JPH0785377A - Light-emitting diode driving circuit - Google Patents

Abstract

PURPOSE:To realize the light-emitting diode driving circuit where the current consumption is minimized and all other light-emitting diode elements are not extinguished regardless of disconnection of one element at the time of simultaneously lighting plural light-emitting diode elements. CONSTITUTION:Seven light-emitting diode elements 12 connected is series are divided into a first light-emitting diode group A including three elements 12a to 12c and a second light-emitting diode group B including four elements 12d to 12g, and a first Zener diode 14 which has the breakdown voltage exceeding the total value of forward voltages of elements 12a to 12c is connected in parallel to the first light-emitting diode group A, and a second Zener diode 16 which has the breakdown voltage exceeding the total value of forward voltages of elements 12d to 12g is connected in parallel to the second light-emitting diode group B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode drive circuit, and more particularly to a light emitting diode drive circuit for driving a plurality of light emitting diode elements to light up simultaneously.

[0002]

2. Description of the Related Art In the case where a plurality of light emitting diode elements are integrated to form a light source such as a display lamp and these are simultaneously driven for lighting, as shown in FIG.
Connecting 12 in series is the simplest, and if connected in this way, the current consumption can be kept low. However, if all the light emitting diode elements 12 are connected in series, if any one of the light emitting diode elements 12 is broken due to a failure, the power supply to the other light emitting diode elements 12 is immediately cut off and the display lamp itself is turned off. Will be done. As a result, when the display lamp is used as, for example, an alarm lamp, it may be turned off due to a disconnection of the light emitting diode element 12 even though it should be turned on originally, or it is not turned on because it is not a state to be turned on. It is not clear from the outside whether or not this is maintained, and it cannot serve as an alarm lamp.

On the other hand, as shown in FIG. 4, when the respective light emitting diode elements 12 are connected in parallel, even if one of the light emitting diode elements 12 is broken, the light emitting diode element 12 is not turned on. Since the other light emitting diode elements 12 can be turned on, the above inconvenience does not occur. However, in this case, there is a problem in that it causes an increase in current consumption and an increase in heat generation amount, which in turn promotes a reduction in the life of the light emitting diode element 12 (deterioration of brightness).

Therefore, as a compromise between the above, as shown in FIG. 5, the required number of light emitting diode elements 12 are divided into a plurality of groups, and each light emitting diode element 12 is connected in series within each group, and each group is It can be connected in parallel.

[0005]

Certainly, by connecting a plurality of light emitting diode elements 12 in series and parallel as described above, even if the light emitting diode elements 12 belonging to any one of the groups are disconnected, the light emitting diode elements 12 belonging to another group are emitted. The diode element 12 can maintain lighting. Moreover, compared with the case where the individual light emitting diode elements 12 are connected in parallel, the current consumption can be suppressed low. However, all light emitting diode elements 12
In comparison with the case of connecting in series, the current consumption was still high, which was still unsatisfactory.

The present invention has been made in view of the above-mentioned problems of the conventional example, and an object thereof is to reduce the current consumption to a minimum when one of the light emitting diode elements is disconnected. Even if there is, it is to realize a light emitting diode drive circuit in which all the other light emitting diode elements are not turned off.

[0007]

In order to achieve the above object, a light emitting diode drive circuit according to the present invention comprises a plurality of light emitting diode elements connected in series, each including one or more light emitting diode elements. The light-emitting diode groups are divided into groups, and constant-voltage elements are connected in parallel for each light-emitting diode group, and the rated voltage of each constant-voltage element is calculated as the total forward voltage value of the light-emitting diode elements belonging to the light-emitting diode group. Configured to set the value to exceed.

[0008]

Since all the light emitting diode elements are connected in series, the current consumption can be kept low even when they are turned on at the same time. On the other hand, when any one of the light emitting diode elements belonging to each light emitting diode group is disconnected, the constant voltage element connected in parallel to the light emitting diode group operates and bypasses the current. Supply is maintained.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the illustrated embodiments. FIG. 1 is a circuit diagram showing a light emitting diode driving circuit according to the present invention. The light emitting diode driving circuit 10 has seven light emitting diode elements 12 connected in series. These light emitting diode elements 12 are divided into a first light emitting diode group A including three light emitting diode elements 12a to 12c and a second light emitting diode group B including four light emitting diode elements 12d to 12g. , A first Zener diode 14 is connected in parallel to the first light emitting diode group A, and a second Zener diode 16 is connected in parallel to the second light emitting diode group B. The light emitting diode drive circuit 10 is connected to an external power source through terminals 18a and 18b, and the power source is rectified by the bridge diode 20 and then supplied to the light emitting diode drive circuit 10. Reference numeral 22 is the first resistance (1.2 kΩ / 1 W), and 24 is the second resistance (1.2 kΩ / 1 W).
kΩ / 1 W) and 26 indicates a third resistance (400Ω / 1 W).

The rated voltage of the first Zener diode 14, that is, the breakdown voltage, is determined by the light emitting diode elements 12a to 12 belonging to the first light emitting diode group A.
It is set to a value exceeding the total value of the forward voltage of c. Further, the breakdown voltage of the second Zener diode 16 is also set to a value exceeding the total value of the forward voltages of the light emitting diode elements 12d to 12g belonging to the second light emitting diode group B. Here, each light emitting diode element 12 is
Although not shown in the figure, the forward voltage of each of the light emitting diode chips is about 9.5 V because it has a structure in which five light emitting diode chips are connected in series. Therefore, one having a breakdown voltage exceeding about 28.5V should be selected as the first Zener diode 14, and one having a breakdown voltage exceeding about 38V should be selected as the second Zener diode 16. In this embodiment, both the first Zener diode 14 and the second Zener diode 16 having a breakdown voltage of 47V are used.

However, in a normal driving state, 100V AC or DC power is supplied from the terminals 18a and 18b, and the first resistor 22, the second resistor 24, and the third resistor 26 are supplied.
When a predetermined DC voltage is applied to the light emitting diode driving circuit 10 via the bridge diode 20 and the bridge diode 20, the rated current (forward current) of each light emitting diode element 12 is 12 [m
DC current of [A] flows to the light emitting diode drive circuit 10,
The light emitting diode elements 12 are turned on at the same time. On the other hand, when any of the light emitting diode elements 12 in the first light emitting diode group A is disconnected, the first zener diode 14 is turned on and the second light emission is performed via the first zener diode 14. Power is supplied to the diode group B. On the contrary, when any of the light emitting diode elements 12 in the second group B is disconnected, the second Zener diode 16 is turned on and the power supply to the first light emitting diode group A is maintained.

In this embodiment, as described above, the forward current of each light emitting diode element 12 is normally about 12
A current of [mA] is designed to flow through the light emitting diode drive circuit 10. On the other hand, the light emitting diode element 12 in the first light emitting diode group A is disconnected and
When the Zener diode 14 of is turned on, about 6 [m
A] current flows, and when the light emitting diode element 12 in the second light emitting diode group B is disconnected and the second Zener diode 16 is turned on, a current of about 9 [mA] will flow. . As a result, the brightness of the light emitting diode element 12 which is maintained to be lit also decreases in accordance with the decrease in the current value, but since it is not completely turned off,
The abnormality can be detected from the outside. The upper limit of the breakdown voltage of the first Zener diode 14 and the second Zener diode 16 is such that the light emitting diode element 12 belonging to either the A or B light emitting diode group is disconnected under the given circuit conditions. Thus, when one of the Zener diodes is turned on, the light emitting diode elements 12 belonging to the remaining light emitting diode groups are regulated to a value that can supply a current that can barely light up.

FIG. 2 shows a display lamp 28 as an application example of the light emitting diode drive circuit 10. The display lamp 28 has seven light emitting diode elements 12 arranged on a tip light emitting surface 30, and each light emitting diode element 12 includes five light emitting diode chips connected in series. Each light emitting diode chip has one red light emitting diode chip 32a disposed in the central portion,
It is composed of four green light emitting diode chips 32b arranged around it, and when they emit light at the same time, yellowish white light similar to that of an incandescent light bulb is obtained. Further, since the convex lens 34 is fitted so as to cover the tip light emitting surface 30, the light from each light emitting diode element 12 is condensed by the convex lens 34. This indicator lamp 28 is intended to be used as a substitute for a conventional incandescent light bulb, and its base 36 is inserted into a socket hole of an instrument panel or the like (not shown) to connect the terminals 18a, 18b.
Connected to an external power source via.

The display lamp 28 has a body 38 in which a first Zener diode 14 and a second Zener diode 16 constituting the light emitting diode drive circuit 10, a bridge diode 20, a first resistor 22, and a second resistor 22 are provided. 2 resistance 24, 3rd
The resistors 26, etc. of the
Is divided into a first light emitting diode group A made up of three light emitting diode elements 12 and a second light emitting diode group B made up of four light emitting diode elements 12,
A first Zener diode 14 and a second Zener diode 16 are connected in parallel with each other. As a result, even if any of the light emitting diode elements 12 of the display lamp 28 is broken, the light emitting diode elements belonging to a group other than the light emitting diode group to which the light emitting diode element 12 belongs
The 12 can be maintained in a so-called semi-lighted state without being turned off.

In the above, the light emitting diode drive circuit
An example in which the seven light emitting diode elements 12a to 12g are divided into three and four light emitting diode groups A and B is shown as 10, but it is subdivided into more light emitting diode groups and a constant voltage is applied to each group. The reliability can be further improved by connecting the elements in parallel. Also,
Zener diodes have been exemplified as the constant voltage elements 14 and 16, but the present invention is not limited to this, and other elements (for example, varistor or avalanche diode) can be used as long as the rated voltage can be freely selected within a certain range. May be used. Further, as an application example of the light emitting diode drive circuit 10, five light emitting diode chips 32a, 32 are provided.
Although the cylindrical display lamp 28 in which the seven light emitting diode elements 12 each including b are arranged in a substantially concentric shape is shown, the invention is not limited to this. For example, it is of course possible to apply a large number of light emitting diode chips or elements to a collective display lamp in which one surface is arranged in a dot matrix form or a lamp module of an illuminated switch.

[0016]

According to the light emitting diode drive circuit of the present invention, since all the light emitting diode elements are connected in series, it is possible to keep the current consumption low even when they are turned on at the same time. Further, even if any of the light emitting diode elements belonging to each light emitting diode group is broken due to a failure, the constant voltage element connected in parallel to the light emitting diode group operates to bypass the current, so that another light emitting diode element The power supply to the group is continued, and the light emitting diode element can maintain the lighting state. Therefore, it is possible to effectively prevent all the remaining light emitting diode elements from being extinguished due to a failure of some of the light emitting diode elements.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a light emitting diode drive circuit according to the present invention.

FIG. 2 is a schematic exploded perspective view showing a display lamp to which the light emitting diode driving circuit is applied.

FIG. 3 is a circuit diagram showing a conventional example.

FIG. 4 is a circuit diagram showing a conventional example.

FIG. 5 is a circuit diagram showing a conventional example.

[Explanation of symbols]

 10 Light emitting diode drive circuit 12 Light emitting diode element 14 First Zener diode 16 Second Zener diode A First light emitting diode group B Second light emitting diode group

Claims (1)

[Claims] 1. A plurality of light emitting diode elements connected in series are divided into a plurality of light emitting diode groups each including one or more light emitting diode elements, and a constant voltage element is connected in parallel for each light emitting diode group. A light emitting diode drive circuit, wherein the rated voltage of each constant voltage element is set to a value exceeding the total value of the forward voltage of the light emitting diode elements belonging to the light emitting diode group.