JP7293923B2 - LIGHT SOURCE LIGHTING DEVICE, LIGHTING EQUIPMENT, LIGHT SOURCE LIGHTING DEVICE CONTROL METHOD - Google Patents

Description

The present invention relates to a light source lighting device, a lighting fixture, and a light source lighting device control method.

2. Description of the Related Art Various light source lighting devices for lighting light emitting elements such as light emitting diodes are known. This type of light source lighting device includes an AC-DC conversion circuit that rectifies and smoothes commercial AC power to generate a DC voltage, and a DC-DC converter that supplies a current suitable for the LED from the obtained DC voltage. Prepare. A high power factor is required in many lighting fixtures. Therefore, a boost chopper type power factor correction circuit disclosed in Patent Document 1 is used as an AC-DC conversion circuit.

In a boost chopper type power factor correction circuit, when a switching element is turned on, current flows through the inductor via the switching element to charge energy. At this time, the inductor current increases linearly. Next, when the switching element turns off, the energy stored in the inductor is discharged to the load side, and the inductor current decreases linearly. Then, when the inductor current drops to zero, it operates in a so-called critical mode that detects this and initiates the next switching. As a result, the on-time of the switching element is controlled so that the peak value of the coil current becomes sinusoidal in each switching cycle, thereby improving the power factor.

Japanese Unexamined Patent Application Publication No. 2010-40400

In a power factor correction circuit operating in critical mode, when the coil current drops to zero, the voltage Vds across the drain and source across the switching element is the parasitic capacitance existing between the inductance component of the inductor and the electrodes of the switching element. oscillate at the resonant frequency due to the component. A control unit that drives and controls the switching element turns on the switching element at the timing of reaching the bottom point where the resonance voltage between the drain and the source is the lowest. By doing so, a state close to zero voltage switching can be achieved, and switching loss can be reduced.

Here, in the control unit, for example, a processing time of the microcomputer is required from the detection of the zero current of the inductor to the start of the next switching. In other words, there is a slight delay time between the detection of zero current and the actual turning on of the switching element. If this delay time is sufficiently short with respect to the period of the resonance voltage between the drain and the source, it becomes possible to turn on near the bottom of the resonance voltage between the drain and the source. On the other hand, if the delay time is not sufficiently short with respect to the period of the resonance voltage between the drain and the source, it becomes impossible to turn on near the bottom of the resonance voltage between the drain and the source.

As described above, the switching element may not be turned on near the bottom of the resonance voltage between the drain and the source due to the processing time in the control unit. This problem is particularly noticeable when a switching element using a wide bandgap semiconductor such as GaN or SiC is driven at a high frequency. When the switching element is driven at a high frequency, the inductance of the inductor becomes small and the parasitic capacitance of the switching element becomes small, so that the resonance period of the resonance voltage generated in the voltage Vds between the drain and source of the switching element becomes short. Then, the influence of the delay time of the control unit from the detection of zero current in the inductor to the start of the next switching cannot be ignored, and the turn-on occurs after the bottom of the resonance voltage in the drain-source voltage is passed. Therefore, switching loss increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems described above, and an object of the present invention is to provide a light source lighting device, a lighting fixture, and a control method for the light source lighting device that can reduce switching loss.

A light source lighting device according to the present disclosure includes: a DC power supply circuit that charges and discharges energy using a switching element and an inductor to generate a DC voltage; a detection winding that is magnetically coupled to the inductor; an integration circuit that integrates and outputs an output voltage; and a control unit that detects the timing of turning on the switching element using the output of the integration circuit and controls the driving of the switching element. is in the vicinity of the bottom, the switching element is turned on .
A light source lighting device according to the present disclosure includes: a DC power supply circuit that charges and discharges energy using a switching element and an inductor to generate a DC voltage; a detection winding that is magnetically coupled to the inductor; an integration circuit that integrates and outputs an output voltage; and a control unit that detects the timing of turning on the switching element using the output of the integration circuit and controls driving of the switching element, the control unit has a zero current detection unit that outputs a zero current detection signal for turning on the switching element when the output of the integration circuit reaches a predetermined detection threshold, and the DC power supply circuit improves the power factor. A circuit, wherein the zero current detection unit changes the detection threshold according to the input voltage of the power factor correction circuit.
A light source lighting device according to the present disclosure includes: a DC power supply circuit that charges and discharges energy using a switching element and an inductor to generate a DC voltage; a detection winding that is magnetically coupled to the inductor; an integration circuit that integrates and outputs an output voltage; and a control unit that detects the timing of turning on the switching element using the output of the integration circuit and controls driving of the switching element, the control unit has a zero current detection unit that outputs a zero current detection signal for turning on the switching element when the output of the integration circuit reaches a predetermined detection threshold, and the DC power supply circuit is a buck converter. and the zero current detector changes the detection threshold in accordance with the input voltage of the buck converter.

A control method for a light source lighting device according to the present disclosure includes: integrating an output voltage of a detection winding magnetically coupled to an inductor of a DC power supply circuit that charges and discharges energy using a switching element and an inductor; outputting a zero current detection signal when the value obtained by the integration reaches a predetermined detection threshold in the course of the current of the decreasing; and receiving the zero current detection signal, generating a drive signal for the switching element, and turning on the switching element by the drive signal , wherein the switching element is turned on when the oscillating voltage across the switching element is near the bottom. and

Other features of the invention will become apparent below.

According to the present invention, when the voltage obtained by inputting the output voltage of the detection winding to the integration circuit reaches the detection threshold value, the ON operation of the switching element starts, so that the switching loss can be reduced.

1 is a circuit configuration diagram of a light source lighting device according to Embodiment 1; FIG. 4 is an operation waveform diagram of the light source lighting device according to Embodiment 1. FIG. FIG. 10 is a circuit configuration diagram of a light source lighting device according to Embodiment 2; FIG. 10 is an operation waveform diagram of the light source lighting device according to Embodiment 2; FIG. 11 is a cross-sectional view of a lighting fixture according to Embodiment 3;

A light source lighting device, a lighting fixture, and a control method for the light source lighting device according to embodiments will be described with reference to the drawings. The same reference numerals are given to the same or corresponding components, and repetition of description may be omitted.

Embodiment 1.
FIG. 1 is a circuit configuration diagram of a light source lighting device 100 according to the first embodiment. The light source lighting device 100 receives power from the AC power supply 1 to light the light source 9 . A light source 9 is connected to the output of the light source lighting device 100 . The light source 9 is, for example, an LED (Light Emitting Diode) module, but any light source can be used. The light source lighting device 100 and the light source 9 constitute a lighting fixture.

According to an example, the light source lighting device 100 comprises a power factor correction circuit 2, a DC-DC converter 3, a PFC control circuit 4 and a DC-DC converter control circuit 5. The power factor correction circuit 2 includes a rectifier circuit DB with a diode bridge that full-wave rectifies the AC power supply. This full-wave rectified voltage is not smoothed while the power factor correction circuit 2 is operating, and becomes a ripple voltage containing twice the frequency of the AC power supply 1 .

According to one example, the power factor correction circuit 2 is a boost chopper type circuit comprising a filter capacitor C1, an inductor L1, a switching element SW1, a diode D1 and a smoothing capacitor C2. A sensing winding L2 is magnetically coupled to the inductor L1. A sensing winding is sometimes called a secondary winding. Furthermore, a voltage dividing resistor R0 is provided between the two wirings that provide the DC output of the rectifier circuit DB. Also, the output voltage of the power factor correction circuit 2 can be detected by an output voltage detection resistor R1 connected in parallel with the smoothing capacitor C2.

The material of the switching element SW1 can be silicon. According to another example, switching element SW1 may be formed of a wide bandgap semiconductor having a larger bandgap than silicon. Wide bandgap semiconductors include, for example, silicon carbide, gallium nitride-based materials, and diamond.

In order to supply a direct current to the light source 9 via the DC-DC converter 3, energy is charged and discharged by the switching element SW1 and the inductor L1 and converted into a desired direct current voltage. Therefore, the power factor correction circuit 2 can be called a DC power supply circuit. An output of the power factor correction circuit 2 is connected to a DC-DC converter 3 for supplying current to the light source 9 .

A PFC control circuit 4 controls the power factor correction circuit 2 . The power factor correction circuit 2 boosts the voltage full-wave rectified by the rectifier circuit DB and smoothes the DC voltage. Further, the power factor correction circuit 2 is controlled by the PFC control circuit 4 so that the input current waveform is sinusoidal and has substantially the same phase as the voltage of the AC power supply 1, thereby improving the power factor.

According to one example, the PFC control circuit 4 includes a voltage comparison section 4a, an integration circuit 4b, a zero current detection section 4c, a drive signal generation section 4d, and a gate drive section 4e. At least part of the PFC control circuit 4 can be configured by a microcomputer. For example, the voltage comparison section 4a, the zero current detection section 4c and the drive signal generation section 4d can be configured by a microcomputer. The voltage comparison section 4a, the zero current detection section 4c, and the drive signal generation section 4d are referred to as a control section 4A. The PFC control circuit 4 controls the ON time of the switching element SW1 so that the output voltage of the power factor correction circuit 2 becomes a preset voltage value, and the input current waveform is substantially in phase with the voltage of the AC power supply 1 and The switching element SW1 is controlled so as to generate a sine wave.

The voltage comparator 4a compares the output voltage signal generated at the output voltage detection resistor R1 with a target voltage E1 corresponding to the target output voltage of the power factor correction circuit 2, and outputs a signal corresponding to the difference between the two. Thus, the voltage comparator 4a outputs a signal corresponding to the difference between the voltage obtained by dividing the output voltage of the DC power supply circuit by the output voltage detection resistor R1 and the predetermined target voltage E1. According to another example, the voltage comparator 4a may output a signal reflecting the difference between the output voltage of the DC power supply circuit and the target voltage E1.

The drive signal generator 4d receives the output signal of the voltage comparator 4a, determines the ON time in one switching cycle of the switching element SW1, and generates a drive signal for the switching element SW1. The drive signal is, for example, a PWM (Pulse Width Modulation) signal.

The integration circuit 4b includes an operational amplifier 41b, a resistance element 42b and a capacitor 43b. An input terminal of the operational amplifier 41b is connected to the detection winding L2 through the resistance element 42b. In other words, one end of the resistance element 42b is connected to the detection winding L2, and the other end of the resistance element 42b is connected to the input side of the operational amplifier 41b. A capacitor 43b connects the input and output of the operational amplifier 41b. The integration circuit 4b integrates the voltage waveform generated at the detection winding L2 and outputs it to the zero current detection section 4c.

The zero current detector 4c outputs a zero current detection signal to the drive signal generator 4d when the output of the integrating circuit 4b reaches a predetermined detection threshold. The zero current detection signal is a signal for turning on the switching element SW1. According to one example, the zero-current detector 4c detects that the output of the integration circuit 4b has reached a predetermined detection threshold by constantly comparing the voltage value input from the integration circuit 4b and the detection threshold. do. The above-described comparison can be performed by providing the zero current detection unit 4c with, for example, a comparator. In addition, for example, the detection threshold can be used by storing the detection threshold in the memory of the zero current detection unit 4c and reading it.

Upon receiving the zero current detection signal, the drive signal generator 4d generates a signal for turning on the switching element SW1. As shown in FIG. 1, the drive signal generator 4d is connected to the zero current detector 4c and the voltage comparator 4a.

The gate drive unit 4e amplifies the gate drive signal output from the drive signal generation unit 4d with a voltage of, for example, about 5 V to a voltage of, for example, about 10 V suitable for driving the switching element SW1, and outputs the signal to the gate terminal of the switching element SW1. output to The switching element SW1 is turned on and off by a gate drive signal output from the gate drive section 4e. Although not shown, for example, a gate resistor or the like may be connected to the gate terminal of the switching element SW1.

The DC-DC converter 3 is driven and controlled by a DC-DC converter control circuit 5 . The DC-DC converter 3 is subjected to constant current feedback control so that the current flowing through the light source 9 becomes a target current value. Although the detailed configuration of the DC-DC converter 3 is not shown here, the DC-DC converter 3 can be configured with a known circuit such as a step-down chopper circuit or a flyback converter.

Next, a control method for the light source lighting device according to the first embodiment will be described. When an AC voltage is applied to the light source lighting device 100 from the AC power supply 1, the rectifier circuit DB full-wave rectifies the input AC voltage, and the rectified voltage is applied across the filter capacitor C1. The filter capacitor C1 is provided for the purpose of removing switching ripples, not for smoothing the frequency component of the AC power supply 1 here. Therefore, during operation of the power factor correction circuit 2, the voltage across the filter capacitor C1 becomes a full-wave rectified voltage that pulsates sinusoidally at twice the frequency of the AC power supply.

The operation of the power factor correction circuit 2 in a steady operating state will be explained. First, consider a state in which the switching element SW1 is turned on by a signal output from the gate driving section 4e. When the switching element SW1 is turned on, the full-wave rectified voltage is applied to the inductor L1, current flows through the path of the inductor L1 and the switching element SW1, and energy is stored in the inductor L1. At this time, the current in inductor L1 increases linearly.

After the ON time of the switching element SW1 set by the drive signal generator 4d has passed, the drive signal generator 4d outputs an OFF signal to turn off the switching element SW1. When the switching element SW1 is turned off, the energy stored in the inductor L1 is released, and current flows through the inductor L1, the diode D1, and the smoothing capacitor C2 in that order. This charges the smoothing capacitor C2. By transmitting energy in this way, the DC-DC converter 3 receives the voltage charged in the smoothing capacitor C2 and supplies current to the light source 9 .

FIG. 2 is a waveform diagram showing the operation of the light source lighting device 100 according to the first embodiment. The operation of the light source lighting device 100 will be described with reference to the waveform diagram of FIG.

(Period t0-t1)
Here, the operation of the power factor correction circuit 2 is in a steady operation state, and the timing at which the switching element SW1 is turned on by the output of the gate driving section 4e will be described. When the switching element SW1 is turned on, a current flows through the switching element SW1 from the inductor L1, and the inductor L1 current increases. At this time, since a voltage is applied to the inductor L1 in the direction of the arrow VL1 in FIG. 1, a voltage is generated in the detection winding L2 in the direction of the arrow VL2. The position indicated by the arrow has a higher voltage than the position opposite to the arrow. As a result, a negative voltage is input from the detection winding L2 to the integrating circuit 4b. When a negative voltage is input to the integration circuit 4b, the output voltage of the integration circuit 4b increases.

(time t1)
When the switching element SW1 is turned on and a predetermined time elapses, the driving signal generator 4d turns off the switching element SW1 via the gate driving section 4e to cut off the current of the switching element SW1. At time t1, switching element SW1 is turned off. The ON time of the switching element SW1 is determined by the comparison result of the voltage comparator 4a. That is, if the output voltage detection signal obtained by the output voltage detection resistor R1 is smaller than the target voltage E1, the ON time is controlled to be longer. On the other hand, if the output voltage detection signal is greater than the target voltage E1, the ON time is controlled to be shortened.

(Period t1-t2)
When the switching element SW1 is turned off at time t1, the energy stored in the inductor L1 is released to the smoothing capacitor C2 via the diode D1, so the current flowing through the inductor L1 decreases as the energy is released. At this time, the voltage generated in the inductor L1 has a polarity opposite to that when the switching element SW1 is on. That is, a voltage is generated in the opposite direction to the arrow VL1 in FIG. As a result, the voltage generated in the detection winding L2 also has a polarity opposite to that of the arrow VL2 in FIG. 1, and a positive voltage is input to the integrating circuit 4b. When a positive voltage is input to the integration circuit 4b, the output voltage of the integration circuit 4b decreases.

(time t2)
The output voltage of the integrating circuit 4b, which tends to decrease, is input to the zero current detector 4c. The zero current detector 4c compares the voltage input from the integration circuit 4b with a preset detection threshold. At time t2, the voltage input from the integration circuit 4b reaches the threshold voltage. Then, the zero current detector 4c transmits a zero current detection signal to the drive signal generator 4d. At this point, the current through inductor L1 has not reached zero. That is, according to one example, the zero current detection signal is output before the current through inductor L1 becomes zero. Thus, when the value obtained by integration reaches a predetermined detection threshold while the current in inductor L1 is decreasing, a zero current detection signal is output.

(Period t2-t3)
When the drive signal generation unit 4d receives the zero current detection signal, it generates and outputs a drive signal for turning on the switching element SW1, and executes processing for turning on the switching element SW1 via the gate drive unit 4e according to the drive signal. Specifically, the drive signal generator 4d generates a drive signal that turns on the switching element SW1 for an ON time corresponding to the output of the voltage comparator 4a after the logic level of the zero current detection signal is inverted.

However, from the time when the drive signal generation unit 4d receives the zero current detection signal to the time when the switching element SW1 is actually turned on, there is a delay time caused by processing in the drive signal generation unit 4d and a delay time caused by processing in the gate drive unit 4e. Therefore, the switching element SW1 cannot be turned on immediately after the drive signal generator 4d receives the zero current detection signal. When the inductor L1 finishes discharging energy during this delay time period and the inductor L1 current becomes zero, a resonance phenomenon occurs due to the parasitic capacitance between the electrodes of the inductor L1 and the switching element SW1, etc., and the detection winding L2 A voltage accompanied by a resonance phenomenon is generated at , and the voltage of L2 drops rapidly.

(Time t3)
When the delay time of the processing in the drive signal generation unit 4d and the delay time in the gate drive unit 4e elapse and the resonance voltage applied to the switching element SW1 reaches near the bottom due to the resonance phenomenon, the ON signal is output from the gate drive unit 4e. and the switching element SW1 is turned on again. FIG. 2 shows that resonance occurs in the voltage Vds across the switching element, and the switching element SW1 is turned on at time t3 near the bottom of the resonance voltage. In order to turn on the switching element SW1 near the bottom of the resonance voltage, the detection threshold is set so that the time t2-t3 matches or substantially matches the total delay time. In other words, considering the delay time of the drive signal generator 4d and the gate driver 4e in advance, the zero current detector 4c uses the zero current detector 4c so as to turn on the timing when the resonance voltage applied to the switching element SW1 is near the bottom. Determine the detection threshold. If the detection threshold is set high, the period t2-t3 is lengthened, and if the detection threshold is set low, the period t2-t3 is shortened, so the period t2-t3 can be adjusted according to the delay time measured in advance. .

When the switching element SW1 is turned on in this manner, a current begins to flow through the inductor L1, returning to the conditions from time t0 to t1, and repeating the same operation. Turning on the switching element SW1 when the oscillating voltage across the switching element SW1 is near the bottom enables the switching element SW1 to be turned on in a state where the voltage across the switching element SW1 is low. As a result, the operation becomes close to zero voltage switching, and the switching loss can be reduced. The output of the DC power supply circuit thus obtained can be used for lighting the light source.

Here, a case where the output voltage of the power factor correction circuit 2 is made variable according to the voltage effective value of the AC power supply 1 will be described. For example, when an AC power supply 1 with an effective value of 100V is input, the output voltage of the power factor correction circuit 2 is set to 350V, and when an AC power supply 1 with an effective value of 200V is input, the output voltage of the power factor correction circuit 2 is set to 400V. Then, the PFC control circuit 4 controls the output voltage. The voltage determination of the AC power supply 1 can be made, for example, by reading the voltage obtained by the voltage dividing resistor R0 provided between the DC output sides of the rectifier circuit DB with the PFC control circuit 4 . In the example of FIG. 1, the voltage obtained by the voltage dividing resistor R0 is input to the zero current detector 4c. In this way, according to the voltage of the AC power supply 1 that is input, the PFC output voltage can be lowered when the input voltage is low, and the PFC output voltage can be raised when the input voltage is high. By doing so, when the input voltage of the AC power supply 1 is low, it is possible to prevent the step-up ratio defined by the output voltage/input voltage from becoming too high, and the circuit efficiency can be improved.

By the way, it is known that the parasitic capacitance between the electrodes of the switching element SW1 made of a semiconductor depends on the voltage applied between the electrodes, that is, the voltage Vds between the drain and the source. In general, the parasitic capacitance between the electrodes decreases as the voltage Vds across the electrodes increases. In the power factor correction circuit 2, the drain-source voltage Vds is applied between the drain and the source when the switching element SW1 is turned off. Therefore, the higher the output voltage, the higher the voltage applied to the switching element SW1, and the parasitic capacitance between the electrodes is reduced. do. Then, since the resonance frequency of the resonance voltage generated between the drain and source of the switching element SW1 increases, the turn-on timing of the switching element SW1 shifts, and the turn-on of the switching element SW1 may not be possible near the bottom of the resonance voltage.

Therefore, according to the output voltage of the power factor improvement circuit or the input voltage of the power factor improvement circuit, the detection threshold value used in the zero current detection unit 4c is adjusted, and the timing at which the oscillating voltage applied to the switching element SW1 is near the bottom. to turn on the switching element SW1. In the example of FIG. 1, the zero current detector 4c that receives the output of the voltage dividing resistor R0 changes the detection threshold. For example, when the output voltage of the power factor correction circuit is 400V, the detection threshold is increased compared to when the output voltage is 350V. As a result, the timing at which the drive signal generator 4d receives the zero current detection signal can be advanced, and the switching element SW1 can be turned on at the timing when the resonance voltage applied to the switching element SW1 is near the bottom. In this example, 100 V and 200 V are assumed as the effective values of the AC power supply, but three or more effective values can be used.

As described above, the rectangular wave voltage generated in the detection winding L2 for detecting zero current in the inductor L1 is converted into a triangular wave voltage or a waveform similar thereto by the integrating circuit 4b, and compared with the detection threshold. By adjusting the detection threshold, it is possible to freely advance the detection timing of zero current. As a result, the timing of zero current detection can be advanced compared to the case where zero current is detected at the falling timing of the rectangular wave voltage of the detection winding L2. Early zero current detection allows the period t2-t3 to match or substantially match the delay time in the PFC control circuit 4. FIG. As a result, the switching element SW1 can be turned on without delay near the bottom of the resonance voltage of the switching element SW1.

Therefore, since the switching element can be turned on with a low voltage applied to it, an operation close to zero voltage switching is possible, and switching loss can be reduced. Thereby, a highly efficient light source lighting device can be provided. Moreover, even when a wide bandgap semiconductor such as a GaN device is employed as the switching element SW1 and driven at a high frequency, an inexpensive microcomputer whose processing speed is not fast can be used, resulting in cost reduction.

The integrating circuit is not limited to the integrating circuit 4b of FIG. 1, and any circuit that integrates the output voltage of the detection winding L2 can be employed. The integration results in a waveform with a non-rectangular slope, allowing determination of whether the detection threshold has been reached. An example of a waveform with a non-rectangular slope is the triangular wave shown in FIG. For example, the integrator circuit can be any circuit with a capacitor that charges and discharges depending on whether the output voltage of the sensing winding is positive or negative.

The control unit 4A uses the output of the integrating circuit 4b to detect the timing of turning on the switching element SW1, and controls the driving of the switching element SW1. The configuration of the control section 4A can be changed to another configuration having such functions.

Modifications, modifications, or alternatives described in Embodiment 1 can be applied to light source lighting devices, lighting fixtures, and light source lighting device control methods according to the following embodiments. With respect to a light source lighting device, a lighting fixture, and a control method of the light source lighting device according to the following embodiments, differences from the first embodiment will be mainly described.

Embodiment 2.
FIG. 3 is a circuit configuration diagram of the light source lighting device 110 according to the second embodiment. In this embodiment, the operation of the DC-DC converter 3 will be mainly described.

The DC-DC converter 3 is, for example, a step-down chopper type. The DC-DC converter 3 includes an inductor L3, a switching element SW2 made of silicon or a wide bandgap semiconductor, a diode D2 and a smoothing capacitor C3. The DC-DC converter 3 receives a DC voltage from the power factor correction circuit 2, charges and discharges energy with the switching element SW2 and the inductor L3, and outputs a DC voltage and a DC current suitable for lighting the light source 9. circuit. Such a DC power supply circuit is called a buck converter. A light source 9 is lit by the output of the DC-DC converter 3 . A sensing winding L4 is magnetically coupled to the inductor L3. The DC-DC converter 3 also has an output current detection resistor R2 for detecting the output current.

A DC-DC converter control circuit 5 is provided to control the DC-DC converter 3 . The DC-DC converter control circuit 5 includes a voltage comparison section 5a, an integration circuit 5b, a zero current detection section 5c, a drive signal generation section 5d, and a gate drive section 5e. The voltage comparison section 5a, the zero current detection section 5c, and the drive signal generation section 5d constitute the control section 5A. At least part of the DC-DC converter control circuit 5 can be configured by a microcomputer. For example, the voltage comparator 5a, the zero current detector 5c, and the drive signal generator 5d can be microcomputers. Also, the microcomputer of the DC-DC converter 3 may be a common microcomputer with the PFC control circuit 4 .

The DC-DC converter control circuit 5 controls the switching element SW2 so that the output current of the DC-DC converter 3, that is, the current flowing through the light source 9 has a predetermined current value. The predetermined current value is determined, for example, by a brightness setting value set by a dimmer attached to a wall surface in the room or by a remote controller. That is, the DC-DC converter control circuit 5 receives a dimming signal output from a dimmer or a remote control, and the DC-DC converter control circuit 5 controls the switching element SW2 so that the current value corresponding to it is obtained. .

The voltage comparator 5a compares the output current signal generated in the output current detection resistor R2 with a target voltage E2 corresponding to the target output current of the DC-DC converter 3, and generates a drive signal based on the difference between the two. Output to the section 5d.

The drive signal generation unit 5d receives the output signal of the voltage comparison unit 5a, determines the ON time in one switching cycle of the switching element SW2, and generates a drive signal for the switching element SW2. The drive signal is, for example, a PWM (Pulse Width Modulation) signal.

The integrating circuit 5b may have the same configuration as the integrating circuit 4b described in the first embodiment, but FIG. 3 shows an integrating circuit 5b different from the integrating circuit 4b of FIG. The integrating circuit 5b includes a diode 51b, resistance elements 52b, 53b, 54b, a charging/discharging switching element 55b, a capacitor 56b, and an inverting element 57b. The integrator circuit 5b can be provided as an RC integrator circuit.

The inverting element 57b is for driving the charging/discharging switching element 55b in a phase opposite to the gate driving signal of the switching element SW2. The charging/discharging switching element 55b is ON/OFF-controlled by an inverting element 57b in the opposite phase of the driving signal output from the control section 5A to the switching element SW2.

The integration circuit 5b integrates and outputs the voltage waveform generated at the detection winding L4, and inputs it to the zero current detection section 5c. When the voltage value input from the integration circuit 5b reaches a preset threshold voltage, the zero-current detector 5c inputs a zero-current detection signal notifying that effect to the drive signal generator 5d. Upon receiving the zero current detection signal, the drive signal generator 5d generates and outputs a signal for turning on the switching element SW2.

The gate driver 5e is connected to the gate terminal of the switching element SW2. The gate drive unit 5e amplifies the gate drive voltage of, for example, 5V output from the drive signal generation unit 5d to a voltage of, for example, 10V suitable for driving the switching element SW2, and outputs the amplified voltage to the gate terminal of the switching element SW2. The switching element SW2 is turned on and off by a gate drive signal output from the gate drive section 5e. For example, a gate resistor or the like may be connected to the gate terminal of the switching element SW2.

FIG. 4 is an operation waveform diagram of the light source lighting device according to the second embodiment. The operation of the light source lighting device 110 will be described with reference to FIG. Here, it is assumed that the power factor correction circuit 2 is in a steady state and that a constant output voltage is input to the DC-DC converter 3 . Also, the DC-DC converter 3 is also in a steady operating state, and the light source 9 is lit with a constant brightness.

(Period t0-t1)
Here, the operation of the DC-DC converter 3 is in a steady operation state, and the timing at which the switching element SW2 is turned on by the gate driving section 5e will be described. When the switching element SW2 is turned on, a current flows through the inductor L3, and the current of the inductor L3 increases linearly. At this time, a voltage VL3 is applied to the inductor L3 in the direction of the arrow in FIG. 3, a voltage VL4 is generated in the detection winding L4 in the direction of the arrow, and a positive voltage is input to the integrating circuit 5b. At this time, the charging/discharging switching element 55b of the integrating circuit 5b is in an off state. Therefore, a charging current for charging the capacitor 56b flows through the path of the diode 51b, the resistance element 52b, the resistance element 54b, and the capacitor 56b. As a result, the voltage of the capacitor 56b, that is, the output voltage of the integration circuit 5b increases.

(time t1)
When a predetermined time elapses, the drive signal generator 5d turns off the switching element SW2 via the gate driver 5e to cut off the current of the switching element SW2. The ON time of the switching element SW2 is determined by the comparison result of the voltage comparator 5a. That is, if the output current detection signal is smaller than the target voltage E2, the ON time is controlled to be longer, and if the output current detection signal is larger than the target voltage E2, the ON time is controlled to be shorter.

(Period t1-t2)
When the switching element SW2 is turned off, the energy stored in the inductor L3 is released to the conductive diode D2 and the smoothing capacitor C3, and the current flowing through the inductor L3 decreases as the energy is released. At this time, the voltage generated in the inductor L3 has a polarity opposite to that when the switching element SW2 is in the ON state. That is, a voltage is generated in the opposite direction to the arrow in FIG. As a result, the voltage generated in the detection winding L4 also has a direction opposite to the direction of the arrow in FIG. 3, and a negative voltage is input to the integration circuit 5b. However, even if a negative voltage is input, the integration circuit 5b does not conduct due to the diode 51b. In addition, since the charging/discharging switching element 55b is turned on during this period, the electric charge of the capacitor 56b charged during the period t0 to t1 is discharged through the resistance elements 54b and 53b. Therefore, the voltage of the capacitor 56b, that is, the output voltage of the integration circuit 5b decreases. In this way, the capacitor 56b connects both ends of the charging/discharging switching element 55b through the resistance elements 53b and 54b, so that the capacitor 56b can be discharged.

(time t2)
The output voltage of the integration circuit 5b is always input to the zero current detector 5c. The zero-current detector 5c compares the voltage input from the integration circuit 5b with a detection threshold, which is a preset voltage. When the voltage input from the integration circuit 5b reaches the detection threshold, the zero current detector 5c transmits a zero current detection signal to the drive signal generator 5d. At this time of sending the zero current detection signal, the current through inductor L3 has not reached zero.

(Time t2-t3)
Upon receiving the zero current detection signal, the drive signal generator 5d outputs a signal for turning on the switching element SW2, and executes processing for turning on the switching element SW2 via the gate driver 5e. However, in order for the drive signal generation unit 5d to actually turn on the switching element SW2 after receiving the zero current detection signal, there is a processing delay time in the drive signal generation unit 5d and a delay time in the gate drive unit 5e. Therefore, the switching element SW2 cannot be turned on immediately. When the inductor L3 finishes discharging energy in the middle of such a delay time and the current of the inductor L3 becomes zero, a resonance phenomenon occurs due to the parasitic capacitance of the inductor L3 and the switching element. Then, a voltage is generated in the detection winding L4 due to a resonance phenomenon, and the voltage VL4 rises rapidly.

(Time t3)
When the delay time of the process in the drive signal generation unit 5d and the delay time of the gate drive unit 5e elapse and the resonance voltage applied to the switching element SW2 due to the resonance phenomenon reaches near the bottom, the ON signal is generated from the gate drive unit 5e. is output, and the switching element SW2 is turned on again. When the switching element SW2 is turned on, a current begins to flow through the inductor L3, returning to the conditions from time t0 to t1, and repeating the same operation. By turning on the switching element SW2 when the resonance voltage applied to the switching element SW2 is near the bottom, the switching element SW2 can be turned on in a state where the voltage across the switching element SW2 is low. Therefore, the operation becomes close to zero voltage switching, and the switching loss can be reduced.

In consideration of the delay time in the driving signal generating section 5d and the delay time in the gate driving section 5e in advance, zero A detection threshold in the current detection unit 5c can be set. When the detection threshold is set high, the period t2-t3 is set long, and when the detection threshold is set low, the period t2-t3 is set short. For example, the detection threshold is adjusted according to the total sum of delay times measured in advance.

The output voltage of the power factor correction circuit 2 is input to the DC-DC converter 3 . When a step-down chopper circuit is used as the DC-DC converter 3, the output voltage of the power factor correction circuit 2 is applied to the switching element SW2 in the turned off state. Therefore, the parasitic capacitance between electrodes varies according to the output voltage of the power factor correction circuit 2 . That is, when the output voltage of the power factor correction circuit 2 is variable according to the input voltage of the AC power supply 1 as described in the first embodiment, the output voltage between the electrodes of the switching element SW2 in the DC-DC converter 3 is changed. , the detection threshold in the zero current detector 5c can be changed according to the output voltage of the power factor correction circuit 2. FIG. For example, when the output voltage of the power factor correction circuit 2 is 400V, the inter-electrode capacitance of the switching element SW2 is smaller than when the output voltage is 350V, so the detection threshold is raised. As a result, the timing at which the drive signal generator 5d receives the zero current detection signal can be advanced, and the switching element SW2 can be turned on at the timing when the resonance voltage applied to the switching element SW2 is near the bottom. The process of changing the detection threshold used by the zero current detector 5c according to the input voltage of the buck converter in this way can be performed by the zero current detector 5c. For example, the input voltage of the DC-DC converter 3 is detected by voltage dividing resistors, and the detected value is input to the zero current detector 5c.

As described above, even in the DC-DC converter 3 such as a step-down chopper circuit, the timing of zero current detection can be detected in the same manner as in the first embodiment, so the delay time of the DC-DC converter control circuit 5 can be corrected. and the switching element SW2 can be turned on without delay near the bottom of the oscillating voltage of the switching element SW2. In addition, the use of an RC integration circuit that combines a resistance element and a capacitor without using an operational amplifier in the integration circuit contributes to cost reduction.

Both the PFC control circuit 4 in FIG. 1 and the DC-DC converter control circuit 5 in FIG. 3 can be used in the light source lighting device. In Embodiments 1 and 2, the timing to turn on the switching element is detected by comparing the value obtained by integrating the output voltage of the detection winding by the integration circuit with the detection threshold value. However, another method can be used to detect the timing of turning on the switching element using the output of the integrating circuit. For example, the zero current detection signal can be output from the zero current detector at the timing when the amount or rate of decrease from the peak value of the output of the integrating circuit reaches a predetermined value.

In Embodiments 1 and 2, the polarity of the detection winding can be reversed, and the output of the integration circuit can be reversed. In this case, the zero-current detector detects that the output voltage of the integrating circuit has reached the detection threshold while the output voltage is rising.

Embodiment 3.
FIG. 5 is a cross-sectional view of lighting fixture 200 according to Embodiment 3. As shown in FIG. The lighting fixture 200 includes a lighting fixture body 60 , a connector 61 , a light source board 62 and a light source lighting device 63 . The lighting fixture main body 60 is a housing for mounting a light source lighting device 63 and the like. The connector 61 is a connecting portion for receiving power supply from an AC power supply such as a commercial power supply. The light source substrate 62 is a substrate on which light sources such as LEDs or organic ELs are mounted.

The circuit configuration of the light source lighting device 63 is the same circuit configuration as any of the light source lighting devices described above. The light source lighting device 63 receives power supply from an AC power supply via a connector 61 and wiring 64 . The light source lighting device 63 converts the input power and supplies power to the light source board 62 via the wiring 65 . The power supplied from the light source lighting device 63 lights the light source mounted on the light source substrate 62 . Thereby, lighting fixture 200 having the advantages of the light source lighting device according to Embodiment 1, 2, or both is provided.

Since the lighting fixture 200 includes the light source lighting device described in Embodiment 1, 2, or both of them, even if high-frequency switching is performed using a switching element made of a wide bandgap semiconductor, it is applied to the switching element. The switching element can be turned on near the bottom of the oscillating voltage applied. Therefore, switching loss can be reduced.

It should be noted that the variations, modifications, or alternatives described so far can be applied to embodiments other than the embodiment for which they are described.

1 AC power supply 2 Power factor correction circuit 3 DC-DC converter 4 PFC control circuit 5 DC-DC converter control circuit 4b, 5b Integration circuit 9 Light source 100, 110 Light source lighting device 200 Lighting fixture

Claims (15)

a DC power supply circuit that charges and discharges energy using a switching element and an inductor to generate a DC voltage;
a sensing winding magnetically coupled with the inductor;
an integration circuit that integrates and outputs the output voltage of the detection winding;
a control unit that detects the timing to turn on the switching element using the output of the integration circuit and controls the driving of the switching element ;
A light source lighting device , wherein the switching element is turned on when an oscillating voltage across the switching element is near a bottom . The control unit includes a zero current detection unit that outputs a zero current detection signal for turning on the switching element when the output of the integration circuit reaches a predetermined detection threshold. The light source lighting device according to claim 1. The control unit
a voltage comparator that outputs a signal corresponding to the difference between the output voltage of the DC power supply circuit or a voltage obtained by dividing the output voltage and a predetermined target voltage;
a drive signal connected to the zero current detection section and the voltage comparison section, for turning on the switching element for an ON time corresponding to the output of the voltage comparison section after the logic level of the zero current detection signal is inverted; 3. The light source lighting device according to claim 2, further comprising a drive signal generation unit that generates a . 4. The light source lighting device according to any one of claims 1 to 3, wherein the integration circuit includes a capacitor that charges and discharges according to whether the output voltage of the detection winding is positive or negative. The integration circuit is
a resistive element having one end connected to the detection winding;
an operational amplifier having an input side connected to the other end of the resistive element,
5. The light source lighting device according to claim 4, wherein the capacitor connects the input and the output of the operational amplifier. The integration circuit is
a charging/discharging switching element that is ON/OFF controlled in the opposite phase of the driving signal output from the control unit to the switching element;
and a resistive element connected to the charging/discharging switching element,
5. The light source lighting device according to claim 4, wherein the capacitor connects both ends of the charging/discharging switching element via the resistance element. The light source lighting device according to any one of claims 1 to 6, wherein the DC power supply circuit is a power factor correction circuit. a DC power supply circuit that charges and discharges energy using a switching element and an inductor to generate a DC voltage;
a sensing winding magnetically coupled with the inductor;
an integration circuit that integrates and outputs the output voltage of the detection winding;
a control unit that detects the timing to turn on the switching element using the output of the integration circuit and controls the driving of the switching element;
The control unit comprises a zero current detection unit that outputs a zero current detection signal for turning on the switching element when the output of the integration circuit reaches a predetermined detection threshold,
The light source lighting device, wherein the DC power supply circuit is a power factor improvement circuit, and the zero current detection section changes the detection threshold according to the input voltage of the power factor improvement circuit. The light source lighting device according to any one of claims 1 to 6, wherein the DC power supply circuit is a buck converter. a DC power supply circuit that charges and discharges energy using a switching element and an inductor to generate a DC voltage;
a sensing winding magnetically coupled with the inductor;
an integration circuit that integrates and outputs the output voltage of the detection winding;
a control unit that detects the timing to turn on the switching element using the output of the integration circuit and controls the driving of the switching element;
The control unit comprises a zero current detection unit that outputs a zero current detection signal for turning on the switching element when the output of the integration circuit reaches a predetermined detection threshold,
The light source lighting device, wherein the DC power supply circuit is a buck converter, and the zero current detection section changes the detection threshold according to the input voltage of the buck converter. The light source lighting device according to any one of claims 1 to 10, wherein the switching element is made of a wide bandgap semiconductor. 12. The light source lighting device according to claim 11, wherein the wide bandgap semiconductor is silicon carbide, a gallium nitride-based material, or diamond. a light source lighting device according to any one of claims 1 to 12;
and an LED connected to an output of the light source lighting device. Integrating the output voltage of a detection winding magnetically coupled to the inductor of a DC power supply circuit that charges and discharges energy using a switching element and an inductor;
outputting a zero current detection signal when the value obtained by the integration reaches a predetermined detection threshold in the course of the inductor current decreasing;
receiving the zero current detection signal, generating a drive signal for the switching element, and turning on the switching element with the drive signal ;
A control method for a light source lighting device , wherein the switching element is turned on when an oscillating voltage across the switching element is near the bottom . 15. The control method of the light source lighting device according to claim 14, wherein the zero current detection signal is output before the current flowing through the inductor becomes zero .

Images