JP2017175885A - Power supply and lighting device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply which can securely start step-down chopper operation.SOLUTION: A power supply 10 includes a step-down chopper circuit, switch means Q3 and a control circuit 14. The step-down chopper circuit includes a switching element Q2 and a diode D2 which is connected to the output terminal of the switching element Q2 so as to prevent a current flow from the output terminal of the switching element Q2 to the ground, to step down an input voltage by the chopping operation of the switching element. The switch means Q3 is connected in parallel with the diode D2. The control circuit 14 controls the switch means Q3 to be in a conduction state before starting the switching control of the switching element Q2, and to be in an open state on starting the switching control of the switching element Q2.SELECTED DRAWING: Figure 1

Description

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

  A power supply apparatus that obtains desired power by boosting a voltage supplied from the outside and then reducing the voltage is known. Boosting is for improving the power factor, and a boost chopper type power factor improving circuit is used in the power supply device. The step-down voltage is for adjusting the voltage for constant current control, and a step-down chopper type step-down circuit is used in the power supply device.

  A step-down chopper type step-down circuit generally uses a field-effect transistor (FET) as a switching element for chopping. The field effect transistor turns on or off the conduction between the drain that is the input terminal and the source due to the potential difference between the base that is the control terminal and the source that is the output terminal.

  In a step-down circuit using this field effect transistor as a switching element, a bootstrap system is widely applied as a driving system for the switching element. When the bootstrap method is applied, a diode is connected between the output terminal of the switching element and the ground in order to generate a regenerative current when the switching element is off. The diode is connected in a direction that prevents a current flowing from the output terminal to the ground. For this reason, when the step-down circuit is not operating, the potential of the output terminal of the switching element is indefinite. For this reason, in order to start the switching element, it is necessary to supply a voltage of a certain value or more with reference to the potential of the output terminal to the control terminal. On the other hand, after activation, the level of the output terminal is lowered to the level of the ground potential by the regenerative current when the switching element is turned off. For this reason, what is necessary is just to supply the voltage more than a fixed value on the basis of ground potential to a control terminal.

  Normally, when the power supply device is started, the operation of the step-up chopper is first started in the power factor correction circuit, and then the operation of the step-down chopper is started in the step-down circuit. At this time, a voltage to be supplied to the control terminal of the switching element in the step-down circuit is generated from the voltage obtained with the operation of the step-up chopper. For this reason, depending on the operating state of the boost chopper, a voltage sufficient to generate a voltage to be supplied to the control terminal of the switching element may not be obtained. In that case, there is a concern that the operation of the step-down chopper does not start normally.

JP 2015-185450 A

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a power supply device that can reliably start the operation of the step-down chopper and a lighting device including the power supply device. is there.

  In one embodiment, the power supply device includes a step-down chopper circuit, a switch means, and a control circuit. The step-down chopper circuit prevents a current from flowing from the output terminal of the switching element to the ground, and a switching element that turns on or off the conduction between the input terminal and the output terminal due to a potential difference between the control terminal and the output terminal. Thus, a diode connected to the output terminal of the switching element is provided, and the input voltage is stepped down by the chopping operation of the switching element. The switch means is connected in parallel with the diode. The control circuit brings the switch means into a conductive state before starting the switching control of the switching element, and opens the switch means when the switching control of the switching element is started.

  According to one embodiment, the operation of the step-down chopper can be reliably started, and a highly reliable power supply device can be provided.

The figure which shows schematically the circuit structure of the illuminating device which concerns on one Embodiment, and its power supply device. The flowchart which shows the main operation | movement sequences of the control circuit which concerns on one Embodiment. The figure which shows schematically the circuit structure of the step-down circuit which concerns on other embodiment. The figure which shows schematically the circuit structure of the step-down circuit which concerns on other embodiment. The figure which shows schematically the circuit structure of the step-down circuit which concerns on other embodiment.

Hereinafter, embodiments of a power supply device that can reliably start a step-down circuit and a lighting device including the power supply device will be described with reference to the drawings.
[First Embodiment]
First, the first embodiment will be described with reference to FIGS. 1 and 2.
FIG. 1 is a circuit diagram of a lighting device 1 and its power supply device 10 according to the first embodiment. In FIG. 1, only circuit components necessary for describing the embodiment are shown, and circuit components not related to the description are not shown.

  The lighting device 1 includes a power supply device 10 and a light source unit 20. The light source unit 20 includes a plurality of light emitting diodes connected in series, and is detachably connected between the output terminals OUT1 and OUT2 of the power supply device 10. In the light source unit 20, the number of light emitting diodes as light emitting elements is arbitrary. Only one light emitting diode may be provided. A plurality of light emitting diode series circuits as shown in FIG. 1 may be connected in parallel. In place of the light emitting diode, another type of light emitting device such as an organic EL (electroluminescence) may be provided.

  The power supply device 10 includes a rectifier circuit 11, a step-up chopper type power factor correction circuit 12, a step-down chopper type step-down circuit 13, a start circuit 15, and a control circuit 14. The power supply device 10 is a DC power supply device that supplies DC power to the light source unit 20 connected as a load. That is, the power supply apparatus 10 performs full-wave rectification on the AC voltage of the commercial AC power supply 30 connected between the input terminals IN <b> 1 and IN <b> 2, for example, AC 100 V, using the rectifier circuit 11. Then, the power supply device 10 boosts the full-wave rectified voltage by the power factor correction circuit 12 to obtain a predetermined DC voltage, and the DC voltage is stepped down to the target voltage by the step-down circuit 13, and the direct current is converted into a light source. Supply to unit 20.

  The rectifier circuit 11 includes a diode bridge circuit DB and a capacitor C1. The diode bridge circuit DB has a pair of input terminals and output terminals. The diode bridge circuit DB connects each input terminal to the input terminals IN1 and IN2 of the power supply device 10, respectively. The diode bridge circuit DB has one output terminal connected to the transformer T of the power factor correction circuit 12 and the other output terminal connected to the ground E. Furthermore, the diode bridge circuit DB connects the capacitor C1 between the pair of output terminals. With this connection, the rectifier circuit 11 full-wave rectifies the AC voltage of the commercial AC power supply 30 with the diode bridge circuit DB and smoothes it with the capacitor C1. The rectifier circuit 11 outputs the smoothed full-wave rectified voltage to the power factor correction circuit 12.

  The power factor correction circuit 12 includes a transformer T, a switching element Q1, an electrolytic capacitor C3, a backflow prevention diode D1, and a resistor R6. The transformer T includes a primary winding e1, a first secondary winding e21, and a second secondary winding e22. The transformer T has one end of the primary winding e1 connected to the positive terminal of the capacitor C1, and the other end connected to the anode of the diode D1. The transformer T has one end of the first secondary winding e21 connected to the GND (ground) terminal of the control circuit 14, and the other end connected to the ZCD terminal of the control circuit 14 via the resistor R3. The transformer T has one end of the second secondary winding e22 connected to the VS terminal of the control circuit 14, and the other end connected to the VB terminal of the control circuit 14 through a series circuit of a capacitor C2 and a diode D4. The primary winding e1 of the transformer T functions as an inductor in the step-up chopper type power factor correction circuit 12.

  The switching element Q1 is, for example, an N-channel field effect transistor (FET). The switching element Q1 has a drain terminal connected to the connection point between the transformer T and the diode D1, a source terminal connected to the ground E via the resistor R6, and a gate terminal connected to the GD terminal of the control circuit 14. With this connection, the switching element Q1 becomes conductive when the gate signal applied to the gate terminal is turned on, and forms a closed circuit of the capacitor C1, the primary winding e1 of the transformer T, the switching element Q1, and the resistor R6. The switching element Q1 is opened when the gate signal applied to the gate terminal is turned off, and interrupts the closed circuit. The switching element Q1 functions as a switching element for chopping the input voltage in the step-up chopper type power factor correction circuit 12.

  The diode D1 has an anode connected to a connection point between the transformer T and the switching element Q1, and a cathode connected to the positive terminal of the electrolytic capacitor C3. The negative terminal of the electrolytic capacitor C3 is connected to the ground E. Both terminals of the electrolytic capacitor C3 are output terminals of the power factor correction circuit 12. With this connection, a series circuit of a diode D1 and an electrolytic capacitor C3 is formed between the drain terminal and the source terminal of the switching element Q1. As a result, the electrolytic capacitor C3 is charged by the output voltage of the rectifier circuit 11 when the switching element Q1 is in the cut-off state, and discharged when it is in the conductive state. Thus, the power factor correction circuit 12 boosts the voltage rectified by the rectifier circuit 11 by the switching operation of the switching element Q1, obtains a predetermined DC voltage, and outputs it to the step-down circuit 13. Here, the primary winding e1, the switching element Q1, and the electrolytic capacitor C3 of the transformer T form a step-up chopper circuit.

  The step-down circuit 13 includes a switching element Q2, inductors L1 and L2, a capacitor C4, a regenerative diode D2, and a resistor R7. The switching element Q2 is, for example, an N-channel field effect transistor (FET). The switching element Q2 has a drain terminal connected to the positive terminal of the electrolytic capacitor C3 that is one output terminal of the power factor correction circuit 12, a source terminal connected to one end of the inductor L1, and a gate terminal connected to the HO of the control circuit 14. Connect to the terminal. The other end of the inductor L1 is connected to one output terminal OUT1 of the power supply device 10. Thus, the step-down circuit 13 is configured as a so-called high-side type in which the switching element Q2 is connected to a higher potential side (high side) than the inductor L1.

  With this connection, the switching element Q2 becomes conductive when the gate signal applied to the gate terminal is turned on, and guides the output current of the power factor correction circuit 12 to the inductor L1. The switching element Q21 opens when the gate signal applied to the gate terminal is turned off, and interrupts the output current of the power factor correction circuit 12.

  The inductor L1 stores the energy when the switching element Q2 is turned on and a DC voltage is applied, and releases the stored energy when the switching element Q2 is turned off and the DC voltage is not applied.

The capacitor C4 has a positive terminal connected to the connection point between the inductor L1 and one output terminal OUT1 of the power supply apparatus 10, and a negative terminal connected to the other output terminal OUT2 of the power supply apparatus 10. The capacitor C4 connects the negative terminal C4 to the ground E through the resistor R7. Thus, the step-down circuit 13 steps down the DC voltage output from the power factor correction circuit 12 and supplies the DC current to the load connected between the output terminals OUT1 and OUT2, that is, the light source unit 20 in this embodiment. Here, switching element Q2, inductor L1, and capacitor C4 form a step-down chopper circuit. The switching element Q2 functions as a switching element for chopping the input voltage in the step-down chopper circuit.
In the step-down circuit 13, the diode D2 has an anode connected to a connection point between the resistor R7 and the ground E, and a cathode connected to one terminal of the inductor L2. The inductor L2 has the other terminal connected to the connection point between the source terminal of the switching element Q2 and the inductor L1. With this connection, a regenerative current flows in the closed loop of the inductor L1, the capacitor C4, the resistor R7, the diode D2, and the inductor L2 due to the energy released from the inductor L1 when the switching element Q2 is turned off. When the regenerative current flows, the source potential of the switching element Q2 becomes the ground potential.

  The starting circuit 15 includes a diode D5 and a switching element Q3. The diode D5 has an anode connected to the source terminal of the switching element Q2, and a cathode connected to the VS terminal of the control circuit 14.

  The switching element Q3 is, for example, an N-channel field effect transistor (FET). The switching element Q3 has a drain terminal connected to the cathode of the diode D5, a source terminal connected to the ground E, and a gate terminal connected to the SC terminal of the control circuit 14. With this connection, the switching element Q3 becomes conductive when the gate signal applied to the gate terminal is turned on, and drops the source potential of the switching element Q2 to the ground potential. The diode D5 limits the current flowing through the switching element Q3 to the output terminal of the switching element Q2. Here, the switching element Q3 constitutes switching means connected in parallel with the diode D2 between the output terminal of the switching element Q2 and the terminal of the ground potential.

The control circuit 14 is an analog IC. The control circuit 14 includes a GND terminal, a VDC terminal, a VCC terminal, a GD terminal, a HO terminal, an SC terminal, a MULT terminal, a ZCD terminal, a VFB terminal, a VS terminal, a VB terminal, a CS terminal, an OCP terminal, and an ABN terminal. It goes without saying that the control circuit 14 may have other terminals.
The GND terminal is connected to the ground E.

  The VDC terminal is connected to the cathode of the diode D1. With this connection, a high-voltage full-wave rectified voltage input to the power factor correction circuit 12 is applied to the VDC terminal. The control circuit 14 has a circuit for generating a circuit operating voltage, for example, +18 V from a high voltage applied to the VDC terminal. The circuit operating voltage is output from the VCC terminal to each circuit.

  The GD terminal is connected to the gate terminal of the switching element Q1. The control circuit 14 has a circuit that generates a gate signal of the switching element Q1. Then, the control circuit 14 outputs a gate signal of gate-on or gate-off from the GD terminal to the gate terminal of the switching element Q1.

  The HO terminal is connected to the gate terminal of the switching element Q2. The control circuit 14 includes a circuit that generates a gate signal for the switching element Q2. Then, the control circuit 14 outputs a gate signal for turning on or off the gate from the HO terminal to the gate terminal of the switching element Q2.

  The SC terminal is connected to the gate terminal of switching element Q3. The control circuit 14 has a circuit that generates a gate signal of the switching element Q3. Then, the control circuit 14 outputs a gate signal of gate on or gate off from the SC terminal to the gate terminal of the switching element Q3.

  The MULT terminal is connected to the midpoint of the voltage dividing resistors R1 and R2. The voltage dividing resistors R1 and R2 are connected between both terminals of the capacitor C1. The control circuit 14 includes a circuit that generates an envelope waveform of a current signal input to the power factor correction circuit 12 from a signal input to the MULT terminal.

  The ZCD terminal is connected to the output side of the first secondary winding e21 via the resistor R3. The control circuit 14 has a circuit that detects a current flowing through the primary winding e1, that is, a so-called inductor current, from a signal input to the ZCD terminal.

  The VFB terminal is connected to the midpoint of the voltage dividing resistors R4 and R5. The voltage dividing resistors R4 and R5 are connected between both terminals of the electrolytic capacitor C3. The control circuit 14 has a circuit that detects the output voltage of the power factor correction circuit 12 from the voltage applied to the VFB terminal.

  The VS terminal is connected to the node n1, and the VB terminal is connected to the node n2. The input side of the second secondary winding e22 is connected to the node n1. The node n1 is connected to the source terminal of the switching element Q2 via a diode D5 having a reverse polarity. The output side of the second secondary winding e22 is connected to the node n2 through a series circuit of a diode D4 having a reverse polarity and a capacitor C2. In addition, a VCC terminal is connected to the node n2 through a diode D3 having a reverse polarity. Further, a capacitor C6 is connected between the node n1 and the node n2. The control circuit 14 includes a circuit that detects the potential of the node n1 from the voltage applied to the VS terminal. The control circuit 14 includes a circuit that detects the potential of the node n2 from the voltage applied to the VB terminal.

  The potential of the node n1 is equal to the potential of the node n3 on the source terminal side of the switching element Q2. This potential is the negative side potential of the capacitor C6. The source terminal of the switching element Q2 is connected to the ground via an inductor L2 and a diode D2 in series. Therefore, when the switching element Q2 is off and no regenerative current is generated, the potential of the node n3 is not a ground potential, that is, a so-called floating state (undefined).

  The potential of the node n2 is equal to the potential of the positive terminal of the capacitor C6. The capacitor C6 is charged by the circuit operating voltage applied from the VCC terminal and the secondary voltage excited by the second secondary winding e22 with reference to the potential of the node n1. The potential of the node n2 varies depending on the degree of charge of the capacitor C6.

  The CS terminal is connected to the source terminal of the switching element Q1 via the resistor R8. The control circuit 14 has a circuit that detects a current flowing through the switching element Q1, that is, a so-called switching current, from a signal input to the CS terminal.

  The OCP terminal is connected to the negative terminal of the capacitor C4 in the step-down circuit 13 through the resistor R9. The control circuit 14 includes a circuit that detects a current flowing into the light source unit 20 from a signal input to the OCP terminal, that is, a so-called load current.

  The ABN terminal is connected to the midpoint of the voltage dividing resistors R10 and R11. The voltage dividing resistors R10 and R11 are connected between the positive terminal of the capacitor C4 in the step-down circuit 13 and the GND terminal of the control circuit 14. Further, a series circuit (differential circuit) of a capacitor C7 and a resistor R12 is connected in parallel to one resistor R10 connected to the positive terminal. The control circuit 14 has a circuit that detects the amount of change in voltage generated in the step-down circuit 13 from a signal input to the ABN terminal.

  Therefore, the control circuit 14 controls the switching operation of the switching element Q1 by the current critical control for the power factor correction circuit 12 in a steady state. That is, when the switching element Q1 is off, the control circuit 14 outputs a gate-on signal from the GD terminal every time the inductor current detected via the ZCD terminal becomes zero. The switching element Q1 is turned on (conductive state) by this gate-on signal. In a state in which the switching element Q1 is on, the control circuit 14 outputs a gate-off signal from the GD terminal at a timing when the peak waveform of the inductor current follows the envelope waveform detected via the MULT terminal. The switching element Q1 is turned off (opened) by this gate-off signal.

  The control circuit 14 controls the switching operation of the switching element Q2 by applying feedback to the step-down circuit 13 so that the load current detected via the OCP terminal becomes a predetermined target value in a steady state. That is, the control circuit 14 alternately outputs a gate-on signal or a gate-off signal from the HO terminal at a predetermined timing. At this time, the control circuit 14 determines the signal levels of the gate-on signal and the gate-off signal with reference to the potential of the node n1 detected via the VS terminal. Thus, in the step-down circuit 13, the switching element Q2 performs switching by the bootstrap operation.

  In addition, the control circuit 14 includes a protection circuit that stops the switching operation of the switching element Q2 when the amount of change in the voltage detected via the ABN terminal exceeds a predetermined level. For example, when the lighting light source unit 20 is removed, the voltage changes instantaneously. The control circuit 14 stops the switching operation of the switching element Q2 with respect to this steep voltage change, so that the circuit components can be prevented from being destroyed by the steep voltage change.

  FIG. 2 is a flowchart showing a main operation sequence of the control circuit 14. Hereinafter, the operation of the power supply device 10 and the lighting device 1 including the power supply device 10 will be described with reference to FIGS. 1 and 2.

  Before the commercial AC power supply 30 is turned on, in the power supply device 10, the switching elements Q1, Q2, and Q3 are all in the off state. When the commercial AC power supply 30 is turned on, the AC voltage of the commercial AC power supply 30, for example, AC 100 volts is full-wave rectified by the rectifier circuit 11 and converted into a full-wave rectified voltage. The full-wave rectified voltage is applied between both terminals of the capacitor C1 and becomes an input voltage to the power factor correction circuit 12. This input voltage is applied to the VDC terminal of the control circuit 14. When an input voltage is applied to the VDC terminal, a circuit operating voltage is generated inside the control circuit 14, and the circuit operating voltage is output to each circuit from the VCC terminal. When the circuit operating voltage is output, the control circuit 14 starts the operation of the procedure shown in FIG.

  First, the control circuit 14 outputs a gate-on signal from the SC terminal to the switching element Q3 of the starting circuit 15 (step S1). The switching element Q3 is turned on by this signal output.

  When switching element Q3 is turned on, the potential of node n1 becomes the ground potential. For this reason, the capacitor C6 is charged by the circuit operating voltage output from the VCC terminal.

  Next, the control circuit 14 starts the switching operation of the switching element Q1 in the power factor correction circuit 12 (step S2). That is, the control circuit 14 outputs a gate-on signal to the switching element Q1 of the power factor correction circuit 12 from the GD terminal. With this signal output, the switching element Q1 is turned on, and the power factor correction circuit 12 is activated. When the power factor correction circuit 12 is activated, the control circuit 14 controls the switching operation of the switching element Q1 by the current critical control described above.

  When the switching element Q1 starts a switching operation, the output voltage from the power factor correction circuit 12 gradually increases. Further, when the switching element Q1 is on, a current is generated in the primary winding e1 of the transformer T, thereby inducing a voltage in the first and second secondary windings e21 and e22. Then, the voltage induced in the second secondary winding e22 is rectified by the capacitor C2 and the diode D4 and then applied to the capacitor C6, whereby the capacitor C6 is further charged.

  Here, although omitted in FIG. 2, the control circuit 14 monitors the voltage applied to the VFB terminal, that is, the output voltage from the power factor correction circuit 12. When this output voltage is less than the protection threshold voltage set higher than the target voltage, the control circuit 14 continues the switching operation of the switching element Q1. On the other hand, when the output voltage exceeds the protection threshold voltage, the control circuit 14 stops the switching operation of the switching element Q1.

  When the switching operation of the switching element Q1 is stopped, no current flows through the primary winding e1 of the transformer T. Therefore, the capacitor C6 is not charged with the voltage induced in the second secondary winding e22. However, the capacitor C6 is charged with the circuit operating voltage output from the VCC terminal as described above.

When the output voltage from the power factor correction circuit 12 exceeds the protection threshold voltage, the switching operation of the switching element Q1 is stopped, so that the output voltage from the power factor improvement circuit 12 decreases. When the output voltage becomes equal to or lower than the restart threshold voltage lower than the protection threshold voltage, the control circuit 14 restarts the switching control of the switching element Q1 by the current critical control.
Incidentally, the voltage value between the protection threshold and the restart threshold is arbitrary as long as the restart threshold is equal to or lower than the protection threshold. The voltage value of each threshold is set in the control circuit 14 at the stage of designing the power supply device 10 or the lighting device 1.

  Next, the control circuit 14 starts the switching operation of the switching element Q2 in the step-down circuit 13 (step S3). That is, the control circuit 14 outputs a gate-on signal from the HO terminal to the switching element Q2 of the step-down circuit 13. Before the gate-on signal is output to the switching element Q2, the step-down circuit 13 stops operating, so the switching element Q2 is in an off state and no regenerative current is generated. For this reason, if the switching element Q3 is in an OFF state, the source potential of the switching element Q2, that is, the potential of the VS terminal is indefinite. However, since the switching element Q3 is turned on in the process of step S1, the source potential of the switching element Q2 drops to the ground potential. Therefore, the switching element Q2 can be turned on by generating a potential having a predetermined potential difference with respect to the ground potential at the gate.

  It is sufficient that the potential having this predetermined potential difference is a circuit operating voltage output from the VCC terminal. At this time, regardless of whether or not the power factor correction circuit 12 is operating, the capacitor C6 is charged at least with the circuit operating voltage. Therefore, the control circuit 14 generates a gate on / off signal based on the potential of the BS terminal and the potential of the VB terminal, and applies it to the gate terminal of the switching element Q2. As a result, the switching element Q2 is activated.

  When the switching element Q2 is activated, the control circuit 14 outputs a gate-off signal from the SC terminal to the switching element Q3 of the starting circuit 15 (step S4). The switching element Q3 is turned off by this signal output.

  Thereafter, the control circuit 14 performs constant current control (step S5). That is, the control circuit 14 adjusts the frequency and duty ratio of the gate signal for the switching element Q2 so that the load current input to the OCP terminal becomes a target constant current.

  At this time, power for operating the step-down circuit 13 is obtained by a bootstrap system. That is, when the switching element Q2 is turned off while the switching element Q2 is repeatedly turned on and off, the regenerative current of the coil L1 flows through the capacitor C4, the resistor R7, the diode D2, and the coil L2. As a result, the source potential of the switching element Q2, that is, the potential of the VS terminal is lowered to near the ground potential. On the other hand, the voltage between the VB terminal and the VS terminal is a circuit operating voltage output from the Vcc terminal if the switching element Q1 is OFF. If the switching element Q1 is on, the voltage between the VB terminal and the VS terminal is the circuit operating voltage, the voltage supplied from the second secondary winding e2 via the capacitor C2 and the diode D4. The added voltage. For this reason, the potential of the VB terminal becomes larger than the potential of the VS terminal, and the capacitor C6 is charged. As a result of this charging, the voltage between the VB terminal and the VS terminal becomes a voltage sufficient for switching the switching element Q2. The control circuit 14 controls the switching operation of the switching element Q2 by generating a gate on / off signal using a voltage between the VB terminal and the VS terminal.

  As described above, the power supply device 10 of the present embodiment includes the diode connected to the output terminal of the switching element Q2 so as to prevent current from flowing from the output terminal of the switching element Q2 to the ground in the step-down circuit 13. In parallel, a switching element Q3 as a switch means is connected. The control circuit 14 brings the switching element Q3 into a conductive state before starting the switching control of the switching element Q2, and when the switching control of the switching element Q2 is started, the switching element Q3 is brought into an open state. Therefore, since the source potential of the switching element Q2 falls to the level of the ground potential before starting the switching control of the switching element Q2, even if the output voltage from the power factor correction circuit 12 exceeds the protection threshold voltage, the switching element Q1 Even when the switching operation is stopped, the switching element Q2 can be stably started.

  If the switching element Q2 can be started, thereafter, in the step-down circuit 13, the operation of the step-down chopper is continued by the bootstrap operation. On the other hand, also in the power factor correction circuit 12, the output voltage is lowered because the switching operation of the switching element Q1 is stopped. When the output voltage becomes equal to or lower than the restart threshold voltage, the switching control of the switching element Q1 by the current critical control is restarted for the power factor correction circuit 12. Therefore, the power supply device 10 can reliably start the operation of the step-down chopper. Therefore, the reliability of the lighting device 1 can be improved by applying the power supply device 10 as an operating power source of the lighting device 1.

[Second Embodiment]
Next, a second embodiment will be described with reference to FIG.
The second embodiment changes a part of the configuration of the step-down circuit 13 in the power supply device 10 of the first embodiment. FIG. 3 is a circuit diagram showing an outline of the step-down circuit 13 in the second embodiment. In addition, the same code | symbol is attached | subjected to the part which is common in the site | part shown in FIG. 1, and the detailed description is abbreviate | omitted.

  As is clear from a comparison between FIG. 1 and FIG. 3, in the second embodiment, the diode D2 is replaced with a switching element Q4 which is a switch means having a parasitic diode. Specifically, a field effect transistor (FET) is used as the switching element Q4. The switching element Q4 is of an N channel, the drain terminal is connected to the source terminal of the switching element Q2 via the inductor L2, the source terminal is connected to the connection point between the ground terminal and the resistor R7, and the gate terminal is the control circuit. Connect to 14 HO terminals. In the first embodiment, the starting circuit 15 constituted by the switching element Q3 and the diode D5 is omitted.

  Then, the control circuit 14 turns on the switching element Q4 at the timing of step S1 when the switching element Q3 is turned on in the first embodiment. Further, the control circuit 14 turns off the switching element Q4 at the timing of step S4 when the switching element Q3 is turned off in the first embodiment.

  When the switching element Q4 is turned on, conduction between the drain and source of the switching element Q4 makes the source potential of the switching element Q2 the ground potential. Therefore, the switching element Q2 can be reliably activated at the timing of step S3. On the other hand, even if the switching element Q4 is turned off, the switching element Q4 has a parasitic diode passing through the current from the source terminal to the drain terminal. Therefore, the regenerative current generated when the switching element Q2 is turned off is It flows through L1, capacitor C4, resistor R7, parasitic diode of switching element Q4, and inductor L2. Therefore, the step-down circuit 13 performs constant current control by a bootstrap operation. Thus, the same effects as those of the first embodiment can be obtained with fewer elements than those of the first embodiment.

[Third Embodiment]
Next, a third embodiment will be described with reference to FIG.
The third embodiment changes a part of the configuration of the step-down circuit 13 in the power supply device 10 of the first embodiment. FIG. 4 is a circuit diagram showing an outline of the step-down circuit 13 in the third embodiment. In addition, the same code | symbol is attached | subjected to the part which is common in the site | part shown in FIG. 1, and the detailed description is abbreviate | omitted.

  As apparent from a comparison between FIG. 1 and FIG. 4, in the third embodiment, a resistor R13 is connected between the gate terminal and the source terminal of the switching element Q2. In parallel with the resistor R13, a series circuit of the resistor R14 and the light receiving side element of the photovoltaic coupler 131 is connected. Further, a series circuit of a diode D6 and a resistor R15 is connected in parallel to the resistor R14. On the other hand, the light emitting side element of the photovoltaic coupler 131 is connected between the HO terminal and the GND terminal of the control circuit 14. The photovoltaic coupler 131 is a kind of photocoupler using a light emitting LED as a light emitting side element and a photodiode array as a light receiving side element.

  Then, the control circuit 14 outputs a gate-on signal from the HO terminal at the timing of step S3 when the switching element Q2 is turned on in the first embodiment, and causes the light emitting side element of the photovoltaic coupler 131 to emit light. When the light emitting side element emits light, the light receiving side element of the photovoltaic coupler 131 receives the light. When the light receiving side element receives light, an electromotive force is generated, and the switching element Q2 is turned on by this electromotive force. Thus, the switching element Q2 starts a switching operation. Thereafter, the switching element Q2 repeats the switching operation every time a gate on / off signal is output from the HO terminal. Thus, the step-down circuit 13 performs constant current control by the bootstrap operation.

  In the third embodiment, since the processes of steps S1 and S4 executed by the control circuit 14 in the first embodiment can be omitted, there is an advantage that the control can be simplified.

[Fourth Embodiment]
Next, a fourth embodiment will be described with reference to FIG.
The fourth embodiment changes a part of the configuration of the step-down circuit 13 in the power supply device 10 of the first embodiment. FIG. 5 is a circuit diagram showing an outline of the step-down circuit 13 in the fourth embodiment. In addition, the same code | symbol is attached | subjected to the part which is common in the site | part shown in FIG. 1, and the detailed description is abbreviate | omitted.

  As is clear from a comparison between FIG. 1 and FIG. 5, in the fourth embodiment, the driver 132 is connected between the gate terminal and the drain terminal of the switching element Q2. The driver 132 includes an npn-type bipolar transistor Tr and a resistor R16. In the driver 132, the collector of the transistor Tr is connected to the drain terminal of the switching element Q2, the emitter is connected to the gate terminal of the switching element Q2, and the base is connected to the positive terminal of the capacitor C4 via the resistor R16. With this connection, the drover 132 drops the drop voltage between the collector and the emitter of the transistor Tr to a voltage necessary for turning on the gate of the switching element Q2.

  Then, in the first embodiment, the control circuit 14 gives a control signal (not shown) to the driver 132 at the timing of step S3 when the switching element Q2 is turned on to operate the driver 132. When the driver operates, a voltage necessary for turning on the gate is applied to the gate terminal of the switching element Q2, and the switching element Q2 is turned on. Thus, the switching element Q2 starts a switching operation. After the switching element Q2 starts the switching operation, the control circuit 14 does not operate the driver 132. Even if the driver 132 is not operated, the step-down circuit 13 performs constant current control by the bootstrap operation.

  Also in the fourth embodiment, as in the third embodiment, the processing of steps S1 and S4 executed by the control circuit 14 can be omitted, so that there is an advantage that the control can be simplified.

  The present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage.

  For example, in the first embodiment, the starting circuit 15 is formed outside the control circuit 14. In another embodiment, the starting circuit 15 may be formed inside the control circuit 14.

  The switch means is not limited to a field effect transistor. Any device may be used as long as it is switched between conduction and non-conduction by a signal from the control circuit 14.

  The circuit configurations of the rectifier circuit 11, the power factor correction circuit 12, and the step-down circuit 13 are not limited to those shown in FIG. Any circuit configuration having a similar function may be used. The circuit that supplies the input voltage to the step-down circuit 13 is not limited to the power factor correction circuit 12. Even in the power supply device including the step-down circuit 13 to which the input voltage is applied via another circuit, the operation of the step-down chopper can be reliably started by applying the configurations of the first to fourth embodiments. Play.

  In the embodiment, the protection circuit protects the output voltage using the change amount of the output voltage. However, the protection circuit may protect the voltage value together with the change amount. The protection circuit may be a protection circuit using an output current instead of a protection circuit using an output voltage. In FIG. 1, the control circuit 14 detects the load current via the OCP terminal. Since this load current cannot be detected when, for example, the resistor R9 fails, the control circuit 14 switches the switching element Q2 of the step-down circuit 13 so that a larger load current flows. As a result, the load current increases and an excessive output may occur, causing the light source unit 20 to fail. Therefore, the value of the load current detected via the OCP terminal is compared with a predetermined threshold by a comparator, and when the time exceeding this threshold becomes longer than the time determined by a predetermined time constant A protection circuit for switching the switching element Q2 is provided. This protection circuit may be inside the control circuit 14 or outside.

  In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, the constituent elements over different embodiments may be combined.

  DESCRIPTION OF SYMBOLS 1 ... Illuminating device, 10 ... Power supply device, 11 ... Rectifier circuit, 12 ... Power factor improvement circuit, 13 ... Step-down circuit, 14 ... Control circuit, 15 ... Starting circuit, 20 ... Light source unit (load), 30 ... Commercial AC power supply , Q1, Q2, Q3, Q4... Switching element, T... Transformer, L1, L2... Inductor, 131.

Claims (4)

A switching element that turns on or off conduction between the input terminal and the output terminal due to a potential difference between the control terminal and the output terminal, and the switching so as to prevent a current from flowing from the output terminal of the switching element to the ground. A step-down chopper circuit comprising a diode connected to the output terminal of the element, and stepping down an input voltage by a chopping operation of the switching element;
Switch means connected in parallel with the diode;
A control circuit for bringing the switch means into a conductive state before starting the switching control of the switching element, and for opening the switch means when the switching control of the switching element is started;
A power supply apparatus comprising: A diode connected to the output terminal of the switching element to block current flowing through the switch means to the output terminal of the switching element;
The power supply device according to claim 1, further comprising: A step-down chopper circuit that includes a switching element that turns on or off conduction between the input terminal and the output terminal by a potential difference between the control terminal and the output terminal, and that steps down the input voltage by a chopping operation of the switching element;
Switch means having a parasitic diode connected to the output terminal of the switching element so as to prevent a current from flowing from the output terminal of the switching element to the ground;
A control circuit for bringing the switch means into a conductive state before starting the switching control of the switching element, and for opening the switch means when the switching control of the switching element is started;
A power supply apparatus comprising: The power supply device according to any one of claims 1 to 3;
A light source connected between the outputs of the power supply device and controlled to be turned on;
A lighting device comprising: