WO2016084144A1

WO2016084144A1 - Led driver circuit and led lighting device

Info

Publication number: WO2016084144A1
Application number: PCT/JP2014/081171
Authority: WO
Inventors: 林　正明; 久保田　健一
Original assignee: 新電元工業株式会社
Priority date: 2014-11-26
Filing date: 2014-11-26
Publication date: 2016-06-02
Also published as: JPWO2016084144A1; JP6231224B2

Abstract

This LED driver circuit is provided with: a switching element which has one end connected to a first battery terminal; a first inductor which has one end connected to a second battery terminal; a capacitor which has one end connected to the other end of the switching element; a second inductor which has one end connected to the other end of the capacitor, while having the other end connected to an output terminal; a first rectifier element which has one end connected to the second battery terminal, while having the other end connected to the other end of the capacitor, such that the direction from the second battery terminal toward the other end of the capacitor is the forward direction; a second rectifier element which has one end connected to the other end of the switching element, while having the other end connected to the other end of the first inductor, such that the direction from the other end of the switching element toward the other end of the first inductor is the forward direction; a third rectifier element which has one end connected to the other end of the first inductor, while having the other end connected to the other end of the capacitor or to the one end of the switching element, such that the direction from the other end of the first inductor toward the other end of the capacitor or toward the one end of the switching element is the forward direction; and a control unit which controls on/off of the switching element on the basis of the current flowing through the second inductor.

Description

LED driver circuit and LED lighting device

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, JP 2006-340432 A, Chinese Utility Model 202005034, JP 2013-099072 A, JP 2013-098297 A). . 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 the output terminals of the LED driver circuit of the 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. 16 and 17, 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 high speed when such a load suddenly changes. It is possible. The LED driver circuits of the

LED lighting devices

100A and 100B (FIGS. 16 and 17) of the first and second comparative examples include coils L101 and L102, a switching element M101, a diode D101, and a capacitor C101. In a state where the LED lighting device 100A of the first comparative example is operating stably, the capacitor C101 is charged to a voltage close to the voltage Vo between the output terminals T101 and T102. On the other hand, in a state where the LED lighting device 100B of the second comparative example is operating stably, the capacitor C101 has a voltage close to 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.

With such a circuit configuration, when the voltage between the output terminals sharply decreases by switching the number of LED elements in the LED lamp with a switch circuit or the like, even if the switching element M101 is turned off, the capacitor C101 at that time Is higher than the voltage between the output terminals, the current discharged from the capacitor C101 flows toward the output terminal T101 or T102. When the voltage between the output terminals drops sharply in this way, a discharge current flows from the capacitor C101 until the capacitor voltage becomes a stable voltage. Thereby, there is a problem that the output current increases and an overcurrent flows through the LED element.

Therefore, an object of the present invention is to provide an LED driver circuit and an LED lighting device that can prevent an overcurrent from flowing to the load when the load is suddenly reduced.

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 second battery terminal;
A capacitor having one end connected to the other end of the switching element;
A second inductor having one end connected to the other end of the capacitor and the other end connected to the output terminal;
A first rectifying element having one end connected to the second battery terminal and the other end connected to the other end of the capacitor, the direction from the second battery terminal toward the other end of the capacitor being a forward direction; ,
One end is connected to the other end of the switching element and the other end is connected to the other end of the first inductor, and a direction from the other end of the switching element toward the other end of the first inductor is a forward direction. A second rectifying element;
One end is connected to the other end of the first inductor and the other end is connected to the other end of the capacitor or one end of the switching element, and the other end of the capacitor is connected to the other end of the capacitor or the switching element. A third rectifying element in which the direction toward one end of the
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 control unit may turn off the switching element when a current flowing through the second inductor exceeds a predetermined current value.

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

In the LED driver circuit,
The second rectifying element is a diode having an anode connected to the other end of the switching element and a cathode connected to the other end of the first inductor.

In the LED driver circuit,
The third rectifying element is a diode having an anode connected to the other end of the first inductor and a cathode connected to the other end of the capacitor or one end of the switching element.

In the LED driver circuit,
The first rectifying element is a diode having an anode connected to the second battery terminal and a cathode connected to the other end of the capacitor.

An LED lighting device according to an aspect of the present invention is provided.
The LED driver circuit;
The LED lamp;
With
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 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 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 second battery terminal;
One end is connected to the other end of the first inductor and the other end is connected to the other end of the switching element, and a direction from the other end of the first inductor toward the other end of the switching element is a forward direction. A first rectifying element;
A capacitor having one end connected to the other end of the first rectifying element;
One end is connected to the other end of the second battery terminal or the capacitor and the other end is connected to the other end of the first inductor, and the first end is connected to the second battery terminal or the other end of the capacitor. A second rectifying element whose forward direction is toward the other end of the inductor;
A second inductor having one end connected to the other end of the capacitor and the other end connected to the output terminal;
A third rectifying element having one end connected to the second battery terminal and the other end connected to the other end of the capacitor, the direction from the other end of the capacitor toward the second battery terminal being a 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 first rectifying element is a diode having an anode connected to the other end of the first inductor and a cathode connected to one end of the capacitor.

In the LED driver circuit,
The second rectifying element is a diode having an anode connected to the second battery terminal or the other end of the capacitor and a cathode connected to the other end of the first inductor.

In the LED driver circuit,
The third rectifying element is a diode having an anode connected to the other end of the capacitor and a cathode connected to the second battery terminal.

The control unit of the LED driver circuit according to one aspect of the present invention turns off the switching element M1 when the current flowing through the second inductor exceeds a specified current value due to a sudden decrease in the load. At this time, the second rectifying element prevents (blocks) the output current from returning to the capacitor through the first inductor L1. Thereby, since there is no path for discharging from the capacitor when the switching element M1 is off, an increase in the output current when the load is suddenly reduced can be suppressed, and an overcurrent can be prevented from flowing through the load.

At this time, the current flowing through the first inductor is released to the input side or the output side by the third rectifier element. Thereby, it is possible to prevent an overvoltage (surge voltage) from being generated in the first inductor.

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 a current path when the load is suddenly decreased in the LED lighting device 100 illustrated in FIG. 1. FIG. 6 is a diagram illustrating an example of a waveform of a current flowing through the LED element 101a before and after the series number of the LED elements 101a rapidly decreases. FIG. 7 is a diagram illustrating an example of the configuration of the LED lighting device 100b according to the second embodiment. FIG. 8 is a diagram illustrating an example of a current path when the load suddenly decreases in the LED lighting device 100b illustrated in FIG. FIG. 9 is a diagram illustrating an example of the configuration of the LED lighting device 100c according to the third embodiment. FIG. 10 is a diagram illustrating an example of a current path when the switching element M1 of the LED driver circuit 102c illustrated in FIG. 9 is turned on. FIG. 11 is a diagram illustrating an example of a current path when the switching element M1 of the LED driver circuit 102c illustrated in FIG. 9 is off. FIG. 12 is a diagram illustrating an example of a current waveform flowing through the LED driver circuit 102c. FIG. 13 is a diagram illustrating an example of a current path when the load suddenly decreases in the LED lighting device 100c illustrated in FIG. FIG. 14 is a diagram illustrating an example of a configuration of an LED illumination device 100d according to the fourth embodiment. FIG. 15 is a diagram illustrating an example of a current path when the load suddenly decreases in the LED lighting device 100d illustrated in FIG. FIG. 16 is a diagram illustrating an example of the configuration of the LED lighting apparatus 100A of the first comparative example. FIG. 17 is a diagram illustrating an example of the configuration of the LED lighting device 100B of the second comparative example.

Hereinafter, embodiments of 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 a plurality of LED elements 101a connected in series, an LED driver circuit 102 for driving the LED lamp 101, Is provided. 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, for example, a two-wheeled vehicle headlamp. 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.

The load of the LED lamp 101 changes by switching the number of the LED elements 101a that are lit in this way.

Also, the LED driver circuit 102 supplies current to the LED lamp 101 to drive 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, capacitor C1, second inductor L2, first rectifier element D1, second rectifier element D2, third rectifier element D3, first detection resistor R1, and second A detection resistor R2, a control unit 103, and terminals T1 to T6 are provided.

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 (anode) of the second rectifying element D2 via the second detection resistor R2. It is connected. 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.

Note that the switching element M1 may be a bipolar transistor.

The first inductor L1 has one end connected to the second battery terminal Ty and the other end connected to the other end (cathode) of the second rectifier element D2.

The capacitor C1 has one end connected to the other end of the switching element M1 via the second detection resistor R2.

The second inductor L2 has one end connected to the other end of the capacitor C1 through the first detection resistor R1, and the other end 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 capacitor C1. In the first rectifying element D1, the direction from the second battery terminal Ty toward the other end of the 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 capacitor C1, as shown in FIG.

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

The second rectifier element D2 has one end connected to the other end of the switching element M1 via the second detection resistor R2 and the other end connected to the other end of the first inductor L1. In the second rectifying element D2, the direction from the other end of the switching element M1 to the other end of the first inductor L1 is a forward direction.

For example, as shown in FIG. 1, the second rectifying element D2 has an anode connected to the other end of the switching element M1 via a second detection resistor R2, and a cathode other than the first inductor L1. It is a diode connected to the end.

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 third rectifying element D3 has one end connected to the other end of the first inductor L1 and the other end connected to the other end of the capacitor C1. In the third rectifying element D3, the direction from the other end of the first inductor L1 toward the other end of the capacitor C1 is a forward direction.

The third rectifying element D3 is, for example, a diode having an anode connected to the other end of the first inductor L1 and a cathode connected to the other end of the capacitor C1, as shown in FIG.

Note that the third rectifying element D3 may be, for example, a switching element. That is, the third rectifying element D3 includes not only a diode but also a switching element.

The first detection resistor R1 is connected in series with the second inductor L2 between the other end of the capacitor C1 and the output terminal Tz.

The second detection resistor R2 is connected between the other end of the switching element M1 and the other end of the first inductor L1.

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). 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 R1.

For example, the control unit 103 turns on the switching element M1 until the first current increases to the first threshold (UPPER LIMIT).

And the control part 103 turns off the switching element M1, when a 1st electric current increases and it becomes a 1st threshold value (UPPER LIMIT).

Then, the control unit 103 turns off the switching element M1 until the first current decreases and becomes a second threshold value (LOWER LIMIT) smaller than the first threshold value (UPPER LIMIT).

Then, the control unit 103 turns on the switching element M1 when the first current decreases and becomes the second 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 first threshold value (UPPER LIMIT) and the second threshold value (LOWER LIMIT). . 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 current flowing through the second inductor L2 exceeds a specified current value, the control unit 103 turns off the switching element M1. Here, the specified current value is larger than the first threshold value.

As a result, when the number of LED elements 101a in the LED lamp 101 in series (the number of lighting) decreases, the load rapidly decreases, and as a result, when the current flowing through the second inductor L2 exceeds the specified current, the switching element M1 turns off. Thus, when the switching element M1 is turned off, the output current is prevented (blocked) from returning to the capacitor C1 through the first inductor L1 by the second rectifying element D2, and thereby the first inductor L1. The path through which the capacitor is discharged is blocked. As a result, it is possible to prevent current from flowing from the capacitor C1 to the LED lamp 101, and thus it is possible to prevent an overcurrent from flowing to the LED lamp 101.

Also, 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 R2. 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 third threshold value that is larger than the first threshold value (UPPER LIMIT).

Thereby, destruction of elements such as the switching element M1 due to overcurrent can be suppressed.

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 control unit 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, and a driver 103d.

The output current detection unit 103a is connected to the first detection resistor R1 via terminals T2 and T3. The output current detector 103a detects the current flowing through the first detection resistor R1.

The input overcurrent detection unit 103b is connected to one end of the second detection resistor R2 through the terminal T4, and is connected to the other end of the second detection resistor R2 through the terminal T5. The input overcurrent detection unit 103b detects a current flowing through the second detection resistor R2. 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 this 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 is 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 first threshold (UPPER LIMIT).

The switch control unit 103c outputs a control signal for turning off the switching element M1 when the first current increases and reaches the first 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 second threshold (LOWER LIMIT) smaller than the first threshold (UPPER LIMIT). Output.

The switch control unit 103c outputs a control signal for turning on the switching element M1 when the first current decreases and reaches the second 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 first threshold (UPPER LIMIT) and the second 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 predetermined current value, the switch control unit 103c outputs a control signal for turning off the switching element M1. By controlling the switch control unit 103c as described above, it is possible to prevent current from flowing from the capacitor C1 to the LED lamp 101, and thus it is possible to prevent overcurrent from flowing to the LED lamp.

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

Further, the driver 103d amplifies the control signal output from the switch control unit 103c to a predetermined voltage and outputs it.

Here, in the LED driver circuit 102, an output capacitor is not provided between the other end of the second inductor L2 and the ground.

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.

The LED driver circuit 102 does not have an output capacitor, so that a faster response is possible. For example, when the number of LED elements in the LED lamp 101 (the number of lighting) changes (when the load changes suddenly) ), It is difficult to be affected by a sudden load change, and the output current can be supplied constant.

(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 first threshold (UPPER LIMIT) (for example, from time t0 to t1 in FIG. At time t2 to t3), the switching element M1 is turned on.

Thereby, a 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 R2. The current I (M1) includes a first current I1a flowing through the first detection resistor R1 (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).

The 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 (current I (L2) flowing through the second inductor L2) to the first threshold (UPPER LIMIT) (for example, time t1 in FIG. 4). , Time t3), 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 R2 is cut off (FIG. 3).

Then, the control unit 103 reduces the first current I1b flowing through the first detection resistor R1 (current I (L2) flowing through the second inductor L2) to be smaller than the first threshold (UPPER LIMIT). The switching element M1 is turned off until the second threshold (LOWER LIMIT) is reached (for example, time t1 to t2 in FIG. 4).

At this time, as shown in FIG. 3, the first current I1b flowing through the first detection resistor R1 (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 rectifying element D1 in order (FIG. 3).

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

Therefore, the current I (D1) flowing through the rectifying 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 R1 (current I (L2) flowing through the second inductor L2) to the second 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 first threshold (UPPER LIMIT) and the second 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).

The LED driver circuit 102 can respond faster by not having an output capacitor. For example, when the number of LED elements 101a in the LED lamp 101 (the number of lighting) changes (the load changes suddenly). ), It is difficult to be affected by a sudden load change, and the output current can be supplied constant (FIG. 4).

That is, according to the LED lighting device 100 according to the present embodiment, it is difficult to be affected by a sudden load change, and an output current can be supplied constantly.

(About the current path at the time of sudden load drop)
Next, a current path when the load of the LED driver circuit 102 suddenly drops will be described. As described above, the control unit 103 turns off the switching element M1 when the current flowing through the second inductor L2 (first current) exceeds a specified current value. At this time, as shown in FIG. 5, the second rectifying element D2 prevents (blocks) the output current from returning to the capacitor C1 through the first inductor L1. As a result, there is no path for discharging from the capacitor C1 when the switching element M1 is in an off state, so that it is possible to prevent an increase in output current (overcurrent) when the number of LED elements 101a is rapidly reduced.

On the other hand, if only the second rectifier element D2 is added to the LED driver circuit 100A according to the first comparative example of FIG. 16, current does not flow to the first inductor L1, so that the first inductor L1 Overvoltage (surge voltage) occurs. Therefore, the LED driver circuit 102 according to the present embodiment is provided with a third rectifier element D3 for releasing the current flowing through the first inductor L1 to the output side. As a result, as shown in FIG. 5, the current I11 flows in the order of the first inductor L1, the third rectifier element D3, the second inductor L2, and the LED element 101a, so that an overvoltage is generated in the first inductor L1. Occurrence can be prevented.

As shown in FIG. 6, immediately after the number of LED elements 101a in series decreases rapidly and the output voltage Vo decreases rapidly (time t4 in FIG. 6), the LED lamp X101 of the LED driver circuit 100A according to the first comparative example. The current Io flowing through becomes excessive. (Area A1 in FIG. 6). On the other hand, in the present embodiment, when the first current exceeds the specified current, the switching element M1 is turned off, and after the switching element M1 is turned off, the first current decreases with time. This is because the discharge path of the capacitor C1, which is a voltage higher than the output voltage Vo in the LED driver circuit 100, is blocked by the second rectifier element D2, so that only the energy of the second inductor L2 is expelled. It is. After that, when the first current falls to the second threshold (LOWER LIMIT), the switching element M1 is turned on. Thereafter, the switching element M1 is repeatedly turned off and on. Thus, immediately after the number of LED elements 101a in series decreases rapidly and the output voltage Vo decreases rapidly (time t5 in FIG. 6), the current Io flowing through the LED lamp 101 (hereinafter referred to as LED current) Io is constant. It falls within the range (area A2 in FIG. 6). That is, the output current supplied from the output terminal Tz to the LED lamp 101 is controlled within a predetermined range.

Further, the electric charge stored in the capacitor C1 is gradually discharged when the switching element M1 is on (see FIG. 6), and is discharged to a voltage close to the output voltage Vo. For this reason, compared with the voltage V (C101) of the capacitor C101 of the LED driver circuit 100A according to the first comparative example, the voltage V (C1) of the capacitor C1 is the output voltage from the time when the number of LED elements 101a in series decreases rapidly. The time until discharging to a voltage close to Vo becomes longer.

As described above, according to the LED driver circuit 102 according to the present embodiment, the current flowing through the second inductor L2 due to the sudden decrease in the load due to the reduction in the number of LED elements 101a in the LED lamp 101 is a predetermined current value. When the value exceeds the value, the control unit 103 turns off the switching element M1. At this time, the second rectifying element D2 prevents (blocks) the output current from returning to the capacitor C1 through the first inductor L1. Thereby, since there is no path for discharging from the capacitor C1 when the switching element M1 is OFF, an increase in output current at the time of sudden decrease in the load can be suppressed, and an overcurrent can be prevented from flowing through the load. At this time, the current flowing through the first inductor L1 is released to the output side by the third rectifying element D3. Thereby, it is possible to prevent an overvoltage (surge voltage) from being generated in the first inductor L1.

(Second Embodiment)
Next, the second embodiment will be described. As shown in FIG. 7, 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. The LED driver circuit 102b in the second embodiment differs from the LED driver circuit 102 in the first embodiment in the connection mode of the third rectifier element D3. That is, the third rectifying element D3 has one end connected to the other end of the first inductor L1 and the other end connected to one end of the switching element M1. In the third rectifying element D3, the direction from the other end of the first inductor L1 toward one end of the switching element M1 is the forward direction. As shown in FIG. 7, the third rectifying element D3 is, for example, a diode having an anode connected to the other end of the first inductor L1 and a cathode connected to one end of the switching element M1.

In addition, the same code | symbol is attached | subjected to the element which is common in the LED lighting apparatus 100 in 1st Embodiment, and the specific description is abbreviate | omitted. The normal control method of the present embodiment is the same as the control method of the first embodiment, and a description thereof will be omitted.

(About the current path at the time of sudden load drop)
Next, a current path when the load of the LED driver circuit 102b having the above configuration is suddenly reduced will be described. Similar to the control unit 103 of the first embodiment, the control unit 103 of the present embodiment switches the switching element M1 when the current flowing through the second inductor L2 (first current) exceeds a specified current value. Turn off. At this time, as shown in FIG. 8, similarly to the first embodiment, the second rectifying element D2 prevents (blocks) the output current from returning to the capacitor C1 through the first inductor L1. . As a result, there is no path for discharging from the capacitor C1 when the switching element M1 is in an off state, so that it is possible to prevent an increase in output current (overcurrent) when the number of LED elements 101a is rapidly reduced.

On the other hand, if only the second rectifier element D2 is added to the LED driver circuit 100A according to the first comparative example of FIG. 16, current does not flow to the first inductor L1, so that the first inductor L1 Overvoltage (surge voltage) occurs. Therefore, the LED driver circuit 102b according to the present embodiment is provided with a third rectifier element D3 for releasing the current flowing through the first inductor L1 to the input side. As a result, as shown in FIG. 8, the current I12 flows in the order of the first inductor L1, the third rectifier element D3, and the battery BAT, thereby preventing an overvoltage from being generated in the first inductor L1. Can do.

As described above, according to the LED driver circuit 102b according to the present embodiment, the current flowing through the second inductor L2 due to the rapid decrease of the load due to the decrease in the number of series of the LED elements 101a in the LED lamp 101 is a specified current value. When the value exceeds the value, the control unit 103 turns off the switching element M1. At this time, the second rectifying element D2 prevents (blocks) the output current from returning to the capacitor C1 through the first inductor L1. Thereby, since there is no path for discharging from the capacitor C1 when the switching element M1 is OFF, an increase in output current at the time of sudden decrease in the load can be suppressed, and an overcurrent can be prevented from flowing through the load. At this time, the current flowing through the first inductor L1 is released to the input side by the third rectifying element D3. Thereby, it is possible to prevent an overvoltage (surge voltage) from being generated in the first inductor L1.

(Third embodiment)
Subsequently, a third embodiment will be described. As shown in FIG. 9, in the configuration of the LED lighting device 100c in the third embodiment, the LED driver circuit 102 is changed to the LED driver circuit 102c with respect to the configuration of the LED lighting device 100 in the first embodiment. It has become 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 102c in the third 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. 9, a battery (DC power supply) BAT, which will be described later, is not shown.

The LED driver circuit 102c 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. 9, the LED driver circuit 102c 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, the first rectifier element D1, the capacitor C1, the second rectifier element D2, the second inductor L2, the third rectifier element D3, the first detection resistor R1, and the second A detection resistor R2, a control unit 103, and terminals T1 to T6 are provided.

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 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.

One end (source) of the switching element M1 is connected to the second battery terminal Ty via the second detection resistor R2, and the other end (drain) is the other end (cathode) of the first rectifying element D1. It is connected to the. The switch element M1 is controlled to be turned on / off by a signal output from the terminal T1 of the control unit 103.

Note that the switching element M1 may be a bipolar transistor.

The first rectifying element D1 has one end connected to the other end of the first inductor L1 and the other end connected to the other end (drain) of the switching element M1. In the first rectifying element D1, the direction from the other end of the first inductor L1 toward the other end of the switching element M1 is a forward direction.

The first rectifying element D1 is, for example, a diode having an anode connected to the other end of the first inductor L1 and a cathode connected to one end of the capacitor C1, as shown in FIG.

Note that 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.

The capacitor C1 has one end connected to the other end (cathode) of the first rectifying element D1.

The second rectifying element D2 has one end connected to the second battery terminal Ty and the other end connected to the other end of the first inductor L1. In the second rectifying element D2, the direction from the second battery terminal Ty toward the other end of the first inductor L1 is the forward direction.

The second rectifying element D2 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 inductor L1, as shown in FIG.

Note that 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 inductor L2 has one end connected to the other end of the capacitor C1, and the other end connected to the output terminal Tz via the first detection resistor R1.

The third rectifying element D3 has one end connected to the second battery terminal Ty and the other end connected to the other end of the capacitor C1. In the third rectifying element D3, the direction from the other end of the capacitor C1 toward the second battery terminal Ty is the forward direction.

The third rectifying element D3 is, for example, a diode having an anode connected to the other end of the capacitor C1 and a cathode connected to the second battery terminal Ty, as shown in FIG.

Note that the third rectifying element D3 may be a switching element. That is, the third rectifying element D3 includes not only a diode but also a switching element.

The first detection resistor R1 is connected in series with the second inductor L2 between the other end of the capacitor C1 (the other end of the third rectifying element D3) and the output terminal Tz.

The second detection resistor R2 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 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 R <b> 1. 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 102c 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 first threshold (UPPER LIMIT) (for example, from time t10 to t11 in FIG. 12, At time t12 to t13), the switching element M1 is turned on, and the current I (M1) is equal to the current flowing through the second detection resistor R2.

Thereby, a current I (M1) flows through the switching element M1 (FIG. 10). The current I (M1) includes a first current I3a flowing through the first detection resistor R1 (current I (L2) flowing through the second inductor L2) and a second current I4a (passing through the first inductor L1). Current (I (L1)) flowing (FIGS. 10 and 12).

At this time, the capacitor C1 is discharged.

Then, the controller 103 increases the first current I3a (current I (L2) flowing through the second inductor L2) to the first threshold (UPPER LIMIT) (for example, time t11 in FIG. 12). , 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 R2 is cut off (FIG. 11).

Then, the control unit 103 reduces the first current I3b flowing through the first detection resistor R1 (the current I (L2) flowing through the second inductor L2) (FIG. 11) and the first threshold (UPPER LIMIT). The switching element M1 is turned off until the second threshold value (LOWER LIMIT) is reached (for example, times t11 to t12 in FIG. 12).

At this time, the first current I3b flowing through the first detection resistor R1 (current I (L2) flowing through the second inductor L2) is the third rectifying element D3, the second battery terminal Ty, and the LED lamp 101. And the output terminal Tz in this order (FIG. 11).

Furthermore, the current I (L1) flowing through the first inductor L1 flows in the order of the capacitor C1 and the third rectifying element D3, and the capacitor C1 is charged (FIG. 11).

Therefore, the current I (D3) flowing through the third rectifying element D3 is the sum of the current I (L1) and the current I (L2) (FIGS. 11 and 12).

Then, the control unit 103 decreases the first current I3b flowing through the first detection resistor R1 (current I (L2) flowing through the second inductor L2) to the second threshold (LOWER LIMIT). When (for example, time t12 in FIG. 4), the switching element M1 is turned on.

Thereafter, the same operation is repeated.

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

Then, as described above, LED driver circuit 102c is provided between the second battery terminal (ground terminal) Ty and the output terminal Tz, the third rectifier element D 3 connected in series with an inductor (second Therefore, even if no output capacitor is provided, a continuous current can be output (FIGS. 10 to 12).

The LED driver circuit 102c does not have an output capacitor, so that a faster response is possible. For example, when the number of LED elements 101a in the LED lamp 101 (the number of lighting) changes (the load changes suddenly). ), It is difficult to be affected by a sudden load change, and the output current can be supplied constantly (FIG. 12).

That is, according to the LED lighting device 100c according to the present embodiment, it is difficult to be affected by a sudden load change, and an output current can be supplied constantly.

(About the current path at the time of sudden load drop)
Subsequently, a current path when the load of the LED driver circuit 102c suddenly drops will be described. Similar to the control unit 103 of the first embodiment, the control unit 103 of the present embodiment switches the switching element M1 when the current flowing through the second inductor L2 (first current) exceeds a specified current value. Turn off. At this time, as shown in FIG. 13, the first rectifying element D1 prevents (blocks) the output current from returning to the first inductor L1 through the capacitor C1. As a result, there is no path for discharging from the capacitor C1 when the switching element M1 is in an off state, so that it is possible to prevent an increase in output current (overcurrent) when the number of LED elements 101a is rapidly reduced.

On the other hand, if only the first rectifying element D1 is added to the LED driver circuit 100B according to the second comparative example of FIG. 17, current does not flow to the first inductor L1, so that the first inductor L1 Overvoltage (surge voltage) occurs. Therefore, the LED driver circuit 102c according to the present embodiment is provided with a second rectifying element D2 for releasing the current flowing through the first inductor L1 to the input side. As a result, as shown in FIG. 13, the current I13 flows in the order of the first inductor L1, the battery BAT, and the second rectifying element D2, thereby preventing an overvoltage from being generated in the first inductor L1. Can do.

As described above, according to the LED driver circuit 102c according to the present embodiment, the current flowing through the second inductor L2 due to the sudden decrease in the load due to the reduction in the number of LED elements 101a in the LED lamp 101 is a specified current value. When the value exceeds the value, the control unit 103 turns off the switching element M1. At this time, the first rectifying element D1 prevents (blocks) the output current from returning to the first inductor L1 through the capacitor C1. Thereby, since there is no path for discharging from the capacitor C1 when the switching element M1 is OFF, an increase in output current at the time of sudden decrease in the load can be suppressed, and an overcurrent can be prevented from flowing through the load. At this time, the current flowing through the first inductor L1 is released to the input side by the second rectifying element D2. Thereby, it is possible to prevent an overvoltage (surge voltage) from being generated in the first inductor L1.

(Fourth embodiment)
Subsequently, a fourth embodiment will be described. As shown in FIG. 14, the configuration of the LED lighting device 100d in the fourth embodiment is changed from the LED driver circuit 102c to the LED driver circuit 102d with respect to the configuration of the LED lighting device 100c in the third embodiment. It has become a thing. The LED driver circuit 102d in the fourth embodiment differs from the LED driver circuit 102c in the third embodiment in the connection mode of the second rectifying element D2. In other words, the second rectifying element D2 has one end connected to the other end of the capacitor C1 and the other end connected to the other end of the first inductor L1. In the second rectifying element D2, the direction from the other end of the capacitor C1 toward the other end of the first inductor L1 is the forward direction. As shown in FIG. 14, the second rectifying element D2 is, for example, a diode having an anode connected to the other end of the capacitor C1 and a cathode connected to the other end of the first inductor L1.

In addition, the same code | symbol is attached | subjected to the element which is common in LED lighting apparatus 100c in 3rd Embodiment, and the specific description is abbreviate | omitted. The normal control method of the present embodiment is the same as the control method of the third embodiment, and a description thereof will be omitted.

(About the current path at the time of sudden load drop)
Next, a current path when the load of the LED driver circuit 102d having the above configuration is suddenly dropped will be described. Similarly to the control unit 103 of the third embodiment, the control unit 103 of the present embodiment causes the switching element M1 to be switched when the current flowing through the second inductor L2 (first current) exceeds a specified current value. Turn off. At this time, as shown in FIG. 15, the first rectifying element D1 prevents (blocks) the output current from returning to the first inductor L1 through the capacitor C1. As a result, there is no path for discharging from the capacitor C1 when the switching element M1 is in an off state, so that it is possible to prevent an increase in output current (overcurrent) when the number of LED elements 101a is rapidly reduced.

On the other hand, if only the first rectifying element D1 is added to the LED driver circuit 100B according to the second comparative example of FIG. 17, current does not flow to the first inductor L1, so that the first inductor L1 Overvoltage (surge voltage) occurs. Therefore, the LED driver circuit 102d according to the present embodiment is provided with a second rectifying element D2 for releasing the current flowing through the first inductor L1 to the input side. As a result, as shown in FIG. 15, the current I14 flows in the order of the first inductor L1, the battery BAT, the LED lamp 101, the second inductor L2, and the second rectifier element D2, thereby causing the first inductor L1. It is possible to prevent the occurrence of overvoltage.

As described above, according to the LED driver circuit 102d according to the present embodiment, the current flowing through the second inductor L2 due to the rapid decrease of the load due to the decrease in the number of series of the LED elements 101a in the LED lamp 101 is a specified current value. When the value exceeds the value, the control unit 103 turns off the switching element M1. At this time, the first rectifying element D1 prevents (blocks) the output current from returning to the first inductor L1 through the capacitor C1. Thereby, since there is no path for discharging from the capacitor C1 when the switching element M1 is OFF, an increase in output current at the time of sudden decrease in the load can be suppressed, and an overcurrent can be prevented from flowing through the load. At this time, the current flowing through the first inductor L1 is released to the input side by the second rectifying element D2. Thereby, it is possible to prevent an overvoltage (surge voltage) from being generated in the first inductor L1.

Although several embodiments of the present invention have been described, these embodiments are presented as examples 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

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 second battery terminal;
A capacitor having one end connected to the other end of the switching element;
A second inductor having one end connected to the other end of the capacitor and the other end connected to the output terminal;
A first rectifying element having one end connected to the second battery terminal and the other end connected to the other end of the capacitor, the direction from the second battery terminal toward the other end of the capacitor being a forward direction; ,
One end is connected to the other end of the switching element and the other end is connected to the other end of the first inductor, and a direction from the other end of the switching element toward the other end of the first inductor is a forward direction. A second rectifying element;
One end is connected to the other end of the first inductor and the other end is connected to the other end of the capacitor or one end of the switching element, and the other end of the capacitor is connected to the other end of the capacitor or the switching element. A third rectifying element in which the direction toward one end of the
A control unit for controlling on / off of the switching element based on a current flowing through the second inductor;
LED driver circuit comprising:
2. The LED driver circuit according to claim 1, wherein the control unit turns off the switching element when a current flowing through the second inductor exceeds a specified current value.
The LED driver circuit according to claim 1, wherein no capacitor is provided between the other end of the second inductor and the ground.
The LED driver circuit according to claim 1, wherein the second rectifying element is a diode having an anode connected to the other end of the switching element and a cathode connected to the other end of the first inductor.
2. The LED driver according to claim 1, wherein the third rectifying element is a diode having an anode connected to the other end of the first inductor and a cathode connected to the other end of the capacitor or one end of the switching element. circuit.
The LED driver circuit according to claim 1, wherein the first rectifying element is a diode having an anode connected to the second battery terminal and a cathode connected to the other end of the capacitor.
An LED driver circuit according to claim 1;
The LED lamp;
With
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 LED lighting device, wherein 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 second battery terminal;
One end is connected to the other end of the first inductor and the other end is connected to the other end of the switching element, and a direction from the other end of the first inductor toward the other end of the switching element is a forward direction. A first rectifying element;
A capacitor having one end connected to the other end of the first rectifying element;
One end is connected to the other end of the second battery terminal or the capacitor and the other end is connected to the other end of the first inductor, and the first end is connected to the second battery terminal or the other end of the capacitor. A second rectifying element whose forward direction is toward the other end of the inductor;
A second inductor having one end connected to the other end of the capacitor and the other end connected to the output terminal;
A third rectifying element having one end connected to the second battery terminal and the other end connected to the other end of the capacitor, the direction from the other end of the capacitor toward the second battery terminal being a 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 8, wherein the control unit turns off the switching element when a current flowing through the second inductor exceeds a specified current value.
The LED driver circuit according to claim 8, wherein a capacitor is not provided between the other end of the second inductor and the ground.
The LED driver circuit according to claim 8, wherein the first rectifying element is a diode having an anode connected to the other end of the first inductor and a cathode connected to one end of the capacitor.
The LED according to claim 8, wherein the second rectifying element is a diode having an anode connected to the second battery terminal or the other end of the capacitor and a cathode connected to the other end of the first inductor. Driver circuit.
The LED driver circuit according to claim 8, wherein the third rectifying element is a diode having an anode connected to the other end of the capacitor and a cathode connected to the second battery terminal.
An LED driver circuit according to claim 8;
The LED lamp;
With
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 LED lighting device, wherein the number of LED elements to be lit is switched by turning on / off the switch circuit.