JPH04303884A - Led lighting circuit - Google Patents

Abstract

PURPOSE:To suppress the increment of the current when the LED elements of a large number of LED driving circuits are lit by connecting plural pairs of LED group driving circuits to a power source via a common current adjusting resistor. CONSTITUTION:In a LED lighting circuit in which the plural pairs of LED group driving circuits 3 consisting of plural LED elements 1R. 1G, and 1B and a switch circuit 2 which controls to put on/off those LED elements 1R, 1G, and 1B simultaneously are connected to the power source 4, respectively, the plural LED group driving circuits 3 are connected in parallel with each other. At parallel circuits consisting of the plural LED group driving circuit 3, a terminal on one side is connected to the pole on one side of the power source 4, and also, another terminal on the other side is connected to the pole on the other side of the power source 4 via the current adjusting resistor RC. Therefore, it follows that the current on each LED group driving circuit 3 flows via the common current adjusting resistor, and a current value can be suppressed.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides a method for displaying a large number of LEDs on a substrate.
In an LED display device that displays characters, figures, etc. by arranging elements, an LED for controlling the lighting of each LED element.
Regarding lighting circuits.

0002

2. Description of the Related Art LED display devices that display characters and figures by controlling the lighting of a large number of LED elements arranged on a substrate have been used in various fields. When displaying such a display in color on a large screen, for example, as shown in FIG.
RGB (red, green, and blue) three primary color LED elements 1R,
A plurality of 1G and 1B are arranged for each color.

A conventional LED lighting circuit in each light emitting region 10 of the LED display device includes a plurality of LED elements 1R, 1G, 1B for each color, as shown in FIG.
are connected in series with the switch circuit 2 to configure the LED group drive circuit 3 for each luminescent color, and these L
The ED group drive circuit 3 is connected in parallel to the power supply 4. As a result, by controlling the switch circuit 2 of each LED group drive circuit 3, the LED elements 1 of the same color are lit at the same time.
Since the brightness of 0 can be increased and the LED elements 1 of different colors can be lit individually, it is possible to arbitrarily change the lighting color of each light emitting area 10. Note that the LEDs in each LED group drive circuit 3
Current stabilizing resistors RR, RG, RB are provided between the D elements 1R, 1G, 1B and the switch circuit 2, respectively.
are connected, and these LED elements 1R, 1G, 1B
The aim is to stabilize the current flowing through the

0004

[Problems to be Solved by the Invention] However, in such an LED lighting circuit, any one of the LED group driving circuits 3
When the switch circuit 2 is turned on and only the LED elements 1 of one color are lit, and when the two LED group drive circuits 3
When lighting in a mixed color of two types of colors,
There are three ways to use all three types of white lighting. Compared to the case where only one type of color LED element 1 is lit, when all three types are lit, this L
A current three times the sum of the current for each LED group driving circuit 3 flows through the ED lighting circuit, and the ratio of the amount of heat generated by this is proportional to the square of the current, so it reaches nine times as much.

Therefore, if the conventional LED lighting circuit is set so that it can supply a current that provides sufficient brightness when only the LED elements 1 of one color are lit, the
Since the amount of heat generated when all types of LED elements 1 are turned on is too large, a structure is required to efficiently dissipate this heat and suppress the temperature rise, which increases design constraints and increases device efficiency. A problem has arisen that leads to an increase in costs.

[0006]

[Means for Solving the Problems] In order to solve the above problems, the present invention further includes a plurality of LED group drive circuits each including a plurality of LED elements and a switch circuit that simultaneously controls turning on or turning off these LED elements. In the LED lighting circuit, each set of which is connected to a power source, a plurality of sets of LED group drive circuits are connected to the power source via a common current adjustment resistor.

[0007]

[Operation] When each of the above LED group drive circuits is connected in parallel to one power source or independently connected to each power source, the LED group drive circuit that lights up the LED elements by the switch circuit. The current will also increase in proportion to the number. However, according to the LED lighting circuit configured as described above, the current of each LED group drive circuit flows through a common current adjustment resistor. Therefore, compared to when current flows only through one LED group drive circuit, when current flows through two LED group drive circuits with the same characteristics, the current commonly connected to these LED group drive circuits increases. The adjustment resistor prevents the current value from doubling, but suppresses it to a smaller value. Further, even when current flows simultaneously to three or more LED group drive circuits, the current value is similarly suppressed to a value smaller than the value proportional to the number of LED group drive circuits.

However, if this current is suppressed too much, when many LED elements of the LED group drive circuit turn on,
The current flowing through each LED group drive circuit becomes smaller, and the LED
The brightness of the element decreases too much. Therefore, the rate of increase in current value due to the LED lighting circuit of the present invention is, for example, when three LED group drive circuits are connected to a power supply via a common current adjustment resistor, one LED group drive circuit LE of
The current that flows when only the D element is lit is 100%, and the current that flows when two LED group drive circuits are used is 14%.
0% to 160% (70% to 80% for each LED group drive circuit)
%), and the current flowing in all LED group drive circuits is 150% to 210% (50% to each LED group drive circuit).
~70%) is appropriate.

As a result, according to the LED lighting circuit of the present invention, when lighting the LED elements of only one LED group drive circuit, while supplying a current that can cause the LED elements to emit light with sufficient brightness,
Even when a large number of LED group drive circuits turn on the LEDs at the same time, the total amount of current can be suppressed to prevent the amount of heat generated from becoming too large.

0010

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows one embodiment of the present invention, and is a circuit diagram of an LED lighting circuit. Note that the same numbers are added to the structural members having the same functions as those of the conventional example shown in FIG. 4.

In this embodiment, three color LED elements 1R of each light emitting area 10 in the LED display device shown in FIG.
, 1G, 1B will be described. The plurality of red LED elements 1R are each connected in series, and are also connected in series with the current stabilizing resistor RR and the switch circuit 2, forming an LED group drive circuit 3 that lights up in red. Further, the plurality of green LED elements 1G are each connected in series, and are also connected in series with a current stabilizing resistor RG and a switch circuit 2 different from the above, and an LED group drive circuit 3 for lighting green. It consists of Additionally, multiple blue LEDs
The elements 1B are also connected in series, and are also connected in series with the current stabilizing resistor RG and another switch circuit 2, forming an LED group drive circuit 3 that lights up in blue.

The switch circuit 2 of each of the LED group drive circuits 3 may use a contact relay or the like, but in reality, it is constituted by a non-contact switch circuit using a switching transistor, an IC, or the like. In addition, each current stabilizing resistor RR, RG, RB is connected to each LED.
This is to alleviate variations in the characteristics of the elements 1R, 1G, and 1B and stabilize the current.

The above three types of LED group drive circuits 3 are connected in parallel to each other. Furthermore, in the parallel circuit formed by these LED group drive circuits 3, one terminal is connected to one pole of the power supply 4, and the other terminal is connected to the current adjustment resistor RC.
It is connected to the other pole of the power supply 4 via.

In the LED lighting circuit having the above configuration, the switch circuit 2 of each LED group drive circuit 3 is connected to a computer (not shown).
The on/off is controlled by the LED elements 1 of the same color are turned on or off at the same time, and the LED elements 1R of different colors are turned on or off at the same time.
1G and 1B are individually controlled to turn on or off. Therefore, by controlling the lighting of the light emitting regions 10 forming each dot using such an LED lighting circuit, it becomes possible to display characters, figures, etc. in color on a large screen.

Further, for example, if the voltage of the power supply 4 in the LED lighting circuit of the above configuration is 20V and the current adjustment resistor RC is 300Ω, the forward equivalent of the series circuit of the LED elements 1R, 1G, 1B in each LED group drive circuit 3 is calculated as follows. Internal resistance (internal resistance when considered as a passive element) is 400Ω
, each current stabilizing resistor RR, RG, RB is 300Ω.
Then, by controlling the switch circuit 2, any one of L
When only the LED element 1 of the ED group drive circuit 3 is turned on, the total combined resistance is 1 kΩ, so a current of 20 mA flows. However, when the LED elements 1 of any two LED group drive circuits 3 are turned on, the total combined resistance becomes 65
Since it is 0Ω, the current flowing through the entire LED lighting circuit is 3
The current is 0.8 mA, which is an increase of only about 1.5 times the above 20 mA. In addition, the LED elements 1R of all the LED group drive circuits 3,
Even when 1G and 1B are lit, the total combined resistance is about 533Ω, so the current flowing through the entire LED lighting circuit is about 37.5mA, which is an increase of slightly less than 1.9 times the above 20mA. Therefore, 1 in this LED lighting circuit.
The ratio of the amount of heat generated when the three colors are lit is less than four times that of the previous one, making it possible to design a device with more leeway in terms of heat countermeasures.

It should be noted that the current flowing through each LED group drive circuit 3 during each of the above lighting states is 20 mA and 1 mA, respectively.
It gradually decreases to 5.4mA and 12.5mA. However, since the number of LED elements 1 that are lit increases, there is no fear that the brightness of the light emitting area 10 as a whole will decrease.

FIG. 2 shows another embodiment of the invention. It should be noted that here as well, the same numbers are added to the constituent members having the same functions as those of the conventional example shown in FIG. 4.

In this embodiment, the LED elements 1 of the same color in each LED group drive circuit 3 are further divided into two groups, each of which is connected in series with current stabilizing resistors RR, RG, and RB. LED elements 1 are connected in parallel. However, in this case as well, the parallel circuits of the two groups of LED elements 1 are connected in series to the switch circuits 2 of the respective LED group drive circuits 3. The lighting will be controlled all at once. The three types of LED group drive circuits 3 configured in this way are also connected in parallel to each other and connected to the power source 4 via the current adjustment resistor RC, similarly to the embodiment shown in FIG. ing.

As a result, also in the LED lighting circuit of this embodiment, the LEDs lit by the LED group drive circuit 3
It becomes possible to suppress an increase in current when the types of elements 1R, 1G, and 1B are increased.

[0021] In each of the above embodiments, one power supply 4 is used.
Although the case where three types of LED group drive circuits 3 are connected is shown in FIG. 1, the present invention can be implemented in the same way with an LED lighting circuit in which each LED group drive circuit 3 is connected to a different power source. However, if you use separate power supplies like this, for example, you can use only the grounding power supply in common.
It is necessary to connect the ground side terminals of each LED group drive circuit 3 to each other and to connect them to the ground via the current adjustment resistor RC.

[0022]

Effects of the Invention As is clear from the above description, the LED lighting circuit of the present invention can
Even when the elements are turned on, the increase in current can be suppressed by the current adjustment resistor commonly connected to these LED group drive circuits, reducing the amount of heat generated and reducing the cost of the device. This has the effect of increasing the degree of freedom in design.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the present invention, in which an LED
It is a circuit diagram of a lighting circuit.

FIG. 2 shows another embodiment of the present invention, in which LE
It is a circuit diagram of a D lighting circuit.

FIG. 3 is a diagram showing the arrangement of LED elements in a light emitting region constituting each dot of an LED display device.

FIG. 4 is a circuit diagram of an LED lighting circuit, showing a conventional example.

[Explanation of symbols]

1 LED element 2 Switch circuit 3 LED group drive circuit 4 Power supply RC current adjustment resistance

Claims (1)

[Claims] 1. An LED lighting circuit comprising a plurality of LED group drive circuits each connected to a power source, each of which includes a plurality of LED elements and a switch circuit that simultaneously controls lighting or extinguishment of these LED elements. An LED lighting circuit characterized in that a drive circuit is connected to a power source via a common current adjustment resistor.