JP4491561B2 - LED lighting circuit for AC of sign display device using LED - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an alternating current LED lighting circuit of a sign display device that displays a sign such as an advertisement or decoration by lighting or blinking of an LED by a commercial power source.
[0002]
[Prior art]
Conventionally, sign display devices used for advertising and decoration are mainly those using neon signs using neon tubes, light bulbs that emit filaments, and fluorescent display tubes as the light source of the light emitters that make up the display area. Yes, it has been used for a long time as a medium that gives a strong impression of color change. As a substitute for these neon signs and light bulb illumination advertisements, sign display devices using LEDs (light emitting diodes) that are advantageous in terms of power consumption and durability are being realized. In addition to the advantages described above, the LED has excellent flexibility in the shape of the light emitting part and freedom of color expression using the three primary colors of light. Since it can be attracted, it is being applied to traffic lights, traffic lights, and the like. As described above, the sign display device using the LED as the light source of the light emitter constituting the display area is not limited to advertisement or decoration, but can be applied as a device for displaying various information.
[0003]
[Problems to be solved by the invention]
By the way, in the sign display device as described above, a commercial power source is used as a power source, but the LED is driven by a direct current in principle, and the voltage is several volts or less. Therefore, when the LED is lit using a commercial power source, a method is adopted in which the current is limited by connecting the LED and a current limiting resistor in series. However, the method of directly lighting an LED with a commercial power source requires that a large number (about 40 to 60) of LEDs and the limiting resistor be connected in series to suppress the heat generation of the current limiting resistor. In addition, this method has a problem in that brightness variation is caused largely by the voltage fluctuation of the commercial power source.
[0004]
The present invention is made from the circumstances as described above, and the object of the present invention is to suppress heat generation by reducing the limiting resistance for lighting each LED as much as possible in a sign display device using a large number of LEDs, An object of the present invention is to provide an AC LED lighting circuit in which the brightness of an LED does not change as much as possible even when the power supply voltage fluctuates. Another object of the present invention is to provide an AC LED lighting circuit that can prevent thermal runaway of the LED, which is likely to occur when the voltage changes.
[0005]
[Means for Solving the Problems]
The present invention relates to an AC LED lighting circuit for a sign display device using LEDs as light emitters constituting a display region, and the above object of the present invention is to provide a commercial AC power supply of AC90V to AC110V, a full-wave rectifier, A current adjustment circuit; a first resistor that feeds back an output of the current adjustment circuit to an adjustment terminal of the current adjustment circuit; a second resistor that divides the output voltage of the current adjustment circuit by the first resistor; A plurality of LEDs each connected in series, connected in series, and directly full-wave rectified by the full-wave rectifier without stepping down the voltage of the commercial AC power supply and supplied to the current adjustment circuit; and by feeding back the voltage applied to the first resistor as a control signal for the current regulating circuit, a current flowing through the LED is accomplished by the configuration you constant. The current adjustment circuit is a three-terminal regulator, and the current applied to the LED is made constant by feeding back the voltage applied to the first resistor to the adjustment terminal of the three-terminal regulator; The circuit is a transistor, the voltage applied to the first resistor is fed back between the emitter and base of the transistor, and the current flowing through the LED is made constant by controlling the collector current; Is achieved.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The AC LED lighting circuit according to the present invention is suitably used for a sign display device that displays a sign of advertisement, decoration, etc. by lighting or flickering of an LED by a commercial power source. As an alternative to this, various sign display devices using LEDs can be provided. In addition, about the whole structure of a sign display apparatus, and the lighting order of the LED which comprises the display area, and control of a lighting speed, it shall assume that a well-known technique can be utilized, description is abbreviate | omitted here, and it refers to this invention below. The configuration of the AC LED lighting circuit will be described.
[0007]
FIG. 1 is a circuit diagram showing an example of an AC LED lighting circuit of a sign display device according to the present invention. The LED 2 of the sign display device is a commercial power supply via a current adjustment circuit 12 in the AC LED lighting circuit 10. (AC power supply) 1 is connected. The current adjusting circuit 12 is a circuit that adjusts the voltage applied to the resistor 13 connected in series with the LED 2 to make the current constant, and always supplies a predetermined current value to the LED regardless of fluctuations in the AC voltage of the commercial power supply 1. As described above, a portion of the AC half-wave current exceeding a predetermined value is cut and adjusted to a constant current. In this example, as the current adjustment circuit 12, an output variable regulator IC (for example, Texas Instruments) having an adjustment terminal in addition to an input / output terminal so that the voltage can be adjusted via an external resistor 13. Three-terminal regulator “TL317” from National Semiconductor, and three-terminal regulator “LM317” from National Semiconductor). In the present invention, the voltage applied to the resistor 13 is fed back as a control signal for the current adjusting circuit 12 so that the LED 2 is always lit at a predetermined current value.
[0008]
In the embodiment shown in FIG. 1, a rectifier 11 (in this example, four diodes) that are components of the AC LED lighting circuit 10 is provided between the commercial power source 1 and the LEDs 2 (D1, D2,..., Dn). (A ring modulation circuit connected in a bridge shape), a current adjustment circuit 12 and a resistor 13 are connected in series, and the voltage applied to the resistor 13 is fed back as a control signal of the current adjustment circuit 12, thereby allowing the LED 2 to On the other hand, a constant current is supplied and a stable output voltage can be supplied. Further, in this example, two resistors 13 (R1, R2) are connected to the output _OUT of the current adjustment circuit 12, and the output of the resistor R1 is fed back to the adjustment terminal _ADJ of the current adjustment circuit 12, thereby providing an output. The voltage V _OUT can be set by a resistor 13 (R2 / R1 ratio).
[0009]
In the configuration as described above, the voltage Vin from the commercial power source 1 which is an AC power source is applied to the rectifier 11 in the AC LED lighting circuit 10, and the AC half-wave current after rectification is supplied to the current adjustment circuit 12. . Then, as shown in FIG. 2, the current adjusting circuit 12 cuts a portion of the AC half-wave limit Li or higher, and a current having a waveform as shown in FIG. 2 flows to the LED 2 to give a constant current value (for example, 20 mA). ) LED2 is lit. By adopting such a lighting system, the limiting resistance can be made as small as possible to suppress heat generation.
[0010]
As shown in the waveform examples of the AC90V and AC110V portions in FIG. 2, the lighting duty (T1 and T2) is slightly different depending on the voltage fluctuation, but the LED is always lit at a predetermined current value. Can do. Therefore, the LED can be turned on with a constant brightness, and deterioration of the LED due to overcurrent can be prevented. Further, the output voltage obtained by rectifying and smoothing the power supply voltage is stabilized by the current adjustment circuit 12, and the voltage for lighting the LED 2 is fed back and stabilized. Accordingly, it is possible to provide a sign display device in which the change in the brightness of the LED is extremely small. In addition, it is possible to prevent thermal runaway of the LED that is likely to occur when the voltage changes.
[0011]
In the embodiment described above, as the current adjustment circuit 12, a transistor or a constant current Zener diode can be used instead of the three-terminal regulator. In the case of using a transistor, for example the emitter of the voltage applied to the resistor 13 transistor is fed back between the base, by controlling the collector current look variations of V _BE, so that a constant current flowing through the LED2 You can do it. However, in the case of a transistor, it is difficult to perform accurate current control as in the case of a three-terminal regulator. Therefore, it is optimal to use a three-terminal regulator as the current adjustment circuit 12. In the above-described embodiment, the commercial power source used for the sign display device has been described by taking the case of 100 V as an example in the waveform example of FIG. 2, but is not limited to 100 V.
[0012]
【The invention's effect】
As described above, according to the present invention, the current adjustment circuit has a current adjustment circuit that cuts a portion of the alternating current half-wave current greater than or equal to a predetermined value to obtain a constant current value. Since the voltage is fed back and the voltage is fed back, changes in brightness due to fluctuations in the power supply voltage can be extremely reduced, and deterioration of the LED due to overcurrent can be prevented. Furthermore, the limiting resistance for turning on each LED can be reduced to suppress heat generation, and thermal runaway of the LED, which easily occurs when the voltage changes, can be prevented. Further, normally, a smoothing capacitor is inserted after rectification by a diode bridge to prevent LED flickering. However, in the present invention, since lighting is performed at a constant current, flickering of the LED does not occur. This is the same as so-called pulse lighting, which has both lighting and non-lighting.
[0013]
Therefore, the application range of the sign display device using the LED is widened, and it is possible to provide a sign display device capable of displaying various information without being limited to advertisements and decorations.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration example of an AC LED lighting circuit of a sign display device according to the present invention.
FIG. 2 is a diagram illustrating an example of a waveform of a current flowing through an LED.
[Explanation of symbols]
1 AC power supply 2 LED
10 LED lighting circuit for AC 11 Rectifier 12 Current adjustment circuit 13 Resistance

Claims (3)

An AC LED lighting circuit of a sign display device using LEDs as light emitters constituting a display area, which is a commercial AC power supply of AC90V to AC110V, a full-wave rectifier, a current adjustment circuit, and an output of the current adjustment circuit A first resistor that feeds back to the adjustment terminal of the current adjustment circuit, a second resistor that divides the output voltage of the current adjustment circuit by the first resistor, and a plurality of LEDs each connected in series. It is connected in series, and is configured to supply full current rectification directly by the full wave rectifier without stepping down the voltage of the commercial AC power supply to the current adjustment circuit, and the voltage applied to the first resistor is current by feeding back a control signal for adjusting the circuit, the AC LED lighting circuit of the signature display device is characterized in that the current flowing in the LED and configuration shall be the constant. It said current adjusting circuit is a three-terminal regulator, claims adapted to a constant current flowing through the LED by feeding back the voltages applied to the first resistor to the adjustment terminal of the three terminal regulator Item 2. An LED lighting circuit for AC of the sign display device according to Item 1. Said current adjusting circuit is a transistor, the emitter of said voltages applied to said first resistor transistor, is fed back between the base, so as to a constant current flowing through the LED by controlling the collector current The alternating current LED lighting circuit of the sign display apparatus of Claim 1.

Images