JP2020014325A - Lighting device and light fixture - Google Patents

Abstract

To provide a lighting device and a light fixture which can perform control in a current critical mode while avoiding an increase in size of a device and deterioration of heat dissipation.SOLUTION: A lighting device comprises: a DC conversion circuit that includes a rectification circuit, a coil in which a current output from the rectification circuit flows, and a switching element for varying increase and decrease of the current flowing in the coil, and converts electric power output from the rectification circuit into DC power while improving a power factor by suppressing a harmonic wave; a control unit that controls the DC conversion circuit; a first voltage divider circuit that divides an output voltage of the rectification circuit; a second voltage divider circuit that divides voltages across the switching element; and a comparator that compares voltages of a first divided voltage output from the first voltage divider circuit and a second divided voltage output from the second voltage divider circuit, and outputs a voltage corresponding to a magnitude relationship between them to the control unit.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lighting device for lighting a light source and a lighting fixture using the lighting device.

  Regulations regarding harmonics of an input current are specified for lighting fixtures using an LED (Light Emitting Diode) as a light source. In Japan, limits are set for harmonics of the input current by Japanese Industrial Standards. Therefore, the lighting device has a PFC (Power Factor Correction) circuit that is a power factor correction circuit for suppressing harmonics of the input current and improving the power factor.

  The lighting device controls the brightness of the LED. Since the brightness of the LED is determined depending on the magnitude of the current of the LED, the lighting device has a current control circuit for controlling the magnitude of the output current to be constant. In particular, there may be a configuration in which the PFC circuit and the current control circuit are realized by one circuit.

JP 2009-213280 A

  Patent Literature 1 discloses that, as timing control for turning on a switching element of a PFC circuit, zero current detection is performed using an output voltage of a secondary winding of a coil. This is called the current critical mode. In this case, since the coil needs to have a transformer structure, the coil becomes large due to the thick winding. Further, since the secondary winding hinders heat radiation of the main winding, there is a problem that the winding temperature rises. In other words, this hinders an increase in the output of the lighting device.

  As another means for detecting the zero current, it is conceivable to detect the coil current by using a shunt resistor. In this case, since a loss occurs in the shunt resistance, there is a problem that the efficiency of the lighting device is reduced.

  Also, a means for detecting the zero current by measuring the voltage between both ends of the coil is conceivable. In this case, if the voltage to be measured fluctuates, zero current cannot be detected correctly, and there is a problem that current critical mode control cannot be performed.

  The present invention has been made in order to solve the above-described problems, and provides a lighting device and a lighting fixture that can perform control in a current critical mode while suppressing an increase in the size of a device and a deterioration in heat dissipation. The purpose is to:

  A lighting device according to the invention of the present application includes a rectifier circuit for rectifying AC power, a coil through which a current output from the rectifier circuit flows, and a switching element that changes an increase or decrease of a current flowing through the coil. A DC conversion circuit that converts the power output from the rectifier circuit into DC power while suppressing a power factor, controls a DC converter circuit, and a first voltage divider that divides an output voltage of the rectifier circuit. A voltage dividing circuit, a second voltage dividing circuit for dividing the voltage between both ends of the switching element, a first divided voltage outputted from the first voltage dividing circuit, and a second voltage dividing outputted from the second voltage dividing circuit. And a comparator for comparing the voltages of the compressed voltages and outputting a voltage according to the magnitude relation to the control unit.

  Other features of the present invention will be clarified below.

  According to the lighting device of the present invention, the voltage across the switching element and the output voltage of the rectifier circuit are divided and compared to detect that the coil current has become zero. Control in the current critical mode while suppressing the deterioration of

FIG. 2 is a diagram illustrating a configuration example of a lighting device and a lighting fixture according to Embodiment 1. FIG. 3 is a diagram illustrating a configuration example of a current control circuit. 5 is a timing chart illustrating an operation of the current control circuit. 5 is a timing chart illustrating an operation of the DC conversion circuit. 5 is a timing chart showing a timing at which a switching element is changed from off to on. FIG. 9 is a diagram illustrating a configuration example of a lighting device and a lighting fixture according to Embodiment 2. 5 is a timing chart showing a timing at which a switching element is changed from off to on. FIG. 14 is a diagram illustrating a configuration example of a lighting device and a lighting fixture according to Embodiment 3. 5 is a timing chart showing a timing at which a switching element is changed from off to on. FIG. 14 is a diagram illustrating a configuration example of a lighting device and a lighting fixture according to Embodiment 4. 5 is a timing chart showing a timing at which a switching element is changed from off to on.

  A lighting device and a lighting device according to an embodiment of the present invention will be described with reference to the drawings. The same or corresponding components are denoted by the same reference numerals, and description thereof may not be repeated. The present invention is not limited by the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a configuration example of a lighting device and a lighting fixture according to Embodiment 1. The lighting fixture 200 is connected to the AC power supply 1. The lighting fixture 200 includes a lighting device 100, a light source 8 that receives and supplies current from the lighting device 100, and a dimmer 10 that outputs a dimming signal for turning on, off, or dimming the light source 8. ing. The lighting device 100 converts the power supplied from the AC power supply 1 into a DC current that can be input to the light source 8 and outputs the power through the input filter 2 that removes a high-frequency component of the AC current output from the AC power supply 1. . The light source 8 is composed of, for example, an LED group in which a plurality of LEDs are connected in series. One end of the LED group is connected to the positive DC bus, and the other end of the LED group is connected to the negative DC bus. Instead of the light source 8 including the LED, the light source 8 including the organic EL may be used.

  The lighting device 100 includes an input filter 2, a rectifier circuit 3 connected to the input filter 2 for rectifying AC power, a capacitor 4 connected in parallel to the rectifier circuit 3, a DC converter circuit 5 as a PFC circuit, and a current control circuit 7. . The lighting device 100 includes a control unit 9 for controlling the DC conversion circuit 5 and the current control circuit 7.

  The lighting device 100 includes a DC conversion circuit 5, a smoothing capacitor 6 for smoothing an output voltage of the DC conversion circuit 5, and a current control circuit 7 for controlling the magnitude of a current output to the light source 8. The DC conversion circuit 5 has a function of suppressing harmonics of a current input from the AC power supply 1 to improve a power factor, and converting power output from the rectification circuit 3 into DC power and supplying the DC power to the light source 8. Have.

  The input filter 2 arranged between the AC power supply 1 and the rectifier circuit 3 has a coil 2a and a filter capacitor 2b, and reduces a high-frequency component superimposed on a current output from the AC power supply 1. The coil 2a is connected to the AC power supply 1 in series. One end of the coil 2a is connected to one end of the AC power supply 1, and the other end of the coil 2a is connected to the filter capacitor 2b and the rectifier circuit 3. The other end of the filter capacitor 2b is connected to the AC power supply 1 and the rectifier circuit 3.

  The rectifier circuit 3 is arranged between the input filter 2 and the DC conversion circuit 5 and converts AC power supplied from the AC power supply 1 into DC power. The rectifier circuit 3 is configured by a diode bridge combining four diodes. The configuration of the rectifier circuit 3 is not limited to this, and may be configured by combining MOSFETs that are unidirectional conductive elements.

  The capacitor 4 is connected in parallel to the output of the rectifier circuit 3 and smoothes the output voltage of the rectifier circuit 3. One end of the capacitor 4 is connected to a positive DC bus, and the other end of the capacitor 4 is connected to a negative DC bus.

  The DC conversion circuit 5 is arranged between the rectifier circuit 3 and the current control circuit 7. The DC conversion circuit 5 has a switching element 5b composed of a MOSFET or the like, a coil 5a, and a diode 5c. When the switching element 5 b is turned on and off by the control unit 9, the output voltage of the rectifier circuit 3 is boosted, and the boosted voltage is output to the smoothing capacitor 6. The DC conversion circuit 5 has a function of suppressing harmonics of the input current and improving the power factor. In the first embodiment, an example in which the DC conversion circuit 5 is configured by a boost chopper circuit will be described. Note that the DC conversion circuit 5 may be configured by a circuit such as a step-up / step-down chopper circuit, a flyback circuit, a flyforward circuit, a SEPIC (Single Ended Primary Inductor Converter), a Zeta converter, or a Cuk converter, in addition to the step-up chopper circuit. .

  The coil 5a is arranged between the capacitor 4 and the switching element 5b on the positive DC bus. The coil 5a can be formed by winding an insulating wire around a core. One end of the coil 5a is connected to one end of the capacitor 4. The other end of the coil 5a is connected to the anode of the diode 5c. Voltages having different polarities are applied to the coil 5a in accordance with the on / off operation of the switching element 5b. When the switching element 5b is turned on, the current output from the rectifier circuit 3 to the coil 5a increases.

  The drain of the switching element 5b is connected to the coil 5a and the anode of the diode 5c on the positive DC bus. The source of the switching element 5b is connected to the other end of the capacitor 4 and the other end of the smoothing capacitor 6 on the negative DC bus. The gate of the switching element 5b is connected to the control unit 9. The control signal output from the control unit 9 is input to the gate of the switching element 5b. The ON / OFF control of the switching element 5b is performed by inputting the control signal.

  The diode 5c is arranged between the switching element 5b and the smoothing capacitor 6 on the positive DC bus. The anode of diode 5c is connected to coil 5a and switching element 5b, and the cathode of diode 5c is connected to smoothing capacitor 6.

  Smoothing capacitor 6 is arranged between DC conversion circuit 5 and current control circuit 7. One end of the smoothing capacitor 6 is connected to a positive DC bus, and the other end of the smoothing capacitor 6 is connected to a negative DC bus.

  The control unit 9 includes a target value output unit 9a, a voltage detection unit 9b, a calculation unit 9c, and a driving unit 9d to control the DC conversion circuit 5.

  The dimmer 10 is connected to the target value output unit 9a. The target value output unit 9a determines an output current target value corresponding to the type of the dimming signal output from the dimmer 10, and outputs the determined output current target value to the calculation unit 9c. The output current target value is a signal that specifies a current target value that the lighting device 100 outputs to the light source 8.

  The voltage detector 9b detects the voltage of the smoothing capacitor 6, and outputs voltage information corresponding to the detected voltage value to the calculator 9c. As the voltage detection unit 9b, a resistance voltage dividing circuit can be exemplified. In the voltage dividing circuit, one end of a series resistor in which two or more resistors are connected in series is connected to a positive DC bus, and the other end of the series resistor is connected to a negative DC bus. This is a circuit for dividing the voltage applied to the smoothing capacitor 6.

  The operation unit 9c outputs a control signal for controlling the DC conversion circuit 5 based on a predetermined output voltage target value and the voltage information input to the voltage detection unit 9b. The current control circuit 7 converts the DC voltage output from the DC conversion circuit 5 into a DC current that can be input to the light source 8 based on the control signal output from the control unit 9.

  FIG. 2 is a diagram illustrating a configuration example of the current control circuit 7. The current control circuit 7 includes a switching element 7a such as a MOSFET, a coil 7b, a diode 7c, and a filter capacitor 7d. Switching element 7a is arranged on the positive DC bus. The drain of switching element 7a is connected to one end of smoothing capacitor 6 shown in FIG. 1 and the cathode of diode 5c. The source of the switching element 7a is connected to the cathode of the diode 7c and one end of the coil 7b. The gate of the switching element 7a is connected to the driving section 9d. The control signal output from the control unit 9 is input to the gate of the switching element 7a. The control signal is a signal for turning on and off the switching element 7a.

  One end of the coil 7b is connected to the source of the switching element 7a and the cathode of the diode 7c. The other end of the coil 7b is connected to one end of the filter capacitor 7d and one end of the light source 8 shown in FIG. The cathode of the diode 7c is connected to the source of the switching element 7a and one end of the coil 7b. The anode of the diode 7c is connected to the other end of the smoothing capacitor 6 shown in FIG. 1, the other end of the filter capacitor 7d, and the other end of the light source 8 shown in FIG.

  Although the current control circuit 7 shown in FIG. 2 is configured by a step-down chopper circuit, in addition to the step-down chopper circuit, a circuit such as a step-up / step-down chopper circuit, a flyback circuit, a flyforward circuit, a SEPIC, a Zeta converter, or a Cuk converter is used. The current control circuit 7 may be configured.

  FIG. 3 is a timing chart showing the relationship between the current flowing through the light source 8, the current flowing through the coil 7b, and the gate voltage of the switching element 7a. FIG. 3 shows, from the top, the current flowing through the light source 8, the current flowing through the coil 7b, and the gate voltage of the switching element 7a. The horizontal axis represents time.

  The switching cycle Tsw is equal to the time from when the control signal of the switching element 7a changes from off to on to when the control signal of the switching element 7a changes from off to on again. The switching cycle Tsw is set in the calculation unit 9c in advance. The on-time Ton is equal to the time from when the control signal of the switching element 7a changes from off to on to when it changes from on to off.

  When the control signal of the switching element 7a changes from the off state to the on state, the switching element 7a is turned on, so that a current path passing through the smoothing capacitor 6, the switching element 7a, the coil 7b and the filter capacitor 7d is formed. As shown in FIG. 7, the current flowing through the coil 7b increases.

  When the control signal of the switching element 7a changes from the on state to the off state, the switching element 7a is turned off, so that a current path passing through the coil 7b, the filter capacitor 7d, and the diode 7c is formed. The flowing current decreases to zero. When the switching cycle Tsw elapses, the control signal of the switching element 7a changes from off to on. As a result, the switching element 7a is turned on again.

  At this time, the current flowing through the coil 7b has a triangular waveform, but the current output to the light source 8 is smoothed by the filter capacitor 7d, and the average value of the current flowing through the coil 7b is output from the current control circuit 7. . After the current flowing through the coil 7b drops to zero, a resonance current is generated in the parasitic capacitance of the switching element 7a and the resonance circuit formed by the coil 7b, but the description is omitted.

  When controlling the current flowing through the light source 8 for dimming the light source 8, the arithmetic unit 9c sets the switching period Tsw for turning on the switching element 7a to be constant, and changes the on-time Ton according to the target value of the output current. The control method of obtaining a specific output by adjusting the ON time Ton in this manner is called duty control because the ratio of the ON time Ton to the switching cycle Tsw is called duty.

  The switching elements 5b and 7a may be made of, for example, a silicon-based semiconductor, or may be made of a wide band gap semiconductor such as silicon carbide or a gallium nitride-based material. By using the wide band gap semiconductors for the switching elements 5b and 7a, the conduction loss of the switching elements can be reduced, and the heat radiation is improved even when the switching frequency, that is, the driving frequency is increased. For this reason, the heat radiation components of the DC conversion circuit 5 and the current control circuit 7 can be reduced in size or omitted, and the size and cost of the lighting device 100 can be reduced.

  Next, the operation of the DC conversion circuit 5 will be described in detail.

  FIG. 4 is a timing chart showing the relationship between the current flowing through the coil 5a shown in FIG. 1, the drain voltage of the switching element 5b, and the gate voltage of the switching element 5b. FIG. 4 shows, in order from the top, the current of the AC power supply 1 input to the lighting device 100, the current flowing through the coil 5a, the zero current detection signal output by the zero current detection circuit 11, the drain voltage of the switching element 5b, and the like. , And the gate voltage of the switching element 5b. The horizontal axis represents time.

  In FIG. 4, for convenience of description, the cycle in which the gate voltage of the switching element 5b is turned on / off is illustrated as being longer than the actual cycle. The cycle in which the gate voltage of the switching element 5b is turned on and off is equal to the time from when the gate voltage of the switching element 5b changes from off to on to when the gate voltage of the switching element 5b changes from off to on again.

  When the switching element 5b is turned on, a current path of the AC power supply 1, the rectifier circuit 3, the coil 5a, and the switching element 5b is formed, and the AC power supply 1 is short-circuited via the coil 5a. Therefore, the current flowing through the coil 5a increases, and energy is stored in the coil 5a.

  When the ON time set in the operation section 9c elapses, the switching element 5b is turned off. Thereby, a current path of the coil 5a, the diode 5c and the smoothing capacitor 6 is formed. In this current path, the energy stored in the coil 5a is released, and the smoothing capacitor 6 is charged.

  When the current flowing through the coil 5a becomes zero, the switching element 5b is turned on again. By the switching element 5b, the increase or decrease of the current flowing through the coil 5a can be changed. The control for turning on the switching element 5b immediately after the current of the coil 5a becomes zero is called a current critical mode.

  By a series of on / off operations of the switching element 5b, the current flowing through the coil 5a has a triangular waveform, and the vertices have a sinusoidal envelope as shown by a dotted line. At this time, a high-frequency component is removed from the current waveform input from the AC power supply 1 by the input filter 2, and the average value of the coil current flowing through the coil 2a is input, thereby forming a sinusoidal waveform.

  At this time, the voltage detector 9b detects the applied voltage of the smoothing capacitor 6, and the feedback control is performed by the controller 9 so that the detected voltage follows the target value, so that the ON time of the switching element 5b is controlled. Is done.

  When the on-time of the switching element 5b is feedback-controlled, if the on-time greatly changes, the envelope of the top of the current flowing through the coil 5a does not become a sine wave, and the input current of the AC power supply 1 becomes a sine wave. Can not do. Therefore, in the control unit 9, the response time of the feedback control is set so that the loop gain of the feedback control is equal to or less than 1 time (0 dB) in a period equal to or more than の of one period of the AC power supply 1. In other words, the response time of the feedback control is set to be equal to or less than 1 time (0 dB) at a frequency equal to or less than twice the frequency of the AC power supply 1.

  More specifically, when the power supply frequency is 50 Hz, the loop gain of the feedback control is set to 1 time (0 dB) or less at a frequency of 100 Hz or less of a half cycle (half wave) of the power supply frequency, that is, at a cycle of 10 msec or more. Thereby, the feedback control is set so as not to respond in a cycle shorter than 1/2 of the power supply cycle. In addition, within a half cycle of the power supply cycle, the fluctuation of the ON time of the switching element 5b is suppressed, and the envelope of the top of the current flowing through the coil 5a has a sinusoidal waveform.

  In the feedback control, the same effect can be obtained by setting the cycle of updating the ON time to a cycle corresponding to half of the cycle of the AC power supply 1 or a cycle longer than a cycle corresponding to half of the cycle of the AC power supply 1. be able to.

  After detecting the zero current, a slight delay time is provided until the switching element 5b is turned on, and the switching element 5b is turned on near the bottom of the drain voltage oscillation during the period when the drain voltage of the switching element 5b is oscillating freely. You can also. This makes it possible to suppress a sharp change in the drain voltage and suppress noise caused by switching.

  When dimming the light source 8, the arithmetic unit 9c performs control to shorten the on-time of the switching element 5b in order to reduce the input current of the AC power supply 1.

  Next, the zero current detection circuit 11 and its operation will be described. FIG. 1 shows a zero current detection circuit 11. The zero current detection circuit 11 includes voltage dividing resistors 11a, 11b, 11c, 11d, and a comparator 11e. The comparator 11e outputs a zero current detection signal for detecting that the current of the coil 5a has become zero.

  One end of the voltage dividing resistor 11a is connected to the capacitor 4, and the other end is connected to the voltage dividing resistor 11b and the input terminal of the comparator 11e. One end of the voltage dividing resistor 11b is connected to the voltage dividing resistor 11a and the input terminal of the comparator 11e, and the other end is connected to the negative DC bus. That is, the voltage dividing resistors 11a and 11b divide the output voltage VDB of the rectifier circuit 3 into a voltage that can be input to the comparator 11e. The voltage dividing resistors 11a and 11b are an example of a first voltage dividing circuit 11A that divides the output voltage VDB of the rectifier circuit 3.

  One end of the voltage dividing resistor 11c is connected to the drain terminal of the switching element 5b, and the other end is connected to the voltage dividing resistor 11d and the input terminal of the comparator 11e. One end of the voltage dividing resistor 11d is connected to the voltage dividing resistor 11c and the input terminal of the comparator 11e, and the other end is connected to the negative DC bus. That is, the voltage dividing resistors 11c and 11d divide the drain voltage Vds of the switching element 5b into a voltage that can be input to the comparator 11e. The voltage dividing resistors 11c and 11d are an example of a second voltage dividing circuit 11B that divides the drain voltage Vds of the switching element 5b. The second voltage dividing circuit 11B can be said to be a circuit for dividing the voltage between both ends of the switching element 5b. The voltage dividing ratios in the first voltage dividing circuit 11A and the second voltage dividing circuit 11B can be made equal.

The comparator 11e compares the output voltage VDB of the rectifier circuit 3 with the drain voltage Vds of the switching element 5b via the voltage dividing resistors 11a and 11b and the voltage dividing resistors 11c and 11d. The drain voltage Vds of the switching element 5b may be simply referred to as Vds, and the output voltage VDB of the rectifier circuit 3 may be simply referred to as VDB. To be precise, the comparator 11e is first divided voltage VDB was pressurized to VDB minute ^- a second divided voltage Vds obtained by dividing the amount Vds ^- comparing the arithmetic unit 9c a signal based on the result of the comparison Output to Hereinafter, the voltage division ratio of the first voltage dividing circuit 11A and the second voltage dividing circuit 11B is equal, the second divided voltage Vds ^- is the first division voltage VDB ^- outputs a high signal is greater than the second minute voltage Vds ^- is the first division voltage VDB ^- described arrangement outputs a low signal is smaller than.

FIG. 5 is a timing chart showing the timing of changing the switching element 5b from off to on. In order from the top in FIG. 5, the current flowing through the coil 5a, the voltage of the coil 5a, the second divided voltage Vds ^- and a zero current detection signal output from the zero current detection circuit 11, the gate voltage of the switching element 5b Are shown. Note that the horizontal axis represents time.

t1 is the timing when the gate voltage of the switching element 5b is changed from on to off. After t1, when the diode 5c is turned on, the output voltage of the DC conversion circuit 5 charged in the smoothing capacitor 6 is applied to the drain of the switching element 5b. After t1, the coil 5a discharges the charged energy to the smoothing capacitor 6, so that the current of the coil 5a decreases. The second divided voltage Vds ^- is the first division voltage VDB ^- larger than, the high signal is output as a zero current detection signal.

t2 is the timing when the current of the coil 5a decreases to zero. When the current of the coil 5a decreases to zero, a resonance voltage is generated in the parasitic capacitance of the switching element 5b and the resonance circuit formed by the coil 5a. The waveform of the voltage of the coil 5a, the second division voltage Vds ^- the dotted line shown in the waveform display area of an auxiliary line indicating a resonance voltage in the subsequent t2. The resonance voltage of the coil 5a to zero, the second divided voltage Vds ^- resonance voltage of VDB ^- a vibration waveform to converge to.

t3 is a timing at which the second divided voltage Vds ⁻ decreases to the first divided voltage VDB ⁻ due to the resonance voltage after the current of the coil 5a has decreased to zero. At t3, a low signal is output as a zero current detection signal. The calculation unit 9c detects that the zero current detection signal has changed from high to low, and thereby determines that the current of the coil 5a has decreased to zero.

  The resonance voltage of Vds changes depending on the magnitude of VDB and the instantaneous value of the output voltage Vpfc of the DC conversion circuit 5. However, since the resonance voltage of Vds converges to VDB, a comparison between the divided voltage of Vds and the divided voltage of VDB allows zero-current detection even when VDB or the output voltage Vpfc of the DC conversion circuit 5 fluctuates. The signal can be changed from high to low. It should be noted that the logic of the zero current detection signal may be reversed from the above-described logic, and control according to the logic may be realized.

  t4 is a timing when the gate of the switching element 5b is changed from off to on. When Vds decreases to near zero, the output of the rectifier circuit 3 is short-circuited via the coil 5a, so that the current of the coil 5a increases after t4, and the coil 5a charges energy. t4 may be, for example, a timing at which the vibration of Vds becomes a minimum value. As Vds at the timing when the switching element 5b is turned on is smaller, a sharp change in voltage can be suppressed and noise can be reduced. Further, the change width of the voltage can be reduced, and the loss can be reduced. Therefore, it is possible to investigate beforehand how long the period from t3 to t4 is to minimize Vds at the timing t4 when the switching element 5b is turned on. The noise and the loss can be suppressed by continuously using the optimal period of t3 to t4 obtained by the investigation.

  By using the zero current detection circuit 11 described above, it is possible to eliminate the need for the secondary winding of the coil, which is conventionally required when performing control in the discontinuous current mode including the current critical mode. This makes it possible to reduce the size of the coil, improve the heat dissipation, suppress the temperature rise of the coil, and increase the output of the lighting device. When a secondary winding is provided, the shape of the coil is limited to a transformer. However, since the present configuration does not require a secondary winding, the degree of freedom of the shape of the coil 5a is improved. For example, an air-core coil, a single-sided substrate planar coil, or a drum coil can be applied as the coil 5a.

The comparator 11e is first divided voltage VDB output from the first voltage dividing circuit 11A ^- a second divided voltage Vds output from the second voltage dividing circuit 11B ^- comparing, in accordance with the magnitude relation It can be said that the voltage is output to the control unit 9. In the first embodiment, the comparator 11e outputs a zero current detection signal to the control unit 9, the first division voltage VDB ^- than the second divided voltage Vds ^- is a zero current detection signal becomes lower by logically inverting . Then, after this logical inversion, the control unit 9 has shown an operation of turning on the switching element 5b. If the voltage dividing ratios of the first voltage dividing circuit 11A and the second voltage dividing circuit 11B are different, more complicated processing is required as compared with the case where the magnitude relation between the first divided voltage and the second divided voltage is compared. .

  The structure described in Embodiment 1 can also be applied to lighting devices and lighting devices according to the following embodiments. Since the lighting device and the lighting fixture according to the following embodiment have many points in common with the first embodiment, the description will focus on differences from the lighting device and the lighting fixture according to the first embodiment.

Embodiment 2 FIG.
FIG. 6 is a diagram illustrating a configuration example of a lighting device 100A and a lighting fixture 200A according to Embodiment 2. Lighting device 200A according to Embodiment 2 differs from lighting device 200 according to Embodiment 1 in that lighting device 100A is used instead of lighting device 100. The difference between the lighting device 100A according to the second embodiment and the lighting device 100 according to the first embodiment is that, in the lighting device 100A, the zero current detection circuit 11C includes a diode 11f and a voltage source 11g.

  The zero current detection circuit 11C includes a diode 11f and a voltage source 11g, which is a DC power supply, in addition to the voltage dividing resistors 11a, 11b, 11c, and 11d and the comparator 11e. The diode 11f and the voltage source 11g constitute a voltage supply unit 11D. The comparator 11e outputs a zero current detection signal for detecting that the current of the coil 5a has become zero.

  The diode 11f has a cathode connected to the voltage dividing resistors 11a and 11b and an input terminal of the comparator 11e, and an anode connected to one end of the voltage source 11g. One end of the voltage source 11g is connected to the anode of the diode 11f. Voltage source 11g provides a voltage greater than the forward voltage of diode 11f.

First voltage divider circuit 11A as described above, the midpoint voltage of the two resistor elements connected in series the first division voltage VDB ^- output as. Therefore, it can be said that the cathode of the diode 11f is connected to the midpoint between the two resistance elements.

The other end of the voltage source 11g is connected to the voltage dividing resistor 11b at the negative DC bus. Dividing resistors 11a, 11b can be input to the comparator 11e the VDB of the first division voltage VDB ^- pressure bisection. First division voltage VDB ^- if falls below the voltage of the voltage source 11g inputs the voltage of the voltage source 11g to the comparator 11e. In the second embodiment, the first division voltage VDB ^- the voltage of the voltage source 11g is provided only to the comparator 11e when is reduced, otherwise the first division voltage VDB ^- to the comparator 11e It can be said that an OR circuit is provided.

As described above, the comparator 11e outputs the zero current detection signal based on the voltage of the voltage source 11g to the calculation unit 9c in addition to the divided voltages of VDB and Vds. Here, as an example, voltage dividing resistors 11a, 11b and the voltage dividing resistors 11c, partial pressure ratio of 11d are the same, the second divided voltage Vds ^- a high signal is greater than ^- the first division voltage VDB A configuration for outputting to the control unit 9 and outputting a low signal to the control unit 9 when the second divided voltage Vds ⁻ is smaller than the first divided voltage VDB ⁻ will be described.

First division voltage VDB inputted to the comparator 11e ^- if larger than the voltage of the voltage source 11g, the diode 11f does not conduct. In this case, since the circuit operation of the zero current detection circuit 11C is the same as the circuit operation of the zero current detection circuit 11 in the first embodiment, the description will be omitted.

On the other hand, the first division voltage VDB ^- is the smaller than the voltage of the voltage source 11g, with reference to FIG. 7, illustrating a circuit operation of the zero current detection circuit 11C.

FIG. 7 is a timing chart showing the timing when the switching element 5b in FIG. 6 is changed from off to on. FIG. 7 shows, from the top, the current flowing through the coil 5a, the voltage of the coil 5a, the second divided voltage Vds ⁻ , the zero current detection signal output by the zero current detection circuit 11C, and the gate voltage of the switching element 5b. Note that the horizontal axis represents time.

t1 is the timing when the gate voltage of the switching element 5b is changed from on to off. Since the diode 5c conducts during the period from t1, the output voltage of the DC converter 5 charged in the smoothing capacitor 6 is applied to the drain of the switching element 5b. After t1, the coil 5a discharges the charged energy to the smoothing capacitor 6, so that the coil current decreases. First division voltage VDB ^- the second divided voltage Vds ^- larger than, the high signal is output as a zero current detection signal.

t2 is the timing when the current of the coil 5a decreases to zero. When the current of the coil 5a decreases to zero, a resonance voltage is generated in the parasitic capacitance of the switching element 5b and the resonance circuit formed by the coil 5a. The waveform of the voltage of the coil 5a, the second division voltage Vds ^- the dotted line shown in the display field of the waveforms are auxiliary lines showing the resonant voltage at the later t2. Further, the voltage of the coil 5a to zero, the second division voltage Vds ^- the first division voltage VDB ^- a vibration waveform to converge to.

t3 is a timing at which the second divided voltage Vds ⁻ decreases to the voltage of the voltage source 11g due to the resonance voltage after the current of the coil 5a has decreased to zero. The second divided voltage Vds ^- when is smaller than the voltage of the voltage source 11g, low signal is outputted from the zero current detection circuit 11C. The calculation unit 9c detects that the zero current detection signal has changed from high to low, and thereby determines that the current of the coil 5a has decreased to zero. Note that the second divided voltage Vds ^- second divided voltage Vds in the process of decreases ^- to produce the timing is less than the voltage of the voltage source 11g, the voltage source 11g is provided to the comparator 11e voltage, the second divided voltage Vds ^- has to be smaller than the maximum value of.

  t4 is the timing when Vds drops to zero due to the resonance voltage after the current of the coil 5a has dropped to zero. When Vds drops to zero, the parasitic diode of the switching element 5b conducts, so that Vds does not drop below zero.

  t5 is a timing at which the gate of the switching element 5b is changed from off to on. When Vds decreases to near zero, the output of the rectifier circuit 3 is short-circuited via the coil 5a, so that the current of the coil 5a increases after t5, and the coil 5a charges energy.

The zero current detection circuit 11 according to the first embodiment has a configuration in which the voltage source 11g is not used. For this reason, when VDB or the first divided voltage VDB ⁻ decreases to near zero, the second divided voltage Vds ⁻ may not become lower than the first divided voltage VDB ^{− in} some cases. In this case, the zero current detection signal cannot be changed from high to low, and zero current cannot be detected. In contrast, the zero current detection circuit 11C shown in the second embodiment by using a voltage source 11g, the first division voltage VDB ^- even when the drops to near zero, the first division voltage VDB ^- instead of Since the voltage of the voltage source 11g is provided to the comparator 11e, zero current can be detected.

  When performing control such as critical mode control that changes the switching element 5b from off to on based on zero current detection, if zero current detection is not possible, the switching operation cannot be restarted after stopping. As a countermeasure, there is a method in which when the zero current cannot be detected, the control unit 9 restarts switching after a predetermined time has elapsed. However, this is not preferable because the switching frequency is reduced, so that the distortion of the input current waveform increases and the harmonics increase.

  Therefore, by using the zero current detection circuit 11C according to the second embodiment, control in the current critical mode or the current discontinuous mode other than the critical mode can be reliably performed. In addition, the secondary winding of the coil, which is conventionally required in the critical mode, can be eliminated. This makes it possible to reduce the temperature of the coil by reducing the size of the coil and improving the heat dissipation, thereby increasing the output of the lighting device. Further, when the secondary winding is provided, the shape of the coil 5a is limited to the transformer, but since this configuration does not require the secondary winding, the degree of freedom of the shape of the coil 5a is improved. Therefore, for example, an air-core coil, a single-sided substrate planar coil, or a drum type coil can be applied as the coil 5a. In addition, even when the VDB drops, such as near the power supply voltage zero crossing or when the power supply voltage sags, a more accurate zero current detection can be performed. Is possible.

Although the voltage source 11g is described as an individual component in the second embodiment, for example, the voltage source may be provided by dividing a control power supply for operating the comparator 11e. Voltage supply unit 11D includes the first division voltage VDB ^- when is smaller than a predetermined value, the first division voltage VDB ^- in place, the first division voltage VDB ^- comparators higher voltage 11e. Another circuit providing such an operation can be employed as the voltage supply unit 11D.

Embodiment 3 FIG.
FIG. 8 is a diagram showing a configuration example of a lighting device 100B and a lighting fixture 200B according to Embodiment 3. Lighting device 200B according to Embodiment 3 and lighting device 200 according to Embodiment 1 are different from lighting device 200B in that lighting device 100B is used instead of lighting device 100 in lighting device 200B. The difference between lighting device 100B according to Embodiment 3 and lighting device 100 according to Embodiment 1 is that in lighting device 100B, zero current detection circuit 11E includes voltage drop diode 11h.

The zero current detection circuit 11E includes a voltage drop diode 11h in addition to the voltage dividing resistors 11a, 11b, 11c, and 11d and the comparator 11e. The voltage drop diode 11h has a cathode connected to the voltage dividing resistors 11a and 11b and an anode connected to the voltage dividing resistors 11c and 11d. More specifically, the cathode of the voltage drop diode 11h is connected to the output of the first voltage dividing circuit having the voltage dividing resistors 11a and 11b. The anode of the voltage drop diode 11h is connected to the output of a second voltage dividing circuit having voltage dividing resistors 11c and 11d. Voltage drop diode 11h second divided voltage Vds ^- lowering. The comparator 11e outputs a zero current detection signal for detecting that the current of the coil 5a has become zero.

The comparator 11e outputs a signal based on the divided voltage of VDB and Vds to the calculation unit 9c. In this example, the voltage dividing ratios of the voltage dividing resistors 11a and 11b and the voltage dividing resistors 11c and 11d are the same. The second divided voltage Vds ^- is the first division voltage VDB ^- comparator 11e outputs a high signal is greater than the second divided voltage Vds ^- less than ^- the first division voltage VDB In this case, the comparator 11e outputs a low signal.

FIG. 9 is a timing chart showing the timing of changing the switching element 5b shown in FIG. 8 from off to on. FIG. 9 shows, in order from the top, a current flowing through the coil 5a, a voltage of the coil 5a, Vds, a second divided voltage Vds ⁻ , a zero current detection signal indicating a timing at which the current flowing through the coil 5a becomes zero, and a switching element. 5b is shown. Note that the horizontal axis represents time.

  t1 is the timing when the gate voltage of the switching element 5b is changed from on to off, and when the diode 5c is turned on, the output voltage of the DC conversion circuit 5 charged in the smoothing capacitor 6 is applied to the drain of the switching element 5b. Is done. After t1, the energy charged in the coil 5a is discharged to the smoothing capacitor 6, so that the current in the coil 5a decreases. Since Vds is larger than VDB, a high signal is output as a zero current detection signal.

At this time, since Vds is larger than VDB and the voltage division ratios of the voltage dividing resistors 11a, 11b, 11c, and 11d are equal, the voltage drop diode 11h conducts. Accordingly, the second divided voltage Vds to be inputted to the comparator 11e ^- is the average value of the output voltage and VDB of the DC converter circuit 5, the voltage obtained by adding the forward voltage of the voltage drop diode 11h.

  t2 is the timing when the current of the coil 5a decreases to zero. When the current of the coil 5a decreases to zero, a resonance voltage is generated in the parasitic capacitance of the switching element 5b and the resonance circuit formed by the coil 5a. The dotted line shown in the display column of the voltage waveform of the coil 5a and the Vds waveform is an auxiliary line showing the resonance voltage after t2. The resonance voltage of the coil 5a is zero and the resonance voltage of Vds is a vibration waveform converging to VDB.

t3 is a timing at which the second divided voltage Vds ⁻ decreases to the first divided voltage VDB ⁻ due to the resonance voltage after the current of the coil 5a has decreased to zero. after t3, the second divided voltage Vds ^- is the first division voltage VDB ^- to become smaller than the low signal is outputted as a zero-current detection signal. The calculation unit 9c detects that the zero current detection signal has changed from high to low, and thereby determines that the current of the coil 5a has decreased to zero. The second divided voltage Vds ^- is the first division voltage VDB ^- becomes smaller than the voltage drop diode 11h becomes non-conductive.

  t4 is a timing when the gate of the switching element 5b is changed from off to on. When Vds decreases to near zero, the output of the rectifier circuit 3 is short-circuited via the coil 5a, so that the current of the coil 5a increases after t5, and the coil 5a charges energy.

Incidentally, the output voltage of the DC conversion circuit 5 may be an overvoltage. For example, when the normal output voltage is 400 V, an output voltage as high as 500 to 600 V may occur. In this case, for example, even if the output voltage of 600V is generated, thereby to comparator 11e is not failed, a second divided voltage Vds ^- shall make smaller. That is, when determining dividing resistors 11c, the resistance value of 11d considers the overvoltage that may occur in the output voltage of the DC converter circuit 5, the second divided voltage Vds ^- to within the breakdown voltage of the comparator 11e There is a need. Therefore, the second divided voltage Vds in the case where an overvoltage does not occur ^- forced to not give so low, resulting in the use of narrow voltage range. Use of a narrow voltage range may cause malfunction. On the other hand, the zero current detection circuit 11E according to the third embodiment can suppress the peak value of the second divided voltage Vds ⁻ by using the voltage drop diode 11h. Then, when no overvoltage occurs, a wide voltage range can be used, and malfunction can be suppressed.

  By using the zero current detection circuit 11E of this configuration, the secondary winding of the coil which is conventionally required when performing the control in the current critical mode or the current discontinuous mode other than the current critical mode is unnecessary. Can be. This makes it possible to reduce the temperature of the coil by reducing the size of the coil and improving the heat dissipation, thereby increasing the output of the lighting device. When a secondary winding is provided, the shape of the coil is limited to a transformer. However, since the present configuration does not require a secondary winding, the degree of freedom of the shape of the coil 5a is improved. As the coil 5a, for example, an air-core coil, a single-sided substrate planar coil, or a drum type coil can be applied. In addition, since the divided voltage input to the comparator 11e can be reduced, an inexpensive comparator 11e having a rough detection resolution can be used, and the lighting device 100B can be reduced in cost.

Embodiment 4 FIG.
FIG. 10 is a diagram illustrating a configuration example of a lighting device 100C and a lighting fixture 200C according to Embodiment 4. Lighting device 200C according to Embodiment 4 and lighting device 200 according to Embodiment 1 are different from lighting device 200C in that lighting device 100C is used instead of lighting device 100 in lighting device 200C. The difference between the lighting device 100C and the lighting device 100 according to Embodiment 1 is that the zero current detection circuit 11F of the lighting device 100C includes an output stop switching element 11i.

  The zero current detection circuit 11F includes, in addition to the voltage dividing resistors 11a, 11b, 11c, 11d, and the comparator 11e, an output stop switching element 11i composed of, for example, a MOSFET. The driving section 9d is connected to the gate of the output stop switching element 11i in addition to the switching element 5b. The drive unit 9d controls the on / off state of the output stop switching element 11i based on the calculation result of the calculation unit 9c.

  The drain terminal of the output stop switching element 11i is connected to the output terminal of the comparator 11e and the operation unit 9c. The source terminal of the output stop switching element 11i is connected to the negative bus voltage. The comparator 11e outputs a zero current detection signal for detecting that the current of the coil 5a has become zero. However, when the output stop switching element 11i is on, the output voltage of the zero current detection circuit 11F is fixed at low. The output stop switching element 11i switches the connection between the output terminal of the comparator 11e and the reference potential. The output stop switching element 11i adds a mask function to the output voltage of the zero current detection circuit 11F.

The comparator 11e outputs a signal based on the divided voltage of VDB and Vds to the calculation unit 9c. In this example, the voltage dividing ratios of the voltage dividing resistors 11a and 11b and the voltage dividing resistors 11c and 11d are the same. The second divided voltage Vds ^- is the first division voltage VDB ^- outputs a high signal is greater than the second divided voltage Vds ^- is the first division voltage VDB ^- low signal is smaller than Will be described.

FIG. 11 is a timing chart showing the timing of changing the switching element 5b shown in FIG. 10 from off to on. In FIG. 10, in order from the top, the current flowing through the coil 5a, the voltage of the coil 5a, the second divided voltage Vds ⁻ , the zero current detection signal output by the zero current detection circuit 11C, the drain voltage of the output stop switching element 11i, and the switching. The gate voltage of element 5b is shown. Note that the horizontal axis represents time.

t1 is the timing when the gate voltage of the switching element 5b is changed from on to off. When the diode 5c conducts, the output voltage of the DC converter 5 charged in the smoothing capacitor 6 is applied to the drain of the switching element 5b. After t1, the coil 5a discharges the charged energy to the smoothing capacitor 6, so that the current of the coil 5a decreases. The second divided voltage Vds ^- is the first division voltage VDB ^- larger than, the high signal is output as a zero current detection signal. At this time, the output stop switching element 11i is changed from ON to OFF.

t2 is the timing when the current of the coil 5a decreases to zero. When the current of the coil 5a decreases to zero, a resonance voltage is generated in the parasitic capacitance of the switching element 5b and the resonance circuit formed by the coil 5a. And the voltage waveform of the coil 5a, the second division voltage Vds ^- the dotted line shown in the display field of the waveforms are auxiliary lines showing the resonant voltage at the later t2. The voltage of the coil 5a to zero, the second division voltage Vds ^- the first division voltage VDB ^- a vibration waveform to converge to.

t3 is a timing at which the second divided voltage Vds ⁻ decreases to the first divided voltage VDB ⁻ due to the resonance voltage after the current of the coil 5a has decreased to zero. At t3, since Vds becomes smaller than VDB, a low signal is output as the zero current detection signal. The calculation unit 9c detects that the zero current detection signal has changed from high to low, and thereby determines that the current of the coil 5a has decreased to zero. When determining that the current of the coil 5a has decreased to zero, the calculation unit 9c outputs a signal for changing the output stop switching element 11i from off to on to the output stop switching element 11i. That is, when receiving the first logical inversion of the zero current detection signal, the control unit 9 turns on the output stop switching element 11i.

  In the fourth embodiment, after detecting that the current of the coil 5a has decreased to zero at t3, a delay time is provided until the switching element 5b is changed from off to on again. By providing the delay time, the switching frequency can be lowered, so that the switching loss generated in the switching element 5b can be suppressed and the high-frequency loss such as iron loss or copper loss generated in the coil 5a can be reduced. Can be.

  As a means for providing a delay time, there is a method of providing a delay after detecting a falling or logical inversion of the zero current detection signal in the arithmetic unit 9c and transmitting a signal for switching the switching element 5b from off to on.

t4, t5 by the resonance voltage after the current in the coil 5a is reduced to zero, the second divided voltage Vds ^- is the first division voltage VDB again ^- it is time to intersect the. In t4, the second divided voltage Vds ^- is the first division voltage VDB ^- tries outputs a high signal to become larger than attempts to output a low signal at t5. When the delay time starts to advance after receiving the first logical inversion of the zero current detection signal at t3, the delay time can be reset when the logical inversion of the zero current detection signal is received again at t4 and t5. In order to prevent such an adverse effect, the output stop switching element 11i is turned on at a timing after t3, and the output of the comparator 11e is fixed at low, so that unnecessary zero current detection during the delay time is provided. Is masked.

  t6 is a timing when the gate of the switching element 5b is changed from off to on, and the drain voltage of the switching element 5b decreases to near zero. Since the output of the rectifier circuit 3 is short-circuited via the coil 5a, the current of the coil 5a increases after t6, and the coil 5a charges energy. The delay time started at t3 continues until, for example, t6.

  By using the zero current detection circuit 11F of the present configuration, it is possible to eliminate the need for the secondary winding of the coil which is conventionally required when performing control in the current critical mode or in the current discontinuous mode other than the critical mode. it can. This makes it possible to reduce the temperature of the coil by reducing the size of the coil and improving the heat dissipation, thereby increasing the output of the lighting device. When a secondary winding is provided, the shape of the coil is limited to a transformer. However, since the present configuration does not require a secondary winding, the degree of freedom of the shape of the coil 5a is improved. As the coil 5a, for example, an air-core coil, a single-sided substrate planar coil, or a drum type coil can be applied. In addition, since the switching frequency can be reduced by providing the delay time, the switching loss generated in the switching element 5b can be suppressed. This reduces high-frequency loss such as iron loss and copper loss generated in the coil 5a, and contributes to increasing the efficiency of the lighting device 100C.

  Note that the output stop switching element 11i is not limited to a MOSFET, and a switching element such as a transistor or a thyristor can be used. The MOSFET is employed in this embodiment because it can perform high-speed switching.

  In the configuration described in the above embodiment, a configuration is described in which a voltage dividing resistor is used as a voltage dividing means used in the zero current detection circuit. As the voltage dividing means, a means for dividing the voltage by connecting capacitors in series can be used. The configuration shown in the above embodiment is an example of the content of the present invention, and can be combined with the second, third, and fourth embodiments, or combined with another known technique. A part of the configuration may be omitted or changed without departing from the scope of the present invention.

  Further, the case where the light source 8 is configured by the LED has been described, but the light source 8 is not limited to the LED, and may be an organic EL (Electro Luminescence).

  Reference Signs List 1 AC power supply, 2 input filter, 3 rectifier circuit, 4 capacitor, 5 DC conversion circuit, 6 smoothing capacitor, 7 current control circuit, 8 light source, 9 control unit, 10 dimmer, 11 zero current detection circuit, 2a, 5a , 7b coil, 2b, 7d filter capacitor, 5b, 7a switching element, 5c, 7c, 11f diode, 11g voltage source, 11h voltage drop diode, 11i output stop switching element, 9a target value output section, 9b voltage detection section, 9c Arithmetic unit, 9d drive unit, 11a, 11b, 11c, 11d voltage dividing resistor, 11e comparator, 100, 100A, 100B, 100C lighting device, 200, 200A, 200B, 200C lighting equipment

Claims (11)

A rectifier circuit for rectifying AC power;
A coil through which the current output from the rectifier circuit flows, and a switching element that changes the increase and decrease of the current flowing through the coil, suppresses harmonics, improves the power factor, and outputs power from the rectifier circuit. A DC conversion circuit for converting the DC power into DC power,
A control unit for controlling a DC conversion circuit;
A first voltage divider circuit for dividing an output voltage of the rectifier circuit;
A second voltage dividing circuit for dividing a voltage between both ends of the switching element;
A first divided voltage output from the first voltage dividing circuit is compared with a second divided voltage output from the second voltage dividing circuit, and a voltage according to a magnitude relationship is output to the control unit. A lighting device, comprising: a comparator. The comparator outputs a zero current detection signal to the control unit, and logically inverts the zero current detection signal when the second divided voltage is lower than the first divided voltage,
The lighting device according to claim 1, wherein the control unit turns on the switching element after the logical inversion occurs.   3. The lighting device according to claim 1, wherein a voltage division ratio in the first voltage division circuit is equal to a voltage division ratio in the second voltage division circuit. 4.   A voltage supply unit that provides a voltage higher than the first divided voltage to the comparator, instead of the first divided voltage, when the first divided voltage becomes smaller than a predetermined value. The lighting device according to claim 1, wherein: The first voltage dividing circuit outputs a midpoint voltage of two series-connected resistance elements as the first divided voltage,
The voltage supply unit includes a diode having a cathode connected to a midpoint between the two resistance elements, and a voltage source connected to an anode of the diode and providing a voltage higher than a forward voltage of the diode. The lighting device according to claim 4, wherein:   The lighting device according to claim 4, wherein a voltage provided to the comparator by the voltage supply unit is smaller than a maximum value of the second divided voltage.   A voltage reducing diode, wherein a cathode is connected to an output of the first voltage dividing circuit and an anode is connected to an output of the second voltage dividing circuit, and the voltage decreasing diode reduces the second divided voltage. The lighting device according to any one of 1 to 6. An output stop switching element for switching the connection between the output terminal of the comparator and a reference potential is provided,
The lighting device according to claim 2, wherein the control unit turns on the output stop switching element when receiving the first logical inversion. A lighting device according to any one of claims 1 to 8,
A light source that receives a current supplied from the lighting device.   The lighting device according to claim 9, wherein the light source includes an LED.   The lighting device according to claim 9, wherein the light source includes an organic EL.

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