JP2014127376A - Lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lighting device with high power efficiency and low noise.SOLUTION: The lighting device comprises a power conversion circuit and a control circuit. The power conversion circuit includes a main switching element, a synchronous rectifier element, a coil, and a capacitor, and converts DC power supply to supply the converted power to a light-emitting diode (LED) load connected in parallel with the capacitor. The control circuit performs ON/OFF control on the main switching element and the synchronous rectifier element. When a current flowing in the coil reaches a first preset value, the main switching element is turned off and after the lapse of a predetermined time, the synchronous rectifier element is turned on, by the control circuit. Also, after a polarity of the current flowing in the coil is inverted from a polarity of the first preset value, the synchronous rectifier element is turned off and after the lapse of a predetermined time, the main switching element is turned on, by the control circuit.

Description

  The present invention relates to a lighting device.

  In a lighting device that drives a light source (load) such as a light emitting diode (hereinafter referred to as LED: Light Emitting Diode), improvement of power conversion efficiency is an important issue. In order to improve power conversion efficiency, lighting devices using switching type power conversion circuits such as step-down choppers, buck-boost choppers, flyback converters, etc. are used, but further improvement in power conversion efficiency is expected. It is rare.

  In order to further improve the power conversion efficiency, Patent Document 1 includes a case where the main switching element that the power conversion circuit originally has for the switching operation including the case where the synchronous rectification is not applied and the case where the synchronous rectification is applied. And a synchronous rectifying element that is a switching element used as a replacement from the free wheel diode, and a lighting device that applies synchronous rectification is described.

JP 2011-151913 A

  In the lighting device described in Patent Document 1, when the synchronous rectifying element is turned off and the main switching element is turned on after a dead time, charging / discharging of the parasitic capacitance (capacitor) that each switching element has between the electrodes occurs. In this charge / discharge, a spike-like current flows through the main switching element, which may cause a turn-on loss and noise. In particular, when synchronous rectification is applied as in Patent Document 1, since a synchronous rectifier element having a small resistance (ON resistance) during conduction is used, the parasitic capacitance between the electrodes is large, and the spike associated with the charge / discharge described above. The current of the shape may also increase.

  An object of the present invention is to provide a lighting device with high power conversion efficiency and low noise.

  In order to solve the above problems, a main switching element, a synchronous rectifying element, a coil, and a capacitor are provided, and a direct current power source is converted to supply power to a light emitting diode (hereinafter referred to as LED) load connected in parallel with the capacitor. A power conversion circuit; and a control circuit for controlling on / off of the main switching element and the synchronous rectifying element, wherein the control circuit is configured to switch the main switching element when a current flowing through the coil reaches a first set value. The element is turned off, the synchronous rectification element is turned on after a predetermined time has elapsed, and the polarity of the current flowing through the coil is reversed from the polarity of the first set value, and then the synchronous rectification element is turned off, for a predetermined time. After the elapse of time, the main switching element is turned on.

  According to the present invention, it is possible to provide a lighting device with high power efficiency and low noise.

It is a basic lineblock diagram of the lighting device of the present invention. It is a figure which shows the operation | movement waveform of the lighting device of this invention. It is a figure which shows the specific example of an electric current detection means and a control circuit. It is a figure which shows another example of a control circuit. It is a figure which shows another example of a power converter circuit. It is a figure which shows the structural example in the case of utilizing AC power supply.

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a basic configuration diagram of a lighting device of the present invention. The lighting device converts the voltage of the DC power supply 100 by the power conversion circuit 101 shown in the broken line and supplies power to the LED load 102. As the DC power source 100, a commercial power source rectified by a rectifier circuit may be used, or a DC power source device connected to the outside may be used. The number of LEDs and the connection form of the LED load 102 are not limited. Further, the LED load 102 may include an LED module incorporating a protection element or the like.

  In FIG. 1, the main circuit of the power conversion circuit 101 is configured as a step-down chopper using a main switching element 103, a synchronous rectifying element 104, a coil 105, a capacitor 106, and current detection means 107. Note that the main circuit of the power conversion circuit 101 may use other types of circuits such as a buck-boost chopper and a flyback converter. In FIG. 1, MOSFETs are shown as examples of the main switching element 103 and the synchronous rectifying element 104, but other types of switching elements such as bipolar transistors and IGBTs may be used. Reference numerals 108 and 109 denote parasitic capacitances (capacitors) of the main switching element 103 and the synchronous rectifying element 104, respectively. However, you may connect a capacitor | condenser separately to the said location.

  The main switching element 103 and the synchronous rectifying element 104 are connected in series. The coil 105 and the capacitor 106 are connected in series. The synchronous rectifying element 104, the coil 105, and the capacitor 106 are connected in parallel. The capacitor 106 and the LED load 102 are connected in parallel. The current detection means 107 is provided between the coil 105 and the capacitor 106 and detects the current flowing through the coil 105.

  A step-down chopper control circuit 110 is shown within a dashed line in FIG. The control circuit 110 includes a current control unit 111, an inversion detection unit 112, and a drive circuit 113. The current control unit 111 outputs a signal for controlling the maximum value of the current (coil current) flowing through the coil 105 detected by the current detection unit 107 to the drive circuit 113. The inversion detection unit 112 detects that the polarity of the coil current detected by the current detection unit 107 is inverted, and outputs a signal corresponding to the detection to the drive circuit 113. Specific examples of these will be described later, but the detailed configuration is not limited as long as an operation waveform shown in FIG. 2 described later can be realized. The driving circuit 113 performs driving for turning on and off the main switching element 103 and the synchronous rectifying element 104 based on signals output from the current control unit 111 and the inversion detection unit 112.

  That is, the control circuit 110 performs on / off control of the main switching element 103 and the synchronous rectification element 104 in accordance with the coil current detected by the current detection unit.

  FIG. 2 is an operation waveform of the lighting device of the present invention. 2, SW1 and SW2 are the on / off states of the main switching element 103 and the synchronous rectifying element 104, IL is a current (coil current) flowing through the coil 105, and Id1 is a drain current (body diode) of the main switching element 103. And Vds1 is the drain-source voltage of the main switching element 103. As the polarities of IL, Id1, and Vds1, the direction of the arrow shown in FIG. 1 is positive.

  When the main switching element 103 is ON (SW1 is ON), the DC power supply 100 (positive side) starts from the main switching element 103, the coil 105, the capacitor 106 and the LED load 102 in parallel, and the DC power supply 100 (negative electrode side). Current flows through the path. As can be seen from FIG. 1, the current detection means 107 is also present on this current path, but is omitted for convenience of explanation. The same applies to the following description. As can be seen from IL and Id1 in FIG. 2, this current increases linearly with time. IL and Id1 are substantially equal. Since the main switching element 103 is on, Vds1 is almost zero.

  When IL reaches the first set value (Imax in FIG. 2) by the current control means 111, the main switching element 103 is turned off (SW1 is turned off), and a predetermined time (dead time, FIG. After td), the synchronous rectifying element 104 is turned on (SW2 is turned on). As a result, the circulating current 1 starts to flow through the path of the coil 105, the parallel body of the capacitor 106 and the LED load 102, the synchronous rectifier element 104, and the coil 105 due to the energy stored in the coil 105.

  Note that when the main switching element 103 is turned off (SW1 is turned off) and the circulating current 1 starts to flow, Vds1 increases to substantially the same voltage as the DC power supply 100. At this time, the DC power supply 100 charges the parasitic capacitance 108 of the main switching element 103. On the other hand, the charge stored in the parasitic capacitance 109 of the synchronous rectifying element 104 is discharged, and the drain-source voltage (Vds2) of the synchronous rectifying element 104 becomes almost zero. This discharge is performed when the circulating current 1 extracts the charge of the parasitic capacitance 109. If this charging / discharging is completed during the dead time (td) period, the turn-on of the synchronous rectifying element 104 becomes zero voltage switching (ZVS), and almost no loss occurs. Note that if an element having a large capacitance of the parasitic capacitance 109 is selected as the synchronous rectifying element 104, the inclination of increasing Vds1 can be suppressed, and the turn-off loss and noise of the main switching element 103 can be reduced.

  As can be seen from the IL in FIG. 2, this reflux current 1 decreases linearly with time. By applying synchronous rectification and applying a low on-resistance element as the synchronous rectifying element 104, the conduction loss of the synchronous rectifying element 104 can be reduced.

  As described in Patent Document 1, in the current critical mode, which is a general control method for a step-down chopper, when the IL becomes zero, the synchronous rectifier element 104 is turned off and the main switching element 103 is turned on. However, in the present invention, the synchronous rectifying element 104 is kept on (SW2 is ON) even after IL becomes zero. As a result, IL becomes negative as shown in FIG. 2, that is, the polarity (direction) is reversed, and a current flows through the path of the capacitor 106, the coil 105, the synchronous rectifier element 104, and the capacitor 106.

  After detecting that the polarity of IL has been reversed from the polarity of the first set value (Imax) or has reached the second set value (Imin in FIG. 2) by the inversion detection means 112, the drive circuit 113 turns off the synchronous rectification element 104 (SW2 is OFF). Further, the drive circuit 113 turns the main switching element 103 on (SW1 is turned on) after the dead time (td in FIG. 2) has elapsed since the synchronous rectifying element 104 is turned off (SW2 is turned off). In this dead time (td) period, current flows through the path of the coil 105, the main switching element 103 (more precisely, the parasitic capacitance 108), the DC power supply 100, the capacitor 106, and the coil 105 due to the energy stored in the coil 105. . This current discharges the charge stored in the parasitic capacitance 108, and Vds1 decreases. If settings such as Imin and td are appropriate, Vds1 decreases to almost zero during the dead time period as shown in FIG. In addition, after Vds1 becomes zero, a current flows through the body diode of the main switching element 103. If the main switching element 103 is turned on after the charging / discharging of the parasitic capacitance 108 is completed and Vds1 is reduced to zero, the main switching element 103 is turned on to zero voltage switching (ZVS) and almost no loss occurs.

  In the conventional current critical mode, the main switching element 103 is turned on before charging / discharging of the parasitic capacitance 108 is completed, that is, before Vds1 is reduced to zero. At this time, a current necessary for completing charging / discharging flows through the main switching element 103, so that loss occurs in the main switching element 103. Further, since this current flows in a spike shape, noise is generated. In particular, when synchronous rectification is applied, since the parasitic capacitance is large, the current required for charging and discharging also increases. Therefore, the control of turning on the main switching element 103 after the charging / discharging is completed by using the energy of the coil 105 as in the present invention is effective for the high efficiency and low noise of the apparatus.

  Even when the control of the present invention is used, for example, when the absolute value of Imin is small and sufficient energy is not stored in the coil 105, there is a situation where the main switching element 103 is turned on before Vds1 decreases to zero. Conceivable. However, also in this case, since the main switching element 103 is turned on in a state where Vds1 is low as compared with the conventional method, loss and noise can be suppressed as compared with the conventional method.

  FIG. 3 shows specific examples of the current detection means 107 of the main circuit in FIG. 1, and the current control means 111 and the inversion detection means 112 in the control circuit 110. The current detection means 107 includes a first resistor 114 and a second resistor 115 which are two resistors. When the main switching element 103 is ON (SW1 is ON), the path of IL is the DC power supply 100 (positive electrode side), the main switching element 103, the coil 105, the parallel body of the capacitor 106 and the LED load 102, and the first resistor 114. Since it becomes the DC power supply 100 (the negative electrode side), IL can be detected as the voltage of the first resistor 114. When the synchronous rectifying element 104 is on (SW2 is on), the description of the current path is omitted, but IL can be detected as the voltage of the second resistor 115. Of course, as a simple method for realizing the current detection means 107, a resistor may be connected in series with the coil 105, and IL may be detected by a potential difference between the resistors.

  The current control unit 111 compares the IL detected by the first resistor 114 with the first set value Imax by the comparator 116. At the moment when IL becomes larger than Imax, the output of the comparator 116 changes from the L level to the H level. Therefore, the rising edge is detected by the control logic 117 in the subsequent stage, and a signal for turning off the main switching element 103 is sent to the driving circuit 113. Can be output.

  The same applies to the inversion detection means 112, and the comparator 118 compares the IL (absolute value) detected by the second resistor 115 and the second set value Imin (absolute value). At the moment when IL becomes smaller than Imin, the output of the comparator 118 changes from the L level to the H level. Can be output.

  By configuring the current detection unit 107 and the control circuit 110 as shown in FIG. 3, the ground of the control circuit 110 can be matched with the negative electrode side of the DC power supply 110, and as a result, the configuration of the control circuit 110 is simplified.

  FIG. 4 is another example of the control circuit 110. Compared with FIG. 3, the configuration of the current control unit 111 is the same, but the configuration of the inversion detection unit 112 and the principle of detecting the inversion of IL are different. In the explanation of the operation waveform in FIG. 2, attention is paid to the process in which IL decreases after the synchronous rectifying element 104 is turned on. The slope at which IL decreases at this time can be calculated from the self-inductance of the coil 105, the voltage of the DC power supply 100, and the voltage of the LED load 102. That is, the time required from when the synchronous rectifying element 104 is turned on (SW2 is turned on) to when IL is inverted and reduced to the desired second set value can also be calculated from these parameters. The inversion detection unit 112 in FIG. 4 includes the SW2 on-time control unit 120 and outputs a signal for obtaining the on-time of the synchronous rectifying element 104 necessary until the IL is inverted to the drive circuit 113. By configuring the inversion detection means 112 as shown in FIG. 4, the resistor 115 in FIG. 3 is unnecessary, and the configuration of the lighting device is simplified. Note that, based on the same idea, the current control unit 111 may be configured to control the on-time of the main switching element 103. As a method of realizing the control circuit 110, there are a method of using a commercially available control IC for LED, a method of configuring by combining discrete components such as a comparator, and a method of implementing software using a microcomputer or a digital signal processor. is there. FIG. 5 shows another example of the power conversion circuit 101, in which the main switching element 103 is connected to the negative side (low side) of the DC power supply 100 and the synchronous rectifier element 104 is connected to the positive side (high side) of the DC power supply 100. It is. At this time, the coil 105, the LED load 102, and the like are connected to the high side. The operation waveform is the same as in FIG. A capacitor may be connected in parallel with the parasitic capacitance 108 of the main switching element 103 or the parasitic capacitance 109 of the synchronous rectification element 104. As a result, the increase in Vds1 when the main switching element 103 is turned off (SW1 is turned off) is moderated, which is effective in reducing turn-off loss and noise.

  FIG. 6 shows a configuration in which the lighting device shown in FIG. 1 is obtained by rectifying the voltage of the AC power source 121 by the rectifier circuit 122 as the DC power source 100. For example, a diode bridge may be used as the rectifier circuit 122. In addition to the components shown in FIG. 6, a fuse, an input filter coil, a capacitor, or the like may be added.

  In the present embodiment, the LED load is used as the light source (load), but this is not the case. For example, the same effect can be obtained even when a light source such as an organic EL is used as a load.

DESCRIPTION OF SYMBOLS 100 DC power supply 101 Power conversion circuit 102 LED load 103 Main switching element 104 Synchronous rectification element 105 Coil 106 Capacitor 107 Current detection means 108 Main switching element parasitic capacitance 109 Synchronous rectification element parasitic capacitance 110 Control circuit 111 Current control means 112 Inversion detection Means 113 Drive circuit 114 Resistance (same as 115)
116 Comparator (118 is the same)
117 Control logic (same for 119)
120 SW2 ON time control means 121 AC power supply 122 Rectifier circuit

Claims (6)

A power conversion circuit that includes a main switching element, a synchronous rectifying element, a coil, and a capacitor, converts a DC power supply, and supplies power to a light emitting diode (hereinafter referred to as LED) load connected in parallel with the capacitor, and the main switching element And a control circuit for controlling on / off of the synchronous rectifier element,
The control circuit includes:
Turning off the main switching element when the current flowing through the coil reaches a first set value, turning on the synchronous rectifying element after a predetermined time;
The LED lighting device, wherein the synchronous rectifying element is turned off after the polarity of the current flowing through the coil is reversed from the polarity of the first set value, and the main switching element is turned on after a predetermined time has elapsed. . The LED lighting device according to claim 1,
The control circuit includes:
The LED lighting device according to claim 1, wherein when the polarity of the current flowing through the coil is reversed from the polarity of the first set value and reaches a second set value, the synchronous rectifying element is turned off. In the LED lighting device according to claim 1 or 2,
The main switching element, the synchronous rectifier element, the first resistor and the second resistor are connected in series in this order,
The main switching element, the synchronous rectifier element and the DC power supply are connected in series,
The coil and the capacitor are connected in series,
The coil and the capacitor are connected in parallel with the synchronous rectifier element and the first resistor,
The LED load is connected in parallel with the capacitor,
The LED lighting device according to claim 1, wherein the first resistor and the second resistor are used as means for detecting a current flowing through the coil. In the LED lighting device according to any one of claims 1 to 2,
The LED lighting device according to claim 1, wherein the DC power source is generated by rectifying an AC power source by a rectifier circuit. In the LED lighting device according to any one of claims 1 to 4,
The LED lighting device, wherein the power conversion circuit includes a capacitor connected in parallel with at least one of the main switching element and the synchronous rectifying element. A DC power supply, a power conversion circuit connected to the DC power supply, and a light source connected to the power conversion circuit,
The power conversion circuit includes a main switching element connected in series with the DC power supply, a synchronous rectifying element connected in series with the main switching element, a coil and a capacitor connected in parallel with the synchronous rectifying element, A light source connected in parallel with the capacitor, and a control circuit for controlling on / off of the main switching element and the synchronous rectification element,
The control circuit controls the main switching element to be turned off when a current flowing through the coil reaches a first set value, and controls the synchronous rectification element to be turned on after a predetermined time has passed to flow to the coil. A lighting device that controls the synchronous rectifying element to be turned off when the polarity of the current is reversed and reaches a second set value, and controls the main switching element to be turned on after a lapse of a desired time.

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