JP2008282855A - Led drive circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an LED drive circuit which significantly reduces the power loss. <P>SOLUTION: A light source system arranged to charge a storage battery from solar cells during daytime and to perform illumination with the electric power stored in the storage battery during nighttime comprises a controller for controlling charge/discharge of the storage battery; an LED light source consisting of one or a plurality of LEDs which is lit with the electric power from the storage battery during nighttime, a step-down DC/DC converter provided in the housing of the LED light source and supplying power from the storage battery to the LED light source, while stepping down the voltage; and a transmission line for supplying power from the storage battery to the step-down DC/DC converter with high voltage. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an LED drive circuit, for example, a drive circuit that can stably drive an LED with high efficiency by reducing direct current resistance loss of a transmission line in an independent LED street light.

  Recently, high-intensity light-emitting diodes (LEDs), such as high-intensity white LEDs, have been put into practical use, and instead of conventional light bulbs or cathode tubes, LEDs are used as light sources for various devices such as street lights, traffic lights, It has been put to practical use for light sources such as guide lights.

  In this type of LED driving circuit, the current flowing through the LED is controlled to be constant by a step-up DC / DC converter and a limiting resistor so that the luminance of the LED does not change greatly even if the power supply voltage varies ( Patent Document 1).

  In addition, solar cells receive light in the daytime to generate electromotive force, thereby charging a capacitor, such as an electric double layer capacitor. (Patent Document 2).

  By utilizing the above-described solar battery, street lights, traffic lights, guide lights, etc. can be constructed as stand-alone types, that is, self-luminous devices, and the spread of LEDs is further expected.

JP 2006-324534 A Japanese Patent Laid-Open No. 04-357908

  By the way, when constructing a stand-alone LED street light, the storage battery and the controller are installed at a low position so that the operator can easily maintain them, and the lamp as the light source is installed at a height of several meters such as the pole tip. There are many cases. In such a case, the power loss due to the direct current resistance of the transmission line is large.

  Further, since the forward voltage of the LED varies greatly and varies depending on each element or due to temperature change, the voltage loss at the limiting resistor is set large, and the power loss is large.

  In the conventional LED driving circuit, the power loss is large due to the direct current resistance and the limiting resistance of the transmission line, and this point is a difficulty in putting an independent LED street light into practical use.

  In view of such problems, the present invention provides an LED drive circuit that can significantly reduce power loss even when a storage battery and a power transmission line between a controller and a lamp are long, such as a street light. This is the issue.

  Therefore, an LED drive circuit according to the present invention includes a controller that controls charging and discharging of a storage battery in a light source system that charges a storage battery from a solar battery in the daytime and illuminates at night with power charged in the storage battery, Alternatively, an LED light source that consists of a plurality of LEDs and is turned on at night by the power of the storage battery, a step-down DC / DC converter that is provided in the housing of the LED light source and that steps down the power of the storage battery to give the LED light source, and a storage battery And a power transmission line for transmitting the power to the step-down DC / DC converter with a high voltage.

  One feature of the present invention resides in that a step-down DC / DC converter is used, the power of the storage battery is transmitted at a high voltage, and the voltage is dropped and applied to the LED light source.

  As a result, the electric power from the storage battery can be transmitted to the step-down DC / DC converter with a high voltage. As a result, even if the transmission line is long such as a street light, the power loss due to the direct current resistance of the transmission line is reduced. There are few, and it is most suitable to apply to an independent type LED street light.

  The step-down DC / DC converter is not limited as long as it can output with a reduced input voltage, but preferably outputs a constant current with a variable current value. As a result, the LED can be substantially driven with the LED forward voltage even when the individual difference or temperature fluctuation of the LED forward voltage is large.

  Further, it is preferable to provide an integration circuit for integrating the daily power generation amount of the solar cell in the casing, and set the output current value of the step-down DC / DC converter corresponding to the integrated value.

  If the integration circuit and step-down DC / DC converter are installed in the housing of the LED light source, the signal line distance between the integration circuit, step-down DC / DC converter and LED light source can be shortened, resulting in improved noise resistance. it can.

  As the step-down DC / DC converter, for example, XC9220 manufactured by Torex can be adopted.

  Hereinafter, the present invention will be described in detail based on specific examples shown in the drawings. 1 to 6 show a preferred embodiment of an LED driving circuit according to the present invention. FIG. 1 shows the overall configuration of the LED drive circuit of this example, which is an example applied to a street lamp. In FIG. 1, 10 is a solar cell that receives sunlight to generate power, 11 is an LED light source composed of one or a plurality of LEDs, 12 is a step-down DC / DC converter, and 13 is an integrated power generation amount of the solar cell per day. An integrating circuit, 14 is an LED light source 11, a step-down DC / DC converter 12 and a lamp housing incorporating the integrating circuit 13, 15 is a lead storage battery, 16 is a controller for controlling charging and discharging of the lead storage battery 15, and 17 is a lead storage battery. 15 is a transmission line for transmitting power from 15 at a high voltage.

  FIG. 2 shows an example of a power supply circuit for the integration control circuit in the lamp housing 14, and a voltage SL (+) (≈12 V) from a charge / integration power module circuit (FIG. 5) described later is used as an input. While the voltage IC20 converts the voltage to a constant voltage VDD of 5V and outputs it, the input voltage of the voltage SL (+) fluctuates at dawn or the like. VDD is held.

  FIG. 3A shows an example of an integration control circuit in the lamp housing 14, which includes a binary counter 30 that outputs the output Qn at a set period, for example, a period of 600 seconds, and a charge control signal from the one-shot multivibrator 31. “H” is output, for example, the charging voltage signal instantaneously falls to “L” every 10 minutes, and the integration control signal rises to “H” in synchronization with this (see FIG. 7). See timing chart).

  FIG. 3 (b) shows an example of an integration reset circuit in the lamp housing 14, and the voltage VIN synchronized with the rising / falling of the lighting power signal LightPW from the controller 16 is input and for about 20 seconds at dawn. The integration reset signal is output.

  FIG. 4 shows an example of a step-down DC / DC converter circuit and an LED light source. The step-down DC / DC converter 40 receives the lighting power signal LightPW, outputs an on signal to the output terminal EXT when the lighting power signal LightPW is “H”, and outputs an off signal to the output terminal EXT when it is “L”. The LED light source 11 is energized through the LED light source 11 so that the voltage between the FB terminal and GND is controlled to a constant voltage, for example, a constant voltage of 0.9 V, and thereby a constant current is supplied to the LED light source 11. It is supposed to be.

  Further, when the voltage signal CCSIG of the integrating circuit is equal to or lower than the set value, only the resistor R1 is connected between the FB terminal and GND, and when the voltage signal CCSIG exceeds the set value, the resistor R1 and the resistor R2 are connected in parallel between the FB terminal and GND. The constant current value of the LED light source 41 is changed.

  FIG. 5 shows an example of the charging / integrating power module circuit (integrating circuit) in the lamp housing 14, which is connected to the output terminal (+) (−) of the solar cell 10, while the voltage SL (+) of 12V. And the integration capacitor 50 is charged every time there is an integration control signal, and while there is a charge control signal, the charging to the integration capacitor 50 is suspended and the charging voltage is held, while the charging voltage of the integration capacitor 50 is changed. Detected by the detection circuit 51, a voltage value CCSIG of “H” is output when a set value, for example, 1.5V or less exceeds “L” and 1.5V, and the integration capacitor 50 is discharged by the input of the integration reset signal. (See the timing chart in FIG. 7).

  FIG. 6 is a diagram illustrating functions of the controller 16. FIG. 7 is a chart of the operation timing of the drive circuit.

  In the daytime, a lead storage battery (for example, 12V rating) 15 is charged from the solar battery 10 via a controller (manufactured by Morningstar; SL-10L-12V) 16. At night, the electric power charged in the lead storage battery 15 is sent through the controller 15 to turn on the LED light source 11.

  In this example, the lighting power signal LightPW becomes “L” with a delay of 5 minutes from the dawn when the output of the solar cell 10 becomes “H”, and the lighting power signal LightPW becomes “H” with a delay of 5 minutes after sunset. . Actually, the controller 16 has a timer function or the like, so that a sufficient power supply voltage holding time of the integrating circuit 13 is provided. The circuit constants in the power supply circuit of FIG. 2 and the integration control circuit of FIG. 3 can be kept for several tens of seconds by design.

  The step-down DC / DC converter 40 adopts XC9220 manufactured by Torex Co., which corresponds to an input voltage of 11 to 16 V, and realizes high conversion efficiency at a constant current output in a range of 0.5 A to 1 A. The constant current is switched in two steps in this example. When the voltage signal CCSIG is at the H level, the LED light source 11 is brightened by setting the energizing current of the LED light source 41 large by parallel driving of the resistors R1 and R2. Can be lit.

  The circuit for charging the lead storage battery 15 from the solar battery 10 is cut off for a very short time, and the integration capacitor 50 is charged by bypassing the circuit during the cut-off period. In the daytime, power is supplied from the solar cell 10 to the integration control / integration reset circuit (FIG. 3), the integration circuit (FIG. 5) and its power supply circuit (FIG. 2), and the current during power generation of the solar cell 10 is directly supplied to the integration capacitor 50. Since it is energized and charged, the circuit configuration is simple.

  Although the accuracy of the integrated value is not high, since the voltage of the lead storage battery 10 at the time of filling is stable at about 13 V, the total output of the day can be converted approximately by integrating the current value of the solar battery 10. In addition, since the integration circuit is continuously charged at regular intervals in the daytime, output fluctuations are averaged, and it can be determined that there is no problem in the performance of determining whether or not the battery is fully charged.

  Here, when the conversion efficiency is actually measured, when the input is 12.4 V and 0.6 A, and the output is 8.45 V and 0.75 A, the conversion efficiency is 85%, which is 68% of the efficiency of the conventional LED driving circuit. It can be seen that it has improved.

  Further, assuming that the consumption amount of the storage battery at night is 50 Wh [5 W × 10 hours], the charge from the solar cell 10 per day is required to be 50 Wh (≈4 Ah) or more. The output Qn of the binary counter 30 in the integration control circuit of FIG. 3 is set to a period of 600 seconds, the pulse output of the one-shot multivibrator 31 is set to 60 mS, the integration capacitor 50 of the integration circuit is set to 1F, and the solar cell 10 When the output current value in cloudy weather is 0.4A, and the sunshine time of the day is 10 hours, the number of energizations to the integration circuit of the day, that is, the number of integrations is 600 seconds / time = 60 times, and the total integration time is 60 Times × 60 mS / times = 3600 mS (3.6 seconds), and the daily charging voltage under the above conditions is V = (I × T) ÷ C = (0.4 A × 3.6 seconds) ÷ 1F≈1 .44V, that is, it is possible to determine whether or not the output of the voltage detection CMOS of the detection circuit 51 of 1.5V is fully charged, and a constant current value may be determined.

It is a figure which shows the whole structure in preferable embodiment of the LED drive circuit which concerns on this invention. It is a figure which shows the example of the power supply circuit in the controller in the said embodiment. It is a figure which shows the example of a circuit of the integral control and integral reset in the controller in the said embodiment. It is a figure which shows the example of the pressure | voltage fall type DC / DC converter circuit and LED light source in the said embodiment. It is a figure which shows the example of the integration circuit in the said embodiment. It is a figure which shows the function of the controller in the said embodiment. It is a chart figure which shows the operation timing in the said embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Solar cell 11 LED light source 12 Step-down DC / DC converter 13 Integration circuit 14 Case 15 Lead acid battery 16 Controller 17 Transmission line

Claims (3)

In a light source system that charges a storage battery from a solar battery in the daytime and illuminates at night with the power charged in the storage battery,
A controller for controlling the charging and discharging of the storage battery;
An LED light source consisting of one or more LEDs, which is lit at night by the power of the storage battery;
A step-down DC / DC converter that is provided in the housing of the LED light source and that steps down the voltage of the power of the storage battery and applies it to the LED light source;
An LED drive circuit comprising: a power transmission line that transmits electric power from a storage battery to a step-down DC / DC converter with a high voltage.   2. The LED drive circuit according to claim 1, wherein the step-down DC / DC converter outputs a constant current having a variable current value.   The casing is provided with an integration circuit for integrating the daily power generation amount of the solar cell, and the step-down DC / DC converter is configured to set an output current value corresponding to the integrated value. Item 3. The LED drive circuit according to Item 2.

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