JP4519613B2 - LED lighting device - Google Patents

Description

  The present invention relates to an LED lighting device for lighting a light emitting diode (hereinafter referred to as LED).

When an LED is used as a light source, for example, in a headlamp for a vehicle, since each LED has a small light emission amount, a plurality of LEDs are simultaneously turned on to obtain brightness suitable for the headlamp.
In a conventional LED lighting device, a constant current circuit is connected in series to a light emitting unit composed of a plurality of LEDs, and a converter circuit is connected as a power source to both ends connected in series. The converter circuit includes a coil to which a power supply is connected, a switching transistor, and a capacitor, stores a back electromotive voltage generated in the coil when the switching transistor is turned on / off, and outputs a voltage across the capacitor. The converter circuit also detects the voltage at the connection point between the light emitting unit and the constant current circuit, controls the output voltage so that the voltage between the terminals of the constant current circuit is constant, and supplies a stabilized voltage to the constant current circuit. To do. The constant current circuit controls the current so that the value of the passing current is constant. As a result, the current passing through the light emitting unit becomes constant, and the plurality of LEDs are driven with a constant current. Some light emitting units have a plurality of LEDs connected in series, and a plurality of LEDs connected in series are connected in parallel. These are configured such that a similar current flows when one constant current circuit is connected to all LEDs. (For example, refer to Patent Document 1).

  Further, as a conventional LED lighting device, there is one in which a power supply voltage is boosted by a boosting circuit to an LED unit in which a plurality of LEDs are connected in series. The LED unit is connected to a booster circuit that applies a boosted voltage at one end, and a constant current circuit is connected to the other end, and the current flowing through the LED unit is controlled by the constant current circuit. The constant current circuit is connected to a voltage detection circuit that detects a voltage from the current flowing through the constant current circuit. The voltage detection circuit compares the detected voltage with a reference voltage taken from the power supply, and generates a boost control signal. The booster circuit includes a coil to which a power supply is connected, a transistor, a rectifying diode, and a smoothing capacitor, and boosts the power supply voltage by a chopper method that turns the transistor on and off at high speed. At this time, the voltage applied to the LED unit is adjusted based on the boost control signal, and the current flowing through the LED unit is kept constant. (For example, refer to Patent Document 2).

JP 2001-215913 A (pages 2 to 5, FIG. 2, FIG. 3, FIG. 7) JP 2003-187614 A (3rd and 4th pages, FIG. 2)

  Since the conventional LED lighting device is configured as described above, a constant current circuit having a large capacity is required because all LEDs are lit by one constant current circuit. Switching power supplies are used in constant current circuits because the power consumption of LEDs is relatively small, but if a large-capacity switching power supply is used to turn on many LEDs, ripples are superimposed on the current and power supply noise increases. There was a problem to do.

  The present invention has been made to solve the above-described problems, and obtains an LED lighting device that can reduce a current ripple due to a switching operation, reduce power supply noise, and stably light a plurality of LEDs. For the purpose.

The LED lighting device according to the present invention includes a plurality of LED circuits in which one or a plurality of LEDs are connected in series, and LED lighting circuits in which a coil and a switching element are connected in series, and the plurality of LED circuits and the LED lighting circuits are used as a power source. Corresponding to the output current of the comparison circuit that switches the ON / OFF operation of the switching element so that the ON / OFF switching timing of the switching element of each LED lighting circuit does not overlap in the LED lighting device configured to be connected in parallel A timing adjustment circuit that shifts the ON / OFF switching timing by changing the reference value to be compared with the voltage value to be operated in accordance with the operation state of the adjacent LED lighting circuit is provided for each of the LED lighting circuits. is there.

According to this invention, it corresponds to the output current of the comparison circuit that switches the ON / OFF operation of the switching elements so that the ON / OFF switching timings of the switching elements of the plurality of LED lighting circuits connected in parallel to the power source do not overlap. Since the reference value to be compared with the voltage value to be changed is changed corresponding to the operation state of the adjacent LED lighting circuit, and the timing adjustment circuit for shifting the ON / OFF switching timing is provided corresponding to each of the LED lighting circuits, The current ripple is reduced, the power supply filter can be reduced in capacity, and the generation of power supply noise can be reduced.

An embodiment of the present invention will be described below.
Embodiment 1 FIG.
1 is a circuit diagram showing a configuration of an LED lighting device according to Embodiment 1 of the present invention. The example illustrated in FIG. 1 is configured by connecting n (n is a natural number excluding 0 and 1) LED circuits a to n in parallel when viewed from the power source 1.
The voltage VB of the power source 1 is applied to the anode of the diode 2a. The cathode of the diode 2a is connected to one end of the resistor 4a and the capacitor 5a. The other end of the resistor 4a is connected to the gate of the FET 3a of the switching element and the collector of the transistor 20a. The other end of the capacitor 5a is connected to the cathode of the flywheel diode 6a, the source of the FET 3a, and one end of the coil 7a. The anode of the flywheel diode 6a is grounded. The FET 3a is an N-channel MOS field effect transistor, and is a switching element that turns on / off the connection between the power source 1 and the coil 7a when the voltage VB of the power source 1 is applied to the drain. The diode 2a, resistor 4a, and capacitor 5a connected in this way constitute a bootstrap drive circuit that drives the FET 3a.

The other end of the coil 7a is connected to the anode of the LED 9a, and the cathode of the LED 9a is connected to the anode of the LED 10a. That is, the coil 7a, the LED 9a, and the LED 10a are connected in series to constitute an LED circuit. The number of LEDs connected in series to the coil 7a is not limited to the two described here.
One end of the shunt resistor 11a and the resistor 12a is connected to the cathode of the LED 10a. The other end of the shunt resistor 11a is grounded. The other end of the resistor 12a is connected to one end of the resistor 13a and the positive input terminal of the comparator 15a. The other end of the resistor 13a is connected to the output terminal of the comparator 15a, and the resistor 13a is a feedback resistor that applies positive feedback to the comparator 15a. The inverting input terminal of the comparator 15a is connected to one end of the resistor 16a and the resistor 18a. A voltage VB is applied to the other end of the resistor 16a, and the other end of the resistor 18a is grounded. One end of the resistor 19a and the resistor 14a is connected to the output terminal of the comparator 15a. A power supply VB is applied to the other end of the resistor 14a, and the resistor 14a is a resistor that pulls up the output signal of the comparator 15a. The other end of the resistor 19a is connected to the base of the transistor 20a. The transistor 20a is an NPN type bipolar transistor, and the emitter is grounded.
The comparator 15a has a hysteresis characteristic, and changes the hysteresis characteristic by a current flowing through an adjacent LED circuit. The comparator 15a forms a timing adjustment circuit in combination with a plurality of resistors.

  The LED circuit a is comprised by each element connected as described so far. When “a” at the end of each symbol is replaced with “b”, each element constituting the LED circuit b is represented. That is, the LED circuit b is configured similarly to the LED circuit a. Further, the LED circuit n shown in FIG. 1 is also configured in the same manner as the LED circuits a and b, and is configured by an element having “n” at the end of each symbol used in the above description. Description of each structure of LED circuit b-n including the LED circuit which abbreviate | omitted illustration comprised similarly to these LED circuit a is abbreviate | omitted.

  In each LED circuit, for example, the LED circuit a and the LED circuit b are connected as follows. One end of the resistor 17a is connected to the inverting input terminal of the comparator 15a of the LED circuit a, and the other end of the resistor 17a is connected to the output terminal of the comparator 15b of the LED circuit b. Also, one end of the resistor 17b is connected to the inverting input terminal of the comparator 15b of the LED circuit b, and the other end of the resistor 17b is connected to the output terminal of the comparator of the LED circuit that is provided next to the LED circuit b and is not shown. To do. Similarly, each LED circuit is connected, and the LED circuit n connected to the LED circuit (not shown) has one end of the resistor 17n connected to the inverting input terminal of the comparator 15n, and the other end of the resistor 17n is connected to the LED circuit a. Connect to the output terminal of the comparator 15a. Thus, the LED circuit a and the LED circuit n provided at both ends of the LED circuits connected in parallel as viewed from the power source 1 are connected.

Next, the operation will be described.
Each of the LED circuits a to n is similarly configured and operates in the same manner. Here, the operation of the LED circuit a will be described as an example.
As described above, the bootstrap drive circuit including the diode 2a, the resistor 4a, and the capacitor 5a is connected to the FET 3a. When the N-channel FET 3a transitions to the ON state, it is necessary to apply a voltage higher than the voltage VB to the gate. The voltage VB of the power supply 1 is applied to the capacitor 5a via the diode 2a, and voltage energy is stored in the capacitor 5a. When the transistor 20a is controlled to be in an OFF state in order to turn on the FET 3a, the current flowing from the diode 2a to which the voltage VB of the power source 1 is applied to the transistor 20a through the resistor 4a is cut off. Is applied to the gate of the FET 3a through the diode 2a and the resistor 4a. At this time, the voltage energy stored in the capacitor 5a moves to the gate of the FET 3a via the resistor 4a, further increasing the gate voltage of the FET 3a, and the FET 3a is in a normal ON state.

  When the FET 3a is turned on, the voltage VB of the power source 1 is applied to one end of the coil 7a via the FET 3a. A current as described later flows through the coil 7a to which this voltage is applied, and this current is described as LED 9a and LED 10a connected in series to the coil 7a (hereinafter, the LED 9a and LED 10a connected in series are referred to as LEDs 9a and 10a). And two LEDs connected in series are also described). The current flowing through the LEDs 9a and 10a returns to the power source 1 through the shunt resistor 11a. At both ends of the shunt resistor 11a, a voltage representing the amount of current flowing through the LEDs 9a and 10a connected to the LED circuit a is generated. This voltage, that is, the voltage at the connection point B shown in FIG. 1, is input to the positive input terminal of the comparator 15a.

When a pulse voltage is applied to the coil, the current flowing through the coil changes like a triangular wave, and specifically changes like an integrated waveform that increases with time. When the FET 3a repeats the switching operation, the pulse voltage is supplied from the FET 3a to the coil 7a, and the current flowing through the coil 7a, that is, the current flowing through the LEDs 9a and 10a increases while the FET 3a is in the ON state. The current flowing through the LEDs 9a and 10a can be adjusted to an arbitrary value by controlling the ON time of the FET 3a. The energization current of the coil 7a in which the LEDs 9a and 10a are connected in series is expressed by the following formula (1).
Energizing current = (voltage applied to coil 7a−forward voltage of LEDs 9a and 10a)
× ON time / inductance of coil 7a (1)
The “forward voltage of the LEDs 9a and 10a” in the above formula (1) is a voltage across the LDE 9a and the LED 10a connected in series, that is, a voltage between the anode of the LED 9a and the cathode of the LED 10a. Thus, the current flowing through the LEDs 9a and 10a increases with the elapsed time that the FET 3a is in the ON state, and increases as the ON time increases.

  The flywheel diode 6a is to recirculate the current flowing out from the LEDs 9a and 10a to the coil 7a when the FET 3a transitions from the ON state to the OFF state, and suppresses a sharp decrease in the current flowing through the LEDs 9a and 10a. Yes. The current returned by the flywheel diode 6a decreases with time.

The comparator 15a compares the voltage representing the amount of current flowing through the LEDs 9a and 10a converted by the shunt resistor 11a with the reference voltage (reference value) obtained by dividing the voltage VB by the resistor 16a and the resistor 18a. The comparison result is output as a high potential or low potential output signal, as will be described later. The output terminal of the comparator 15a is pulled up by the resistor 14a. A voltage representing the current flowing through the LEDs 9a and 10a is input to the positive input terminal of the comparator 15a via the resistor 12a, and positive feedback is applied by the resistor 13a. Thus, the comparator 15a has a hysteresis characteristic since positive feedback is applied.
The reference voltage generated by dividing the voltage VB by the resistors 16a and 18a as described above is input to the inverting input terminal of the comparator 15a. The comparator 15a determines the output signal by comparing the voltage input to the positive input terminal with the reference voltage.

  For example, when the FET 3a is in the ON state, that is, when the transistor 20a is open and the ground connection of the gate of the FET 3a is opened and the gate voltage becomes high, the base of the transistor 20a becomes low. As described above, a low-potential output signal is output from the comparator 15a. When the FET 3a is turned on in this way, a current flows through the coil 7a, and this current increases with the passage of time. A similar current flows through the LEDs 9a and 10a, and the magnitude of this current is converted into a voltage magnitude by the shunt resistor 11a. The comparator 15a inputs this voltage to the positive input terminal via the resistor 12a, and compares the voltage of the positive input terminal with the reference voltage input to the inverting input terminal. At this time, since the output signal of the comparator 15a is at a low potential, the voltage at the positive input terminal to which positive feedback is applied is pulled down. In this state where the voltage is pulled down by positive feedback, the voltage representing the current flowing through the LEDs 9a and 10a rises and the voltage at the positive input terminal rises.

  When the voltage input to the positive input terminal of the comparator 15a increases as the current flowing through the LEDs 9a and 10a increases and becomes greater than the reference voltage, the comparator 15a inverts the output signal from a low potential to a high potential. At this time, the voltage at the positive input terminal to which positive feedback is applied is raised, the base voltage of the transistor 20a transits to a high potential, the transistor 20a is turned on, and the gate of the FET 3a is grounded. The FET 3a transits to the OFF state, and the current supplied from the FET 3a to the coil 7a is interrupted. The current supplied from the flywheel diode 6a flows through the coil 7a, and the current flowing through the LEDs 9a and 10a gradually decreases. This current change is expressed as a voltage change by the shunt resistor 11a, and this voltage is input to the positive input terminal of the comparator 15a through the resistor 12a as described above.

At this time, the voltage of the positive input terminal is pulled up by positive feedback as described above, and a voltage indicating the amount of current flowing through the LEDs 9a and 10a is added to this state, so that the current flowing through the LEDs 9a and 10a is reduced. Accordingly, the voltage at the positive input terminal decreases. When the voltage at the positive input terminal gradually decreases and becomes lower than the reference voltage, the comparator 15a inverts the output signal from a high potential to a low potential.
Since the comparator 15a inputs a voltage indicating the amount of current flowing to the LEDs 9a and 10a to the positive input terminal, the comparator 15a is pulled up above the reference voltage by positive feedback, and is pulled down below the reference voltage. Compared with This comparison operation can obtain the same effect as the operation of comparing with the voltage indicating the current flowing in the LEDs 9a and 10a by alternately using two reference voltages of high potential and low potential generated by the hysteresis characteristic of the comparator 15a. .
As described above, the LED circuit a repeats the switching operation of the FET 3a by the operation using the current flowing through the coil 7a and the hysteresis characteristic of the comparator 15a to perform a self-excited oscillation operation.

  When all the LED circuits a to n performing the switching operation are simultaneously turned on, instantaneous power consumption at this time increases. Also, switching noise increases when transitioning from the ON state to the OFF state or when transitioning from the OFF state to the ON state. In order to suppress instantaneous power consumption, the LED circuit a changes the reference voltage input to the inverting input terminal of the comparator 15a so that the switching operations of all the LED circuits a to n are not synchronized, and the switching operation of the FET 3a. The timing is shifted. As described above, the voltage obtained by dividing the voltage VB by the resistors 16a and 18a is input to the inverting input terminal of the comparator 15a, and the output signal of the comparator 15b is further input via the resistor 17a.

  FIG. 2 is an explanatory diagram illustrating the operation of the LED lighting device according to the first embodiment. This figure is a timing chart showing the temporal change of the voltage at the connection point A, the current flowing through the connection point B, and the ON / OFF state of the FET 3a shown in FIG. The upper waveform in the figure is the voltage at the connection point A shown in FIG. 1, and is the output signal of the comparator 15b of the LED circuit b. Since this voltage is input to the base of the transistor 20b, the high potential indicates the OFF state of the FET 3b, and the low potential indicates the ON state. The middle waveform in FIG. 2 shows the change in the current at the connection point B shown in FIG. 1, that is, the voltage across the shunt resistor 11a, and the change in the current flowing through the LEDs 9a and 10a of the LED circuit a. The lower waveform in FIG. 2 shows the ON / OFF state of the FET 3a. The high potential indicates the ON state and the low potential indicates the OFF state. Note that the dashed line added to the waveform shown in the middle part of FIG. 2 indicates the threshold voltage of the comparator 15a corresponding to the waveform, and the current of the current when the increase / decrease in the current at the connection point B is reversed is shown. The size is easy to understand.

  The current flowing through the LEDs 9a and 10a, that is, the current flowing through the shunt resistor 11a at the connection point B, changes in a triangular waveform as shown in the middle of FIG. 2 by the action of the coil 7a. The voltage generated across the shunt resistor 11a representing this current is input to the positive input terminal of the comparator 15a via the resistor 12a. On the other hand, the reference voltage and the output signal of the comparator 15b are input to the inverting input terminal of the comparator 15a. As described in the explanation of the operation of the LED circuit a, the current at the connection point B, that is, the voltage across the shunt resistor 11a increases when the FET 3a is in the ON state and decreases when the FET 3a is in the OFF state. Also, when the FET 3a transitions from the OFF state to the ON state, the current at the connection point B reverses from decrease to increase, and when the FET 3a transitions from the ON state to the OFF state, the current at connection point B reverses from the increase to the decrease. To do.

When the FET 3b of the LED circuit b provided next to the LED circuit a is in the ON state, the output signal of the comparator 15b, that is, the voltage at the connection point A is low. The voltage at the connection point A at a low potential is input to the inverting input terminal of the comparator 15a of the LED circuit a via the resistor 17a, and the voltage at the inverting input terminal is lowered. That is, the reference voltage generated by the resistor 16a and the resistor 18a input to the inverting input terminal is pulled down.
At this time, when the FET 3a is in the OFF state and the current at the connection point B is decreasing, the reference voltage input to the comparator 15a is lowered more than before, so that the comparator 15a The output signal is inverted at the hold voltage L1, and the current at the connection point B drops for a long time. Further, the timing at which the comparator 15a inverts the output signal is delayed, and the timing at which the FET 3a transitions from the OFF state to the ON state is delayed.
Further, when the FET 3a is in the ON state and the current at the connection point B is increased, the reference voltage input to the comparator 15a is lowered more than before, so that the comparator 15a has a threshold. The output signal is inverted at the voltage H1, and the time for the current at the connection point B to rise is shortened. Further, the timing at which the comparator 15a inverts the output signal is advanced, and the timing at which the FET 3a transitions from the ON state to the OFF state is advanced.

When the FET 3b is in the OFF state, the output signal of the comparator 15b, that is, the voltage at the connection point A is at a high potential. The voltage at the connection point A, which is at a high potential, is input to the inverting input terminal of the comparator 15a of the LED circuit a through the resistor 17a, and the voltage at the inverting input terminal is raised. That is, the reference voltage generated by the resistor 16a and the resistor 18a input to the inverting input terminal is raised.
At this time, when the FET 3a is in the OFF state and the current at the connection point B is decreasing, the reference voltage input to the comparator 15a is raised more than before, so that the comparator 15a The output signal is inverted at the hold voltage L2, and the time during which the current at the connection point B decreases is shortened. Further, the timing at which the comparator 15a inverts the output signal is advanced, and the timing at which the FET 3a transitions from the OFF state to the ON state is advanced.
Further, when the FET 3a is in an ON state and the current at the connection point B is increased, the reference voltage input to the comparator 15a is raised more than before, so that the comparator 15a has a threshold. The output signal is inverted at the voltage H2, and the time during which the current at the connection point B rises becomes longer. Further, the timing at which the comparator 15a inverts the output signal is delayed, and the timing at which the FET 3a transitions from the ON state to the OFF state is delayed.
Note that the threshold voltage H1 of the comparator 15a is lower than the threshold voltage H2, and the threshold voltage L1 is lower than the threshold voltage L2.

  As described above, by using the output signal of the comparator 15b of the LED circuit b provided next to the reference voltage input to the comparator 15a, the hysteresis characteristic of the comparator 15a changes and the output signal of the comparator 15a changes. The timing of inversion changes. For this reason, the FET 3a of the LED circuit a performs a switching operation without synchronizing with the switching timing of the FET 3b of the LED circuit b. Similarly, each LED circuit is configured to operate without synchronizing the switching timing with the adjacent LED circuit by using the output signal of the comparator of the LED circuit provided adjacently. The terminal LED circuit n shown in FIG. 1 adjusts the switching timing of the FET 3n by inputting the output signal of the comparator of the tip LED circuit a.

Note that the configuration and operation for shifting the operation timing of the FET 3a to FET 3n are not limited to those described here.
Further, since each LED circuit an operates by shifting the switching timing, the power supply current and the ripple superimposed on the circuit current are reduced and the power supply noise is reduced. Therefore, the power supply noise not shown in FIG. A power filter having a small capacity can be used as the power supply filter provided for removing the power.

As described above, according to the first embodiment, the LED circuits a to n are connected in parallel, and the operation is performed so that the switching timings of the FETs 3a to 3n of the LED circuits a to n are not synchronized. There is an effect that current ripple can be reduced and power supply noise can be reduced.
Also, for example, when the FET 3b is in the ON state, the timing of transition from the ON state of the FET 3a to the OFF state is advanced, and when the FET 3b is in the OFF state, the timing of transition from the ON state of the FET 3a to the OFF state is delayed. There is an effect that it is possible to reduce the probability that the FET 3b is simultaneously turned ON / OFF.

Embodiment 2. FIG.
FIG. 3 is a circuit diagram showing a configuration of an LED lighting device according to Embodiment 2 of the present invention. The same reference numerals are used for the same or corresponding parts as those shown in FIG. 1, and the description thereof is omitted. FIG. 3 shows an LED circuit a of the LED lighting device according to Embodiment 2, and illustration of LED circuits b to n configured in the same manner as the LED circuit a is omitted. Here, the configuration of the LED circuit a will be described as an example, and the description of the configurations of the other LED circuits b to n will be omitted. Also, the description of the parts configured in the same manner as shown in FIG. 1 is omitted, and the configuration of the parts that are characteristic of the LED lighting device according to Embodiment 2 will be described.

The voltage VB of the power source 1 is applied to one end of the resistor 30a. The other end of the resistor 30a is connected to one end of the resistor 31a and the inverting input terminal of the comparator 34a. The voltage VB of the power source 1 is applied to one end of the resistor 32a. The other end of the resistor 32a is connected to the cathode of the Zener diode 33a and the positive input terminal of the comparator 34a. The other end of the resistor 31a and the anode of the Zener diode 33a are grounded. The output terminal of the comparator 34a is connected to one end of the resistor 35a and the base of the transistor 36a. The voltage VB is applied to the other end of the resistor 35a. The resistor 35a is a pull-up resistor connected to the output terminal of the comparator 34a. The transistor 36a is composed of, for example, an NPN-type bipolar transistor. The collector is connected to the gate of the FET 3a, the other end of the resistor 4a, and the collector of the transistor 20a, and the emitter is grounded. The resistors 30a, 31a, 32a, the Zener diode 33a, the comparator 34a, the resistor 35a, and the transistor 36a constitute a power supply voltage detection circuit (power supply voltage detection means).
The resistors 30a to 32a lower the voltage VB to a voltage range that can be input by the comparator 34a. When the voltage VB is a normal voltage, the voltage divided by the resistors 30a and 31a is the same voltage VB. The respective resistance values are set so as to be higher than the Zener voltage of the Zener diode 33a via the resistor 32a. Other parts are configured in the same manner as the LED circuit a shown in FIG.

Next, the operation will be described.
Description of operations similar to those of the LED lighting device shown in FIG. 1 is omitted, and operations that characterize the LED lighting device according to Embodiment 2 will be described. When the voltage VB of the power supply 1 decreases, the current flowing through the LEDs 9a and 10a decreases. The voltage across the shunt resistor 11a representing this current cannot rise to a voltage at which the output signal of the comparator 15a is inverted, the comparison result of the comparator 15a becomes constant and the output signal is not inverted, and the base of the transistor 20a Is followed by a state in which an output signal having a low potential is input. The gate of the FET 3a is always in a state where the ground connection is opened. In such a state, the bootstrap type driving circuit composed of the resistor 4a, the capacitor 5a and the like cannot operate normally, and the FET 3a is incompletely turned on, which causes problems such as heat generation and increased power consumption. appear.

  In order to avoid such a state, the LED device shown in FIG. 3 turns off the FET 3a when the voltage VB becomes lower than a predetermined value by the power supply voltage detection circuit using the comparator 34a or the like. is there. A voltage obtained by dividing the voltage VB by the resistor 30a and the resistor 31a is input to the inverting input terminal of the comparator 34a. The Zener voltage of the Zener diode 33a from the voltage VB through the resistor 32a is input as a reference voltage to the positive input terminal of the comparator 34a.

  When the voltage divided by the resistor 30a and the resistor 31a is V− and the Zener voltage of the Zener diode 33a is V +, the comparator 34a has the input voltage V + at the positive input terminal smaller than the input voltage V− at the inverting input terminal. When the output voltage saturates to a low potential. Further, when the input voltage V + is larger than the input voltage V−, the output voltage is saturated to a high potential. If the voltage VB is equal to or higher than a predetermined value, the voltage V− is larger than the voltage V + of the positive input terminal grounded by the Zener diode 33a, and a low potential output signal is output from the comparator 34a to the base of the transistor 36a. The At this time, the transistor 36a is turned off, and the gate voltage of the FET 3a is controlled by the ON / OFF operation of the transistor 20a.

When the voltage VB decreases and falls below a predetermined value, the voltage divided by the resistors 30a and 31a also decreases. The comparator 34a compares the voltage V− input at this time with the voltage V +. When the voltage V− becomes smaller than the voltage V +, the comparator 34a outputs a high-potential output signal to the base of the transistor 36a. Then, the transistor 36a is turned on, the gate of the FET 3a is grounded, and the FET 3a is turned off.
Further, by configuring the other LED circuits b to n in the same manner as the LED circuit a described here, the LED circuit also operates in the same manner, and similar operational effects can be obtained.

  As described above, according to the second embodiment, for example, the LED circuit a is configured so that the FET 3a is turned off by the comparator 34a connected to the Zener diode 33a when the voltage VB of the power source 1 becomes smaller than a predetermined value. Therefore, when the voltage VB of the power supply 1 is lowered and the switching operation of the FET 3a is stopped, the current supplied to the LEDs 9a and 10a can be cut off, and each LED circuit configured similarly to the LED circuit a There is an effect that the occurrence of a failure can be prevented.

Embodiment 3 FIG.
FIG. 4 is a circuit diagram showing a configuration of an LED device according to Embodiment 3 of the present invention. The same reference numerals are used for the same or corresponding parts as those shown in FIG. 1, and the description thereof is omitted. In this figure, illustration of LED circuits b to n configured similarly to the LED circuit a is omitted. Here, the configuration of the LED circuit a will be described as an example, and the description of the configurations of the other LED circuits b to n will be omitted. Also, the description of the parts configured in the same manner as the LED circuit a shown in FIG. 1 is omitted, and the configuration of the parts that characterize the LED lighting device according to Embodiment 3 will be described.
The LED lighting device of FIG. 4 has a plurality of coils 7a1 to 7am (m is a natural number other than 0 and 1) connected in parallel to the drain of the FET 3a instead of the coil 7a shown in FIG. 1, and is connected to the LED 9a shown in FIG. The corresponding LEDs 9a1 to 9am and the LEDs 10a1 to 10am corresponding to the LEDs 10a are provided, and the others are configured in the same manner as shown in FIG.

For example, one end of the coil 7a1 is connected to the source of the FET 3a, the other end of the coil 7a1 is connected to the anode of the LED 9a1, and the cathode of the LED 9a1 is connected to the anode of the LED 10a1. That is, the coil 7a1, the LED 9a1, and the LED 10a1 are connected in series, the coil 7a2, the LED 9a2, and the LED 10a2 are connected in series, and the coils 7a3 to 7am, the LEDs 9a3 to 9am, and the LEDs 10a3 to 10am are connected in series. Make it.
Further, the cathodes of the LEDs 10a1 to 10am are all connected to the connection point B and connected to the shunt resistor 11a and the resistor 12a. The LEDs 9a1 and 10a1 and the LEDs 9a2 and 10a2 are connected in parallel. Similarly, the two LEDs connected in series up to the LEDs 9am and 10am including the LEDs not shown in the figure are connected in parallel. The number of LEDs connected in series is not limited to two.

Next, the operation will be described.
Description of operations similar to those of the LED device shown in FIG. 1 will be omitted, and operations that characterize the LED device according to Embodiment 3 will be described.
The current flowing through the LEDs 9a1, 10a1 to LED9am, 10am generally flows into the shunt resistor 11a, and a voltage representing the total amount of current flowing through all the LEDs 9a1, 10a1 to LED9am, 10am is generated at both ends of the shunt resistor 11a. The comparator 15a inputs this voltage to the positive input terminal via the resistor 12a. Other operations are similar to those of the LED lighting device according to the first embodiment.
Further, when the LED circuits b to n not shown are configured in the same manner as the LED circuit a in FIG. 4, these LED circuits b to n operate in the same manner.
FIG. 4 shows the LED lighting device shown in FIG. 1 having coils 7a1 to 7am, LEDs 9a1 to 9am, and LEDs 10a1 to 10am instead of the coils 7a, LED 9a, and LED 10a. Instead of the coil 7a, LED 9a, and LED 10a of the LED lighting device shown in FIG. 6, the coils 7a1 to 7am, LEDs 9a1 to 9am, and LEDs 10a1 to 10am may be provided, and the operation is the same.

As described above, according to the third embodiment, for example, the coils 7a1 to 7am are connected in parallel to the FET 3a, and the LEDs 9a1, 10a1 to LED9am, 10am are connected to the coils 7a1 to 7am, respectively. As a result, there is an effect that a large number of LEDs can be turned on.
In the first to third embodiments, the comparison reference value is changed according to the state of the current flowing in the adjacent LED circuit, and the operation timing of the switching element in the LED circuit is shifted. For example, a separate timing signal generation circuit is provided, and the operation timing of the switching elements of the plurality of LED circuits connected in parallel to the power supply is shifted by a predetermined time by the signal generated by the timing signal generation circuit, and sequentially turned ON / OFF It is also possible to configure it.

Embodiment 4 FIG.
FIG. 5 is an explanatory diagram showing lighting fixtures such as ceiling lighting and a stand in which the LED lighting device according to the first to third embodiments is applied to lighting control of a large number of LEDs constituting the light source. The same reference numerals are used for parts that are the same as or correspond to those shown in FIGS. The illuminating device 40 is similar to the illuminating lamp main body 41 including a plurality of LEDs such as LEDs 9a, 10a to 9n, 10n as light sources, and the LED lighting device described in any of the first to third embodiments. And a control unit 42 having a circuit.
The control unit 42 operates in the same manner as the LED lighting device described in any of the first to third embodiments, and controls lighting of a large number of LEDs 9a, 10a to 9n, 10n.

  FIG. 6 is an explanatory view showing a liquid crystal display device using LEDs as a backlight. The same reference numerals are used for portions that are the same as or correspond to those shown in FIGS. 1 and 3 to 5, and descriptions thereof are omitted. The liquid crystal display device 50 includes a liquid crystal panel 51 and a backlight 52 behind the liquid crystal panel 51. The backlight 52 includes a plurality of LEDs such as LEDs 9a, 10a to 9n, 10n and the control unit 42. The LEDs 9a, 10a to 9n, 10n are arranged so as to illuminate the liquid crystal panel 51 uniformly. The control unit 42 operates in the same manner as described in any one of the first to third embodiments, and controls the lighting of the LEDs 9a, 10a to 9n, 10n.

  FIG. 7 is an explanatory view showing a headlamp of a vehicle using a number of LEDs as a light source. For example, the arrangement of each component when the headlamp unit 60 is viewed from the side is shown. The same reference numerals are used for the same or corresponding parts as those shown in FIGS. 1 and 3 to 6, and the description thereof is omitted. The headlamp unit 60 includes, for example, a reflecting mirror 61, a light shielding wall 62, a lens 63, and LEDs 9a and 10a to LEDs 9n and 10n as light sources. A control unit 42 is provided in the deep part of the headlamp unit 60, and a plurality of LEDs such as the LEDs 9a, 10a to 9n, 10n connected to the control unit 42 irradiate light in an irradiation range required as a headlamp. As shown, the orientation and the like are adjusted to be arranged inside the reflecting mirror 61.

The LED lighting device provided in the control unit 42 has a large number of LEDs 9a, 10a to 9n as light sources arranged inside the reflecting mirror 61 in the same manner as described in any of the first to third embodiments. , 10n, etc. are controlled to light.
Moreover, you may use many LED9a, 10a-LED9n, 10n etc. for a traffic signal light as a light source similarly to the above.

As described above, according to the fourth embodiment, a large number of LEDs 9a, 10a to 9n, 10n, etc. are used as light sources, and the large number of LEDs are controlled by the LED lighting device of the present invention provided in the control unit 42. Thus, there is an effect that current ripple due to switching operation can be reduced, power supply noise can be reduced, and a plurality of LEDs can be lit stably.
In addition, even when one LED is disconnected, all the LEDs are not turned off at the same time, and there is an effect that it is possible to avoid a danger caused by sudden turn-off.

It is a circuit diagram which shows the structure of the LED lighting device by Embodiment 1 of this invention. FIG. 5 is an explanatory diagram showing the operation of the LED lighting device according to Embodiment 1. It is a circuit diagram which shows the structure of the LED lighting device by Embodiment 2 of this invention. It is a circuit diagram which shows the structure of the LED lighting device by Embodiment 3 of this invention. It is explanatory drawing which shows the lighting fixture which applied the LED lighting device of this invention by Embodiment 1-3 to lighting control of many LED which comprises a light source. It is explanatory drawing which showed the liquid crystal display device which uses LED as a backlight. It is explanatory drawing which showed the headlamp of the vehicle which uses many LED as a light source.

Explanation of symbols

  1 power supply, 2a-2n diode, 3a-3n FET, 4a-4n resistor, 5a-5n capacitor, 6a-6n flywheel diode, 7a-7n coil, 9a-9n, 10a-10n LED, 11a-11n shunt resistor, 12a-12n resistor, 13a-13n resistor, 14a-14n resistor, 15a-15n comparator, 16a-16n resistor, 17a-17n resistor, 18a-18n resistor, 19a-19n resistor, 20a-20n transistor, 30a-32a resistor, 33a Zener diode, 34a Comparator, 35a Resistor, 36a Transistor, 40 Illumination device, 41 Illumination lamp body, 42 Control unit, 50 Liquid crystal display device, 51 Liquid crystal panel, 52 Backlight, 60 Headlamp unit, 61 Reflection , 62 light shielding wall, 63 lenses.

Claims (6)

An LED circuit in which one or more LEDs are connected in series;
A plurality of LED lighting circuits in which a coil and a switching element are connected in series;
In the LED lighting device configured to connect the plurality of LED circuits and the LED lighting circuit in parallel to the power source,
Adjacent LEDs that have a reference value to be compared with the voltage value corresponding to the output current of the comparison circuit that switches the ON / OFF operation of the switching element so that the ON / OFF switching timing of the switching element of each LED lighting circuit does not overlap. LED lighting devices each provided with a timing adjustment circuit corresponding to each of the LED lighting circuits, which is changed corresponding to the operating state of the lighting circuit to shift the ON / OFF switching timing.   2. The LED lighting device according to claim 1, wherein the timing adjustment circuit shifts the operation timing of the switching element in the corresponding LED circuit by changing the reference value for comparison according to the state of the current flowing in the adjacent LED circuit. 3. The LED lighting device according to claim 1, wherein an N-channel field effect transistor is used as the switching element, and a bootstrap driving circuit for driving the field effect transistor is provided . The power supply voltage detection means which detects a power supply voltage and controls a switching element to an OFF state, if the said voltage falls below predetermined value, The power supply voltage detection means in any one of Claims 1-3 characterized by the above-mentioned. LED lighting device. The LED lighting device according to any one of claims 1 to 4, wherein a plurality of LED circuits are connected in parallel to the switching element . The LED lighting device according to any one of claims 1 to 5, wherein a set of LEDs formed of a plurality of LED circuits constitutes a light source of a headlight of a vehicle .

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