JP2013004586A - Led drive circuit and method for driving led - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED drive circuit capable of reducing the number of components in the LED drive circuit, while giving less influences to the whole when trouble occurs in LEDs, and a method for driving the same.SOLUTION: An LED drive circuit comprises: LED rows in which a plurality of LEDs and at least of one resistance are connected each other in series; LED units in which LED rows are connected each other in parallel; an LED block in which a plurality of LED units are connected each other in a latticed pattern and in series; an LED drive part for supplying current to drive the LED block; and a functional part for setting current flowing through the LED drive part to a predetermined current value.

Description

  The present invention relates to a driving circuit and a driving method of a light emitting diode (hereinafter referred to as “LED”).

  With the advent of pseudo-white LEDs and the improvement in luminous efficiency accompanying technological advances, various attempts have been made to commercialize lighting devices using LEDs as light sources. By using an LED as a light source, it is possible to achieve higher energy efficiency than incandescent bulbs that have been frequently used as a conventional light source, and further, the device can be reduced in size, weight, and life.

  Unlike a voltage-driven incandescent bulb, the brightness and color tone of an LED are adjusted by controlling the current flowing through the LED. Therefore, a drive circuit unique to LEDs is required, which is different from the drive circuit of an illumination device that uses an incandescent bulb as a light source. As a general LED drive circuit, a resistance type drive circuit is known in which a plurality of series circuits in which a plurality of LEDs and current limiting resistors are connected in series are connected in parallel. In this resistance type driving circuit, the value of the current limiting resistance is set so that the rated current flows through the LEDs in the series circuit.

  In addition, a circuit for driving LEDs at a constant current by connecting a plurality of LEDs and a constant current circuit in series is also known. Patent Document 1 discloses an example of a drive circuit using a constant current circuit. The drive circuit of Patent Document 1 is configured by connecting a plurality of LEDs and a plurality of LED units connected in series with a constant current driver for causing a constant current to flow through the LEDs.

JP 2004-319583 A

  Although there are various merits by using an LED as a light source, since an LED is a semiconductor, there are individual differences in its electrical and optical characteristics. Therefore, if only the quality of the manufactured product is determined and used as it is, differences in brightness and color tone will occur between individual products. Specifically, since the forward voltage of the LED (hereinafter referred to as “Vf”) varies, the current flowing through the LEDs in the series circuit varies in the resistance-type driving circuit, and the luminance varies depending on the column. Differences may occur, and in some cases, the drive circuit itself may not operate. In order to suppress such variations, it may be possible to strictly select the characteristics of the LEDs to be used. However, if such a strict selection is performed, the productivity is lowered and the product cost is significantly increased. There is a risk of inviting.

  In addition, as described in Patent Document 1, when the LEDs are driven for each column using a constant current circuit, the above-described variations are almost no problem, but there are as many constant current circuits as the number of LED columns. Necessary. In particular, in an LED lighting device using a large number of LEDs, an increase in the number of components accompanying an increase in the number of LED rows is remarkable, and there is a possibility that the product cost will be significantly increased as in the case described above. In addition, when a failure occurs in any of the LEDs in the row, all the LEDs in the row are not turned on, which affects the luminance of the lighting device. If the number of LEDs in series is increased in order to reduce the number of LED columns (that is, to reduce the number of constant current circuits), the number of affected LEDs also increases.

  The present invention has been made in view of the above problems, and realizes a reduction in the number of components in an LED drive circuit and an LED drive circuit capable of suppressing the influence on the whole when a failure occurs in the LED. And a driving method.

  In order to solve the above problems, according to the present invention, an LED array in which a plurality of LEDs and at least one resistor are connected in series, an LED unit in which a plurality of LED arrays are connected in parallel, and a plurality of LED units are connected in series and parallel in a grid pattern An LED drive circuit comprising: the LED block, an LED drive unit that supplies a current for driving the LED block, and a functional unit that sets a current flowing through the LED drive unit to a predetermined current value Is provided.

  Moreover, the LED drive circuit of this invention is good also as a structure provided with two or more LED drive parts and functional parts.

  Further, the resistance value in the LED drive circuit of the present invention may be set based on the difference in forward voltage due to the individual difference of the plurality of LEDs in the LED array so as to suppress the difference in current flowing in the plurality of LED arrays. .

  Furthermore, according to the present invention, an LED block in which a plurality of LEDs and LED arrays in which at least one resistor are connected in series is connected in parallel is further connected in series and parallel to form a LED block; An LED driving method is provided, including supplying a current for driving the LED and setting a current flowing in the LED driving unit to a predetermined current value.

In the driving circuit of the present invention, the following effects can be obtained.
(1) Even when some failure occurs in one of the plurality of LED units, the influence on the other LED units can be suppressed to a low level, and a device with high fault tolerance can be realized.
(2) Since it becomes possible to suppress variations in the brightness of LEDs without strictly selecting the characteristics of the LEDs to be used, it is possible to contribute to the improvement of productivity and to prevent an increase in product costs. Become.
(3) Since a plurality of LED units connected in series and parallel are driven as one LED block, the number of circuits for driving the LEDs can be reduced, and the product cost can be reduced.
(4) The system can be easily expanded by connecting an arbitrary number of LED units and their drive circuits in series, in parallel, or in series-parallel.

It is a circuit diagram which shows the LED drive circuit in embodiment of this invention. It is a circuit diagram which shows the application example of the LED drive circuit in embodiment.

  Hereinafter, an LED drive circuit according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit diagram showing an LED drive circuit 100 according to an embodiment of the present invention. As shown in FIG. 1, the LED drive circuit 100 in the present embodiment includes a plurality of LED units 101 to 12n including a plurality of LEDs 1, an LED drive unit 20 that supplies current for driving the LED units 101 to 12n, And a current control unit 30 for setting a current flowing through the LED driving unit 20 to a predetermined value. Further, VD shown in FIG. 1 is an LED power source, and VE is a drive unit power source.

In this embodiment, a feedback type constant current circuit is used as the current control unit 30. Specifically, the current control unit 30 includes a reference voltage setting unit 35 for setting a current value. The reference voltage setting unit 35 includes a variable resistor Rv, and can change the reference voltage by changing the value of the variable resistor Rv. That is, the current flowing through the LED units 101 to 12n is set to a desired value by the variable resistor Rv. The current control unit 30 includes an amplifier 31. The amplifier 31 receives the reference voltage set by the reference voltage setting unit 35 as one input, and the current value of the LED drive unit 20 connected to the LED units 101 to 12n. Is input to the other through a feedback circuit including feedback resistors Rf ₁ and Rf ₂ .

  The LED driving unit 20 includes a driving transistor Tr, and an emitter resistance Re and a base resistance Rb are connected to an emitter and a base of the driving transistor Tr, respectively. Information on the current value flowing through the LED units 101 to 12n is detected as a voltage generated in the emitter resistor Re. And the electric current which flows into LED unit 101-12n is controlled by inputting the detected voltage value into the amplifier 31 via a feedback circuit.

  Each of the LED units 101 to 12n is configured by connecting a plurality of LEDs 1 and a plurality of LEDs 1 connected in series to each other and a single resistor R10. The number of LEDs 1 in series in LED array 2 and the number of LEDs 2 in parallel may be two or more, and are appropriately set based on the luminance required for the apparatus and the number of LEDs.

  As described above, since the Vf (forward voltage) of the LED varies depending on individual differences, the total value of Vf is the smallest when constant current driving is performed by simply connecting LEDs in series and parallel. Current concentrates on the LED strings. As a result, only some of the LED rows are lit brightly, while some of the LED rows are hardly illuminated. In order to prevent such a problem, in this embodiment, by inserting the resistor R <b> 10 into each LED row 2, the occurrence of a difference in current flowing through each LED row 2 is suppressed.

  The value of the resistor R10 of this embodiment is calculated as follows. First, when n stages of LEDs are connected in series, a voltage difference of (Vfmax−Vfmin) × n at the maximum occurs in each LED row 2. Here, Vfmax is the maximum value of Vf of LED1, and Vfmin is the minimum value of Vf of LED. Therefore, by setting the voltage drop value of the resistor R10 connected in series to be k times the voltage difference, the variation in Vf can be absorbed. Here, it is desirable to set k to a value of at least 3 or more, and by making it larger (for example, around 10), variations can be almost ignored. However, since the loss of voltage due to the resistor R10 is increased by setting k large, it is practical to set k to a value around 5 in consideration of the balance between variation absorption and loss.

  In the present embodiment, as shown in FIG. 1, the LED units 101 to 12n are connected in series and parallel in a lattice shape, and are driven by the LED driving unit 20 as one LED block. Specifically, first, a row in which a plurality of LED units 101 to 10n are connected in series, a row in which a plurality of LED units 111 to 11n are connected in series, and a row in which a plurality of LED units 121 to 12n are connected in series. Are connected in parallel, and LED units (for example, LED units 102, 112, and 122) in adjacent rows are further connected. Thereby, the connection point of each LED unit 101-12n is arrange | positioned at a grid | lattice form.

  The number of LED units in the LED drive circuit 100 can be set as appropriate based on the brightness required for the device and the number of LEDs. However, increasing the number of LED units increases the power supply voltage value. The power supply voltage value may be set to be a predetermined value or less (for example, 48 V or less). Moreover, in this embodiment, since the dispersion | variation in Vf of LED1 is absorbed by resistance R10 as mentioned above, an electric current flows stably through LED1 in each LED unit 101-12n. Therefore, there is almost no potential difference between the LED units 101 to 10n, the LED units 111 to 11n, and the LED units 121 to 12n, and the plurality of LED units 101 to 12n are driven in a balanced manner. The

  Here, in the case where the plurality of LED units 101 to 12n are simply connected in series and driven, if any one of the LED units connected in series has a failure such as a broken wiring on the substrate, the effect Extends to all the LED units connected in series, and the LEDs in all the LED units will not light up. On the other hand, in this embodiment, such a problem can be prevented by connecting a plurality of LED units 101 to 12n in series and parallel in a lattice shape. For example, when a failure occurs in the LED unit 112, the current supplied from the LED drive unit 20 is shunted to the LED units 102 and 122 and supplied to the LED unit 111 via the LED units 102 and 122. Thus, in this embodiment, since the influence on LED units other than the LED unit in which a failure has occurred can be suppressed, the fault tolerance and reliability of the apparatus are improved.

  Further, in each LED unit 101 to 12n, even when a failure occurs in any one LED in the LED row, the LEDs included in the LED row other than the LED row to which the failed LED is connected are faulty. It is also possible to continue lighting without being affected by the. Furthermore, since the plurality of LED units 101 to 12n are driven by one LED driving unit 20, the number of circuits for driving can be reduced as compared with the case where constant current driving is performed for each column. Further, by absorbing the variation in Vf of the LED 1 by the resistor R10, it is possible to suppress the difference in the current flowing through each LED row 2 and to suppress the variation in brightness. Moreover, since the variation in Vf of the LED 1 can be absorbed by the resistor R10, it is not necessary to strictly select the LEDs in advance.

  Furthermore, according to the present invention, it is possible to drive a large number of LEDs stably and with reduced current variation in a single LED unit. Therefore, even when a plurality of LED units are connected in series, the LED units can be driven in a stable manner and with reduced variations, as in the case of a single LED unit. As a result, the system can be easily expanded by arbitrarily increasing the number of LED units connected.

  In addition, the present invention is not limited to the circuit configuration shown in FIG. 1, and a plurality of LED units 101 to 12n are connected in parallel as in the LED driving circuit 110 shown in FIG. It is also possible to drive with the drive unit 20 and the current control unit 30. By setting it as such a structure, the electric current supplied to LED unit 101-12n can be increased, and it becomes possible to drive more LED units. Furthermore, even when any of the LED driving units 20 or the current control unit 30 fails, the LED units 101 to 12n can be continuously driven by the other LED driving unit 20 and the current control unit 30. Improves fault tolerance.

  The above is the description of the exemplary embodiments of the present invention. Specific aspects of the embodiments of the present invention are not limited to those described above, and can be arbitrarily changed within the scope of the technical idea expressed by the description of the scope of claims. For example, in the above embodiment, a feedback type constant current circuit is used as the current control unit 30, but the present invention is not limited to this, and a constant voltage circuit is used instead of the constant current circuit, or other known These circuits can be used. In the above embodiment, one resistor R10 is connected in series in the LED array 2, but two or more resistors R10 may be connected in series or in parallel.

1 LED
2 LED row R10 Resistance 20 LED drive unit 30 Current control unit 31 Amplifier 35 Reference voltage setting unit 100 LED drive circuits 101 to 12n LED unit

Claims (4)

An LED string in which a plurality of LEDs and at least one resistor are connected in series;
An LED unit in which a plurality of the LED rows are connected in parallel;
LED blocks in which the LED units are connected in series and parallel in a plurality of grids;
An LED driving unit for supplying a current for driving the LED block;
A functional unit for setting a current flowing through the LED driving unit to a predetermined current value;
An LED drive circuit comprising:   The LED drive circuit according to claim 1, comprising a plurality of the LED drive units and functional units.   The resistance value is set based on a difference in forward voltage due to an individual difference of the plurality of LEDs in the LED array so as to suppress a difference in current flowing in the plurality of LED arrays. 3. The LED driving circuit according to 1 or 2. LED blocks in which a plurality of LEDs and at least one resistor are connected in series, and LED units in which a plurality of LEDs are connected in parallel are further connected in series and parallel to form a LED block;
Supplying a current for driving the LED block;
Setting the current flowing through the LED driver to a predetermined current value;
An LED driving method including:

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