JP2009266855A - Led lighting device - Google Patents

Abstract

An LED illumination device capable of stably controlling brightness to low illuminance while reducing power loss.
A current control means 16 controls a base voltage of a transistor 14 so that a current flowing through an LED unit 12 in which an LED 13, a transistor 14 which is a semiconductor element, and a resistor 15 are connected in series becomes a predetermined value, and a switch The means 18 controls on / off of the transistor 14 by a control signal. When the LED non-energization detecting unit 21 does not detect the LED current non-energized state, the input power control unit 20 is configured so that the collector voltages Va to Vc of the transistor 14 become the predetermined reference value V1. During the period when the LED non-energization detecting means 21 detects the non-energized state of the LED current, the output voltage of the DC power supply 11 is set to a value immediately before the non-energized state or a predetermined fixed value. Hold.
[Selection] Figure 1

Description

  The present invention relates to an LED lighting device having an LED unit in which a semiconductor switch element for controlling a current flowing in an LED is connected in series to the LED.

  The LED lighting device stabilizes the current flowing into the LED and suppresses variations in illuminance. As what stabilizes the electric current which flows into LED, there exists what made it connect high resistance in series with LED. When a high resistance is connected in series with the LED, the voltage drop and power loss due to the high resistance are large and the efficiency is deteriorated. Therefore, as a method for stabilizing the current flowing into the LED, a simple constant current circuit is connected in series with the LED to minimize power loss and at the same time reduce variation in illuminance (see, for example, Patent Document 1). .

This is provided with a plurality of LED units in which a constant current circuit composed of a single transistor and a resistor and an LED are connected in series. The current flowing through the LED unit is detected as a voltage drop of the resistor, and the constant current reference circuit The voltage is compared and amplified and fed back to the base of the transistor for automatic control, and the control is performed so that the voltage drop of the resistor is always constant to keep the current of the LED unit at a constant value. Then, the sum of the voltage drop between the transistor and the resistor in the plurality of LED units is input to the lowest voltage detection device, the smallest voltage among the LED units is detected, and the power supply unit so that this voltage becomes the target value. The output voltage is controlled.
JP 2006-278304 A

  However, in Patent Document 1, when the dimming control is performed by the LED lighting device, the current of the LED of the LED unit is controlled to be extremely small. The voltage drop value of the resistors connected in series is minimized, and current detection becomes difficult.

  Therefore, it is conceivable to control the on / off ratio of the LED current of the LED unit. However, when a period in which the LEDs of all the LED units are turned off by the on / off ratio control of the LED current, the LEDs of all the LED units are controlled. The voltage applied to the constant current circuit (the sum of the voltage drop between the transistor and the resistor) is high during the period when is turned off, and the output voltage of the power supply section is Since the sum of the voltage drops is controlled to be the target value of the minimum voltage detecting device, the output voltage of the power supply unit is controlled to decrease when the applied voltage of the constant current circuit increases. Thereafter, at the moment when the ON signal is output to the LED of any of the LED units, the output voltage of the power supply unit is insufficient, so that the LED does not light immediately. In order to prevent this, the target value of the minimum voltage detection device is set higher. However, in this case, the power loss consumed by the transistors and resistors of the constant current circuit increases during continuous lighting.

  The objective of this invention is providing the LED illuminating device which can control brightness stably to low illumination intensity, reducing power loss.

  An LED lighting device according to a first aspect of the present invention is an LED unit in which an LED to which DC power is input and a semiconductor switch element for controlling a current flowing through the LED are connected in series; a current flowing through the LED unit is predetermined Current control means for controlling the semiconductor switch element to have a value; switch means for on / off control of the semiconductor switch element by an external control signal; and the semiconductor switch element is turned off by control of the switch means, LED non-energization detecting means for detecting a non-energized state in which no current is supplied to the LED from a DC power supply; and when the LED non-energized detection means does not detect a non-energized state of the LED current, the semiconductor switch The DC power input to the LED is controlled so that the voltage between the terminals of the element becomes a predetermined reference value. During the period when the LED deenergization detecting means detects the deenergized state of the LED current, the input power that holds the DC power input to the LED at a value immediately before the deenergized state or a predetermined fixed value. And a control means.

  In the present invention and the following inventions, definitions and technical meanings of terms are as follows. The DC power input to the LED is supplied from, for example, a DC power source. The direct current power source includes a direct current power source that generates direct current by converting alternating current into direct current. The LED includes a plurality of LEDs connected in series. The semiconductor switch element connected in series with the LED is, for example, a transistor. When the semiconductor switch element is a transistor, for example, the LED unit is formed by connecting an LED and a collector of a transistor, and further connecting an emitter of the transistor and a resistor.

  The current flowing through the LED unit is the current flowing through the series connection circuit of the LED and the semiconductor switch element, and the magnitude is determined by the base voltage of the transistor when the semiconductor switch element is a transistor. The base voltage of the transistor is controlled to a predetermined value by the current control means. The predetermined current value is set to the value of the LED current that should flow through the LED according to the rating.

  The switch means is an element having an on / off function, such as a transistor or a thyristor. The control signal from the outside is, for example, a PWM control signal. When the semiconductor switch element connected in series with the LED is a transistor, the switch means is connected between the base and emitter of the transistor and is turned on to forcibly reduce the transistor base voltage to zero. Turn off.

  The LED non-energization detecting means detects a non-energized state in which the semiconductor switch element is turned off by the switch means and no current is supplied to the LED. When a plurality of LED units are connected in parallel to a power source that supplies DC power, a non-energized state occurs when no current is supplied to all the LED units.

  The input power control means feeds back the voltage across the terminals of the semiconductor switch element and controls the output voltage of the DC power supply. The terminal voltage of the semiconductor switch element is a collector voltage when the semiconductor switch element is a transistor.

  When the LED non-energization detecting means does not detect the non-energized state of the LED current, the output voltage of the DC power supply is controlled so that the voltage between the terminals of the semiconductor switch element becomes a predetermined reference value. This reference value is preferably the lowest value of the voltage across the terminals of the semiconductor switch element that lights the LED. Actually, the margin is set to a value that is larger than the minimum value of the voltage between the terminals of the semiconductor switch element in which the LED is turned on with an allowance.

  Further, during the period in which the LED non-energization detecting means detects the non-energized state of the LED current, the output voltage of the DC power supply is held at a value immediately before the non-energized state or a predetermined fixed value. This is to prevent the input power control means from controlling the output voltage of the DC power supply to be lowered when the current is not supplied to all the LED units and the voltage between the terminals of the semiconductor switch element becomes high. .

  According to the first aspect of the present invention, when the current flows through the LED, the output voltage of the DC power supply is controlled so that the collector voltage of the transistor becomes a predetermined reference value, and when the current does not flow through the LED. Holds the output voltage of the DC power supply at the voltage value immediately before the current is flowing or a predetermined fixed value, so that the output voltage of the DC power supply is controlled to be lowered when no current flows through the LED. Can be prevented. Therefore, when dimming control is performed, the brightness can be stably controlled to low illuminance by the on / off ratio control of the LED current while reducing power loss.

  FIG. 1 is a circuit configuration diagram of an LED lighting device according to an embodiment of the present invention. A plurality of LED units 12 are connected in parallel via a capacitor C to a DC power source 11 that outputs DC power. FIG. 1 shows a case where three LED units 12a to 12c are connected. The three LED units 12a to 12c have the same configuration.

  The LED units 12a to 12c are configured by connecting a plurality of LEDs 13a to 13c connected in series, transistors 14a to 14c as semiconductor switch elements, and resistors 15a to 15c in series. The base voltages of the transistors 14a to 14c of the LED units 12a to 12c are controlled by the current control means 16, and the current flowing through the transistors 14a to 14c (the LED current flowing through the LEDs 13a to 13c) is controlled. That is, the operational amplifier 17 of the current control means 16 has the bases of the transistors 14a to 14c through the diodes Da1 to Dc1 so that the emitter voltages of the transistors 14a to 14c (voltages of the resistors 15a to 15c) become the predetermined voltage value V1. Control the voltage. When the predetermined voltage value V1 is large, the current (LED current) flowing through the LED units 12a to 12c increases, and when the predetermined voltage value V1 is small, the current (LED current) flowing through the LED units 12a to 12c decreases.

  Further, switch means 18a to 18c are provided between the bases and emitters of the transistors 14a to 14c. The switch means 18a to 18c are turned on and off by the PWM control signals PWM1 to PWM3 from the external PWM control means 19 to control the transistors 14a to 14c on and off. The PWM control signals PWM1 to PWM3 determine the current ratio of energization and non-energization of the LED current. When the switch means 18a to 18c are on, the bases and emitters of the transistors 14a to 14c are short-circuited. The base voltages of the transistors 14a to 14c are forced to be zero. Therefore, the transistors 14a to 14c are turned off, and the LED current is turned off. Thus, the transistors 14a to 14c are turned on / off by the PWM control signals PWM1 to PWM3, and the transistors 14a to 14c are controlled to be turned on / off.

  Next, the input power control means 20 controls the output voltage of the DC power supply 11 so that the collector voltages Va to Vc of the transistors 14a to 14c become predetermined reference values. Here, since the power loss can be reduced as the output voltage V1 of the operational amplifier 17 and the collector voltages Va to Vc of the transistors 14a to 14c are smaller, this reference value is the collector of the transistors 14a to 14c in which the LEDs 13a to 13c are lit. The minimum value of voltages Va to Vc is set. Actually, the margin is set to a value larger than the minimum value of the collector voltages Va to Vc of the transistors 14a to 14c for which the LEDs 13a to 13c are lit up in anticipation of the margin.

  In addition, there are provided LED non-energization detecting means 21a to 21c for detecting a non-energized state in which the transistors 14a to 14c are turned off by the switch means 18a to 18c and no current is supplied from the DC power supply 11 to the LEDs 13a to 13c. . The LED non-energization detecting means 21a to 21c are turned on / off by the base voltages of the transistors 14a to 14c. Therefore, the same operation as the on / off operation of the transistors 14a to 14c is performed. Then, when all the LED non-energization detection units 21 a to 21 c are off, the high signal non-conduction detection signal V <b> 2 is input to the input power control unit 20.

  Here, the reason why the LED non-energization detecting means 21a to 21c are provided will be described below. 2 is an operation waveform diagram when the LED non-energization detection means 21a to 21c are not provided, and FIG. 3 is an operation waveform diagram when the LED non-energization detection means 21a to 21c are provided. As shown in FIG. 2, when the LED non-energization detecting means 21a to 21c are not provided, a period Ti (i = 1, the total of LED currents supplied from the DC power supply 11 to the LED units 12a to 12c becomes zero. 2, 3...), The sum of voltage drops between the transistors 14 a to 14 c and the resistors 15 a to 15 c (collector voltages of the transistors 14 a to 14 c) increases. As a result, the input power control means 20 controls the collector voltages of the transistors 14a to 14c so as to become a predetermined reference value, and as a result, controls so that the output voltage of the DC power supply 11 decreases. Then, since the output voltage of the DC power supply 11 remains lowered at the moment when the transistors 14a to 14c are turned on thereafter, the DC voltage is insufficient, and the DC voltage necessary for lighting the LEDs 13a to 13c is supplied. I can't.

  Therefore, as shown in FIG. 3, the LED non-energization detection means 21 a to the period Ti (i = 1, 2, 3...) In which the total LED current supplied from the DC power supply 11 to the LED units 12 a to 12 c is zero. Detect at 21c. That is, in the period Ti in which the total LED current is zero, the LED non-energization detection means 21 a to 21 c are turned off, and the high signal non-conduction detection signal V 2 is output to the input power control means 20. When the non-conduction detection signal V2 is a high signal, the input power control means 20 sets the output voltage of the DC power source 11 (DC power input to the LED) to a value immediately before the non-energized state or a predetermined fixed value. Hold. As a result, it is possible to prevent the collector voltage from increasing, so that the output voltage of the DC power supply 11 is not controlled to decrease.

  That is, during the period in which the LED currents of all three LED units 12a to 12c are in a non-energized state, the collector voltages Va to Vc of all the transistors 14a to 14c of the LED units 12a to 12c are high, and the input power Since the control means 20 operates so as to control the collector voltage with the minimum voltage, it operates so as to lower the output voltage of the DC power supply 11. Then, since the output voltage of the DC power supply 11 remains lowered at the moment when the transistors 14a to 14c are turned on thereafter, the DC voltage is insufficient, and the DC voltage necessary for lighting the LEDs 13a to 13c is supplied. Since it is not possible, the LEDs 13a to 13c do not shine immediately.

  Therefore, LED non-energization detecting means 21a to 21c for detecting a period in which no current flows through the LEDs 13a to 13c is provided, and the input power control means 20 is configured such that all the LED non-energization detecting means 21a to 21c are in a non-energized state of LED current During the period during which the output of the DC power source 11 is detected, the output voltage of the DC power supply 11 is held at a value immediately before the non-energized state or a predetermined fixed value, and the LED currents of all the LED units 12a to 12c are DC The output voltage of the power supply 11 is prevented from decreasing. Thus, even when the transistors 14a to 14c are turned on from the non-energized state of the LED current, the LEDs 13a to 13c can be immediately illuminated.

  When the PWM control signals PWM1 to PWM3 of the PWM control means 19 are Low, the LED current flows through the LEDs 13a to 13c, and the LED non-energization detection means 21a to 21c are on. On the other hand, when all of the three transistors 14a to 14c are turned off and the LED current stops flowing, all of the LED non-energization detecting units 21a to 21c are turned off, and a high signal is output as the non-conduction detection signal V2. . When even one of the three transistors 14a to 14c has an LED current flowing, the non-conducting detection signal V2 becomes a low signal, and the DC power supply 11 is stably at the lowest value of the collector voltages Va to Vc. Feedback controlled.

  According to the embodiment of the present invention, the input power control means 20 is when the LED non-energization detection means 21a-21c does not detect the non-energization state of the LED current (when the non-conduction detection signal V2 is a Low signal). Controls the output voltage of the DC power supply 11 so that the collector voltages Va to Vc of the transistors 14a to 14c become predetermined reference values, so that the DC power supply 11 stably performs feedback control with the lowest value of the collector voltages Va to Vc. Is done. Therefore, power loss in the transistors 14a to 14c and the resistors 15a to 15c can be reduced.

  On the other hand, during the period in which the LED non-energization detection means 21a to 21c detect the non-energized state of the LED current (when the non-conduction detection signal V2 is a high signal), the output voltage of the DC power supply 11 is set immediately before the non-conductive state. Or a predetermined fixed value, it is possible to prevent the output voltage of the DC power supply 11 from being lowered while the LED currents of all the LED units 12a to 12c are in a non-energized state. Therefore, even when the transistors 14a to 14c are turned on from the non-energized state of the LED current, the LEDs 13a to 13c can be immediately illuminated. In this way, by using the time ratio control, it is possible to stably control to low illuminance while reducing power loss in the transistors 14a to 14c and the resistors 15a to 15c.

The circuit block diagram of the LED lighting apparatus concerning embodiment of this invention. The operation | movement waveform diagram when not providing the LED non-energization detection means in embodiment of this invention. The operation | movement waveform diagram in case the LED non-energization detection means in embodiment of this invention is provided.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... DC power supply, 12 ... LED unit, 13 ... LED, 14 ... Transistor, 15 ... Resistance, 16 ... Current control means, 17 ... Operational amplifier, 18 ... Switch means, 19 ... PWM control means, 20 ... Input power control means 21 ... LED non-energization detecting means, 22 ... AC power supply, 23 ... rectifier, 24 ... boost chopper

Claims (1)

An LED unit in which an LED to which DC power is input and a semiconductor switch element for controlling a current flowing in the LED are connected in series;
Current control means for controlling the semiconductor switch element such that a current flowing through the LED unit becomes a predetermined value;
Switch means for controlling on / off of the semiconductor switch element by an external control signal;
LED non-energization detecting means for detecting a non-energized state in which the semiconductor switch element is turned off by the control of the switch means and no current is supplied to the LED from the DC power supply;
When the LED non-energization detecting means does not detect the non-energized state of the LED current, the DC power input to the LED is controlled so that the voltage between the terminals of the semiconductor switch element becomes a predetermined reference value. During the period when the LED non-energization detecting means detects the non-energized state of the LED current, the DC power input to the LED is held at a value immediately before the non-energized state or a predetermined fixed value. Input power control means;
An LED lighting device comprising:

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