JP6243063B2 - LED driver circuit and LED lighting device - Google Patents

Description

  The present invention relates to an LED driver circuit and an LED lighting device.

  Conventionally, a battery that is a DC power supply, a step-up / step-down LED driver circuit (converter, switching power supply) that converts the battery power and outputs a predetermined output current, and is connected in series and supplied with an output current There is an LED lighting device including an LED lamp having a plurality of LED elements to be lit (see, for example, Japanese Patent Laid-Open No. 2006-340432, Chinese Utility Model 202005034, Japanese Patent Laid-Open No. 2013-099072, Japanese Patent Laid-Open No. 2013-098297). . This conventional LED lighting device is used for a headlight of a vehicle such as a two-wheeled vehicle, for example.

  Conventionally, an output capacitor is connected between output terminals of an LED driver circuit included in an LED lighting device. In this conventional LED driver circuit, the brightness of one LED element does not change when the number of LED elements in the LED lamp in series (the number of lighting) changes by switching between high beam and low beam during operation. As described above, there is a problem that the output voltage cannot be changed at high speed.

  On the other hand, as shown in FIGS. 11 and 12, the LED driver circuit is configured such that no output capacitor is connected between the output terminals so that the output voltage can be changed at a high speed when the load suddenly changes. It is possible. The LED driver circuits of the LED lighting devices 100A and 100B (FIGS. 11 and 12) of the first and second comparative examples include coils L101 and L102, a switching element M101, a diode D101, and a first capacitor C101. In a state where the LED lighting device 100A of the first comparative example is operating stably, the first capacitor C101 is charged to a voltage close to the voltage Vo between the output terminals T101 and T102. On the other hand, in the state in which the LED lighting device 100B of the second comparative example is operating stably, the first capacitor C101 has the sum of the voltage Vi between the input terminals T103 and T104 and the voltage Vo between the output terminals T101 and T102. Charged to near voltage.

  With such a circuit configuration, at the moment when the connection state of the load such as the LED lamp is released while the LED driver circuit is operating, the energy stored in the inductor L102 connected in series to the output terminal is released immediately before that. Is done. Therefore, in the LED driver circuit 100A of the first comparative example of FIG. 11, the voltage of the output terminal rapidly rises, and in the LED driver circuit 100B of the second comparative example of FIG. 12, the voltage of the output terminal suddenly drops. As a result, there is a problem that electric discharge occurs between the output terminal T101 and the ground.

  Then, an object of this invention is to provide the LED driver circuit and LED lighting apparatus which can suppress the change of the voltage of an output terminal when the connection state of load becomes open | released.

An LED driver circuit according to one embodiment of the present invention includes:
A first battery terminal connected to the positive electrode of the battery;
A second battery terminal connected to the negative electrode of the battery and connected to the cathode side of the LED lamp;
An output terminal connected to the anode side of the LED lamp;
A switching element having one end connected to the first battery terminal;
A first inductor having one end connected to the other end of the switching element and the other end connected to the second battery terminal;
A first capacitor having one end connected to one end of the first inductor;
A second inductor having one end connected to the other end of the first capacitor and the other end connected to the output terminal;
One end is connected to the second battery terminal and the other end is connected to the other end of the first capacitor, and the direction from the second battery terminal toward the other end of the first capacitor is the forward direction. A first rectifying element;
A second capacitor having one end connected to the second battery terminal;
One end is connected to the other end of the second inductor, the other end is connected to the other end of the second capacitor, and the direction from the other end of the second inductor to the other end of the second capacitor is A second rectifying element in the forward direction;
A control unit for controlling on / off of the switching element based on a current flowing through the second inductor;
It is characterized by providing.

In the LED driver circuit,
The second capacitor is configured to be capable of discharging through a resistor.

In the LED driver circuit,
The control unit stops the switching operation of the switching element when a voltage based on a voltage at the other end of the second capacitor exceeds a first threshold.

In the LED driver circuit,
The controller restarts the switching operation of the switching element when a voltage based on the voltage at the other end of the second capacitor falls below a second threshold value that is smaller than the first threshold value.

In the LED driver circuit,
The first threshold value is set to a value based on a voltage value larger than twice the voltage of the output terminal in a steady state.

In the LED driver circuit,
The resistance is
A first voltage dividing resistor having one end connected to the other end of the second capacitor;
A second voltage dividing resistor having one end connected to the other end of the first voltage dividing resistor and the other end connected to one end of the first inductor;
Have
The voltage based on the voltage at the other end of the second capacitor is a voltage at the other end of the first voltage dividing resistor.

In the LED driver circuit,
A capacitor is not provided between the other end of the second inductor and the second battery terminal.

An LED lighting device according to an aspect of the present invention is provided.
The LED driver circuit;
The LED lamp,
The LED lamp is
A plurality of LED elements connected in series;
A switch circuit connected in parallel with any of the plurality of LED elements;
Including
The number of LED elements to be lit is switched by turning on / off the switch circuit.

An LED driver circuit according to another aspect of the present invention includes:
A first battery terminal connected to the positive electrode of the battery;
A second battery terminal connected to the negative electrode of the battery and connected to the anode side of the LED lamp;
An output terminal connected to the cathode side of the LED lamp;
A first inductor having one end connected to the first battery terminal;
A switching element having one end connected to the other end of the first inductor and the other end connected to the second battery terminal;
A first capacitor having one end connected to the other end of the first inductor;
A second inductor having one end connected to the other end of the first capacitor and the other end connected to the output terminal;
One end is connected to the other end of the first capacitor and the other end is connected to the second battery terminal, and the direction from the other end of the first capacitor toward the second battery terminal is the forward direction. A first rectifying element;
A second capacitor having one end connected to the second battery terminal;
One end is connected to the other end of the second capacitor, the other end is connected to the other end of the second inductor, and the direction from the other end of the second capacitor toward the other end of the second inductor is A second rectifying element in the forward direction;
A control unit for controlling on / off of the switching element based on a current flowing through the second inductor;
It is characterized by providing.

In the LED driver circuit,
The second capacitor is configured to be capable of discharging through a resistor.

In the LED driver circuit,
The controller may stop the switching operation of the switching element when a voltage based on a voltage at the other end of the second capacitor falls below a first threshold.

In the LED driver circuit,
The controller restarts the switching operation of the switching element when a voltage based on the voltage at the other end of the second capacitor exceeds a second threshold value that is greater than the first threshold value.

In the LED driver circuit,
The resistance is
A first voltage dividing resistor having one end connected to the other end of the second capacitor;
A second voltage dividing resistor having one end connected to the other end of the first voltage dividing resistor and the other end connected to a second battery terminal;
Have
The voltage based on the voltage at the other end of the second capacitor is a voltage at the other end of the first voltage dividing resistor.

In the LED driver circuit,
A capacitor is not provided between the other end of the second inductor and the second battery terminal.

An LED lighting device according to an aspect of the present invention is provided.
The LED driver circuit;
The LED lamp,
The LED lamp is
A plurality of LED elements connected in series;
A switch circuit connected in parallel with any of the plurality of LED elements;
Including
The number of LED elements to be lit is switched by turning on / off the switch circuit.

  An LED driver circuit according to an aspect of the present invention includes a second capacitor via a second rectifier element at a moment when a connection state of a load is released and a voltage of an output terminal greatly increases during operation of the switching element. By storing energy in the output terminal, it is possible to suppress an increase in voltage at the output terminal. That is, it is possible to suppress a change in the voltage of the output terminal when the load connection state is released.

  In addition, the LED driver circuit according to another aspect of the present invention is configured so that the connection state of the load is released during the operation of the switching element, and the voltage of the output terminal greatly drops via the second rectifier element. When the second capacitor is charged with a negative voltage with respect to the ground, the voltage drop at the output terminal can be suppressed. That is, it is possible to suppress a change in the voltage of the output terminal when the load connection state is released.

FIG. 1 is a diagram illustrating an example of the configuration of the LED lighting device 100 according to the first embodiment. FIG. 2 is a diagram illustrating an example of a current path when the switching element M1 of the LED driver circuit 102 illustrated in FIG. 1 is turned on. FIG. 3 is a diagram illustrating an example of a current path when the switching element M1 of the LED driver circuit 102 illustrated in FIG. 1 is turned off. FIG. 4 is a diagram illustrating an example of a current waveform flowing in the LED driver circuit 102. FIG. 5 is a diagram illustrating an example of voltage waveforms before and after the load connection state is released in the LED lighting device 100 illustrated in FIG. 1. FIG. 6 is a diagram illustrating an example of the configuration of the LED lighting device 100b according to the second embodiment. FIG. 7 is a diagram illustrating an example of a current path when the switching element M1 of the LED driver circuit 102b illustrated in FIG. 6 is turned on. FIG. 8 is a diagram illustrating an example of a current path when the switching element M1 of the LED driver circuit 102b illustrated in FIG. 6 is off. FIG. 9 is a diagram illustrating an example of a waveform of a current flowing through the LED driver circuit 102b. FIG. 10 is a diagram illustrating an example of voltage waveforms before and after the load connection state is released in the LED lighting device 100 illustrated in FIG. 6. FIG. 11 is a diagram illustrating an example of the configuration of the LED lighting apparatus 100A of the first comparative example. FIG. 12 is a diagram illustrating an example of the configuration of the LED lighting device 100B of the second comparative example.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings.

(First embodiment)
As shown in FIG. 1, the LED lighting device 100 according to the first embodiment includes an LED lamp 101 having one or a plurality of LED elements 101 a connected in series, and an LED driver circuit that drives the LED lamp 101. 102. In FIG. 1, a battery (DC power supply) BAT, which will be described later, is not shown.

  The LED lamp 101 includes a plurality of LED elements 101a connected in series and a switch circuit SW connected in parallel with any of the plurality of LED elements 101a.

  The number of LED elements 101a to be lit is switched by turning on / off the switch circuit SW. The switch circuit SW can be switched on / off by the user.

  The LED lamp 101 is a headlamp of a two-wheeled vehicle, for example. The LED element 101a to which the switch circuit SW is not connected in parallel is, for example, a Low beam LED element. The LED element 101a connected in parallel to the switch circuit SW is, for example, a Hi beam LED element.

  Then, when the switch circuit SW is controlled to be turned off by the user, a current flows through all the LED elements 101a.

  On the other hand, when the switch circuit SW is turned on by the user, the LED element 101a connected in parallel to the switch circuit SW is in a state where no current flows.

  Thus, the number of LED elements 101a to be lit is switched by turning on / off the switch circuit SW.

  By switching the number of LED elements 101a to be lit in this way, the load on the LED lamp 101 changes.

  The LED driver circuit 102 drives the LED lamp 101 by supplying a current to the LED lamp 101.

  As shown in FIG. 1, the LED driver circuit 102 includes, for example, a first battery terminal Tx, a second battery terminal (ground terminal) Ty, an output terminal Tz, a switching element M1, and a first inductor. L1, a first capacitor C1, a second inductor L2, a first rectifier element D1, a second capacitor C2, a second rectifier element D2, a first voltage dividing resistor R1, 2 voltage dividing resistor R2, first detecting resistor R3, second detecting resistor R4, control unit 103, and terminals T1 to T7.

  The first battery terminal Tx is connected to the positive electrode TBa of the battery BAT.

  The second battery terminal Ty is connected to the negative electrode TBb of the battery BAT and to one end (cathode side) 22 of the LED lamp 101.

  The output terminal Tz is connected to the other end (anode side) 21 of the LED lamp 101.

  The switching element M1 has one end (drain) connected to the first battery terminal Tx and the other end (source) connected to one end of the first inductor L1 via the second detection resistor R4. . The switch element M1 is controlled to be turned on / off by a signal output from the terminal T1 of the control unit 103.

  The switching element M1 is, for example, a MOS transistor as shown in FIG. In this case, the signal output from the terminal T1 of the control unit 103 is supplied to the gate of the MOS transistor.

  The switching element M1 may be a bipolar transistor.

  The first inductor L1 has one end connected to the other end of the switching element M1 and the other end connected to the second battery terminal Ty.

  One end of the first capacitor C1 is connected to one end of the first inductor L1.

  One end of the second inductor L2 is connected to the other end of the first capacitor C1 via the first detection resistor R3, and the other end is connected to the output terminal Tz.

  The first rectifying element D1 has one end connected to the second battery terminal Ty and the other end connected to the other end of the first capacitor C1. In the first rectifying element D1, the direction from the second battery terminal Ty toward the other end of the first capacitor C1 is the forward direction.

  The first rectifying element D1 is, for example, a diode having an anode connected to the second battery terminal Ty and a cathode connected to the other end of the first capacitor C1, as shown in FIG.

  The first rectifying element D1 may be a switching element, for example. That is, the first rectifying element D1 includes not only a diode but also a switching element.

  One end of the second capacitor C2 is connected to the second battery terminal Ty.

  The second rectifying element D2 has one end connected to the other end of the second inductor L2 and the other end connected to the other end of the second capacitor C2. In the second rectifying element D2, the direction from the other end of the second inductor L2 toward the other end of the second capacitor C2 is the forward direction.

  The second rectifier element D2 is, for example, a diode having an anode connected to the other end of the second inductor L2 and a cathode connected to the other end of the second capacitor C2, as shown in FIG. .

  Note that the second rectifying element D2 may be a switching element, for example. That is, the second rectifying element D2 includes not only a diode but also a switching element.

  The second capacitor C2 is configured to be able to discharge through a resistor. More specifically, a resistor is connected between the other end of the second capacitor C2 and one end of the first inductor L1. In the present embodiment, this resistor includes a first voltage dividing resistor R1 and a second voltage dividing resistor R2.

  Here, one end of the first voltage dividing resistor R1 is connected to the other end of the second capacitor C2, and the other end is connected to the terminal T7.

  The second voltage dividing resistor R2 has one end connected to the other end of the first voltage dividing resistor R1 and the other end connected to one end of the first inductor L1.

  The first detection resistor R3 is connected in series with the second inductor L2 between the other end of the first capacitor C1 and the output terminal Tz.

  The second detection resistor R4 is connected between the other end of the switching element M1 and one end of the first inductor L1.

  The control unit 103 is based on a voltage based on the voltage at the other end of the second capacitor C2 (specifically, the voltage at the other end of the first voltage dividing resistor R1 with reference to the reference potential of the control unit 103). The stop or restart of the switching operation of the switching element M1 is determined. For example, when the voltage based on the voltage at the other end of the second capacitor C2 exceeds the first threshold, the control unit 103 stops the switching operation of the switching element M1. Thereby, when the overvoltage of the output voltage is detected, the switching operation of the switching element M1 can be stopped.

  The control unit 103 has a voltage based on the voltage at the other end of the second capacitor C2 (specifically, the voltage at the other end of the first voltage dividing resistor R1 with reference to the reference potential of the control unit 103). When the value falls below a second threshold value that is smaller than the first threshold value, the switching operation of the switching element M1 is resumed. Accordingly, the switching operation of the switching element M1 can be stopped until the voltage based on the voltage at the other end of the second capacitor C2 reaches the second threshold value, and no current flows through the switching element M1 during that time. Therefore, the heat generation of the element can be reduced accordingly.

  Here, the terminal T5 is connected to the reference potential of the control unit 103, but the reference potential of the control unit 103 is floating from the ground terminal. Therefore, the reference potential of the control unit 103 is not fixed, and when the voltage at the output terminal Tz is V1 when the switching element M1 is in a switching operation (steady state), the switching element M1 is off. The potential of the terminal T5 of the control unit 103 decreases to -V1. Since the potential at the other end of the second capacitor C2 is V1, the voltage between the other end of the second capacitor C2 and the reference potential of the control unit 103 is 2 × V1. Therefore, the control unit 103 stops the switching operation of the switching element M1 when the voltage at the other end of the second capacitor C2 exceeds a voltage value larger than 2 × V1 with respect to the reference potential of the control unit 103. In addition, the first threshold value is set to a value based on a specified voltage value that is larger than twice the voltage V1 of the output terminal in the steady state (2 × V1). Specifically, the first threshold value is a voltage value at the other end of the first voltage dividing resistor R1 with the reference potential of the control unit 103 at the specified voltage value as a reference point.

  The control unit 103 performs on / off control of the switching element M1 based on a current flowing through the second inductor L2 (hereinafter referred to as a first current). Note that, for example, as illustrated in FIG. 1, the control unit 103 acquires the value of the first current by detecting the current flowing through the first detection resistor R3. For example, the control unit 103 turns on the switching element M1 until the first current increases to reach the third threshold (UPPER LIMIT).

  Then, the control unit 103 turns off the switching element M1 when the first current increases to reach the third threshold (UPPER LIMIT).

  Then, the control unit 103 turns off the switching element M1 until the first current decreases and reaches a fourth threshold value (LOWER LIMIT) that is smaller than the third threshold value (UPPER LIMIT).

  Then, the control unit 103 turns on the switching element M1 when the first current decreases to reach the fourth threshold (LOWER LIMIT).

By such control of the control unit 103, the first current flowing through the second inductor L2 is controlled to transition between the third threshold (UPPER LIMIT) and the fourth threshold (LOWER LIMIT). . That is, the output current supplied from the output terminal Tz to the LED lamp 101 is controlled within a predetermined range.
Further, the control unit 103 acquires the value of the second current flowing through the switching element M1 by detecting the current flowing through the second detection resistor R4. The control unit 103 forcibly turns off the switching element M1 when the second current flowing through the switching element M1 becomes equal to or greater than a fifth threshold value that is larger than the third threshold value (UPPER LIMIT).

  Thereby, destruction of elements, such as switching element M1 by overcurrent, can be suppressed.

  Note that the control unit 103 is connected to the positive electrode TBa of the battery BAT via the terminal T6 and the first battery terminal Tx. The controller 103 is supplied with the voltage Vcc of the battery BAT via the terminal T6 and the first battery terminal Tx.

  For example, as shown in FIG. 1, the control unit 103 includes an output current detection unit 103a, an input overcurrent detection unit 103b, a switch control unit 103c, a driver 103d, and an output overvoltage detection unit 103e. Prepare.

  The output current detection unit 103a is connected to the first detection resistor R3 via terminals T2 and T3. The output current detection unit 103a detects a current flowing through the first detection resistor R3.

  The input overcurrent detection unit 103b is connected to one end of the second detection resistor R4 through the terminal T4, and is connected to the other end of the second detection resistor R4 through the terminal T5. The input overcurrent detection unit 103b detects a current flowing through the second detection resistor R4. The other end of the second detection resistor R2 is connected to the reference potential of the control unit 103 via the terminal T5. In this embodiment, the reference potential is floating from the ground terminal.

  For example, as in the present embodiment, when the switching element M1 is an n-ch MOS transistor, the source potential is a floating potential from the ground potential. Therefore, if the reference potential of the control unit 103 is the ground potential, the high side driver I need it. However, the high-side driver is not required by adopting a configuration in which the reference potential of the control unit 103 is floated from the ground.

  The switch control unit 103c outputs a control signal based on the current detected by the input overcurrent detection unit 103b and the current detected by the output current detection unit 103a.

  For example, the switch control unit 103c outputs a control signal for turning on the switching element M1 until the first current increases to reach the third threshold (UPPER LIMIT).

  Then, the switch control unit 103c outputs a control signal for turning off the switching element M1 when the first current increases to reach the third threshold (UPPER LIMIT).

  Then, the switch control unit 103c outputs a control signal for turning off the switching element M1 until the first current decreases and becomes a fourth threshold value (LOWER LIMIT) smaller than the third threshold value (UPPER LIMIT). Output.

  Then, the switch control unit 103c outputs a control signal for turning on the switching element M1 when the first current decreases to reach the fourth threshold (LOWER LIMIT).

  By such control of the switch control unit 103c, the first current flowing through the second inductor L2 is controlled to transition between the third threshold (UPPER LIMIT) and the fourth threshold (LOWER LIMIT). The That is, the output current supplied from the output terminal Tz to the LED lamp 101 is controlled within a predetermined range.

  On the other hand, when the first current exceeds a specified current value, the switch control unit 103c outputs a control signal for turning off the switching element M1.

  In addition, the switch control unit 103c outputs a control signal for forcibly turning off the switching element M1 when the second current becomes equal to or greater than a fifth threshold value that is larger than the third threshold value (UPPER LIMIT). .

  Thereby, destruction of elements, such as switching element M1 by overcurrent, can be suppressed.

  The driver 103d controls the gate voltage of the switching element M1 according to the control signal output by the switch control unit 103c.

  The output overvoltage detection unit 103e is connected to the other end of the first voltage dividing resistor R1 via the terminal T7. The output overvoltage detection unit 103e is a voltage based on the voltage at the other end of the second capacitor C2 (specifically, the voltage at the other end of the first voltage dividing resistor R1 with the reference potential of the control unit 103 as a reference point). ) To stop or restart the switching operation of the switching element M1. For example, the output overvoltage detection unit 103e stops the switching operation of the switching element M1 when the voltage based on the voltage at the other end of the second capacitor C2 exceeds the first threshold. Thereby, when the overvoltage of the output voltage is detected, the switching operation of the switching element M1 can be stopped.

  The output overvoltage detection unit 103e is a voltage based on the voltage at the other end of the second capacitor C2 (specifically, the voltage at the other end of the first voltage dividing resistor R1 with the reference potential of the control unit 103 as a reference point). When the voltage is lower than the second threshold value which is smaller than the first threshold value, the switching operation of the switching element M1 is resumed. Accordingly, the switching operation of the switching element M1 can be stopped until the voltage based on the voltage at the other end of the second capacitor C2 reaches the second threshold value, and no current flows through the switching element M1 during that time. Therefore, the heat generation of the element can be reduced accordingly.

  Here, in the LED driver circuit 102, no output capacitor is provided between the other end of the second inductor L2 and the second battery terminal Ty.

  The LED driver circuit 102 has a configuration in which a first rectifier element D1 and a second inductor L2 connected in series are provided between the second battery terminal (ground terminal) Ty and the output terminal Tz. . For this reason, the LED driver circuit 102 can output a continuous current even if an output capacitor is not provided, as will be described later.

(Regarding the normal control method)
Next, an example of a normal control method for the LED driver circuit 102 having the above configuration will be described.

  As described above, the control unit 103 performs on / off control of the switching element M1 based on the first current flowing through the second inductor L2.

  For example, the control unit 103 increases the first current (the current I (L2) flowing through the second inductor L2) to the third threshold (UPPER LIMIT) (for example, time t0 to t1, FIG. At time t2 to t3), the switching element M1 is turned on.

  Thereby, the current I (M1) flows through the switching element M1 (FIG. 4). The current I (M1) is equal to the current flowing through the second detection resistor R4. The current I (M1) includes a first current I1a flowing through the first detection resistor R3 (current I (L2) flowing through the second inductor L2) and a second current I2a (passing through the first inductor L1). And the sum of the flowing current I (L1)) (FIGS. 2 and 4).

  A current I (L2) flowing through the second inductor L2 is supplied to the LED lamp 101 as an output current. As a result, the LED lamp 101 is turned on.

  At this time, the capacitor C1 is discharged.

  Then, the control unit 103 increases the first current I1a (the current I (L2) flowing through the second inductor L2) to reach the third threshold (UPPER LIMIT) (for example, time t1 in FIG. 4). , Time t3), the switching element M1 is turned off.

  As a result, the current I (M1) of the switching element M1, that is, the current of the second detection resistor R4 is cut off (FIG. 3).

  Then, the control unit 103 reduces the first current I1b flowing through the first detection resistor R3 (current I (L2) flowing through the second inductor L2) to be smaller than the third threshold (UPPER LIMIT). The switching element M1 is turned off until the fourth threshold value (LOWER LIMIT) is reached (for example, times t1 to t2 in FIG. 4).

  At this time, as shown in FIG. 3, the first current I1b flowing through the first detection resistor R3 (current I (L2) flowing through the second inductor L2) is the output terminal Tz, the LED lamp 101, the second It flows through the battery terminal Ty and the first rectifying element D1 in order (FIG. 3).

  Furthermore, the current I (L1) flowing through the first inductor L1 flows through the first rectifier element D1 and the first capacitor C1 in order (FIG. 3).

  Therefore, the current I (D1) flowing through the first rectifier element D1 is the sum of the current I (L1) and the current I (L2) (FIGS. 3 and 4).

  Then, the control unit 103 decreases the first current I1b flowing through the first detection resistor R3 (current I (L2) flowing through the second inductor L2) to the fourth threshold (LOWER LIMIT). When (for example, time t2 in FIG. 4), the switching element M1 is turned on.

  Thereafter, the same operation is repeated.

  By the operation of the LED driver circuit 102 described above, the current I (L2) flowing through the second inductor L2 is controlled to transition between the third threshold (UPPER LIMIT) and the fourth threshold (LOWER LIMIT). The

  That is, the output current supplied from the output terminal Tz to the LED lamp 101 is controlled within a predetermined range.

  As described above, the LED driver circuit 102 includes the first rectifier element D1 and the inductor (second circuit) connected in series between the second battery terminal (ground terminal) Ty and the output terminal Tz. Since the inductor L2) is provided, a continuous current can be output without an output capacitor (FIGS. 2 to 4).

(Current path when releasing the load)
Next, the operation of the LED driver circuit 102 when the connection state of the load (LED element 101a) is released during the operation of the switching element M1 will be described.

  When the connection state of the LED element 101a is released during the operation of the switching element M1 as indicated by the gate voltage V (G) of the switching element M1 in FIG. 5 (for example, at time t4 in FIG. 5), the output terminal Tz. At the moment when the voltage Vo rises significantly, electric charge is stored in the second capacitor C2 via the second rectifying element D2. Thereby, the voltage rise of the output terminal Tz is suppressed. Then, as the voltage V (C2) of the capacitor C2 increases, the voltage V (T7) of the terminal T7 increases, so that the voltage V (T7) of the terminal T7 with the reference potential of the control unit 103 as the reference point becomes the first. When the threshold value of 1 is exceeded (for example, at time t5 in FIG. 5), the control unit 103 stops the switching operation of the switching element M1.

  After that, the electric charge once stored in the second capacitor C2 is held even after the potential Vo of the output terminal Tz becomes 0, via the first voltage dividing resistor R1 and the second voltage dividing resistor R2. It is gradually discharged. The control unit 103 performs the switching operation of the switching element M1 until the voltage V (T7) at the terminal T7 with the reference potential of the control unit 103 as a reference point decreases to a second threshold value that is smaller than the first threshold value. Leave it stopped. When the voltage V (T7) at the terminal T7 with the reference potential of the control unit 103 as a reference point falls below the second threshold (for example, time t6 in FIG. 5), the control unit 103 switches the switching element M1. Resume operation.

  Thereafter, the same operation is repeated.

  As described above, in the LED driver circuit 102 according to the first embodiment, the connection state of the load is released during the operation of the switching element M1, and the voltage of the output terminal greatly increases via the second rectifier element D2. By storing energy in the second capacitor C2, an increase in voltage at the output terminal can be suppressed. That is, a change in the voltage of the output terminal Tz when the load connection state is released can be suppressed.

  In addition, when the voltage of the second capacitor C2 rises and the voltage at the other end of the first resistor R1 with the reference potential of the control unit 103 as a reference point exceeds the first threshold, the control unit 103 Then, the switching operation of the switching element M1 is stopped. Thereafter, the electric charge stored in the second capacitor C2 is gradually discharged through the first resistor R1 and the second resistor R2. The LED driver circuit 102 then switches the switching element M1 until the voltage at the other end of the first resistor R1 with the reference potential of the control unit 103 as a reference point falls below a second threshold value (which is smaller than the first threshold value). By maintaining the stop of the switching operation, energy loss in the absence of a load can be suppressed.

(Second Embodiment)
Next, the second embodiment will be described. As shown in FIG. 6, the configuration of the LED lighting device 100b in the second embodiment is changed from the LED driver circuit 102 to the LED driver circuit 102b with respect to the configuration of the LED lighting device 100 in the first embodiment. It is a thing. In the LED driver circuit 102 according to the first embodiment, the switching element M1, the capacitor C1, and the second inductor L2 are connected in series between the first battery terminal Tx and the output terminal Tz, and one end of the capacitor C1. Is connected to the second battery terminal Ty via the first inductor L1. In contrast, in the LED driver circuit 102b in the second embodiment, the first inductor L1, the capacitor C1, and the second inductor L2 are connected in series between the first battery terminal Tx and the output terminal Tz. One end of the capacitor C1 is connected to the second battery terminal Ty via the switching element M1. In FIG. 6, a battery (DC power supply) BAT, which will be described later, is not shown.

  The LED driver circuit 102b supplies current to the LED lamp 101 and drives the LED lamp 101 in the same manner as the LED driver circuit 102 in the first embodiment.

  As shown in FIG. 6, the LED driver circuit 102b includes, for example, a first battery terminal Tx, a second battery terminal (ground terminal) Ty, an output terminal Tz, a first inductor L1, and a switching element. M1, a first capacitor C1, a second inductor L2, a first rectifier element D1, a second capacitor C2, a second rectifier element D2, a first detection resistor R3, 2 detection resistors R4, a control unit 103, and terminals T1 to T7.

  The first battery terminal Tx is connected to the positive electrode TBa of the battery.

  The second battery terminal Ty is connected to the negative electrode TBb of the battery and is connected to one end (anode side) 22 of the LED lamp 101.

  The output terminal Tz is connected to the other end (cathode side) 21 of the LED lamp 101.

  One end of the first inductor L1 is connected to the first battery terminal Tx.

  The switching element M1 has one end (drain) connected to the other end of the first inductor L1, and the other end (source) connected to the second battery terminal Ty via the second detection resistor R4. ing. The switch element M1 is controlled to be turned on / off by a signal output from the terminal T1 of the control unit 103.

  The switching element M1 is, for example, a MOS transistor as shown in FIG. In this case, the signal output from the terminal T1 of the control unit 103 is supplied to the gate of the MOS transistor.

  The switching element M1 may be a bipolar transistor.

  One end of the first capacitor C1 is connected to the other end of the first inductor L1.

  One end of the second inductor L2 is connected to the other end of the first capacitor C1, and the other end is connected to the output terminal via the first detection resistor R3.

  The first rectifying element D1 has one end connected to the other end of the first capacitor C1 and the other end connected to the second battery terminal Ty. In the first rectifying element D1, the direction from the other end of the first capacitor C1 toward the second battery terminal Ty is the forward direction.

  For example, as shown in FIG. 6, the first rectifying element D1 is a diode having an anode connected to the other end of the first capacitor C1 and a cathode connected to the second battery terminal Ty.

  The first rectifying element D1 may be a switching element. That is, the first rectifying element D1 includes not only a diode but also a switching element.

  One end of the second capacitor C2 is connected to the second battery terminal Ty.

  The second rectifying element D2 has one end connected to the other end of the second capacitor C2 and the other end connected to the other end of the second inductor L2 via the first detection resistor R3. In the second rectifying element D2, the direction from the other end of the second capacitor C2 toward the other end of the second inductor L2 is the forward direction.

  For example, as shown in FIG. 6, the second rectifying element D2 has an anode connected to the other end of the second capacitor C2, and a cathode connected to the second inductor via the first detection resistor R3. This is a diode connected to the other end of L2.

  The second rectifying element D2 may be a switching element. That is, the second rectifying element D2 includes not only a diode but also a switching element.

  The second capacitor C2 is configured to be able to discharge through a resistor. More specifically, a resistor is connected between the other end of the second capacitor C2 and the second battery terminal Ty. In the present embodiment, this resistor includes a first voltage dividing resistor R1 and a second voltage dividing resistor R2.

  Here, one end of the first voltage dividing resistor R1 is connected to the other end of the second capacitor C2, and the other end is connected to the terminal T7.

  The second voltage dividing resistor R2 has one end connected to the other end of the first voltage dividing resistor R1 and the other end connected to the second battery terminal Ty.

  The first detection resistor R3 is connected in series with the second inductor L2 between the other end of the first capacitor C1 (one end of the first rectifying element D1) and the output terminal Tz. .

  The second detection resistor R4 is connected between the other end of the switching element M1 and the second battery terminal Ty. Note that the other end of the second detection resistor R2 is connected to the ground via a terminal T5.

  The control unit 103 is connected to the positive electrode TBa of the battery via the terminal T6 and the first battery terminal Tx. The controller 103 is supplied with the battery voltage Vcc via the terminal T6 and the first battery terminal Tx.

  The control unit 103 stops or restarts the switching operation of the switching element M1 based on the voltage based on the voltage at the other end of the second capacitor C2 (specifically, the voltage at the other end of the first voltage dividing resistor R1). To decide. For example, when the voltage based on the voltage at the other end of the second capacitor C2 falls below the first threshold, the control unit 103 stops the switching operation of the switching element M1. For example, when the voltage based on the voltage at the other end of the second capacitor C2 exceeds a second threshold value that is greater than the first threshold value, the control unit 103 resumes the switching operation of the switching element M1.

  Further, the control unit 103 performs on / off control of the switching element M1 based on the current (first current) flowing through the second inductor L2. Note that, for example, as illustrated in FIG. 9, the control unit 103 acquires the value of the first current by detecting the current flowing through the first detection resistor R3. Since the configuration of the control unit 103 is the same as the configuration of the control unit 103 according to the first embodiment, a detailed description thereof is omitted.

Next, an example of a method for controlling the LED driver circuit 102b having the above configuration will be described.
As described above, the control unit 103 performs on / off control of the switching element M1 based on the current (first current) flowing through the second inductor L2.

  For example, the control unit 103 increases the first current (the current I (L2) flowing through the second inductor L2) to the third threshold (UPPER LIMIT) (for example, from time t10 to t11 in FIG. At time t12 to t13), the switching element M1 is turned on.

  Thereby, the current I (M1) flows through the switching element M1 (FIG. 7). The current I (M1) includes a first current I3a flowing through the first detection resistor R3 (current I (L2) flowing through the second inductor L2) and a current I (L1) flowing through the first inductor L1. And the second current I4a (FIGS. 7 and 9).

  A current I (L2) flowing through the second inductor L2 is supplied to the LED lamp 101 as an output current. As a result, the LED lamp 101 is turned on.

  Then, the control unit 103 increases the first current I3a (the current I (L2) flowing through the second inductor L2) to the third threshold (UPPER LIMIT) (for example, time t11 in FIG. 9). , Time t13), the switching element M1 is turned off.

  Thereby, the current I (M1) of the switching element M1, that is, the current of the second detection resistor R4 is cut off (FIG. 8).

  Then, the control unit 103 reduces the first current I3b flowing through the first detection resistor R3 (current I (L2) flowing through the second inductor L2) to be smaller than the third threshold (UPPER LIMIT). The switching element M1 is turned off until the fourth threshold value (LOWER LIMIT) is reached (for example, times t11 to t12 in FIG. 9).

  At this time, the first current I3b flowing through the first detection resistor R3 (current I (L2) flowing through the second inductor L2) is the first rectifying element D1, the second battery terminal Ty, and the LED lamp 101. And the output terminal Tz in this order (FIG. 8).

  Furthermore, the current I (L1) flowing through the first inductor L1 flows in the order of the first capacitor C1 and the first rectifier element D1 (FIG. 8).

  Therefore, the current I (D1) flowing through the first rectifier element D1 is the sum of the current I (L1) and the current I (L2) (FIGS. 8 and 9).

  Then, the control unit 103 decreases the first current I3b (current I (L2) flowing through the second inductor L2) flowing through the first detection resistor R3 to the fourth threshold (LOWER LIMIT). When (for example, time t12 in FIG. 9), the switching element M1 is turned on.

  Thereafter, the same operation is repeated.

  By the operation of the LED driver circuit 102b described above, the current I (L2) flowing through the second inductor L2 is controlled to transition between the third threshold (UPPER LIMIT) and the fourth threshold (LOWER LIMIT). The

  That is, the output current supplied from the output terminal Tz to the LED lamp 101 is controlled within a predetermined range.

  As described above, the LED driver circuit 102b includes the first rectifier element D1 and the inductor (second circuit) connected in series between the second battery terminal (ground terminal) Ty and the output terminal Tz. Since the inductor L2) is provided, a continuous current can be output even if no output capacitor is provided (FIGS. 7 to 9).

(Current path when releasing the load)
Next, the operation of the LED driver circuit 102b when the connection state of the load (LED element 101a) is released during the operation of the switching element M1 will be described.

  When the connection state of the LED element 101a is released during the operation of the switching element M1 as indicated by the gate voltage V (G) of the switching element M1 in FIG. 10 (for example, time t14 in FIG. 10), the output terminal Tz. At the moment when the voltage Vo greatly decreases, the second capacitor C2 is charged with a negative voltage with respect to the ground via the second rectifying element D2. Thereby, the voltage drop of the output terminal Tz is suppressed. Then, when the voltage V (T7) at the terminal T7 falls as the voltage V (C2) of the second capacitor falls, the voltage V (T7) at the terminal T7 falls below the first threshold (for example, , Time t15 in FIG. 10, the control unit 103 stops the switching operation of the switching element M1.

  Thereafter, the negative voltage once charged in the second capacitor C2 is held even after the potential Vo of the output terminal Tz rises to 0, and the first voltage dividing resistor R1 and the second voltage dividing resistor R2 are connected. The voltage gradually rises in a direction approaching the ground potential. The control unit 103 keeps the switching operation of the switching element M1 stopped until the voltage V (T7) at the terminal T7 rises to a second threshold value that is larger than the first threshold value. When the voltage V (T7) at the terminal T7 exceeds the second threshold (for example, time t16 in FIG. 10), the control unit 103 resumes the switching operation of the switching element M1.

  Thereafter, the same operation is repeated.

  As described above, the LED driver circuit 102b according to the second embodiment passes through the second rectifier element D2 at the moment when the connection state of the load is released and the voltage at the output terminal greatly drops during the operation of the switching element M1. Thus, the second capacitor C2 is charged with a negative voltage with respect to the ground, so that a voltage drop at the output terminal Tz can be suppressed. That is, a change in the voltage of the output terminal Tz when the load connection state is released can be suppressed.

  In addition, when the voltage of the second capacitor C2 drops and the voltage at the other end of the first resistor R1 falls below the first threshold, the control unit 103 stops the switching operation of the switching element M1. Thereafter, the negative voltage charged in the second capacitor C2 is gradually discharged through the first voltage dividing resistor R1 and the second voltage dividing resistor R2, and the voltage increases in a direction approaching the ground potential. . Then, the LED driver circuit 102b keeps the switching operation of the switching element M1 stopped until the voltage at the other end of the first voltage dividing resistor R1 exceeds the second threshold (greater than the first threshold). Thus, it is possible to suppress the heat generation of the element in the absence of a load.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

Claims (15)

A first battery terminal connected to the positive electrode of the battery;
A second battery terminal connected to the negative electrode of the battery and connected to the cathode side of the LED lamp;
An output terminal connected to the anode side of the LED lamp;
A switching element having one end connected to the first battery terminal;
A first inductor having one end connected to the other end of the switching element and the other end connected to the second battery terminal;
A first capacitor having one end connected to one end of the first inductor;
A second inductor having one end connected to the other end of the first capacitor and the other end connected to the output terminal;
One end is connected to the second battery terminal and the other end is connected to the other end of the first capacitor, and the direction from the second battery terminal toward the other end of the first capacitor is the forward direction. A first rectifying element;
A second capacitor having one end connected to the second battery terminal;
One end is connected to the other end of the second inductor, the other end is connected to the other end of the second capacitor, and the direction from the other end of the second inductor to the other end of the second capacitor is A second rectifying element in the forward direction;
A control unit for controlling on / off of the switching element based on a current flowing through the second inductor;
An LED driver circuit comprising:   The LED driver circuit according to claim 1, wherein the second capacitor is configured to be dischargeable via a resistor.   2. The LED driver circuit according to claim 1, wherein when the voltage based on the voltage at the other end of the second capacitor exceeds a first threshold, the control unit stops the switching operation of the switching element.   The control unit according to claim 3, wherein when the voltage based on the voltage at the other end of the second capacitor falls below a second threshold value that is smaller than the first threshold value, the control unit resumes the switching operation of the switching element. LED driver circuit.   4. The LED driver circuit according to claim 3, wherein the first threshold value is set to a value based on a voltage value larger than twice the voltage of the output terminal in a steady state. The resistance is
A first voltage dividing resistor having one end connected to the other end of the second capacitor;
A second voltage dividing resistor having one end connected to the other end of the first voltage dividing resistor and the other end connected to one end of the first inductor;
Have
The LED driver circuit according to claim 2, wherein the voltage based on the voltage at the other end of the second capacitor is a voltage at the other end of the first voltage dividing resistor.   The LED driver circuit according to claim 1, wherein no capacitor is provided between the other end of the second inductor and the second battery terminal. An LED driver circuit according to claim 1;
The LED lamp,
The LED lamp is
A plurality of LED elements connected in series;
A switch circuit connected in parallel with any of the plurality of LED elements;
Including
An LED lighting device in which the number of LED elements to be lit is switched by turning on / off the switch circuit. A first battery terminal connected to the positive electrode of the battery;
A second battery terminal connected to the negative electrode of the battery and connected to the anode side of the LED lamp;
An output terminal connected to the cathode side of the LED lamp;
A first inductor having one end connected to the first battery terminal;
A switching element having one end connected to the other end of the first inductor and the other end connected to the second battery terminal;
A first capacitor having one end connected to the other end of the first inductor;
A second inductor having one end connected to the other end of the first capacitor and the other end connected to the output terminal;
One end is connected to the other end of the first capacitor and the other end is connected to the second battery terminal, and the direction from the other end of the first capacitor toward the second battery terminal is the forward direction. A first rectifying element;
A second capacitor having one end connected to the second battery terminal;
One end is connected to the other end of the second capacitor, the other end is connected to the other end of the second inductor, and the direction from the other end of the second capacitor toward the other end of the second inductor is A second rectifying element in the forward direction;
A control unit for controlling on / off of the switching element based on a current flowing through the second inductor;
LED driver circuit comprising:   The LED driver circuit according to claim 9, wherein the second capacitor is configured to be dischargeable via a resistor.   The LED driver circuit according to claim 9, wherein the control unit stops the switching operation of the switching element when a voltage based on a voltage at the other end of the second capacitor falls below a first threshold.   The control unit according to claim 11, wherein when the voltage based on the voltage at the other end of the second capacitor exceeds a second threshold value that is greater than the first threshold value, the control unit restarts the switching operation of the switching element. LED driver circuit. The resistance is
A first voltage dividing resistor having one end connected to the other end of the second capacitor;
A second voltage dividing resistor having one end connected to the other end of the first voltage dividing resistor and the other end connected to a second battery terminal;
Have
The LED driver circuit according to claim 10, wherein a voltage based on a voltage at the other end of the second capacitor is a voltage at the other end of the first voltage dividing resistor.   The LED driver circuit according to claim 9, wherein no capacitor is provided between the other end of the second inductor and the second battery terminal. An LED driver circuit according to claim 9;
The LED lamp,
The LED lamp is
A plurality of LED elements connected in series;
A switch circuit connected in parallel with any of the plurality of LED elements;
Including
An LED lighting device in which the number of LED elements to be lit is switched by turning on / off the switch circuit.

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