JP2010225742A - Led driving circuit, led lighting system, and method of driving led - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an LED driving circuit that causes little blinking. <P>SOLUTION: An LED driving circuit inputs an alternating voltage and drives at least two LEDs (LED units LED1 to LEDn) connected in series. The LED driving circuit includes a voltage control circuit 2 that detects an input voltage of the LED driving circuit or a rectified input voltage and one or more switch circuits SW1 to SWn. In the LED driving circuit, the voltage control circuit 2 controls the ON/OFF of the switch circuits SW1 to SWn such that as the absolute value of the input voltage of the LED driving circuit increases, the number of serially connected LEDs into which the input voltage of the LED driving circuit or the rectified input voltage is to be supplied may increase. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an LED drive circuit that inputs an alternating voltage and drives an LED (Light Emitting Diode), an LED illumination device including the LED drive circuit, and an LED drive method.

  2. Description of the Related Art Conventionally, there is a configuration in which a plurality of LEDs are connected in series and a constant current circuit is connected to the LEDs as a circuit for rectifying an alternating current such as a commercial power source.

  In order to improve flicker, a switch circuit is provided in parallel with the constant current circuit, and the LED is lit over a wide range of AC voltage waveforms by controlling ON / OFF of the switch circuit according to the input voltage. Thus, a measure for reducing the flickering of the LED has been proposed (see, for example, Patent Document 1).

  Here, a schematic configuration of the LED drive circuit disclosed in Patent Document 1 is shown in FIG. The LED drive circuit shown in FIG. 12 is a circuit for driving a series LED group 102 in which a large number of LEDs are connected in series, and a rectifier circuit 101 composed of a diode bridge for full-wave rectification of an AC power supply AC, and each LED in parallel. A bypass resistor group 103 in which a number of bypass resistors Rb to be connected are connected in series, an npn transistor Q101, an npn transistor Q102, a constant current driving circuit 104 that drives the transistor Q101 with constant current, and an n-channel electric field. An effect transistor Q103, and a voltage comparison switching drive circuit 105 that includes an n-channel field effect transistor Q104 and resistors R103 to R106 and switches the transistor Q103 are provided.

  A parallel circuit including a series LED group 102 and a bypass resistor group 103, a transistor Q101, and a resistor R101 of the constant current drive circuit 104 are connected in series to the output terminal of the rectifier circuit 101. A transistor Q103 is connected in parallel to a series circuit including the transistor Q101 and the resistor R101. Each bypass resistor Rb is used to prevent all LEDs from being extinguished by causing a current to flow to an adjacent LED via the bypass resistor Rb when the LEDs connected in parallel are disconnected. Hereinafter, the operation of the LED drive circuit shown in FIG. 12 will be described.

  As will be described later, when the transistor Q103 is in the OFF state, a current for driving the series LED group 102 to emit light flows to the transistor Q101 and the constant current drive circuit 104 side. On the other hand, when the transistor Q103 is in the ON state, most of the current for driving the series LED group 102 to emit light flows to the transistor Q103 side.

  The transistor Q103 is turned on by the voltage comparison switching drive circuit 105 when the power supply voltage is low. The voltage dividing resistors R105 and R106 of the voltage comparison switching drive circuit 105 generate a potential according to the full-wave rectified power supply voltage at the voltage dividing point c. The transistor Q103 of the voltage comparison switching drive circuit 105 is turned on when the potential at the voltage dividing point c is equal to or higher than a predetermined value. When the power supply voltage increases in accordance with the cycle and the potential at the voltage dividing point b exceeds a predetermined value, the transistor Q104 is turned on, and the potential at the voltage dividing point c by the voltage dividing resistors R105 and R106 is substantially 0 [V]. Transistor Q103 is instantaneously turned off.

  When the transistor Q103 is turned off, current flows to the transistor Q101 and the constant current drive circuit 104 side. Further, the current divided to the constant current drive circuit 104 side flows through the resistor R102 into the base of the transistor Q101. When the base current Ib1 of the transistor Q101 increases as the power supply voltage increases, the emitter current Ie1 of the transistor Q101 increases and the collector current (current that flows through the LED) Ic1 of the transistor Q101 increases.

  The base of the transistor Q102 is connected to a connection point a between the emitter of the transistor Q102 and the current detection resistor R101. Transistor Q102 causes collector current Ic2 to flow according to the potential at connection point a, and decreases base current Ib1 of transistor Q101. As a result, the emitter current Ie1 of the transistor Q101 decreases and the collector current Ic1 of the transistor Q101 decreases. Accordingly, the collector current Ic1 of the transistor Q101 is controlled to be substantially constant.

  As described above, since the LED current flows to the ground through the transistor Q103 in the region where the power supply voltage is low, the power supply voltage is all applied to the LED and the LED is lit, and in the region where the power supply voltage is high. Since the current of the LED flows to the ground through the transistor Q101 and the resistor 101 of the constant current drive circuit 104, a specified current flows through the LED and lights up. Thus, the flickering of the LED is reduced by turning on the LED over a wide range of the power supply voltage.

JP-A-11-307815

  When the LED is turned on using an AC power supply, it is necessary to rectify the AC voltage as in the LED driving circuit shown in FIG. 12 described above. Here, the voltage waveform after full-wave rectification of the AC voltage is shown in FIG. The voltage waveform 106 obtained by full-wave rectification of alternating current has a valley portion where the voltage becomes 0 [V]. In order to light the LED, it is necessary to apply a voltage equal to or higher than the forward voltage drop (VF) of the LED to the LED, but the portion before and after this valley is lower than the forward voltage drop (VF) of the LED. The section where does not light up. In particular, in an LED lighting device that directly uses a commercial AC voltage such as 100 [V], a large number (approximately 20) of LEDs are connected in series. More than that.

  In FIG. 13, a luminance waveform 107 shows a temporal change in the light emission luminance of the LED when the LED lighting period is small. When the lighting section is short, that is, when the extinction section is long, the human eye feels that the LED is extinguished for a moment, and therefore the LED appears to flicker.

  In FIG. 13, a luminance waveform 108 shows a temporal change in LED emission luminance when the LED lighting section is long. When the lighting period is long, that is, when the extinguishing period is short, the LED appears to shine almost continuously to the human eye, and therefore the LED flickers less.

  As described above, in order to suppress the flickering of the LED, it is necessary to shorten the extinguishing section as much as possible.

  In the LED drive circuit shown in FIG. 12, when the output voltage of the rectifier circuit 101 is less than or equal to the sum of the forward voltage drops (VF) of the LEDs, even if the on-resistance of the transistor Q103 is 0 [Ω], There was a problem that flickering occurred because a sufficient current could not flow, the brightness of the LED was very small, and a section where the LED did not emit light remained. In particular, the larger the number of LEDs connected in series, the wider the LED turn-off interval, and the more flickering becomes noticeable.

  Flickering can be reduced by reducing the number of LEDs connected in series so that the LED is lit even when the output voltage of the rectifier circuit 101 is low. However, if the number of LEDs connected in series is reduced, the voltage applied to the constant current drive circuit 104 increases when the output voltage of the rectifier circuit 101 increases, and the power loss in the constant current drive circuit 104 increases. was there.

  In addition, when a phase control dimmer is provided between the LED drive circuit and the AC power supply AC shown in FIG. 12 to provide a dimmable LED lighting system, the brightness is reduced by the phase control dimmer. However, there is a problem in that a large amount of current flows through the LED to emit light, and the brightness cannot be reduced.

  In the LED drive circuit shown in FIG. 12, the current in the region where the AC voltage of the AC power source AC is low is larger than the current in the region where the AC voltage of the AC power source AC is high, and the output voltage waveform of the rectifier circuit 101 and the rectifier circuit 101 The shape of the output current waveform differs greatly, causing a problem that the power factor is poor and harmonic noise is generated.

  Furthermore, in the LED drive circuit shown in FIG. 12, the transistor Q101 driven by the constant current drive circuit 104 has a loss and generates heat, so a heat sink is necessary. Since the current of all LEDs is concentrated on the transistor Q101, there is a problem that heat is concentrated and the heat sink becomes large.

  Further, the LED driving circuit shown in FIG. 12 has a problem in that the lifetime of the LEDs is shortened because a large current is caused to flow transiently through all the LEDs in a range where the output voltage of the rectifier circuit 101 is low.

  In view of the above situation, an object of the present invention is to provide an LED driving circuit with little flicker, an LED lighting device including the LED driving circuit, and an LED driving method.

  In order to achieve the above object, an LED driving circuit according to the present invention is an LED driving circuit that inputs an alternating voltage and drives at least two LEDs connected in series, the input of the LED driving circuit. A voltage control circuit that detects a voltage or a voltage obtained by rectifying the input voltage, and at least one switch circuit, and the LED drive circuit increases as the absolute value of the input voltage of the LED drive circuit increases. The voltage control circuit is configured to control ON / OFF of the switch circuit (first configuration) so that the number of LEDs supplied with the input voltage or the voltage obtained by rectifying the input voltage is increased.

  According to such a configuration, as the absolute value of the input voltage of the LED drive circuit increases, the number of LEDs supplied with the input voltage of the LED drive circuit or a voltage obtained by rectifying the input voltage is increased. Therefore, the LED is lit even in a range where the input voltage of the LED drive circuit is low, and the ratio of the lighting period to the cycle of the input voltage of the LED drive circuit is increased. Thereby, flicker can be reduced.

  The first configuration further includes a current limiting circuit that limits a current flowing through the LED, and the current limiting circuit has a current limiting value as the absolute value of the input voltage of the LED driving circuit increases. The current limiting circuit may be configured to increase (second configuration).

  According to such a configuration, the input current waveform of the current limiting circuit is close to the input voltage waveform of the current limiting circuit, and the power factor is improved. In addition, when a phase control type dimmer is provided between the LED illumination device having the second configuration and the AC power source to obtain a dimmable LED illumination system, the brightness is reduced by the phase control type dimmer. Even in the region, it is possible to solve the problem that a large amount of current flows through the LED to emit light, and the brightness cannot be reduced.

  In the first configuration, the switch circuit may have a function of limiting a current flowing through the LED (third configuration).

  According to such a configuration, the heat source (the switch circuit in the third configuration and the current limit circuit in the configuration in which the current limiting circuit is provided in the first configuration) is distributed more than the configuration in which the current limiting circuit is provided in the first configuration. Therefore, the heat generation points are dispersed and the local temperature rise is suppressed, so that the heat sink can be downsized.

  Further, in the first or third configuration, the at least two or more LEDs connected in series are configured by at least two types of LEDs having different luminances at a specified current, and are input to the LED driving circuit. As the absolute value of the voltage increases, the voltage control circuit may control ON / OFF of the switch circuit so that the LEDs are lit in order from the LED having the lowest luminance at the specified current.

  According to such a configuration, since the difference in luminance between when the absolute value of the input voltage of the LED driving circuit is low and when it is high, the flicker can be further reduced.

  In the third configuration, the at least two or more LEDs connected in series include at least two types of LEDs having different forward currents at a specified voltage, and the at least one or more switches. The circuit is composed of a plurality of switch circuits and at least two types of switch circuits having different current limit values. As the absolute value of the input voltage of the LED drive circuit increases, The voltage control circuit may control ON / OFF of the switch circuit so that the LED is turned on in order from the LED with the largest forward current and the current limit value of the switch circuit that is turned on becomes small.

  According to such a configuration, when the absolute value of the input voltage of the LED driving circuit is low, the number of lit LEDs is small, but the switch circuit with a large current limit value is turned on, and the forward direction at the specified voltage Since the LED having a large current is lit, the individual brightness of the lit LED is increased. On the other hand, when the absolute value of the input voltage of the LED drive circuit becomes high, the switch circuit with a small current limit value is turned on, so that the current limit value becomes small and the individual brightness of the LEDs that have been lit up so far is reduced. As the voltage decreases, an LED with a small forward current at the specified voltage is additionally lit. As a result, the difference in luminance between when the absolute value of the input voltage of the LED driving circuit is low and when it is high becomes small, so that the flicker can be further reduced.

  Further, when the absolute value of the input voltage of the LED drive circuit is high, the switch circuit having a small current limit value is turned on as described above, so that the current limit value is small and the LED generates a large forward current at a specified voltage. Will be reduced and the life will be extended.

  Further, in the third configuration, the at least one or more switch circuits are a plurality of switch circuits, and are configured by at least two types of switch circuits having different current limit values, and the input of the LED drive circuit The voltage control circuit may control ON / OFF of the switch circuit so that the current limit value of the switch circuit that is turned on increases as the absolute value of the voltage increases.

  According to such a configuration, the input current waveform of the LED driving circuit becomes close to the input voltage waveform of the LED driving circuit, and the power factor is improved. In addition, when a phase control type dimmer is provided between the LED illumination device having such a configuration and the AC power source to provide a dimmable LED illumination system, the LED can be used even in a region where the brightness is reduced by the phase control dimmer. In this case, the problem that a large amount of current flows to emit light and the brightness cannot be reduced can be solved.

  In order to achieve the above object, an LED lighting device according to the present invention includes an LED drive circuit having any one of the above-described configurations and at least two LEDs connected in series driven by the LED drive circuit. It is set as the structure provided.

  In order to achieve the above object, an LED driving method according to the present invention is an LED driving method for driving at least two LEDs connected in series using an alternating voltage, the alternating voltage or A step of detecting a voltage obtained by rectifying the alternating voltage, and a step of increasing the series number of LEDs supplied with the alternating voltage or a voltage obtained by rectifying the alternating voltage as the absolute value of the alternating voltage increases. Be prepared.

  According to such a method, as the absolute value of the alternating voltage increases, the number of LEDs connected to the alternating voltage or a voltage obtained by rectifying the alternating voltage increases, so that the alternating voltage is low. The LED is also lit in the range, and the ratio of the lighting period to the cycle of the alternating voltage is increased. Thereby, flicker can be reduced.

  According to the present invention, as the absolute value of the alternating voltage used when driving at least two or more LEDs connected in series increases, the alternating voltage or a voltage obtained by rectifying the alternating voltage is supplied. Since the number of LEDs in series is increased, the LEDs are lit even in a range where the alternating voltage is low, and the ratio of the lighting period to the cycle of the alternating voltage is increased. Thereby, flicker can be reduced.

These are the block diagrams of the LED lighting apparatus which concerns on 1st Embodiment of this invention. These are figures which show a specific example of the LED illuminating device shown in FIG. These are figures which show a specific example of the current limiting circuit with which the LED lighting apparatus shown in FIG. 2 is provided. These are figures which show a specific example of the current limiting circuit with which the LED lighting apparatus which concerns on 2nd Embodiment of this invention is provided. These are figures which show the output voltage and electric current waveform of the rectifier circuit in the LED lighting apparatus which concerns on 1st and 2nd embodiment of this invention. These are block diagrams of the LED lighting apparatus which concerns on 3rd Embodiment of this invention. These are figures which show a specific example of the switch circuit with a current limiting function with which the LED lighting apparatus shown in FIG. 6 is equipped. These are figures which show the output waveform of the rectifier circuit in the LED illuminating device which concerns on 1st, 3rd, and 4th embodiment of this invention, and the luminance waveform of the whole LED unit. These are figures which show the output voltage and electric current waveform of the rectifier circuit in the LED lighting apparatus concerning 3rd and 6th embodiment of this invention. These are figures which show the schematic structural example of a bulb-shaped LED lighting fixture. These are figures which show the external appearance of an electric lamp type, an annular | circular shape, and a straight tube | pipe type LED lighting fixture. These are figures which show the example of schematic structure of the conventional LED drive circuit. These are figures which show a voltage waveform and a luminance waveform at the time of lighting LED using AC power supply.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings used for the following description, the same portions are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated. In the following description, n is a natural number of 2 or more.

<First Embodiment>
FIG. 1 shows a block diagram of the LED lighting device according to the first embodiment of the present invention. The LED illumination device shown in FIG. 1 includes a plurality of LED units LED1 to LEDn connected in series and an LED drive circuit that drives the plurality of LED units LED1 to LEDn. Each of the plurality of LED units LED1 to LEDn is configured by one LED or a plurality of LEDs connected in series.

  The LED drive circuit for driving the plurality of LED units LED1 to LEDn includes connection terminals L and N, a rectifier circuit 1, a voltage detection control circuit 2, a current limit circuit CS0 having a fixed current limit value, Switch circuits SW1 to SWn are provided.

  When an AC voltage output from a commercial power supply is applied between the connection terminal L and the connection terminal N, the AC voltage is rectified by the rectifier circuit 1 and a pulsating voltage is output from the rectifier circuit 1. Note that the negative-side output end of the rectifier circuit 1 is fixed to a ground potential (hereinafter referred to as a ground potential) in the LED lighting device.

  The input side of the current limiting circuit CS0 is connected to the positive output side of the rectifier circuit 1. The current limiting circuit CS0 limits the maximum value of the current flowing through the plurality of LED units LED1 to LEDn, and prevents the current from flowing excessively through the LEDs.

  The plurality of LED units LED1 to LEDn are connected in series to the output side of the current limiting circuit CS0, and one switch circuit SW1 to SWn is connected to each cathode side of the plurality of LED units LED1 to LEDn.

  The voltage detection control circuit 2 monitors the pulsating voltage output from the rectifying circuit 1, and switches the switch circuits SW1 to SWn on / off according to the value of the pulsating voltage. When the pulsating voltage output from the rectifier circuit 1 is low, only the switch circuit SW1 is turned on so that the current flows only through the LED unit LED1, and when the pulsating voltage output from the rectifier circuit 1 increases, only the switch circuit SW2 is supplied. When the current is made to flow only to the LED units LED1 and LED2 and the pulsating voltage output from the rectifier circuit 1 is further increased, the switch circuit that is turned on so that the current flows to more LED units is switched.

  A specific example of the LED lighting device shown in FIG. 1 is shown in FIG. In FIG. 2, the bridge diode BD1 functions as the rectifier circuit 1, and includes a reference voltage source REF1, reference voltage dividing resistors R1 to Rn, pulsating voltage dividing resistors DR1 and DR2, comparators A1 to An-1, and an inverter gate. A circuit composed of INV1 to INVn-1 and AND gates AND2 to ANDn-1 (however, when n = 2, the AND gate AND1 is not provided) functions as the voltage detection control circuit 2. Moreover, in FIG. 2, each unit of the plurality of LED units LED1 to LEDn is configured by one LED.

The voltage dividing resistors R1 to Rn divide the reference voltage V _REF1 output from the reference voltage source REF1 to generate divided voltages V _{D1 to} V _Dn-1, and to the inverting input terminals of the comparators A1 to An-1. Supply. The ratio of the resistance values of the voltage dividing resistors R1 to Rn is equal to the ratio of the forward voltage drop VF of the LED units LED1 to LEDn. That is, if the forward voltage drops VF of the LED units LED1 to LEDn are all the same, the resistance values of the voltage dividing resistors R1 to Rn may be all the same.

The voltage dividing resistors DR1 and DR2 divide the pulsating voltage output from the bridge diode BD1, generate a divided voltage V _D0 , and supply it to the non-inverting input terminals of the comparators A1 to An-1. The ratio of the resistance values of the voltage dividing resistors DR1 and DR2 is set so that all of the LED units LED1 to LEDn are turned on when the pulsating voltage output from the bridge diode BD1 becomes maximum, that is, the following equation (1): Set to meet. However, in the equation (1), V _BD1MAX indicates the maximum value of the pulsating voltage output from the bridge diode BD1, DR1 indicates the resistance value of the voltage _dividing resistor DR1, and DR2 indicates the resistance value of the voltage _dividing resistor DR2.
V _REF1 ≈ V _BD1MAX × DR1 / (DR1 + DR2) (1)

Comparator Ak the partial pressure compared with the values of the partial pressures V _Dk of V _D0, the value of the partial pressure V _D0 becomes high level when is greater than the value of the partial pressure V _Dk, of the partial pressure V _D0 values An output signal that is at a low level is output when is equal to or less than the value of the partial pressure V _Dk (k is an arbitrary natural number between 1 and n−1).

  The output signal of the comparator A1 is supplied to the inverter gate INV1 and the first input terminal of the AND gate AND2, and the signal output from the inverter gate INV1 (inverted signal of the output signal of the comparator A1) is supplied to the control terminal of the switch circuit SW1. Is done. The output signal of the comparator Am is supplied to the inverter gate INVm and the first input terminal of the AND gate ANDm + 1, and the signal output from the inverter gate INVm (the inverted signal of the output signal of the comparator Am) is the second signal of the AND gate ANDm. A signal supplied to the input terminal and output from the AND gate ANDm is supplied to the control terminal of the switch circuit SWm (m is an arbitrary natural number of 2 or more and n-2 or less). The output signal of the comparator An-1 is supplied to the inverter gate INVn-1 and the switch circuit SWn, and the signal output from the inverter gate INVn-1 (the inverted signal of the output signal of the comparator An-1) is the AND gate ANDn-. 1 is supplied to the second input terminal, and the signal output from the AND gate ANDn-1 is supplied to the control terminal of the switch circuit SWn-1.

  The AND gates AND1 to ANDn-1 output a high level output signal only when both of the signal input to the first input terminal and the signal input to the second input terminal are at the high level, and are output to the first input terminal. When at least one of the input signal and the signal input to the second input terminal is at low level, a low level output signal is output.

  The switch circuits SW1 to SWn are turned on when a high level signal is supplied to their control terminals, and a current flows. When the low level signal is supplied to their control terminals, they are turned off and a current flows. There is no switch circuit.

Assuming that the pulsating voltage output from the bridge diode BD1 is 0 [V], the divided voltage V _D0 input to each non-inverting input terminal of the comparators A1 to An-1 is 0 [V]. The output signals of the comparators A1 to An-1 are all low level, the output signals of the inverter gate INV1 are high level, the output signals of the AND gates AND2 to ANDn-1 are all low level, and only the switch circuit SW1 is ON. Thus, the switch circuits SW2 to SWn are turned off, and a current flows only to the LED unit LED1.

Next, when the pulsating voltage output from the bridge diode BD1 slightly increases and the divided voltage V _D0 input to each non-inverting input terminal of the comparators A1 to An-1 exceeds the divided voltage V _D1 , The output signal becomes high level, the output signal of the inverter gate INV1 becomes low level, and the switch circuit SW1 is turned off. On the other hand, since the divided voltages V _D0 inputted to the non-inverting input terminals of the comparators A1 to An-1 are equal to or lower than the divided voltage V _D2 , all the output signals of the comparators A2 to An-1 are at a low level. Since the output signal of the comparator A2 is low level, the output signal of the inverter gate INV2 is high level, and the output signal of the comparator A1 and the output signal of the AND gate AND2 that receives the output signal of the inverter gate INV2 are high level. The switch circuit SW2 is turned on. Further, the output signals of the comparators A2 to An-1 are all at a low level, the output signals of the AND gates AND3 to ANDn-1 are all at a low level, and the switch circuits SW3 to SWn are turned off. Therefore, only the switch circuit SW2 is turned on, the switch circuits SW1 and SW3 to SWn are turned off, and a current flows only through the LED units LED1 and LED2.

Next, when the pulsating voltage output from the bridge diode BD1 further increases and the divided voltage V _D0 input to each non-inverting input terminal of the comparators A1 to An-1 exceeds the divided voltage V _D2 , In addition to the output signal, the output signal of the comparator A2 becomes high level, the output signals of the inverter gates INV1 and INV2 become low level, and the switch circuits SW1 and SW2 are turned off. On the other hand, since the divided voltage V _D0 inputted to each non-inverting input terminal of the comparators A1 to An-1 is equal to or lower than the divided voltage V _D3 , the output signals of the comparators A3 to An-1 are all at a low level. Since the output signal of the comparator A3 is low level, the output signal of the inverter gate INV3 is high level, and the output signal of the comparator A2 and the output signal of the AND gate AND3 that receives the output signal of the inverter gate INV3 are high level. The switch circuit SW3 is turned on. Further, the output signals of the comparators A3 to An-1 are all at a low level, the output signals of the AND gates AND4 to ANDn-1 are all at a low level, and the switch circuits SW4 to SWn are turned off. Accordingly, only the switch circuit SW3 is turned on, the switch circuits SW1, SW2, and SW4 to SWn are turned off, and a current flows only through the LED units LED1 to LED3.

  As described above, the number of LED units through which current flows increases as the pulsating voltage output from the bridge diode BD1 increases. When the pulsating voltage output from the bridge diode BD1 approaches the maximum value, the voltage at the non-input terminal in all the comparators A1 to An-1 exceeds the voltage at the inverting input terminal according to the above equation (1). The output signals of the comparators A1 to An-1 are all at the high level, the switch circuit SWn is turned on, and the second input terminals of all the AND gates AND2 to ANDn-1 are at the low level, which is the inverted state of the output signals of the comparators. Therefore, all the output signals of the AND gates AND2 to ANDn-1 become low level, the switch circuits SW1 to SWn-1 are turned OFF, and a current flows through all the LED units LED1 to LEDn.

  As described above, as the pulsating voltage output from the bridge diode BD1 increases, the number of LED units connected to the pulsating voltage output from the bridge diode BD1 increases. As a result, even in the range where the power supply voltage in which the LED is not lit in the conventional LED drive circuit is low, in the LED lighting device according to the first embodiment of the present invention, current flows through the LED, the LED emits light, and the period of the power supply voltage Since the ratio of the lighting period is large, flicker can be reduced.

  In addition, since the LEDs are lit even in a range where the power supply voltage is low, even if the number of LEDs connected in series is increased, the range in which the LEDs are turned off does not increase, and flickering hardly occurs. For this reason, the number of LEDs connected in series can be increased, the applied voltage of the current limiting circuit can be kept low, and the power loss in the current limiting circuit can be reduced.

  Since the current flowing through the LED passes through the current limiting circuit CS0, the maximum current value is limited so that excessive current does not flow through the LED.

  A specific example of the current limiting circuit CS0 is shown in FIG. The current limiting circuit shown in FIG. 3 includes terminals A and B, an NPN transistor Qcs, bias resistors Rcsb and Rcse, and a constant voltage diode ZD1. The collector of the transistor Qcs is connected to the terminal A, the emitter of the transistor Qcs is connected to the terminal B via the bias resistor Rcse, the collector and base of the transistor Qcs are connected via the bias resistor Rcsb, and the terminal B and the transistor Qcs The base is connected via a constant voltage diode ZD1.

The terminal A is connected to the positive output side of the bridge diode BD1, and the terminal B is connected to the anode side of the LED unit LED1. When a voltage is applied to the terminal A, a current flows from the terminal A toward the terminal B and flows into the LED. Inside the current limiting circuit CS0, a current flows through the bias resistor Rcsb to the constant voltage diode ZD1, and a Zener voltage Vz [V] (constant value) is generated at both ends of the constant voltage diode ZD1. Further, since the base-emitter voltage of the transistor is about 0.7 [V], the current Ics [A] flowing through the bias resistor Rcse is expressed by the following equation (2). However, in the formula (2), Rcse indicates the resistance value of the bias resistor Rcse.
Ics = (Vz−0.7) / Rcse (2)

  The current flowing from the terminal A to the terminal B is the sum of the current Ics and the current flowing through the constant voltage diode ZD1, but generally the current flowing through the constant voltage diode ZD1 is less than the current Ics0, so the terminal A The current flowing from terminal to terminal B can be approximated to the current Ics.

  The circuit configuration shown in FIG. 3 is merely an example, and for example, a PNP transistor may be used instead of the NPN transistor Qcs.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. The LED lighting device according to the second embodiment of the present invention removes the current limiting circuit CS0 from the LED lighting device according to the first embodiment of the present invention shown in FIG. 1 and replaces the current limiting circuit CS0 with a current limiting circuit CS0 ′. Is provided.

  In the current limiting circuit CS0 ', the current limiting value increases as the pulsating voltage output from the rectifying circuit 1 increases. A specific example of the current limiting circuit CS0 'is shown in FIG. The current limiting circuit CS0 'shown in FIG. 4 includes terminals A and B, PNP transistors Qcs1 and Qcs2, and resistors Rcse1, Rcse2, and Rcsc. The emitter of the transistor Qcs1 is connected to the terminal A via the resistor Rcse1, the emitter of the transistor Qcs2 is connected to the terminal A via the resistor Rcse2, and the collector of the transistor Qcs1 is connected to the ground via the resistor Rcsc. The collector is connected to the terminal B, and the base and collector of the transistor Qcs1 and the base of the transistor Qcs2 are connected in common.

The terminal A is connected to the positive output side of the rectifier circuit 1, and the terminal B is connected to the anode side of the LED unit LED1. When a voltage is applied to the terminal A, a current flows through the resistor Rcse1, the transistor Qcs1, and the resistor Rcsc. Since the base and collector of the transistor Qcs1 are connected in common, the emitter-collector voltage of the transistor Qcs1 is approximately 0.7 [V]. Further, if a resistor having a relatively small resistance value is used as the resistor Rcse1 and the voltage applied to both ends of the resistor Rcse1 is set to be sufficiently smaller than the voltage applied to the terminal A, the current Icse1 flowing through the resistor Rcse1 is Approximated by the following equation (3). In the equation (3), V _A indicates a voltage applied to the terminal A, and Rcsc indicates a resistance value of the resistor Rcsc.
Icse1 = (V _A −0.7) / Rcsc (3)

The transistors Qcs1 and Qcs2 are transistors having uniform characteristics and constitute a current mirror circuit. When the resistance value of the resistor Rcse1 is set sufficiently smaller than the resistance value of Rcsc, the emitter-collector of the transistor Qcs2 A current Ics2 that flows between them, that is, a current that flows from the terminal A to the terminal B is a current that flows in the LED, and is expressed by the following equation (4). However, in the equation (4), Rcse1 indicates the resistance value of the resistor Rcse1, and Rcse2 indicates the resistance value of the resistor Rcse2.
Ics2 = {(V _A −0.7) / Rcsc} × (Rcse1 / Rcse2) (4)

  From the above equation (4), it is understood that in the current limiting circuit CS0 'shown in FIG. 4, the current limiting value increases as the pulsating voltage output from the rectifying circuit 1 increases. Thereby, when it is set as the LED lighting system which can be dimmed by providing a phase control type dimmer between the LED lighting apparatus according to the second embodiment of the present invention and the AC power supply AC, the phase control type dimmer Even in a region where the brightness is reduced, a large amount of current flows through the LED to emit light, and the problem that the luminance cannot be reduced can be solved. Further, the output current waveform of the rectifier circuit 1 becomes close to the output voltage waveform of the rectifier circuit 1, and the power factor is improved (see FIG. 5). FIG. 5 shows an output voltage waveform 3 of the rectifier circuit 1 in the LED lighting device according to the first and second embodiments of the present invention, and an output voltage waveform 4 of the rectifier circuit 1 in the LED lighting device according to the first embodiment of the present invention. It is a figure which shows the output voltage waveform 5 of the rectifier circuit 1 in the LED lighting apparatus which concerns on 2nd Embodiment of this invention. FIG. 5 shows a case where n = 2.

<Third Embodiment>
Next, a third embodiment of the present invention will be described. The LED lighting device according to the third embodiment of the present invention removes the current limiting circuit CS0 and the switch circuits SW1 to SWn from the LED lighting device according to the first embodiment of the present invention shown in FIG. Instead, a switch circuit with current limiting function CS1 to CSn is provided.

  When an AC voltage output from a commercial power supply is applied between the connection terminal L and the connection terminal N, the AC voltage is rectified by the rectifier circuit 1 and a pulsating voltage is output from the rectifier circuit 1. Note that the negative output terminal of the rectifier circuit 1 is fixed to the ground potential.

  The plurality of LED units LED1 to LEDn are connected in series to the positive output side of the rectifier circuit 1, and one switch circuit CS1 to CSn with a current limiting function is connected to each cathode side of the plurality of LED units LED1 to LEDn. Has been.

  The voltage detection control circuit 2 monitors the pulsating voltage output from the rectifying circuit 1, and switches on / off the switch circuits CS1 to CSn with a current limiting function according to the value of the pulsating voltage. Since the specific example and operation of the voltage detection control circuit 2 are as described in the first embodiment, description thereof will be omitted.

  Further, the first embodiment described above also relates to the operation when the number of LED units to which the pulsating voltage output from the rectifying circuit 1 is supplied increases as the pulsating voltage output from the rectifying circuit 1 increases. Since it is as having described in the form, description is abbreviate | omitted.

  A current flows through the LED in response to an increase in the pulsating voltage output from the rectifier circuit 1, and the current is switched on in the switch circuit CSk with a current limiting function (k is an arbitrary natural number between 1 and n). When the current is limited by the switch circuit CSk with a current limiting function, excessive current does not flow to the LED.

  The LED lighting device according to the third embodiment of the present invention has the same effects as the LED lighting device according to the first embodiment of the present invention. Furthermore, in the LED lighting device according to the third embodiment of the present invention, the heat generation source (switch circuits CS1 to CSn with a current limiting function in the third embodiment, and the current limiting circuit CS0 in the first embodiment) is from the first embodiment. Since the heat generation points are dispersed and the local temperature rise is suppressed, the heat sink can be downsized.

  Here, a specific example of the switch circuits CS1 to CSn with a current limiting function is shown in FIG. The switch circuit CS1 includes NPN transistors Qu1 and Qd1, resistors Rb1 and Re1, a control signal input terminal t1, and a switch input terminal t1 '. Similarly, the switch circuit CS2 includes NPN transistors Qu2 and Qd2, resistors Rb2 and Re2, a control signal input terminal t2, and a switch input terminal t2 ′. The switch circuit CSn includes NPN transistors Qun and Qdn, resistors Rbn and Ren, a control signal input terminal tn, and a switch input terminal tn ′ are provided. When the switch circuits CS1 to CSn with current limiting function shown in FIG. 7 are used, the LED lighting device according to the third embodiment of the present invention is a circuit for supplying a bias voltage to the switch circuits CS1 to CSn with current limiting function ( A circuit comprising a reference voltage source REF2, an NPN transistor Qcs0, and resistors Rcsc0 and Rcse0). Further, each output from the voltage detection control circuit 2 is supplied to the control signal input terminals t1 to tn.

The reference voltage source REF2 outputs a reference voltage _VREF2 . When the resistance value of the resistor Rcse0 is set sufficiently smaller than the resistance value of the resistor Rcsc0, the current Ics0 flowing from the collector to the emitter of the transistor Qcs0 can be approximated by the following equation (5). However, in the equation (5), Rcsc0 indicates the resistance value of the resistor Rcsc0.
_{Ics0 = (V REF2 -0.7) /} Rcsc0 ... (5)

  The transistors Qcs0 and Qd1 to Qdn are transistors with uniform characteristics and constitute a current mirror circuit.

The maximum value Ics1 of the current flowing into the switch input terminal t1 ′ is expressed by the following equation (6). In Equation (6), Re1 represents the resistance value of the resistor Re1, and Rcse0 represents the resistance value of the resistor Rcse0.
Ics1 = (Re1 / Rcse0) × Ics0 (6)

Similarly, the maximum value Ics2 of the current flowing into the switch input terminal t2 ′ is expressed by the following equation.
Ics2 = (Re2 / Rcse0) × Ics0

Similarly, the maximum value Icsn of the current flowing into the switch input terminal tn ′ is expressed by the following equation.
Icsn = (Ren / Rcse0) × Ics0

  Therefore, the current flowing through the LED can be changed by adjusting the resistance values of the resistors Re1 to Ren. Embodiments to which this is applied are the fifth and sixth embodiments to be described later.

<Fourth embodiment>
Next, a fourth embodiment of the present invention will be described. The block diagram of the LED lighting device according to the fourth embodiment of the present invention is the same as that of the first embodiment or the third embodiment (see FIG. 1 or FIG. 6). The specific circuit example in the fourth embodiment is also the same as the specific circuit example in the first embodiment or the third embodiment (see FIG. 2, FIG. 3 or FIG. 7), and the luminance of the LED. Only the difference.

  In the fourth embodiment, a high-brightness LED is used as an LED unit that is lit when the pulsating voltage output from the rectifier circuit 1 is low, and the LED unit that does not illuminate until the pulsating voltage output from the rectifier circuit 1 is high. The LED of low brightness is used. Specifically, each LED unit has the following relationship: (luminance at the specified current of the LED unit LED1)> (luminance at the specified current of the LED unit LED2)> ...> (luminance at the specified current of the LED unit LEDn) Select the LED to be used in. As a result, the difference in luminance between when the pulsating voltage output from the rectifier circuit 1 is low and when it is high is reduced, so that flicker can be further reduced (see FIG. 8). FIG. 8 shows the output voltage waveform 3 of the rectifier circuit 1 in the LED lighting device according to the first, third, and fourth embodiments of the present invention, and the LED in the LED lighting device according to the first and third embodiments of the present invention. It is a figure which shows the luminance waveform 6 of unit LED1-LEDn whole, and the luminance waveform 7 of LED unit LED1-LEDn whole in the LED illuminating device which concerns on 4th Embodiment of this invention. FIG. 8 shows a case where n = 2, but by increasing n, the time during which the LED is turned off can be further reduced, and flicker can be further reduced.

<Fifth Embodiment>
Next, a fifth embodiment of the present invention will be described. The fifth embodiment of the present invention is an application of the third embodiment, and the block diagram of the LED lighting device according to the fifth embodiment of the present invention is the same as that of the third embodiment (see FIG. 6). The specific circuit example in the fifth embodiment is also the same as the specific circuit example in the third embodiment (see FIG. 7).

  In the fifth embodiment, the LED unit that is lit when the pulsating voltage output from the rectifier circuit 1 is low uses an LED having a large forward current at a specified voltage, and the pulsating voltage output from the rectifier circuit 1 is high. For the LED unit that does not light up until it becomes, an LED having a small forward current at a specified voltage is used. Specifically, (forward current at the specified voltage of the LED unit LED1)> (forward current at the specified voltage of the LED unit LED2)> ...> (forward current at the specified voltage of the LED unit LEDn) Thus, the LED used in each LED unit is selected.

  In the fifth embodiment, the current limit value of the switch circuit with a current limiting function connected to the cathode of the LED unit that is lit when the pulsating voltage output from the rectifier circuit 1 is low is increased. The current limit value of the switch circuit with a current limiting function connected to the cathode of the LED unit that does not light up until the output pulsating voltage becomes high is reduced. Specifically, (current limit value of switch circuit CS1 with current limit function)> (current limit value of switch circuit CS2 with current limit function)>...> (Current limit value of switch circuit CSn with current limit function) As described above, the current limit values of the switch circuits CS1 to CSn with current limit function are set.

  As a result, when the pulsating voltage output from the rectifier circuit 1 is low, the number of LEDs that are lit is small, but the switch circuit with a current limiting function having a large current limit value is turned ON, and the forward direction at the specified voltage Since the LED having a large current is lit, the individual brightness of the lit LED is high. On the other hand, when the pulsating voltage output from the rectifier circuit 1 becomes high, the switch circuit with a current limiting function having a small current limiting value is turned on, so that the current limiting value becomes small and the LEDs that have been lit up until then are turned on. As each luminance decreases, an LED with a small forward current at a specified voltage is additionally lit. As a result, the luminance waveform of the entire LED units LED1 to LEDn becomes the same as the luminance waveform 7 shown in FIG. 8, and the luminance difference between when the pulsating voltage output from the rectifier circuit 1 is low and high is small. Therefore, flicker can be further reduced.

  Further, when the pulsating voltage output from the rectifier circuit 1 is high, the switch circuit with a current limiting function having a small current limiting value is turned on as described above, so that the current limiting value becomes small and the forward current at the specified voltage is reduced. The heat generation of large LEDs is reduced and the life is extended.

<Sixth Embodiment>
Next, a sixth embodiment of the present invention will be described. The sixth embodiment of the present invention is an application of the third embodiment, and the block diagram of the LED lighting device according to the sixth embodiment of the present invention is the same as that of the third embodiment (see FIG. 6). The specific circuit example in the sixth embodiment is also the same as the specific circuit example in the third embodiment (see FIG. 7).

  In the sixth embodiment, the current limit value of the switch circuit with a current limiting function connected to the cathode of the LED unit that is lit when the pulsating voltage output from the rectifier circuit 1 is low is reduced, and is output from the rectifier circuit 1. The current limit value of the switch circuit with a current limiting function connected to the cathode of the LED unit that does not light up until the pulsating voltage increases is increased. Specifically, (current limit value of switch circuit CS1 with current limiting function) <(current limit value of switch circuit CS2 with current limiting function) <... (Current limit value of switch circuit CSn with current limiting function). As described above, the current limit values of the switch circuits CS1 to CSn with current limit function are set. Thereby, the output current waveform of the rectifier circuit 1 becomes close to the output voltage waveform of the rectifier circuit 1, and the power factor is improved (see FIG. 9). FIG. 9 shows the output voltage waveform 3 of the rectifier circuit 1 in the LED lighting device according to the third and sixth embodiments of the present invention, and the switch circuit CS1 with current limiting function in the LED lighting device according to the third embodiment of the present invention. It is a figure which shows the output voltage waveform 8 of the rectifier circuit 1 when each current limiting value of CSn is the same, and the output voltage waveform 9 of the rectifier circuit 1 in the LED lighting apparatus according to the sixth embodiment of the present invention. Although FIG. 9 shows the case where n = 2, the output current waveform of the rectifier circuit 1 is closer to the output voltage waveform of the rectifier circuit 1 by increasing n and switching the current limit value in finer steps. Thus, the power factor is further improved.

  From the voltage waveform 3 and the current waveform 9 in FIG. 9, it is understood that in the sixth embodiment, the current limit value increases as the pulsating voltage output from the rectifier circuit 1 increases. Thereby, when it is set as the LED illumination system which can be dimmed by providing a phase control dimmer between the LED illumination device according to the sixth embodiment of the present invention and the AC power supply AC, the phase control dimmer Even in a region where the brightness is reduced, a large amount of current flows through the LED to emit light, and the problem that the luminance cannot be reduced can be solved.

<Others>
The voltage input to the LED lighting device according to the present invention is not limited to a sinusoidal AC voltage, and may be another alternating voltage (for example, an alternating voltage output from a phase control dimmer). Further, when the current flowing through the LED unit has a sufficient margin with respect to the rated current of the LED, it is also possible not to provide a current limiting circuit or a current limiting function.

  In the above-described embodiment, the switch circuit SWn or the switch circuit CSn with a current limiting function is provided. However, the LED unit to which the pulsating voltage output from the rectifier circuit 1 is not supplied without providing them is in the ON state. Since it is short-circuited to the ground by the switch circuit or the switch circuit with a current limiting function, the same effect as that of the above-described embodiment can be obtained. For example, when the switch circuit SWn is not provided in the circuit configuration shown in FIG. 2, the output signal of the AND gate An-1 may be supplied only to the inverter gate INVn-1.

  Further, a modification in which the anode side of the LED unit LED1 and the cathode side of the LED unit LEDn-k are connected via the switch circuit SWk or the switch circuit CSk with a current limiting function is possible (k is 1 or more and n-1 or less). Natural number).

  Further, in FIG. 7 of a specific example of the switch circuits CS1 to CSn with current limiting function in the third embodiment of the present invention, the reference voltage source REF2, the transistors Qcs0, Qd1, Qd2, Qdn, resistors Rcsc0, Rcse0, Re1, Re2 , Ren are removed, the emitters of the transistors Qu1, Qu2, and Qu are connected to the ground potential, a resistor Rc1 is connected between the collector of the transistor Qu1 and the switch input terminal t1 ′, and the collector of the transistor Qu2 and the switch input terminal t2 ′ are connected. Even if the resistor Rc2 is connected between the collector and the resistor Rcn between the collector of the transistor Qun and the switch input terminal tn ′, the accuracy of the current limit value is reduced, but a switch circuit with a current limit function is simply configured. (The figure is omitted). In this embodiment, the current limit value is determined by the resistance values of the resistors Rc1, Rc2, and Rcn.

  Moreover, although all the LED lighting apparatuses mentioned above are provided with the rectifier circuit, a rectifier circuit is not an essential component with respect to the LED lighting apparatus which concerns on this invention. In the configuration in which the rectifier circuit is not provided, for example, two LED modules having different forward directions (a module composed of n LED units) are provided, and for each LED module, a voltage detection control circuit, a current limiting circuit, and n pieces of LED modules are provided. The switch circuit is provided with a voltage detection control circuit and n number of switch circuits with a current limiting function. In such a configuration, the rectifier circuit is unnecessary, the power supply efficiency is slightly improved because the rectifier circuit is unnecessary, and the duty ratio of the LED drive current is half that of the system driven after full-wave rectification. As a result, there is a merit such as extending the life of the LED (= reducing the decrease in luminous flux), but on the other hand, the number of LEDs is doubled, resulting in a demerit.

  The LED lighting device according to the present invention can be implemented, for example, in the form of a lamp. FIG. 10 shows a schematic structural example of an LED illumination lamp that is an embodiment of the LED illumination device according to the present invention. In FIG. 10, the bulb-shaped LED lighting fixture 10 is shown in a partially cutaway view. The bulb-shaped LED lighting fixture 10 includes a housing or substrate 12, n or 2n LED units 11 installed on the front surface (bulb-shaped head side) of the housing or substrate 12, and the housing or substrate. The LED drive circuit 13 according to the present invention is installed inside the back surface of 12 (the lower side of the light bulb shape).

  An LED illumination lamp mounting portion 14 to which a bulb-shaped LED illumination lamp 10 is screwed and mounted, and a light controller 15 are connected in series to an AC power source AC. The LED illumination lamp mounting part 14 is disposed on, for example, an indoor ceiling wall surface, and the light controller 15 is disposed on, for example, an indoor side wall surface.

  Since the bulb-shaped LED illumination lamp 10 is detachable from the LED illumination lamp mounting portion 14, for example, in existing illumination apparatuses and illumination systems that conventionally used illumination lamps such as incandescent lamps and fluorescent lamps, It is easy to replace an illumination lamp such as a lamp or a fluorescent lamp with a bulb-shaped LED illumination lamp 10.

  FIG. 10 shows the appearance of the light controller 15 when the light controller 15 is a phase control dimmer, and the degree of dimming can be changed by a knob type volume. The device 15 may be a light control device other than the phase control dimmer, for example, a light control device including a push switch and a firefly circuit.

  In the above description, the light controller is one that is directly operated by a person using a knob-type volume or a push button switch. However, the light controller is not limited to this, and may be one that is remotely operated by a radio signal such as a remote controller. That is, a wireless signal receiving unit is provided in the light controller main body on the receiving side, and a light control signal (for example, a remote control transmitter, a portable terminal, etc.) Remote control can be performed by providing a wireless signal transmission unit that transmits a dimming signal, a light ON / OFF signal, and the like.

  Further, the LED illumination lamp is not limited to a light bulb-shaped LED illumination lamp, and is, for example, an electric LED illumination lamp 16, an annular LED illumination lamp 17, or a straight tube LED illumination lamp 18 shown in FIG. Also good. In any shape, the LED illumination lamp has a structure including at least an LED and an LED drive circuit.

DESCRIPTION OF SYMBOLS 1 Rectification circuit 2 Voltage detection control circuit 3 Voltage waveform 4, 5 Current waveform 6, 7 Luminance waveform 8, 9 Current waveform 10 Light bulb-shaped LED lighting fixture 11 n or 2n LED unit 12 Case or board 13 This invention LED driving circuit 14 LED lighting fixture mounting portion 15 Light controller 16 Electric LED lighting fixture 17 Annular LED lighting fixture 18 Straight tube LED lighting fixture 101 Rectifier circuit 102 Series LED group 103 Bypass resistance group 104 Current drive circuit 105 Voltage comparison switching drive circuit 106 Voltage waveform 107, 108 Luminance waveform A, B Terminal A1-An-1 Comparator AC AC power supply AND2-ANDn-1 AND gate BD1 Bridge diode CS0, CS0 'Current limit circuit CS1-CSn Switch times with current limiting function Path DR1, DR2 Dividing resistance of pulsating voltage INV1-INVn-1 Inverter gate L, N Connection terminal LED1-LEDn LED unit Q101, Q102 npn transistor Q103, Q104 n-channel field effect transistor Qcs NPN transistor Qcs1, Qcs2 PNP transistor Qd1 ~ Qdn, Qu1-Qun, Qcs0 NPN transistor R1-Rn Reference voltage divider resistor R101-R106 Resistor Rcsb, Rcse Bias resistor Rcse1, Rcse2, Rcsc resistor Rb1-Rbn, Re1-Ren, Rcsc0, Rcse0 resistor REF1, REF2 Reference Voltage source SW1 to SWn Switch circuit t1 to tn Control signal input terminal t1 ′ to tn ′ Switch input terminal ZD1 Constant voltage diode

Claims (8)

An LED driving circuit that inputs an alternating voltage and drives at least two or more LEDs connected in series,
A voltage control circuit for detecting an input voltage of the LED driving circuit or a voltage obtained by rectifying the input voltage;
And at least one switch circuit,
As the absolute value of the input voltage of the LED driving circuit increases, the voltage control is performed so that the number of LEDs supplied with the input voltage of the LED driving circuit or a voltage obtained by rectifying the input voltage is increased. An LED driving circuit, wherein the circuit controls ON / OFF of the switch circuit. A current limiting circuit for limiting a current flowing through the LED;
The LED driving circuit according to claim 1, wherein the current limiting circuit is a current limiting circuit in which a current limiting value increases as an absolute value of an input voltage of the LED driving circuit increases.   The LED drive circuit according to claim 1, wherein the switch circuit has a function of limiting a current flowing through the LED. The at least two or more LEDs connected in series are composed of at least two types of LEDs having different brightness at a specified current,
As the absolute value of the input voltage of the LED drive circuit increases, the voltage control circuit controls ON / OFF of the switch circuit so that the LEDs are lit in order from the LED having the lowest luminance at the specified current. The LED driving circuit according to claim 1, wherein the LED driving circuit is characterized in that: The at least two LEDs connected in series are composed of at least two types of LEDs having different forward currents at a specified voltage,
The at least one switch circuit is a plurality of switch circuits, and is composed of at least two types of switch circuits having different current limit values,
As the absolute value of the input voltage of the LED drive circuit increases, the current limit value of the switch circuit that is turned on in order from the LED with the larger forward current at the specified voltage and turned on becomes smaller. The LED drive circuit according to claim 3, wherein the voltage control circuit controls ON / OFF of the switch circuit. The at least one switch circuit is a plurality of switch circuits, and is composed of at least two types of switch circuits having different current limit values,
The voltage control circuit controls ON / OFF of the switch circuit so that the current limit value of the switch circuit that is turned on increases as the absolute value of the input voltage of the LED drive circuit increases. The LED driving circuit according to claim 3. The LED driving circuit according to any one of claims 1 to 6,
An LED lighting device comprising: at least two LEDs connected in series driven by the LED driving circuit. An LED driving method for driving at least two or more LEDs connected in series using an alternating voltage,
Detecting the alternating voltage or a voltage obtained by rectifying the alternating voltage;
And increasing the series number of LEDs supplied with the alternating voltage or a voltage obtained by rectifying the alternating voltage as the absolute value of the alternating voltage increases.

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