JP2018057100A - Power supply device and illumination apparatus including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reliably enable starting of step-down chopper operation.SOLUTION: A power supply device of an embodiment includes a step-up chopper circuit, a step-down chopper circuit provided with a bootstrap circuit, and a control circuit. The bootstrap circuit includes a first switch which, when being ON, boosts an output end of a switching element by applying output voltage from the bootstrap circuit thereto, and a second switch which, when being ON, gives output voltage from the bootstrap circuit to the ground. The control circuit performs switching control such that the first switch is ON during starting of the switching element and is switched to an OFF state after the starting, and the second switch is OFF during starting of the switching element and is switched to an ON state after the starting.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a power supply device and a lighting device including the power supply device.

  2. Description of the Related Art Generally, a configuration including a step-up chopper circuit and a step-down chopper circuit, which are power factor correction (PFC) circuits, is known as a power supply device that is used in lighting devices and the like and realizes harmonic improvement and constant current characteristics. . For example, in a lighting lighting device that uses a solid state light source LED as a load as a power supply device, a commercial AC input voltage is full-wave rectified, the boosted chopper circuit boosts this rectified voltage, and the power factor is improved. A configuration in which the output voltage (VDC) of a circuit is controlled with constant current using a step-down chopper circuit is widely used.

  The power supply device is started by first starting the operation of the step-up chopper circuit and then starting the operation of the step-down chopper circuit. The step-down chopper circuit uses the voltage obtained from the step-up chopper circuit to generate a voltage for controlling the switching element. For this reason, there is a case where a voltage sufficient to reliably operate the switching element cannot be obtained. As a countermeasure, there is a configuration in which a bootstrap circuit is connected to the source side in the case of a switching element using an n-ch FET.

JP 2016-110874 A

  As a power supply device including the above-described bootstrap circuit, for example, Patent Document 1 discloses a bootstrap circuit that generates a drive voltage that is always connected to and driven by a switching element, and a power source that supplies power to the bootstrap circuit at a normal time. A drive circuit including a circuit and a power supply circuit that supplies power in an emergency has been proposed.

  In the configuration as in Patent Document 1, a dropper is configured from the output voltage from the PFC circuit and used as a power source for the bootstrap circuit. However, since power is obtained from a high potential via a resistor, The loss of is great. Therefore, when the load is an LED light source, unnecessary lighting occurs depending on the forward voltage Vf of the LED light source, and in the case of a load having a resistance for mounting detection, the voltage for mounting detection is normal. There is a possibility that it cannot be read.

  Accordingly, it is an object of the present invention to provide a power supply device that obtains a driving power source for a high-side switch element without affecting the state of a load with little loss, and a lighting device including the power supply device.

  To achieve the above object, a power supply apparatus according to an embodiment of the present invention includes a DC power supply unit that outputs rectified DC power; an input terminal connected to the output terminal of the DC power supply unit, and an input to a control terminal At least one switching element that is turned on / off by a signal; an inductor having one end connected in series to the output terminal of the switching element; a capacitor connected to the other end of the inductor and smoothing a voltage supplied to a load; A diode connected to the low potential side of the capacitor and connected to the output terminal of the switching element to circulate the energy of the inductor; a bootstrap generating a voltage to be supplied to the control terminal of the switching element; One end of the circuit is connected to the output end of the bootstrap circuit, and the other end is connected to the output end of the switching element. A second switch that has one end connected to the output end of the bootstrap circuit, the other end connected to the ground, and connects the output end of the bootstrap circuit to the ground when turned on And before turning on the switching element, turning off the first switch, turning on the second switch, turning on the first switch when starting the switching element, and turning off the second switch. And a control circuit that performs switching control.

  According to the embodiment, it is possible to provide a power supply device that obtains a driving power source for the high-side switch element without affecting the load state with little loss, and a lighting device including the power supply device.

FIG. 1 is a diagram illustrating a conceptual configuration in which a bootstrap circuit according to an embodiment is mounted on a step-down chopper circuit. FIG. 2 is a diagram illustrating a configuration example in which the bootstrap circuit according to the embodiment is mounted on the power supply circuit of the lighting device.

Hereinafter, embodiments will be described in detail with reference to the drawings.
FIG. 1 is a diagram illustrating a conceptual configuration in which a bootstrap circuit according to an embodiment is mounted on a step-down chopper circuit.
The step-down chopper circuit 30 includes a switching element Q31 composed of an n-ch FET (n-channel field effect transistor), a coil (inductor) L31 whose input end side is connected in series with the output end (source) of the switching element Q31, A capacitor (smoothing capacitor) C31 connected between the output terminal of the coil L31 and the ground line (low potential side), an anode connected to the low potential side of the capacitor C31, and a cathode connected to the output terminal of the switching element Q31. And a diode D31 that circulates the energy of the coil L31. A light source unit 1 of a solid light source such as an LED is connected to both ends of the capacitor C31.

  The step-down chopper circuit 30 uses a configuration in which the drain of the FET that is the switching element Q31 is supplied to the VDC and the switching element Q31 is arranged on the high side. With such a configuration, the VDC is prevented from being directly output to the output side. When driving the switching element Q31 (FET) on the high side, the source potential of the switching element Q31 does not necessarily match the ground potential, so a power supply based on the source potential is required. However, in the case of the step-down chopper circuit 30 In this case, since the reference potential varies depending on the state of the output voltage, it is necessary to obtain a driving power source for the FET.

  Therefore, in the present embodiment, two switches S31 and S32 are added to the bootstrap circuit 50 including the capacitor C32 and the diode D33 that boosts the output terminal potential (source potential) of the switching element Q31 of the step-down chopper circuit 30. Is provided. A bootstrap circuit 50 including switches S31 and S32 may be used.

  In the bootstrap circuit 50, a diode D33 has an anode connected to a power source that outputs a Vcc voltage described later, and a cathode connected to one end (input end) of a capacitor C32. The diode D33 and the capacitor C32 are connected in series. The diode D33 prevents the reverse current from flowing from the charged capacitor C32 to the power supply side (Vcc side) by connecting the cathode to the capacitor C32. The other end (output end) of the capacitor C32 is connected to the output end of the switching element Q31 via the switch S31 [first switch], and further to the ground line via the switch S32 [second switch]. Also connected to. These switches S31 and S32 are switched and controlled by a control circuit 40 or the like to be described later.

  Considering that the potential of the capacitor C31 is indefinite at the time of starting the power supply device (at the time of starting lighting, which will be described later), first, the switch S31 is turned off and the switch S32 is turned on to disconnect from the source of the switching element Q31. The output side of the capacitor C32 is connected to the ground potential, and the capacitor C32 is charged. Next, by turning on the switch S31 and turning off the switch S32, a voltage output from the terminal HO that is input to the control terminal of the switching element Q31 is generated using the voltage VB with reference to the reference potential Vs of the bootstrap circuit 50. To do. Thereafter, a drive voltage based on the reference potential Vs is obtained from the bootstrap circuit 50.

Therefore, in this embodiment, by combining these two switches with the bootstrap circuit 50 and performing switching control, there is little power loss, and the high side of the switching element Q31 is not affected without affecting the state of the load (light source unit). Power can be supplied to drive to the side.
When the step-down chopper circuit 30 is driven, even if the reference potential varies depending on the state of the output voltage, the voltage of the bootstrap circuit 50 is input to the switching element Q31 to boost the source potential, and the switching element Q31 is stabilized. Drive can be obtained.

  Next, a configuration example in which the bootstrap circuit of the above-described embodiment is mounted on a power supply device for driving a lighting device will be described. FIG. 2 is a diagram illustrating a configuration example in which the bootstrap circuit according to the embodiment is mounted on a power supply device of a lighting device. Note that FIG. 2 shows a circuit necessary for mounting the bootstrap circuit of the present embodiment, and some of the elements included in the actual power supply apparatus are not shown.

  The illumination device 100 includes a light source unit 1 and a power supply device 3. The light source unit 1 is detachable with respect to the main body of the lighting device 100 in order to allow replacement. The power supply device 3 is fixedly provided in the lighting device main body.

  The light source unit 1 includes a light emitting diode (LED) D11 and a resistor R11, which are at least one solid-state light source serving as a light source, and these are connected in series. The number of light emitting diodes is set based on the required brightness. The resistor R11 is connected to the cathode which is the current output terminal in the series circuit of the light emitting diode D11. In addition, in FIG. 1, although the series circuit of the light emitting diode D11 of 1 row is shown, the structure of multiple parallel may be sufficient.

  Terminals T11 and T12 for detachably connecting to the power supply device 3 are provided at the current input terminal and the current output terminal in the series circuit including the light emitting diode D11 and the resistor R11. A terminal T13 is provided between the cathode of the light emitting diode D11 and the resistor R11. In the present embodiment, a light emitting diode is taken as an example of a solid light source, but is not limited, and may be another light source such as an organic EL (electroluminescence).

The power supply device 3 receives power supplied from an external power supply 200 such as a commercial power supply, and generates power to be supplied to the light source unit 1 for causing the light emitting diode D11 to emit light.
The power supply device 3 is roughly divided into a rectifier circuit 10, a power factor correction [PFC (power factor correction)] circuit 20, a step-down chopper circuit 30, and a control circuit 40. In addition, as shown in FIG. 2, it includes a plurality of capacitors, a plurality of resistors, and a plurality of diodes, each of which shows only a part related to the present embodiment.

  The rectifier circuit 10 (DC power supply unit) is composed of, for example, a bridge-type rectifier circuit, and an external power supply 200 such as a commercial power supply is supplied to the pair of input terminals T21 and T22 to rectify AC power into DC power. Output. The capacitor (smoothing capacitor) C1 has one end connected to the output end of the rectifier circuit 10 and the other end connected to the ground (ground potential). The DC power output from the output terminal of the rectifier circuit 10 is smoothed by the capacitor C 1 and supplied to the PFC circuit 20.

  Resistors R2 and R3 are connected in series and provided between the output terminal of the rectifier circuit 10 and the ground. These resistors R2 and R3 divide the output voltage supplied to the PFC circuit 20 by the resistance ratio, and the divided voltage is input to the MULT terminal of the control circuit 40.

  The PFC circuit 20 is a boost chopper circuit that boosts the supplied DC power for power factor improvement. The PFC circuit 20 includes at least a coil 21, a diode D20, a switching element Q21, an electrolytic capacitor C21, and a resistor R21.

  The cathode of the diode D20 is connected to one end of the electrolytic capacitor C21 and serves as the output end of the PFC circuit 20. The other end of the electrolytic capacitor C21 is connected to the ground potential. As for the output of the PFC circuit 20, the potential difference between the cathode potential of the diode D20 and the ground potential becomes the output voltage VDC. The output voltage VDC is supplied to the step-down chopper circuit 30 and to the VDC terminal of the control circuit 40.

  The switching element Q21 of this embodiment uses an FET, and its source is connected to the ground potential via the CS terminal of the control circuit 40 and the resistor R21. The gate of the switching element Q21 is connected to the GD terminal of the control circuit 40. The PFC circuit 20 performs self-excited oscillation control by turning on / off the switching element Q21 under the control of the control circuit 40. The switching signal for turning on / off the switching element Q21 is a high-frequency signal of about 40 to 50 kHz, for example.

  The resistors R4 and R5 are connected in series and provided between the output terminal of the PFC circuit 20 and the ground. These resistors R4 and R5 divide the output voltage supplied to the step-down chopper circuit 30 by the resistance ratio, and the divided voltage is input to the VFB terminal of the control circuit 40.

  The step-down chopper circuit 30 includes at least a switching element Q31, a coil L31, a diode D31, and a capacitor C31, and further incorporates the bootstrap circuit 50 of the present embodiment. The step-down chopper circuit 30 uses a configuration in which VDC is supplied to the drain of the FET that is the switching element Q31, and the switching element Q31 made of an n-ch FET is disposed on the high side. Although the coil L32 connected to the diode D31 is used as a filter, it is not essential.

  The drain of the switching element Q31 is connected to one end of a capacitor 21 that is an output end of the PFC circuit 20. The drain of the switching element Q31 corresponds to the input terminal of the step-down chopper circuit 30. Further, the gate of the switching element Q31 is connected to the HO terminal of the control circuit 40, and the source which is the output end is connected to one end of the coil L31. The other end of the coil L31 is connected to the output terminal 31 of the step-down chopper circuit 30.

  The source of the switching element Q31 is connected to the ground potential via a series circuit of a coil L32 and a diode D31. The anode of the diode D31 is connected to the ground potential. The resistor R31 is for detecting the current flowing through the light emitting diode D11, and generates a potential having a magnitude corresponding to the current at a connection point between the capacitor C31 and the resistor R31. A connection point between the capacitor C31 and the resistor R31 is connected to the OCP terminal of the control circuit 40 via the resistor R6.

The connection point between the coil L31 and the capacitor C31 corresponds to the output terminal of the step-down chopper. This connection point is connected to a terminal T31 that contacts the terminal T11 of the light source unit.
The resistor R32 is connected at both ends to terminals T32 and T33 which are in contact with the terminals T12 and T13 of the light source unit, respectively. The connection point between the resistor R32 and the terminal T32 is connected to the OP-terminal of the control circuit 40. The terminal T33 is connected to the ground potential via the resistor R31.

The bootstrap circuit 50 includes a capacitor C32 and a diode D33. The diode D33 has an anode connected to the Vcc terminal of the control circuit 40 and a cathode connected to the VB terminal. The diode D33 passes the current output from the Vcc terminal of the control circuit 40 so as to be input to the VB terminal. Further, the diode D33 prevents backflow with respect to the VS terminal.
The capacitor C32 is connected to the VS terminal and the VB terminal of the control circuit 40, respectively.

  In the bootstrap circuit 50, the other end (output end) of the capacitor C32 is connected to the output end of the switching element Q31 via the switch S31 and to the ground line via the switch S32. The switches S31 and S32 are controlled by the control circuit 40 so as to be switched on and off individually. The bootstrap circuit 50 may be configured to be incorporated in the control circuit 40 of the lighting device 100 together with the two switches S31 and S32. The bootstrap circuit 50 continues the bootstrap operation with an arbitrary power supply after the step-down chopper is activated.

  In the control circuit 40, all elements (components) may be mounted as an integrated circuit (IC), or a part of the elements may be mounted outside the IC. All elements may be constituted by analog circuits. Furthermore, a part of processing performed in each circuit included in the control circuit 40, for example, an operation sequence can be realized by software processing using a computer.

Each terminal provided in the control circuit 40 will be described.
The terminals described in the control circuit 40 shown in FIG. 1 are a MULT terminal, a CS terminal, a VS terminal, a VB terminal, a GD terminal, a VFB terminal, a VDC terminal, an OCP terminal, and an OP-terminal. Of course, the present invention is not limited to these terminals, and a plurality of other terminals are provided, but those relating to the present embodiment are described.

The MULT terminal is a terminal for monitoring the input voltage to the PFC circuit 20.
The potential of the CS terminal changes according to the current flowing between the drain and source of the switching element Q21. That is, the CS terminal is a terminal for monitoring the magnitude of the current.
The potential of the VS terminal is a terminal for determining the reference potential of the HO terminal and the VB terminal. The VS terminal is connected between the capacitor C32 of the bootstrap circuit 50 and the switch S31.

.
The VB terminal is connected between the capacitor C32 of the bootstrap circuit 50 and the cathode of the diode D33. The voltage supplied from the Vcc terminal is supplied based on, for example, a voltage generated by a coil (not shown) magnetically coupled to the coil L31 of the step-down chopper circuit 30.

The VFB terminal has a potential corresponding to the voltage VDC output from the PFC circuit 20. That is, the VF terminal is a terminal for monitoring the magnitude of the voltage VDC.
The VDC terminal is a terminal for taking in the voltage VDC as the operating voltage of the control circuit 40.
The potential of the OCP terminal is a potential corresponding to the current flowing through the resistor R31. The current flowing through the resistor R31 is the current flowing through the light emitting diode D11. That is, the OCP terminal is a terminal for monitoring the magnitude of the current supplied to the light emitting diode D11, and is used for overcurrent protection in this embodiment.

  The potential of the OP-terminal is a voltage corresponding to a voltage drop based on the current flowing through the light emitting diode D11 and the resistor R11, and is a potential difference generated between the terminals T12 and T13. The magnitude of the resistance value of the resistor R11 is set according to the load of the light emitting diode D11, that is, it is set according to the current value to be passed, and the value of OP− matches the preset target value. The output current of the power supply device 3 is feedback controlled. When the terminal T12 of the light source unit 1 is not in contact with the terminal T32, the detection voltage is not input to the OP-terminal. On the other hand, if the value of OP− does not match the target value for a certain time, an abnormality of the power supply device 3 is estimated. Therefore, in the present embodiment, the OP-terminal is also used as a terminal for monitoring whether or not the light source unit 1 is normally mounted, and for monitoring the abnormality of the power supply device 3.

Next, the starting operation of the lighting device 100 equipped with the bootstrap circuit 50 configured as described above will be described.
Before the lighting device 100 is started (before lighting is started), both the switching element Q21 and the switching element Q31 are in the off state. Before startup, the switches S31 and S32 of the bootstrap circuit 50 are set to an off state. Alternatively, the switch S31 is set to an off state and the switch S32 is set to an on state.

  First, when a power switch (not shown) of the lighting device 100 is turned on, AC power is supplied to the rectifier circuit 10 to start a rectification operation. The DC power obtained by the rectifier circuit 10 and the capacitor C1 is supplied to the PFC circuit 20. When the DC power voltage VDC is supplied from the PFC circuit 20 to the control circuit 40, the control circuit 40 is started. The control circuit 40 maintains the switch S31 in the off state and turns on the switch S32. If the switch S31 is set to an off state and the switch S32 is set to an on state before starting, these states are maintained without a switching operation.

  By this switching operation, the output end of the bootstrap circuit 50 and the source of the switching element Q31 are electrically disconnected, the output side of the capacitor C32 is connected to the ground potential, and the capacitor C32 is charged. When the switch S31 is turned on and the switch S32 is turned off, a drive voltage based on the potential Vs is obtained from the bootstrap circuit 50, and a steady operation state is obtained.

This steady operation state is a state in which the light source unit is lit, and the PFC circuit 20 performs step-up chopping so that the voltage VDC becomes a predetermined target voltage while performing phase compensation. The control circuit 40 is configured such that the voltage supplied to the PFC circuit 20, the difference between the voltage VDC and its target value, the upper limit value of the current set according to the current flowing through the switching element Q21, and the current flowing through the primary coil L21 are zero. By adjusting the switching signal for driving the switching element Q21 according to the timing when it becomes, the boost chopping is controlled by the well-known self-excited oscillation method.
According to the present embodiment, the PFC circuit 20 of the power supply device 3 can output DC power with a power factor improved.

  The above-described embodiment is presented as an example, does not limit the scope of the invention, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Light source unit, 3 ... Power supply device, 10 ... Rectifier circuit, 20 ... PFC circuit, 21 ... Capacitor, 30 ... Step-down chopper circuit, 31 ... Output terminal, 40 ... Control circuit, 50 ... Bootstrap circuit, 100 ... Illumination device 200, external power source, C1, C31, C32 ... capacitor, C21 ... electrolytic capacitor, D11 ... light emitting diode, D20, D31, D33 ... diode, L21, L31, L32 ... coil, Q21, Q31 ... switching element, R2, R4 , R6, R11, R21, R31, R32 ... resistors, S31, S32 ... switches, T11, T12, T13, T31, T32, T33 ... terminals.

Claims (3)

A DC power supply unit that outputs rectified DC power;
At least one switching element having an input terminal connected to the output terminal of the DC power supply unit and turned on / off by a signal input to the control terminal;
An inductor having one end connected in series to the output end of the switching element;
A capacitor connected to the other end of the inductor and smoothing a voltage supplied to a load;
A diode having an anode connected to the low potential side of the capacitor and connected to the output terminal of the switching element to return the energy of the inductor;
A bootstrap circuit for generating a voltage to be supplied to the control terminal of the switching element;
A first switch having one end connected to the output end of the bootstrap circuit and the other end connected to the output end of the switching element;
A second switch having one end connected to the output end of the bootstrap circuit, the other end connected to the ground, and connecting the output end of the bootstrap circuit to the ground when turned on;
Switching control for turning off the first switch before starting the switching element, turning on the second switch, turning on the first switch when starting the switching element, and turning off the second switch A control circuit for performing;
A power supply apparatus comprising:   The power supply device according to claim 1, wherein the switching element is an n-ch field effect transistor, and the bootstrap circuit generates a voltage to be supplied to a gate of the n-ch field effect transistor.   The lighting device including the power supply device according to claim 1, wherein the load is a solid light source, and the solid light source is driven.