JP6473569B2 - LED drive circuit - Google Patents

Description

  The present invention relates to an LED driving circuit.

  FIG. 9 shows a conventional LED driving circuit. Reference numeral 51 is a voltage input terminal, 52 and 53 are LED groups in which a plurality of LEDs are connected in series, 54 is a PWM terminal to which a PWM signal is input, and 55 is a drive circuit.

  When the voltage VIN of the voltage input terminal 51 is low, the circuit shown in FIG. 9A in which the LED groups 52 and 53 are connected in parallel is used. When the voltage VIN of the voltage input terminal 51 is high, the LED A circuit shown in FIG. 9B in which the groups 52 and 53 are connected in series is used.

  However, this method requires two types of circuits. Or when wiring is different and it is configured on the same substrate, four LED groups are required, leading to an increase in expensive components and an increase in substrate area.

  On the other hand, in Patent Document 1, as shown in FIG. 10, when the forward voltage Vf of the LEDs of the LED groups 63 and 64 is small, the terminal 65 is connected by a resistor, and the LED is connected between the terminals 61 and 62. A configuration is described in which the groups 63 and 64 are connected in series, and when the forward voltage Vf of the LEDs of the LED groups 63 and 64 is large, the terminals 66 and 67 are connected by resistors, and the LED groups 63 and 64 are connected in parallel. Has been.

  However, this selects one of the series connection and the parallel connection of the LED groups 63 and 64 according to the magnitude of the forward voltage Vf of the LED to be used. It is not clear how to connect. Further, it is not clear whether the forward voltage Vf of each LED of the LED groups 63 and 64 in series connection is determined from the terminal 61 side or from the terminal 62 side. Further, when the terminal 65 is connected by a transistor, it is not clear how to determine the bias setting. Therefore, there is a problem that luminance design cannot be performed.

  Further, in Patent Document 2, in a video camera device in which an illumination unit is provided between a voltage input terminal and an internal voltage generation unit, the illumination unit is configured by a plurality of LEDs, and the illumination unit is configured according to the voltage of the voltage input terminal. A configuration is described in which the series / parallel connection of LEDs is switched so that the voltage input to the voltage generator is within a predetermined range.

  However, this illumination unit realizes voltage adjustment by switching LEDs in series / parallel at the same time as the illumination function, and there is no special description about LED brightness setting.

JP 2009-059636 A JP 2012-053144 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide an LED drive circuit that can automate the series / parallel switching of two LED groups in accordance with the input voltage, and can set the same brightness in either series / parallel. That is.

In order to achieve the above object, the invention according to claim 1 includes a first LED group including a series circuit of n (n is an integer of 1 or more) LEDs, and a high voltage side connected to a voltage input terminal; A first drive unit that supplies a first drive current, a first switch circuit that connects the low voltage side of the first LED group and the first drive unit, and a series circuit of n LEDs A second LED group, a second switch circuit connecting the high voltage side of the second LED group and the voltage input terminal, and a second drive for supplying the same drive current as the first drive current , A third switch circuit connecting the low voltage side of the second LED group and the second drive unit, a low voltage side of the first LED group, and a high voltage of the second LED group A fourth switch circuit for connecting the first side and the second input circuit according to the voltage of the voltage input terminal. A first control circuit that turns on and off the third and fourth switch circuits, and the first control circuit is configured to output the first, second, and third signals when the voltage at the voltage input terminal is low. The switch circuit is turned on, the fourth switch circuit is turned off, the series connection circuit of the first LED group and the first driving unit, the series of the second LED group and the second driving unit. A connection circuit is connected in parallel to the voltage input terminal, and when the voltage at the voltage input terminal is high, the first and second switch circuits are turned off, and the third and fourth switch circuits are turned on. The first and second LED groups and the second driver are connected in series to connect to the voltage input terminal, and the first switch circuit has a collector connected to the first LED. Connected to the low voltage side of the group, The third switch circuit is connected to the low-voltage side of the second LED group, and is configured by a first NPN transistor to which a constant voltage is applied to the base when turned on. The emitter is connected to the second driving unit, and is configured by a second NPN transistor in which a constant voltage is applied to the base when the emitter is turned on.

According to a second aspect of the present invention, in the LED driving circuit according to the first aspect, a voltage stabilizing circuit that stabilizes a voltage at the voltage input terminal is provided, and the voltage stabilizing circuit includes the first and second driving circuits. And a voltage obtained by dividing the stabilization voltage is supplied to the base of the second NPN transistor when the third switch circuit is on .

According to a third aspect of the present invention, in the LED drive circuit according to the first or second aspect, the fourth switch circuit includes an emitter connected to the low voltage side of the first LED group, and the second LED. A PNP transistor having a collector connected to the high voltage side of the group, and when the first LED group and the second LED group are connected in series, the voltage of the voltage input terminal is connected to the base of the PNP transistor A voltage obtained by dividing the voltage is applied.

According to a fourth aspect of the present invention, in the LED drive circuit according to the first, second, or third aspect, the second drive circuit is connected to an external control terminal, and the second control circuit includes the external control terminal. On / off switching of the first, second, third and fourth switch circuits and the value of the first drive current of the first and second drive units according to a control signal input from It is characterized by doing.

According to a fifth aspect of the present invention, in the LED drive circuit according to the first, second, third, or fourth aspect, a connection other than one of the parallel connection and the serial connection of the first and second LED groups is provided. A time adjustment circuit to be avoided is provided on the output side of the first control circuit .

  According to a sixth aspect of the present invention, in the LED drive circuit according to the first, second, third, fourth, or fifth aspect, a reverse connection prevention circuit is connected to the voltage input terminal.

  According to the first aspect of the present invention, the series / parallel of the first and second LED groups is automatically switched by the first control circuit in accordance with the voltage of the voltage input terminal. In this case, the same current can be supplied to the first and second LED groups, and the same luminance can be realized.

  According to the invention of claim 2, even if the voltage at the voltage input terminal fluctuates, a stable voltage can be supplied to the first control circuit and the drive circuit, and variation in luminance of each LED group can be prevented. it can.

  According to the third aspect of the invention, it becomes possible to destabilize the first switch circuit and prevent backflow.

  According to the invention of claim 4, the first and second LED groups can be switched in series / parallel from the outside regardless of the voltage at the voltage input terminal, and the current at that time is also set from the outside. Will be able to.

  According to the invention concerning Claim 5, connection states other than serial / parallel of the 1st, 2nd LED group can be avoided.

  According to the sixth aspect of the present invention, the internal circuit can be protected even if the voltage input terminal is connected to the power supply line with the reverse polarity.

It is a circuit diagram of the LED drive circuit of the 1st Example of this invention. It is a circuit diagram of the LED drive circuit of the 2nd Example of this invention. It is a circuit diagram of the LED drive circuit of the 3rd Example of this invention. It is a circuit diagram of the LED drive circuit of the 4th Example of this invention. It is a circuit diagram of the LED drive circuit of the 5th Example of this invention. It is a circuit diagram of the LED drive circuit of the 6th Example of this invention. It is a circuit diagram of the LED drive circuit of the 7th Example of this invention. It is a circuit diagram of the LED drive circuit of the 8th Example of this invention. It is a circuit diagram of the conventional LED drive circuit. It is a circuit diagram of another conventional LED drive circuit.

  The present invention will be described below with reference to the drawings. The members and arrangements described below do not limit the present invention, and various modifications can be made within the scope of the gist of the present invention. In the drawings, the same number indicates the same or the same part.

<First embodiment>
FIG. 1 shows an LED driving circuit of the first embodiment. 1 is a voltage input terminal, 2 is a first LED group in which n (n is an integer of 1 or more) LEDs are connected in series, 3 is also a second LED group in which n LEDs are connected in series, 4 is PWM terminal. Reference numeral 5 denotes a first control circuit, a voltage detection circuit 51 that detects the level of the voltage VIN input to the voltage input terminal 1, and a switch control circuit 52 that outputs a control signal corresponding to the detection result of the voltage detection circuit 51. including. Reference numeral 6 denotes a drive circuit, which includes a first drive unit 61 for driving the LED group 2 and a second drive unit 62 for driving the LED group 3 or the series circuit of the LED groups 2 and 3, which have a predetermined current. A value is set and the current is turned on / off by a PWM signal input to the PWM terminal 4. Reference numerals 7 to 10 denote switch circuits whose ON / OFF is individually controlled by the switch control circuit 52.

  A high voltage or a low voltage VIN is input to the voltage input terminal 1. At this time, when the input voltage VIN is detected as a low desired voltage in the power supply detection circuit 51 of the control circuit 5, the switch control circuit 52 controls the switch circuits 7, 8, and 10 to be turned on. The circuit 9 is controlled off. Thereby, the LED groups 2 and 3 are connected in parallel to the voltage input terminal 1. The drive units 61 and 62 of the drive circuit 6 are set to the same current value and controlled by the same PWM signal, so that the LEDs of the LED groups 2 and 3 emit light with the same brightness according to the PWM control. .

  As described above, when the input voltage VIN is low, the LED groups 2 and 3 are connected in parallel. At this time, since the number of LEDs connected in series to the voltage input terminal 1 is reduced, the dynamic range of the circuit can be increased, and an LED having a large forward voltage Vf can also be used.

  On the other hand, when the input voltage VIN is detected as a high desired voltage in the power supply detection circuit 51 of the control circuit 5, the switch circuits 8 and 9 are controlled to be turned on by the switch control circuit 52. 10 is controlled off. Thereby, the LED groups 2 and 3 are connected in series to the voltage input terminal 1. At this time, the drive unit 62 of the drive circuit 6 is PWM-controlled, so that the LED groups 2 and 3 emit light with luminance according to the PWM control.

  As described above, when the input voltage VIN is high, the LED groups 2 and 3 are connected in series. At this time, the current value of the drive unit 62 is controlled by the switch control circuit 52 to the same current value as the current value that has flowed to the LED group 3 when being connected in parallel, so that the LED groups 2 and 3 are connected in parallel. When the same PWM signal as the input PWM signal is input, the luminance level of each LED of the LED groups 2 and 3 connected in series can be set to the same level as the luminance level at the time of parallel connection.

<Second embodiment>
FIG. 2 shows an LED drive circuit according to the second embodiment. In the present embodiment, in the LED drive circuit of FIG. 1, a stabilized power supply circuit 11 is newly provided, and a first voltage attenuation circuit 12 is inserted and connected between the voltage input terminal 1 and the stabilized power supply circuit 11, A second voltage attenuation circuit 13 is inserted and connected between the voltage input terminal 1 and the LED groups 2 and 3.

  When the value of the input voltage VIN is not stable, the control circuit 5 and the drive circuit 6 are affected by the fluctuation of the input voltage VIN, and the LED groups 2 and 3 cannot realize a predetermined luminance. Therefore, in this embodiment, the stabilized power supply circuit 11 is provided, and the stabilized voltage VDD is generated and supplied here, so that the control circuit 5 and the drive circuit 6 are not affected by the fluctuation of the input voltage VIN. Like that. Further, the voltage attenuating circuit 12 is inserted and connected, so that the voltage applied to the stabilized power supply circuit 11 is lowered so that the elements constituting the stabilized power supply circuit 11 do not have insufficient withstand voltage. Further, the voltage attenuating circuit 13 is inserted and connected, so that the voltage applied between the both ends of the switch circuits 7 and 8 is lowered, so that the elements constituting the switch circuits 7 and 8 do not have insufficient withstand voltage.

For example, when the LED groups 2 and 3 are connected in parallel, the voltage applied to the switch circuits 7 and 8 is that the input voltage is VIN and the output voltage of the stabilized power supply circuit 11 is VDD.
High voltage side voltage of switch circuit 7 = VIN−n · Vf
The low voltage of the switch circuit 7 is lower than VDD, and the desired voltage at which the first driver 61 can operate. The high voltage of the switch circuit 8 = VIN−n · Vf
The low-voltage side voltage of the switch circuit 8 is lower than VDD, and becomes a desired voltage at which the second drive unit 62 can operate.

On the other hand, when the LED groups 2 and 3 are connected in series, the voltage applied to the switch circuit 8 is
High voltage side voltage of the switch circuit 8 = VIN-2n · Vf
The low-voltage side voltage of the switch circuit 8 is lower than VDD, and becomes a desired voltage at which the second drive unit 62 can operate.

  Accordingly, when the input voltage VIN is high or when the forward voltage Vf of the LED is small, a large withstand voltage is particularly required for the switch circuits 7 and 8, but the voltage attenuation circuit 13 is inserted as described above. Thus, the breakdown voltage required for the switch circuits 7 and 8 can be reduced.

<Third embodiment>
FIG. 3 shows an LED driving circuit of the third embodiment. In this embodiment, an activation circuit 14 and a voltage application circuit 15 are added to the LED drive circuit of FIG.

  When the LED groups 2 and 3 are used in series connection, the switch circuit 9 is controlled to be on, but the voltage applied to the switch circuit 9 and the LED group 3 when the input voltage VIN rises (starts up). Is undefined. At this indefinite time, the switch circuit 9 may be fixed to a certain state and become inoperable. In addition, when the low voltage side voltage of the LED group 2 is supplied as the high voltage side voltage of the LED group 3, a large voltage is applied across the switch circuit 9.

  Therefore, by supplying a desired voltage to the switch circuit 9 at the time of startup, the high voltage side of the LED group 3 is connected to the low voltage side of the LED group 2, and the desired voltage is set as the high voltage side voltage of the LED group 3 from the switch circuit 9. To prevent voltage instability and sticking. Further, the supply voltage from the switch circuit 9 to the LED group 3 is a voltage that takes into consideration the forward voltage Vf and the dynamic range of the LED groups 2 and 3.

<Fourth embodiment>
FIG. 4 shows an LED driving circuit of the fourth embodiment. In this embodiment, a reverse current prevention circuit 16 is inserted in series with the switch circuit 9 in the first embodiment.

  When the LED groups 2 and 3 are connected in series, the voltage of the switch circuit 9 on the LED group 2 side is high, the voltage on the LED group 3 side is low, and the reverse voltage is not obtained. However, when connected in parallel, the voltage on the LED group 3 side of the switch circuit 9 is high, the voltage on the LED group 2 side is low, a reverse voltage is applied to the switch circuit 9, and the current flows in the reverse direction. Deterioration of the element may occur.

  In order to prevent this, a reverse current prevention circuit 16 is inserted. Note that the same effect can be obtained even if the reverse current prevention circuit 16 is inserted between the switch circuit 9 and the LED group 3.

<Fifth embodiment>
FIG. 5 shows an LED drive circuit of the fifth embodiment. In the present embodiment, a second control circuit 18 connected to the external control terminal 17 and controlling the control circuit 5 and the drive circuit 6 is added to the embodiment of FIG.

  In this embodiment, when the control circuit 18 receives a control signal input from the outside to the external control terminal 17, the switch circuit 52 of the control circuit 5 is related to the detection result of the voltage detection circuit 51 by the control circuit 18. Without being controlled, the series connection or parallel connection of the LED groups 2 and 3 can be switched, or the current values of the drive units 61 and 62 of the drive circuit 6 can be switched.

<Sixth embodiment>
FIG. 6 shows an LED drive circuit according to the sixth embodiment. In this embodiment, the time adjustment circuit 19 is inserted on the output side of the switch control circuit 52 of the control circuit 5 in the embodiment of FIG.

  When the switch circuits 7 to 10 are switched and controlled by the switch control circuit 52, there may be a time region in which the LED groups 2 and 3 are neither in series nor in parallel, or a time region in which series / parallel occurs simultaneously. Therefore, when the LED groups 2 and 3 are switched in series / parallel by the switch control circuit 52, a time difference is provided in the switching when the switch circuits 7 to 10 are switched by the time adjustment circuit 19, and the above-described series is provided. Avoid the occurrence of a time domain that is neither / parallel nor a time domain where serial / parallel occurs simultaneously. By the time adjustment circuit 19, for example, the switch circuits 7 and 10 are always turned on / off at the same time, and the switch circuit 9 is turned off / on, that is, synchronized with the reverse operation. The switch 8 may be always turned on.

<Seventh embodiment>
FIG. 7 shows an LED drive circuit of the seventh embodiment. In this embodiment, the reverse connection prevention circuit 20 is inserted and connected to the voltage input terminal 1 in the embodiment of FIG.

  The LED drive circuit that realizes series connection or parallel connection of the LED groups 2 and 3 can be realized with a small number of elements, and the board size of a printed circuit board or the like for constructing the circuit becomes small, making it difficult to visually recognize the board orientation. . In such a case, reverse connection of the power supply line is likely to occur during assembly work, and if this reverse connection occurs, there is a possibility of circuit destruction during operation. Therefore, the reverse connection prevention circuit 20 is inserted and connected to the voltage input terminal 1 to prevent circuit destruction even when the reverse connection of the power supply line occurs.

<Eighth embodiment>
FIG. 8 shows an LED drive circuit of the eighth embodiment. This embodiment is a specific circuit having all of the configurations described with reference to FIGS. D1 is a diode, R1 to R19 are resistors, CP1 and CP2 are comparators, Q1 to Q6 are transistors, and C1 is a capacitor.

  The reverse connection prevention circuit 10 is composed of a diode D1, the voltage attenuation circuit 12 is composed of a resistor R1, and the voltage attenuation circuit 13 is composed of a resistor R2.

  The voltage detection circuit 51 of the control circuit 5 includes a voltage Va obtained by dividing the reference voltage Vref obtained by dividing the output voltage VDD of the stabilized power supply circuit 11 by resistors R3 and R4 and the input voltage VIN by resistors R5 and R6. Are compared by a comparator CP1. When Va ≧ Vref, the output voltage V1 of the comparator CP1 is “H”, and when Va <Vref, the output voltage V1 of the comparator CP1 is “L”.

  The switch control circuit 52 is configured to compare the reference voltage Vref and the output voltage V1 of the comparator CP1 by the comparator CP2. When V1 = “H”, the output voltage V2 of the comparator CP2 is V2 = “L”, and when V1 = “L”, V2 = “H”.

  The switch circuit 7 includes a transistor Q1, the switch circuit 8 includes a transistor Q2, the switch circuit 9 includes a transistor Q3, and the switch circuit 10 includes a transistor Q4.

  When the input voltage VIN is low and the voltage V1 = “L” (voltage V2 = “H”), the transistor Q1 is turned on, and the transistor Q6 is turned on to turn on the transistor Q4. The transistor Q3 is turned off when the transistor Q5 is turned off. The transistor Q2 is turned on by a base voltage obtained by dividing the stabilization voltage VDD by the resistors R18 and R19. Thus, at this time, the LED groups 2 and 3 are connected in parallel.

  On the other hand, when the input voltage VIN is high and the voltage V1 = “H” (when the voltage V2 = “L”), the transistor Q1 is turned off, and the transistor Q6 is turned off to turn off the transistor Q4. The transistor Q3 is turned on when the transistor Q5 is turned on. The transistor Q2 is turned on by a base voltage obtained by dividing the stabilization voltage VDD by the resistors R18 and R19. From the above, at this time, the LED groups 2 and 3 are connected in series.

  The starting circuit 14 and the voltage applying circuit 15 described with reference to FIG. 3 and the backflow prevention circuit 16 described with reference to FIG. 4 include a transistor Q3 and resistors R15 and R16. When the input voltage VIN is high at start-up and the output voltage V1 of the comparator CP1 is “H”, the transistor Q5 is turned on and a voltage obtained by dividing the input voltage VIN by the resistors R15 and R16 is applied to the base of the transistor Q3. Let For this reason, the transistor Q3 is reliably turned on even when it is activated. Since the transistor Q3 is a PNP type in which the emitter is connected to the low voltage side of the LED group 2 and the collector is connected to the high voltage side of the LED group 3, even when the LED groups 2 and 3 are connected in parallel, the LED group 3 No back flow from the high voltage side to the low voltage side of the LED group 2 occurs.

<Other examples>
8 does not include the control circuit 18 of FIG. 5 or the time adjustment circuit 19 of FIG. 6, it goes without saying that it can of course be included. That is, an LED drive circuit including all the configurations described in the first to seventh embodiments can be configured.

  1: voltage input terminal, 2, 3: LED group, 4: PWM terminal, 5: first control circuit, 51: voltage detection circuit, 52: switch control circuit, 6: drive circuit, 61: first drive unit 62: second drive unit, 7-10: switch circuit, 11: stabilized power supply circuit, 12, 13: voltage attenuation circuit, 14: start-up circuit, 15: voltage application circuit, 16: backflow prevention circuit, 17: External control terminal, 18: second control circuit, 19: time adjustment circuit, 20: reverse connection prevention circuit

Claims (6)

a first LED group consisting of a series circuit of n (n is an integer of 1 or more) LEDs, the high voltage side of which is connected to the voltage input terminal; a first drive unit for supplying a first drive current; A first switch circuit connecting the low voltage side of the first LED group and the first drive unit, a second LED group comprising a series circuit of n LEDs, and a high level of the second LED group A second switch circuit that connects the voltage side and the voltage input terminal; a second drive unit that supplies the same drive current as the first drive current; a low voltage side of the second LED group; A third switch circuit that connects two driving units, a fourth switch circuit that connects a low voltage side of the first LED group and a high voltage side of the second LED group , and a voltage input terminal A first for turning on / off the first, second, third and fourth switch circuits in accordance with a voltage; And a control circuit,
The first control circuit turns on the first, second and third switch circuits and turns off the fourth switch circuit when the voltage at the voltage input terminal is low, and turns off the first LED. A series connection circuit of a group and the first drive unit, a series connection circuit of the second LED group and the second drive unit are connected in parallel to the voltage input terminal, and the voltage of the voltage input terminal is high When the first and second switch circuits are turned off and the third and fourth switch circuits are turned on, the first and second LED groups and the second drive unit are connected in series . Operate to connect a circuit to the voltage input terminal;
The first switch circuit has a collector connected to the low voltage side of the first LED group, an emitter connected to the first driver, and a constant voltage applied to the base when turned on. Of NPN transistors,
In the third switch circuit, a collector is connected to the low voltage side of the second LED group, an emitter is connected to the second driving unit, and a constant voltage is applied to the base when turned on. Composed of NPN transistors
An LED drive circuit characterized by that.
The LED driving circuit according to claim 1,
A voltage stabilization circuit for stabilizing the voltage of the voltage input terminal ;
The voltage stabilization circuit supplies a stabilization voltage to the first and second drive units, and distributes the stabilization voltage to the base of the second NPN transistor when the third switch circuit is on. An LED driving circuit characterized by supplying a pressed voltage . The LED drive circuit according to claim 1 or 2,
The fourth switch circuit includes a PNP transistor having an emitter connected to the low voltage side of the first LED group and a collector connected to the high voltage side of the second LED group,
The LED driving circuit, wherein when the first LED group and the second LED group are connected in series, a voltage obtained by dividing the voltage of the voltage input terminal is applied to the base of the PNP transistor. In the LED drive circuit according to claim 1, 2, or 3,
A second control circuit connected to the external control terminal;
The second control circuit switches on / off of the first, second, third and fourth switch circuits and the first and second driving according to a control signal input from the external control terminal. An LED drive circuit that controls a value of the first drive current of the unit. In the LED drive circuit according to claim 1, 2, 3, or 4,
An LED drive characterized in that a time adjustment circuit for avoiding connection other than one of the parallel connection and the series connection of the first and second LED groups is provided on the output side of the first control circuit. circuit. In the LED drive circuit according to claim 1, 2, 3, 4 or 5,
An LED drive circuit comprising a reverse connection prevention circuit connected to the voltage input terminal.

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