JP6305908B2 - LED lighting device and control method of LED lighting device - Google Patents

Description

  The present invention relates to an LED lighting device capable of switching the number of LED elements in series and a method for controlling the LED lighting device.

  2. Description of the Related Art Conventionally, a battery that is a direct current power source, an LED driver circuit that converts electric power of the battery and outputs a predetermined output current, and an LED illumination device that includes an LED lamp that has a plurality of LED elements that are lit when supplied with the output current Is known (see, for example, Patent Document 1). This LED illumination device is used for a headlight of a vehicle such as a motorcycle.

  The LED driver circuit has a step-down chopper, which is a step-down converter, and controls the switching element with a fixed off width (fixed off time) so that the peak value of the current flowing through the switching element of the step-down chopper is constant. Yes.

  The LED driver circuit responds to a sudden load change so that the brightness of one LED element does not change even when the series number (lighting number) of LED elements in the LED lamp changes by switching between high beam and low beam. A high-speed response is required.

Special table 2010-527223

  By the way, when the number of LED elements in series changes, the voltage across the LED lamp (the sum of the forward voltages VF of the LED elements) changes, so the unit current per unit time that flows through the LED lamp after the switching element is turned off The amount of decrease (slope) changes. Here, as shown in FIG. 4, since the OFF time (OFF width) of the switching element is constant, the minimum current value changes according to the number of LED elements in series. As a result, the ripple of the current flowing through the LED lamp changes according to the number of LED elements in series, and as a result, the average current value varies greatly. A large variation in the average current value is not preferable from the viewpoint of the reliability of the LED lamp.

  Then, an object of this invention is to provide the control method of the LED lighting apparatus which can suppress the fluctuation | variation of the average electric current value which flows into a LED lamp, and a LED lighting apparatus.

An LED lighting device according to an aspect of the present invention is provided.
An LED lamp having a plurality of LED elements connected in series;
A changeover switch for switching the series number of the plurality of LED elements;
A step-down converter having a switching element through which the current of the LED lamp flows, and stepping down a power supply voltage by a switching operation of the switching element and supplying the voltage to the LED lamp;
When the current flowing through the switching element that is turned on reaches a predetermined peak current value, the switching element is switched off for a certain period, and the switching element is switched on after the certain period has elapsed. A first control circuit;
A second control circuit that shortens the certain period as the voltage across the LED lamp increases;
It is characterized by providing.

In the LED lighting device,
The second control circuit may extend the certain period as the voltage across the LED lamp decreases.

In the LED lighting device,
The second control circuit may make the voltage between both ends of the LED lamp inversely proportional to the certain period.

In the LED lighting device,
The second control circuit may control the certain period so that a minimum value of a current flowing through the switching element is constant regardless of a voltage between both ends of the LED lamp.

In the LED lighting device,
The second control circuit includes:
A charging circuit that outputs a charging current according to a voltage between both ends of the LED lamp;
A capacitive element to which the charging current is supplied to one end;
A discharge switch connected between one end of the capacitive element and ground, turned on when the switching element is switched on, and turned off when the switching element is switched off;
A comparator that causes the first control circuit to switch on the switching element when a voltage at one end of the capacitive element is equal to or higher than a reference voltage value;
You may have.

In the LED lighting device,
The step-down converter
A diode having a cathode to which the power supply voltage is supplied and connected to an anode side terminal of the LED lamp;
An inductor having one end connected to the cathode side terminal of the LED lamp and the other end connected to the anode of the diode;
One end of the switching element may be connected to the other end of the inductor.

The control method of the LED lighting device according to one aspect of the present invention includes:
An LED lamp having a plurality of LED elements connected in series, a changeover switch for switching the series number of the plurality of LED elements, a switching element, and stepping down a power supply voltage by a switching operation of the switching element, the LED A step-down converter for supplying to a lamp, and a control method of an LED lighting device comprising:
When the current flowing through the switching element that is turned on reaches a predetermined peak current value, the switching element is turned off for a certain period, and after the certain period has elapsed, the switching element is turned on. ,
The certain period is shortened as the voltage across the LED lamp increases.

  According to the present invention, the OFF time is controlled to be shorter as the voltage across the LED lamp increases, so that the number of LED elements in series increases and the voltage across the LED lamp increases. , The off time is shortened. When the voltage between both ends of the LED lamp is increased, the amount of reduction per unit time of the current flowing through the LED lamp after the switching element is turned off increases. Here, by shortening the off time, the minimum value of the current flowing through the LED lamp can be made substantially equal to the value before switching the number of LED elements in series. That is, the change in the ripple of the current flowing through the LED lamp can be suppressed. Therefore, fluctuations in the average current value flowing through the LED lamp can be suppressed.

It is a circuit diagram of the LED lighting apparatus which concerns on one Embodiment. FIG. 2 is a circuit diagram of the off-time control circuit in FIG. 1. It is waveform diagrams, such as the electric current which flows through the LED lamp of FIG. It is a wave form diagram of the electric current which flows through the conventional LED lamp.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. This embodiment does not limit the present invention.

  FIG. 1 is a circuit diagram of an LED lighting device according to an embodiment. As shown in FIG. 1, the LED lighting device includes an LED lamp 1, a changeover switch SW1, a step-down converter 2, a switching control circuit (first control circuit) 3, and a UVLO circuit (low voltage malfunction prevention circuit) 4. And an off-time control circuit (second control circuit) 5.

  The LED lamp 1 includes a plurality of LED elements 1a (for example, six LED elements 1a) connected in series.

  The changeover switch SW1 is connected in parallel with one or a plurality of LED elements 1a connected in series (for example, three LED elements 1a). The change-over switch SW1 is turned on or off by the user and switches the number of LED elements 1a in series, that is, the number of LED elements 1a to be lit.

  The LED lamp 1 is, for example, a motorcycle headlight. Here, when the changeover switch SW1 is OFF, the number of LED elements 1a in series is six, and a current flows through all the LED elements 1a, resulting in a high beam state. When the changeover switch SW1 is turned on, the number of LED elements 1a in series is three, and no current flows through the three LED elements 1a connected in parallel to the changeover switch SW1, and a low beam state is established.

  A voltage VLED between both ends 1A and 1B of the LED lamp 1 is a sum of forward voltages VF of six or three LED elements 1a. Accordingly, the voltage VLED between both ends 1A and 1B of the LED lamp 1 when the changeover switch SW1 is on is lower than the voltage VLED when the changeover switch SW1 is off.

  Step-down converter 2 includes a switching element NM1, a diode D1, and an inductor L1. The step-down converter 2 steps down the power supply voltage Vcc by the switching operation of the switching element NM1, and supplies it to the LED lamp 1. The current Iout of the LED lamp 1 flows through the switching element NM1 when it is on. The switching element NM1 is, for example, an N-type MOS transistor.

  The diode D1 is supplied with the power supply voltage Vcc and has a cathode connected to the anode side terminal 1A of the LED lamp 1. A current Iout flows through the diode D1 when the switching element NM1 is off.

The inductor L1 has one end connected to the cathode side terminal 1B of the LED lamp 1 and the other end connected to the anode of the diode D1.
One end (drain) of the switching element NM1 is connected to the other end of the inductor L1.

  An output capacitor is not connected between both ends 1A and 1B of the LED lamp 1. Therefore, a faster response is possible, and even when the number of LED elements 1a in series (the number of lighting) changes (when the load changes suddenly), it is not easily affected by the sudden change in load, and an excessive output current Iout Can be suppressed.

  The switching control circuit 3 switches the switching element NM1 to the off time (predetermined period) when the current flowing through the switching element NM1 that has been turned on reaches a predetermined peak current value Ip, and the off time has elapsed. After that, the switching element NM1 is switched on again. As will be described later, this off time is a variable time controlled by the off time control circuit 5.

  Here, the switching control circuit 3 includes a resistor R1, a comparator CMP1, a flip-flop FF1, a logic circuit 31, and a buffer 32.

  The resistor R1 is connected between the other end (source) of the switching element NM1 and the ground, and detects a current flowing through the switching element NM1.

  The comparator CMP1 has a non-inverting input terminal connected to the other end of the switching element NM1, an inverting input terminal to which the reference voltage V1 is supplied, and an output terminal connected to the reset terminal R of the flip-flop FF1. The comparator CMP1 outputs a high signal RESET when the current flowing through the switching element NM1 reaches the peak current value Ip, and outputs a low signal RESET when the current flowing through the switching element NM1 is less than the peak current value Ip. Output.

  The UVLO circuit 4 outputs a low signal when the power supply voltage Vcc is lower than the operation threshold voltage, and outputs a high signal when the power supply voltage Vcc is equal to or higher than the operation threshold voltage.

  When the output signal of the UVLO circuit 4 changes from low to high, the logic circuit 31 outputs a high signal SET only for a short period. Thereby, the LED illumination device is activated. Thereafter, while the output signal of the UVLO circuit 4 is high, the logic circuit 31 supplies the signal SET having the same logic as the control signal S1 from the off-time control circuit 5 to the set terminal S of the flip-flop circuit FF1.

  The flip-flop circuit FF1 is an RS flip-flop, and outputs a high signal QOUT from the output terminal Q when a high signal SET is supplied to the set terminal S when the signal RESET at the reset terminal R is low. The flip-flop circuit FF1 outputs a low signal QOUT from the output terminal Q when the high signal RESET is supplied to the reset terminal R when the signal SET at the set terminal S is low.

  The buffer 32 drives the switching element NM1 according to the signal QOUT.

  The off time control circuit 5 shortens the off time as the voltage VLED between both ends 1A and 1B of the LED lamp 1 increases. The off-time control circuit 5 increases the off-time as the voltage VLED between the both ends 1A and 1B of the LED lamp 1 decreases. For example, the off time control circuit 5 may lengthen the off time in proportion to the decrease in the voltage VLED. Further, the off time control circuit 5 may make the voltage VLED and the off time in inverse proportion. The off time control circuit 5 outputs a control signal S1 for controlling the off time.

  FIG. 2 is a circuit diagram of the off-time control circuit 5 of FIG. As shown in FIG. 2, the off-time control circuit 5 includes a charging circuit 51, a capacitor element C1, a discharge switch SW2, and a comparator CMP2.

  The charging circuit 51 outputs a charging current Ic corresponding to the voltage VLED between both ends 1A and 1B of the LED lamp 1. Here, the charging circuit 51 includes an amplifier circuit AMP1, an operational amplifier OP1, an N-type MOS transistor NM2, P-type MOS transistors PM1 and PM2, and a resistor R2.

  The amplifier circuit AMP1 amplifies the voltage VLED with a predetermined amplification factor (for example, an amplification factor of less than 1) and supplies it to the non-inverting input terminal of the operational amplifier OP1.

  The inverting input terminal of the operational amplifier OP1 is connected to the source of the N-type MOS transistor NM2. The output terminal of the operational amplifier OP1 is connected to the gate of the N-type MOS transistor NM2.

  The source of the N-type MOS transistor NM2 is also connected to one end of the resistor R2. The other end of the resistor R2 is grounded.

  The drain of the N-type MOS transistor NM2 is connected to the drain and gate of the P-type MOS transistor PM1 and the gate of the P-type MOS transistor PM2.

  A power supply voltage Vcc is supplied to the sources of the P-type MOS transistors PM1 and PM2. The drain of the P-type MOS transistor PM2 outputs a charging current Ic.

  With such a configuration, the charging circuit 51 increases the charging current Ic as the voltage VLED increases, and decreases the charging current Ic as the voltage VLED decreases.

The capacitive element C1 has a charging current Ic supplied to one end and the other end grounded.
The discharge switch SW2 is connected between one end of the capacitive element C1 and the ground. The discharge switch SW2 is turned on when the switching element NM1 is turned on in response to the signal QOUT from the flip-flop FF1, and turned off when the switching element NM1 is turned off.

  The comparator CMP2 changes the control signal S1 from low to high when the voltage at one end of the capacitive element C1 becomes equal to or higher than a predetermined reference voltage value V2, and causes the switching control circuit 3 to switch on the switching element NM1. .

  Therefore, when the discharge switch SW2 is turned on, the capacitive element C1 is discharged through the discharge switch SW2, and the control signal S1 becomes low. When the discharge switch SW2 is turned off, the capacitive element C1 is charged with the charging current Ic, and the control signal S1 becomes high after an off time has elapsed since the discharge switch SW2 was turned off.

  As the voltage VLED increases, the charging current Ic increases and the capacitor element C1 is charged at high speed, so that the off-time is shortened. On the other hand, as the voltage VLED is lowered, the charging current Ic is decreased and the charging of the capacitive element C1 is slowed down.

Next, the operation of the LED lighting device will be described in more detail with reference to FIG.
FIG. 3 is a waveform diagram of the current Iout and the like flowing through the LED lamp 1 of FIG. Specifically, FIG. 3 shows a waveform 300 of the current Iout when the changeover switch SW1 is off and the series number of the LED elements 1a is large, and a current Iout when the changeover switch SW1 is on and the series number of the LED elements 1a is small. The waveform 301 is shown. FIG. 3 shows a part of the waveforms of the signals QOUT, SET, and RESET when the number of series LED elements 1a is large.

First, a case where the number of LED elements 1a in series is large will be described.
At time t1, the signal SET becomes high so that the signal QOUT becomes high. As a result, the switching element NM1 is turned on and the current Iout starts to increase. Further, when the signal QOUT becomes high, the discharge switch SW2 is turned on. As a result, at time t2, the control signal S1 and the signal SET become low.

  Next, when the current Iout flowing through the switching element NM1 reaches the peak current value Ip at time t3, the signal RESET becomes high, and the signal QOUT becomes low. As a result, the switching element NM1 is turned off and the current Iout starts to decrease. Further, when the signal QOUT becomes low, the discharge switch SW2 is turned off. Thereby, charging of the capacitive element C1 is started. When the current Iout decreases, the signal RESET goes low at time t4.

  Next, when the voltage at one end of the capacitive element C1 becomes equal to or higher than the reference voltage value V2 at time t5, the control signal S1 and the signal SET become high. Therefore, the period between time t3 and time t5 is the off time. Thereby, the same operation as after time t1 is performed. The subsequent waveforms of signals QOUT, SET, and RESET are not shown.

  On the other hand, when the number of LED elements 1a in series is small, the charging current Ic decreases, so that the time required for charging the capacitive element C1 becomes long. Therefore, at time t5A later than time t5, the signal SET becomes high (not shown). That is, the time between time t3 and time t5A is the off time, and the off time in this case is longer than the off time when the number of series LED elements 1a is large.

  Thus, compared to the case where the number of series of LED elements 1a is small, when the number of series is large, the voltage VLED between the both ends 1A and 1B of the LED lamp 1 is high, and therefore the LED after the switching element NM1 is turned off. A decrease amount per unit time of the current Iout flowing through the lamp 1 increases (waveform 300). That is, the absolute value of the negative slope of the current Iout increases. Therefore, by shortening the off time, the minimum value Im of the current Iout flowing through the LED lamp 1 can be prevented from becoming too small.

  Therefore, as shown in FIG. 3, the peak current value Ip of the current Iout is substantially constant and the minimum value Im is also substantially constant regardless of the number of LED elements 1a in series. As a result, the ripple of the current Iout becomes almost constant regardless of the number of LED elements 1a in series.

  Thus, in the off-time control circuit 5, the minimum value Im of the current Iout flowing through the switching element NM1 is substantially constant regardless of the number of LED elements 1a in series, that is, the voltage VLED between both ends 1A and 1B of the LED lamp 1. Thus, it can be said that the off-time is controlled.

  Thus, according to this embodiment, since the OFF time is controlled to be shorter as the voltage VLED between the both ends 1A and 1B of the LED lamp 1 is higher, the number of LED elements 1a in series is increased and the voltage VLED is increased. When becomes higher, the off time becomes shorter. When the voltage VLED increases, the amount of decrease per unit time in the current Iout flowing through the LED lamp 1 after the switching element NM1 is turned off increases. Here, by shortening the OFF time, the minimum value Im of the current Iout can be made substantially equal to the value before switching the number of LED elements 1a in series. That is, a change in the ripple of the current Iout can be suppressed. Therefore, fluctuations in the average current value flowing through the LED lamp 1 can be suppressed. Therefore, the reliability of the LED lamp 1 can be improved.

  By the way, in the conventional LED lighting device in which the off time does not change, when both ends of the LED lamp are short-circuited for some reason, the average current increases with the passage of time. The reason is that the decrease per unit time of the current flowing through the inductor after the switching element is turned off due to a short circuit is further reduced and the off time is constant, so the current does not decrease sufficiently while the switching element is off. Because. Moreover, the ON time of the switching element does not become zero because there is a minimum value due to the delay of the circuit. Therefore, when the switching element is turned on again after the off time has elapsed, the current exceeds the peak current value. By repeating such an operation, the average current increases with time. Therefore, the reliability of the LED lighting device may be reduced.

  On the other hand, in this embodiment, when both ends 1A and 1B of the LED lamp 1 are short-circuited, the off time becomes long, so that the current is sufficiently reduced during the off time. Accordingly, even if the switching element NM1 is turned on again after the off time has elapsed, the current Iout does not exceed the peak current value Ip. Therefore, the average current does not increase with the passage of time, and the reliability of the LED lighting device can be improved.

In addition, although the above embodiment demonstrated the LED illuminating device in which the output capacitor was not connected in parallel with the LED lamp 1, such an output capacitor may be connected.
Also, the high and low of each signal may be reversed.

  The aspect of the present invention is not limited to the individual embodiments described above, and includes various modifications that can be conceived by those skilled in the art, and the effects of the present invention are not limited to the contents described above. That is, various additions, changes, and partial deletions can be made without departing from the concept and spirit of the present invention derived from the contents defined in the claims and equivalents thereof.

DESCRIPTION OF SYMBOLS 1 LED lamp 1a LED element SW1 Changeover switch 2 Buck converter 3 Switching control circuit (1st control circuit)
4 UVLO circuit 5 OFF time control circuit (second control circuit)
NM1 Switching element D1 Diode L1 Inductor R1, R2 Resistor CMP1 Comparator FF1 Flip-flop 31 Logic circuit 32 Buffer 51 Charging circuit C1 Capacitance element SW2 Discharge switch CMP2 Comparator AMP1 Amplifier circuit OP1 Operational amplifier NM2 N-type MOS transistor PM1, PM2 P-type MOS transistor

Claims (5)

An LED lamp having a plurality of LED elements connected in series;
A changeover switch for switching the series number of the plurality of LED elements;
A step-down converter having a switching element through which the current of the LED lamp flows, and stepping down a power supply voltage by a switching operation of the switching element and supplying the voltage to the LED lamp;
When the current flowing through the switching element that is turned on reaches a predetermined peak current value, the switching element is switched off for a certain period, and the switching element is switched on after the certain period has elapsed. A first control circuit;
A second control circuit that shortens the certain period as the voltage across the LED lamp increases;
Equipped with a,
The second control circuit lengthens the certain period as the voltage across the LED lamp decreases.
Said second control circuit, LED lighting device according to claim Rukoto in inverse proportion to the voltage and the predetermined period across the LED lamp. Said second control circuit, so that the minimum value of the current flowing to the switching element irrespective of the voltage across the LED lamp is constant, according to claim 1, wherein controlling a period of time, characterized in that LED illuminating device of description. The second control circuit includes:
A charging circuit that outputs a charging current according to a voltage between both ends of the LED lamp;
A capacitive element to which the charging current is supplied to one end;
A discharge switch connected between one end of the capacitive element and ground, turned on when the switching element is switched on, and turned off when the switching element is switched off;
A comparator that causes the first control circuit to switch on the switching element when a voltage at one end of the capacitive element is equal to or higher than a reference voltage value;
LED lighting device according to claim 1 or claim 2, characterized in that it has a. The step-down converter
A diode having a cathode to which the power supply voltage is supplied and connected to an anode side terminal of the LED lamp;
An inductor having one end connected to the cathode side terminal of the LED lamp and the other end connected to the anode of the diode;
LED lighting device according to any one of claims 1 to 3, one end of the switching element is connected to the other end of the inductor, it is characterized. An LED lamp having a plurality of LED elements connected in series, a changeover switch for switching the series number of the plurality of LED elements, a switching element, and stepping down a power supply voltage by a switching operation of the switching element, the LED A step-down converter for supplying to a lamp, and a control method of an LED lighting device comprising:
When the current flowing through the switching element that is turned on reaches a predetermined peak current value, the switching element is turned off for a certain period, and after the certain period has elapsed, the switching element is turned on. ,
The higher the voltage across the LED lamp, the shorter the fixed period, and the lower the voltage across the LED lamp, the longer the fixed period, the voltage across the LED lamp and the fixed period Ru in inverse proportion, the control method of the LED illumination apparatus, characterized in that.

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