected by the PFC voltage detection circuit 6 is input to the base of the switching element Q2. When the detection voltage Va2 becomes equal to or higher than the threshold voltage Vbe of the switching element Q2, the switching element Q2 is turned on. As a result, the base voltage of the PNP transistor Q3 becomes L level, and the PNP transistor Q3 is turned on. When the PNP transistor Q3 is turned on, the gate voltage of the switching element Q1 becomes L level, the switching element Q1 is turned off, and the self-excited resonance oscillation operation is stopped. As a result, the PFC voltage Vpfc is limited to a predetermined range.
The limit voltage of the PFC voltage Vpfc can be set by the voltage division ratio of the resistors R5, R6, and R7 that constitute the PFC voltage detection circuit 6. Here, the PFC voltage detection circuit 6 is set so that the limit voltage of the PFC voltage Vpfc is 200V.

  The PFC voltage Vpfc is set to be within a predetermined range at a predetermined AC voltage Vac. The DC-DC conversion circuit 2 supplies a direct current obtained by converting the PFC voltage Vpfc to the light source 10 to light it. It is desirable that the direct current supplied to the light source 10 be limited to a predetermined range so as not to reduce the lifetime of the light source. Since the self-excited resonance type power factor correction circuit 1 of the first embodiment limits the voltage range of the PFC voltage Vpfc, fluctuations in the direct current supplied to the light source 10 can be suppressed.

(Second Embodiment)
FIG. 4 is a circuit diagram illustrating a configuration of the light source driving device 100a according to the second embodiment. The same reference numerals are given to the same components as those of the light source driving device 100 of the first embodiment.
As shown in FIG. 4, the light source driving device 100a includes a self-excited resonance type power factor correction circuit 1 and a DC-DC conversion circuit 2a similar to those in the first embodiment.

The DC-DC conversion circuit 2a includes a transformer T2, a feedback circuit 7, a switch circuit 8, a voltage correction circuit 9, a reference voltage generation circuit 11, a smoothing capacitor Ca2, a diode D2, a switching element Q4, and a Zener. A diode ZD2, a current detection resistor Ra2, and resistors R10, R13, and R14 are included. The DC-DC conversion circuit 2a is a self-excited resonant step-down converter for a step-down chopper. The DC-DC conversion circuit 2a is a buck converter system, and generates an average output voltage lower than the input voltage.
The light source 10 and the smoothing capacitor Ca2 are connected in parallel, the positive terminal of the self-excited resonance type power factor correction circuit 1 is connected to the first terminal, and the second terminal is connected to the first terminal of the coil L3 of the transformer T2. Connected. The light source 10 is an LED that emits light when a predetermined constant current is passed in the direction of the coil L3 from the positive terminal of the self-excited resonance type power factor correction circuit 1. The smoothing capacitor Ca <b> 2 smoothes the voltage across the light source 10.

The transformer T2 (second transformer) is configured by magnetically coupling a primary coil L3 (third coil) and a secondary coil L4 (fourth coil) to each other. In the transformer T2, the coil L3 is excited by a current supplied from the self-excited resonance type power factor correction circuit 1. The first end of the coil L3 is connected to the second end of the parallel connection of the light source 10 and the smoothing capacitor Ca2. The second end of coil L3 is connected to the drain of switching element Q4. The first end of the coil L4 is connected to a connection node between the resistors R8 and R9 and the capacitor C4 that constitute the bias setting circuit of the feedback circuit 7. The second end of coil L4 is connected to the cathode of Zener diode ZD2, the gate of switching element Q4, and the emitter of PNP transistor Q5.
The switching element Q4 (third switching element) is, for example, an FET, the source is connected to the ground via the current detection resistor Ra2, and the gate (control terminal) is connected to the second end of the coil L4 of the transformer T2. The switching element Q4 switches whether or not a current flows through the coil L3 of the transformer T2. The current detection resistor Ra2 (second current detection resistor) detects the current flowing through the light source 10 and the coil L3 as a voltage value.
The diode D2 (second diode) is forward-connected in the direction from the connection node between the coil L3 of the transformer T2 and the drain of the switching element Q4 to the positive electrode of the self-excited resonance type power factor correction circuit 1. The diode D2 flows a regenerative current that regenerates the electromagnetic energy accumulated in the coil L3 of the transformer T2 when the switching element Q4 is off.

The feedback circuit 7 (second feedback circuit) includes a bias setting circuit in which resistors R8 and R9 and a capacitor C4 are connected in series, and a coil L4 of the transformer T2. The feedback circuit 7 is induced in the coil L4 while the switching element Q4 is turned on and current flows from the self-excited resonance type power factor correction circuit 1 through the path of the light source 10, the coil L3, the switching element Q4, and the current detection resistor Ra2. The positive voltage is fed back to the gate of the switching element Q4, and the ON operation of the switching element Q4 is continued. Furthermore, when the current flowing through the coil L3 becomes zero, the feedback circuit 7 outputs a voltage based on the PFC voltage Vpfc to the gate (control terminal) of the switching element Q4 via the coil L4. Turn on.
A bias setting circuit, which is a series connection of resistors R8, R9 and a capacitor C4, is connected between the positive electrode of the self-excited resonance type power factor correction circuit 1 and the ground.
Zener diode ZD2 is connected between the gate of switching element Q4 and the ground. The zener diode ZD2 clamps the gate voltage of the switching element Q4 so as not to exceed the rated gate voltage when the self-excited resonance type power factor correction circuit 1 is turned off. In a normal operation state, no current flows through the Zener diode ZD2.

The second end of the coil L4 is connected to the gate of the switching element Q4 and the switch circuit 8. Thus, a positive feedback loop that causes self-excited oscillation is formed by the switching element Q4 and the coil L3.
The switch circuit 8 (second switch circuit) includes a comparator U2 and a PNP transistor Q5. In the switch circuit 8, the reference voltage generation circuit 11 determines a corrected detection voltage V7 obtained by superimposing a detection voltage Va3 obtained by dividing the PFC voltage Vpfc on the detection voltage V6 detected by the current detection resistor Ra2 by a resistor R15 and a resistor R16. When the reference voltage Vb2 (predetermined value) is exceeded, the switching element Q4 is turned off.
The voltage correction circuit 9 includes a series circuit of resistors R15 and R16. The detection voltage Va3 is applied to the first end of the resistor R15. The second end of the resistor R15 is connected to the first end of the resistor R16. A second end of the resistor R16 is connected to the source of the switching element Q4. The connection node of the resistors R15 and R16 is connected to the inverting input terminal of the comparator U2. The voltage correction circuit 9 divides the detection voltage Va3 obtained by dividing the PFC voltage Vpfc into the voltage value detected by the current detection resistor Ra2 by the resistors R15 and R16 and the current detection resistor Ra2 (hereinafter referred to as a superimposed voltage). The correction detection voltage V7 (correction detection signal) is generated.
In the corrected detection voltage V7, when the PFC voltage Vpfc increases, the detection voltage Va3 increases and the superimposed voltage increases. As a result, when the corrected detection voltage V7 exceeds the reference voltage Vb2, the switch circuit 8 turns off the switching element Q4 regardless of the positive voltage induced in the coil L4, so that the detection voltage V6 is corrected to be small. be able to. Further, when the PFC voltage Vpfc decreases, the correction detection voltage V7 decreases the detection voltage Va3, and the superimposed voltage decreases. As a result, when the corrected detection voltage V7 becomes equal to or lower than the reference voltage Vb2, the switch circuit 8 does not turn off the switching element Q4, so that the detection voltage V6 can be corrected to increase.
Therefore, the detection voltage Va3 increases or decreases due to the increase or decrease of the PFC voltage Vpfc, and the current flowing through the switching element Q4 increases or decreases contrary to the PFC voltage Vpfc, and the stability of the output current with respect to the PFC voltage Vpfc is maintained. It is.

The reference voltage generation circuit 11 includes a shunt regulator REG1 and resistors R11 and R12. The reference voltage generation circuit 11 is a circuit that generates a reference voltage.
The positive terminal of the shunt regulator REG1 is connected to the connection node of the resistors R8 and R9 via the resistor R10. The shunt regulator REG1 has a negative terminal grounded to the ground and a feedback terminal connected to a connection node of the resistors R11 and R12. The resistor R11 is connected between the positive terminal of the shunt regulator REG1 and the feedback terminal. The resistor R12 is connected between the feedback terminal and the negative terminal of the shunt regulator REG1. As a result, a reference voltage is generated at the positive terminal of the shunt regulator REG1. The positive terminal of the shunt regulator REG1 is connected to a series circuit of resistors R13 and R14. A reference voltage Vb2 obtained by dividing the reference voltage of the shunt regulator REG1 is generated at the connection node of the resistors R13 and R14.

  Comparator U2 has an inverting input terminal connected to a connection node of resistors R15 and R16, and a non-inverting input terminal connected to a connection node of resistors R13 and R14. The output terminal of the comparator U2 is connected to the base of the PNP transistor Q5. The PNP transistor Q5 has a collector grounded and an emitter connected to the gate (control terminal) of the switching element Q4. The comparator U2 generates a comparison signal that compares the reference voltage Vb2 output from the reference voltage generation circuit 11 with the corrected detection voltage V7 generated by the resistors R15 and R16 and the current detection resistor Ra2. The comparator U2 outputs this comparison signal to the gate (control terminal) of the switching element Q4 via the PNP transistor Q5, and controls the ON operation of the switching element Q4. Therefore, the DC-DC conversion circuit 2a can flow a stable predetermined constant current to the light source 10 that is not affected by the ambient temperature.

When the corrected detection voltage V7 exceeds the reference voltage Vb2, the comparator U2 quickly turns on the PNP transistor Q5 and outputs a comparison signal for setting the gate voltage of the switching element Q4 to L level. Therefore, the DC-DC conversion circuit 2a can obtain good line regulation (regulation of the output current with respect to the PFC voltage Vpfc and regulation of the output current with respect to the voltage of the light source 10).
Furthermore, the switch circuit 8 can stably turn on the switching element Q4 with respect to environmental changes such as temperature and voltage fluctuations by the comparator U2 and the reference voltage generation circuit 11 having good responsiveness. As a result, the DC-DC conversion circuit 2a can pass a predetermined constant current having a stable environmental performance and flowing to the light source 10.

Hereinafter, the operation of the light source driving device 100a will be described. When the self-excited resonance type power factor correction circuit 1 starts operation, the DC-DC conversion circuit 2a starts operation.
In the initial state of operation, the starting voltage is applied to the gate (control terminal) of the switching element Q4 via the resistors R8 and R9 and the coil L4 by the bias setting circuit of the feedback circuit 7. At this time, since no current flows through the light source 10, the coil L3 of the transformer T2, and the current detection resistor Ra2, the corrected detection voltage V7 applied to the inverting input terminal of the comparator U2 is equal to or lower than the reference voltage Vb2. At this time, the output of the comparator U2 becomes H level, and the PNP transistor Q5 is turned off. Thereby, the switching element Q4 is turned on, and an on-current flows through the light source 10 and the coil L3.

  The on-current that flows through the light source 10 and the coil L3 of the transformer T2 flows through the current detection resistor Ra2 via the drain / source of the switching element Q4. Due to the current flowing through the coil L3, a positive voltage is generated in the coil L4 of the transformer T2. This positive voltage is fed back to the gate (control terminal) of the switching element Q4. As a result, the switching element Q4 is kept on. A voltage corresponding to the on-current is generated at both ends of the current detection resistor Ra2.

  The comparator U2 of the switch circuit 8 compares the correction detection voltage V7 generated by the voltage correction circuit 9 with the reference voltage Vb2 of the reference voltage generation circuit 4. When the corrected detection voltage V7 exceeds the reference voltage Vb2, the comparator U2 sets the gate of the switching element Q4 to the L level via the PNP transistor Q5. That is, the PNP transistor Q5 is turned on and the switching element Q4 is turned off. When the switching element Q4 is turned off, the regenerative current of the coil L3 of the transformer T2 flows to the light source 10 via the diode D2.

  While the regenerative current of the coil L3 of the transformer T2 flows through the light source 10, a negative voltage is generated in the coil L4 of the transformer T2. This negative voltage is fed back to the gate (control terminal) of the switching element Q4, and the switching element Q4 remains off.

When the regenerative current of the coil L3 of the transformer T2 becomes zero, the negative voltage generated in the coil L4 of the transformer T2 decreases to zero. Thereby, the starting voltage by the bias setting circuit is applied to the gate (control terminal) of the switching element Q4, and the switching element Q4 is turned on again.
The DC-DC conversion circuit 2a can cause a predetermined constant current to flow through the light source 10 and perform a self-resonant (oscillation) operation by repeatedly turning on and off the switching element Q4. The DC-DC conversion circuit 2a is a resonance type (critical operation) drive circuit, and when the regenerative current of the coil L3 of the transformer T2 becomes zero, the switching element Q4 is turned on from off.

  According to the light source driving device 100a of the second embodiment, a zero current switch resonant self-excited oscillation type driving device can be realized with a circuit configuration with a small number of components. Here, the zero current switch is to turn on the switching element Q1 with the zero current of the transformer T1, or to turn on the switching element Q4 with the zero current of the transformer T2. Therefore, the light source driving device 100a can obtain high efficiency by reducing the switching loss of the switching elements Q1, Q4. As a result, the light source driving device 100a does not require a heat sink for heat dissipation, and the cost can be reduced and the circuit unit (device) can be downsized.

FIG. 5 is a graph showing the power factor of the light source driving device 100a. The horizontal axis of the graph indicates the AC voltage Vac input to the light source driving device 100a. The vertical axis of the graph indicates the power factor of the light source driving device 100a.
When the AC voltage Vac is 100V, the power factor K3 approaches 1.00. As described above, the light source driving device 100a can obtain a high power factor even though it is an inexpensive and simple circuit configuration using existing passive elements and active elements without providing a dedicated IC.

In addition, the specific configuration can be appropriately changed without departing from the gist of the present invention. For example, there are the following (a) and (b).
(A) The light source 10 is not limited to an LED, and may be, for example, an organic EL (Organic Electro-Luminescence) element or an inorganic EL (Inorganic Electro-Luminescence) element.
(B) The switching elements Q1 and Q4 are not limited to FETs, and may be bipolar transistors or the like.

1 self-excited resonance type power factor correction circuit 2, 2a DC-DC conversion circuit 3 feedback circuit (first feedback circuit)
4 Reference voltage generation circuit 5 Switch circuit (first switch circuit)
6 PFC voltage detection circuit 7 Feedback circuit (second feedback circuit)
8 Switch circuit (Second switch circuit)
9 Voltage correction circuit 10 Light source 11 Reference voltage generation circuit 100, 100a Light source driving device BD1 Rectifier circuit C1 Capacitors L1, L2 coils (first coil, second coil)
L3, L4 coil (3rd coil, 4th coil)
T1, T2 transformer (first transformer, second transformer)
Q1, Q2, Q4 switching elements (first to third switching elements)
ZD1, ZD2 Zener diode Ra1, Ra2 Current detection resistor (first current detection resistor, second current detection resistor)
D1, D2 diode (first and second diode)
Ca1, Ca2 smoothing capacitors (first and second smoothing capacitors)
R10, R13, R14 resistance

Claims (8)

A rectifier circuit that outputs a rectified voltage obtained by full-wave rectification of an AC voltage;
A first transformer including a first coil and a second coil magnetically coupled, and excited by a current supplied from the rectifier circuit;
A first switching element having a gate-drain capacitance, switching the current to flow through the first diode by choppering the first coil;
A first smoothing capacitor for smoothing a PFC (Power Factor Correction) voltage output from the first diode;
The feedback voltage induced in the second coil is fed back to the gate terminal of the first switching element, and when the current flowing through the first coil becomes zero, the voltage based on the rectified voltage is applied to the second coil. A first feedback circuit that outputs to the gate terminal via the first switching element and turns on the first switching element;
A first Zener diode connected between a gate terminal of the first switching element and a ground to clamp a gate-source voltage of the first switching element;
A first current detection resistor connected between the source terminal of the first switching element and the ground and detecting a current flowing through the first switching element as a voltage value;
A reference voltage generation circuit that generates a first reference voltage obtained by dividing the rectified voltage;
A first switch circuit that sets a voltage at a gate terminal of the first switching element to an L level if a voltage value detected by the first current detection resistor exceeds the first reference voltage;
A self-excited resonance type power factor correction circuit comprising:   The first feedback circuit includes:
  A resistor connected between the output terminal of the rectifier circuit and one end of the second coil;
  A capacitor connected between one end of the second coil and the ground;
  Comprising
  The other end of the second coil is connected to the gate terminal of the first switching element.
  The self-excited resonance type power factor correction circuit according to claim 1. The reference voltage generation circuit and the first current detection resistor are set so that the PFC voltage is within a predetermined range at a predetermined input voltage.
The self-excited resonance type power factor correction circuit according to claim 1 or 2 . A second switching element having a voltage at the gate terminal of the first switching element of L level;
A voltage dividing resistor connected between the cathode of the first diode and the ground and applying a divided value of the PFC voltage to a control terminal of the second switching element;
With
The voltage dividing resistor, the PFC voltage is set so as to turn on the pre-Symbol second switching element if exceeding the threshold,
Self-resonance type power factor correction circuit according to any one of claims 1 to 3, wherein the this. A self-excited resonance type power factor correction circuit according to any one of claims 1 to 4 ,
A DC-DC conversion circuit that receives the PFC voltage and supplies a direct current to the light source;
A light source driving device comprising: A self-excited resonance type power factor correction circuit according to claim 4 ,
The PFC voltage is input to supply a direct current to the light source, and a direct current supplied to the light source is output from the self-excited resonance type power factor correction circuit and supplied to the light source based on a voltage corresponding to the PFC voltage. A DC-DC conversion circuit that is controlled to be constant;
A light source driving device comprising: The DC-DC conversion circuit includes:
A second smoothing capacitor connected in parallel to the light source;
A second transformer including a magnetically coupled third coil and a fourth coil, which is excited by a current supplied from the self-excited resonance power factor correction circuit;
A third switching element having a gate-drain capacitance and switching whether or not to pass a current through the third coil;
A second diode that regenerates energy stored in the third coil when the third switching element is off;
The positive voltage induced in the fourth coil is fed back to the gate terminal of the third switching element, and when the current flowing through the third coil becomes zero, the voltage based on the PFC voltage is set to the fourth coil. A second feedback circuit that outputs via the first switching element to turn on the third switching element;
A second Zener diode connected between the gate terminal of the third switching element and the ground to clamp the gate-source voltage of the third switching element;
A second current detection resistor for detecting a current flowing through the third coil as a voltage value;
A voltage correction circuit that generates a correction detection signal in which a voltage obtained by dividing the PFC voltage is superimposed on a voltage value detected by the second current detection resistor;
A second switch circuit for setting the voltage of the gate terminal of the third switching element to an L level if the correction detection signal exceeds a predetermined value;
The light source driving device according to claim 5 , wherein the light source driving device is a self-excited resonance type.   The second feedback circuit includes:
  A resistor connected between an output terminal of the self-excited resonance type power factor correction circuit and one end of the fourth coil;
  A capacitor connected between one end of the fourth coil and the ground;
  Comprising
  The other end of the fourth coil is connected to the gate terminal of the third switching element.
  The light source driving device according to claim 7.

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