KR20190106416A - Lighting control device - Google Patents

Abstract

A lighting control device according to an embodiment includes: a sensor unit configured to sense an object; a PWM signal generating unit configured to generate a PWM input signal according to the signal sensed by the sensor unit; a first photocoupler to which a single output from the PWM signal generating unit is input; an output unit to which a signal output from the first photocoupler is input; a power supply unit configured to supply power to the sensor unit and the PWM signal generating unit; and a power switching unit configured to selectively supply power to the PWM signal generating unit and the sensor unit according to a dimming operation signal, wherein the first photocoupler may electrically insulate the PWM signal generating unit and the output unit. In the embodiment, power is switched according to whether a dimming operation mode or a standby mode is on, so it is possible to effectively prevent power loss generated during the standby mode.

Description

Lighting control device {LIGHTING CONTROL DEVICE}

Embodiments relate to a lighting control device for reducing standby power consumption.

Light Emitting Diodes (LEDs) are a type of semiconductor device that converts electrical energy into light. Light emitting diodes have the advantages of low power consumption, semi-permanent life, fast response speed, safety and environmental friendliness compared to conventional light sources such as fluorescent and incandescent lamps. In particular, the LED lighting device can perform a variety of production by controlling the flashing order, the emission color and the brightness of the LED arranged in a plurality.

Accordingly, many researches are being conducted to replace conventional light sources with light emitting diodes, and light emitting diodes are increasingly used as light sources for lighting devices such as various lamps, liquid crystal displays, electronic displays, and street lamps that are used indoors and outdoors. . In particular, it is used for general lighting in the interior, stage lighting for creating a specific atmosphere, advertising lighting and landscape lighting.

The lighting device may be installed on an exterior wall of a building, a park, a street lamp, a bridge railing, or a performance hall as lapsed illumination, and its size and application system may vary depending on the intended use, object, or location. In other words, the exterior wall of the building is simply displayed in the form of a band on the exterior wall of the building, or simply expressed in a single color or a combination of colors. It is used to change.

The lighting device includes a driving driver for driving the LED module, a sensor for sensing an external object, and a dimming controller for controlling a dimming signal of the LED module by a sensing value sensed by the sensor.

In the conventional lighting device, when an external object is detected, the sensor and the dimming control unit must be operated to control the LED module. Therefore, the sensor unit and the dimming control unit should always be activated. This causes a lot of problems in standby power consumption.

The embodiment aims to provide a lighting control device for reducing standby power consumption.

The lighting control apparatus according to the embodiment includes a sensor unit for sensing an object, a PWM signal generator for generating a PWM input signal according to the signal detected from the sensor unit, and a signal output from the PWM signal generator. A photo coupler, an output unit to which the signal output from the first photo coupler is input, a power supply unit supplying power to the sensor unit and the PWM signal generator, and the PWM signal generator and the sensor according to a dimming operation signal And a power switching unit for selectively supplying power to the unit, and the first photo coupler may electrically insulate the PWM signal generator and the output unit.

The electronic device may further include a first switch configured to provide an on-off signal to the power switching unit according to the dimming operation signal.

The power switching unit is disposed between the power supply unit and the PWM signal generating unit, and the power switching unit is turned off to cut off power to the PWM signal generating unit when the first switch is turned off and the second photo coupler and the second. The electronic device may further include a second switch branched between the photo coupler and the PWM signal generator and disposed between the power supply unit and the sensor unit.

The second switch includes a BJT circuit, wherein the BJT circuit is turned on and off by a potential difference between a first node between the power supply unit and the BJT circuit and a second node between the second photo coupler and the PWM signal generator. Can be.

When the first switch is turned on, the second switch may be turned off so that power of the power supply unit may be applied to the PWM signal generator.

The electronic device may further include a sensing detector configured to output a low signal generated from the sensor unit through the first photo coupler.

The sensing detector may include a third switch disposed between the sensor unit and the first photo coupler and turned on by the high signal of the sensor unit when the first switch is turned off and turned off when the signal is switched to the low signal. .

The apparatus may further include a bias current controller configured to control the bias current of the second photo coupler by the on / off signal of the first switch.

The bias current controller may increase the bias current of the first photo coupler when an on signal of the first switch is received, and decrease the bias current of the first photo coupler when an off signal of the first switch is received. .

The bias current controller includes a MOSFET circuit and a tenth and eleventh resistors connected in parallel between the fourth switch and the gate terminal and the source terminal of the fourth switch and the fourth switch turned on and off according to the signal of the first switch, An eighth resistor may be connected between the source terminal of the third switch and the first photo coupler in parallel with the tenth resistor.

According to the embodiment, power is switched according to the dimming operation mode and the standby mode, thereby effectively preventing power loss generated during the standby mode.

In addition, the embodiment has an effect that can effectively output the low signal generated from the sensor by designing the sensing detector with a simple structure consisting of a switch and a passive element.

In addition, the embodiment has the effect of preventing the distortion of the signal by controlling the bias current of the photo coupler.

1 is a circuit diagram illustrating a lighting control device according to an embodiment.
2 and 3 are circuit diagrams for describing an operation of a power switch of the lighting control apparatus according to the embodiment.
4 is a circuit diagram illustrating an operation of a sensing detector of a lighting control apparatus according to an embodiment.
5 and 6 are circuit diagrams for describing an operation of the bias current controller of the lighting control apparatus according to the embodiment.
7 is a diagram illustrating waveforms in an operation mode and a standby mode of a current controller.

The following embodiments are provided as examples to sufficiently convey the spirit of the present invention to those skilled in the art to which the present invention pertains. Therefore, the present invention is not limited to the embodiments described below and may be embodied in other forms. Like numbers refer to like elements throughout the specification.

Advantages and features of the present invention, and methods for achieving them will be apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms. In addition, only the embodiments are provided to make the disclosure of the present invention complete, and to fully inform the scope of the invention to those skilled in the art. Moreover, the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout.

In describing the embodiments of the present disclosure, when it is determined that a detailed description of a known function or configuration may unnecessarily obscure the subject matter of the present disclosure, the detailed description thereof will be omitted. Terms to be described below are terms defined in consideration of functions in the embodiments of the present invention, and may vary according to intentions or customs of users or operators. Therefore, the definition should be made based on the contents throughout the specification.

The spatially relative terms "under, below, beneath", "lower", "on, above", "upper", and the like are shown as one element as shown in the drawings. Or it may be used to easily describe the correlation of the components with other elements or components. The spatially relative terms are to be understood as terms that include different directions of the device in use or operation in addition to the directions shown in the figures. For example, when flipping a device shown in the figure, a device described as "below" or "beneath" of another device may be placed "above" of another device. Thus, the exemplary term "below" may include both an orientation of above and below.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In this specification, the singular also includes the plural unless specifically stated otherwise in the phrase. As used herein, “comprise” and / or “comprising” refers to a component, step, operation and / or element that is present in one or more other components, steps, operations and / or elements. Or does not exclude additions.

1 is a circuit diagram illustrating a lighting control device according to an embodiment, FIGS. 2 and 3 are circuit diagrams for describing an operation of a power switching unit of the lighting control device according to an embodiment, and FIG. 4 is a lighting control device according to an embodiment. 5 and 6 are circuit diagrams for describing an operation of a bias current controller of a lighting control apparatus according to an embodiment, and FIG. 7 is a diagram illustrating an operation mode and a standby mode of a current controller. Is a diagram showing waveforms.

Referring to FIG. 1, the lighting control apparatus according to the embodiment includes a sensor unit 100 for detecting an object and a PWM signal generator 300 for generating a PWM input signal according to a signal detected from the sensor unit 100. And a first photo coupler PC1 to which a signal output from the PWM signal generator 300 is input, an output unit 400 to which a signal output from the first photo coupler PC1 is input, and the sensor. A power supply unit 500 for supplying power to the unit 100 and the PWM signal generator 300, and selectively supply power to the PWM signal generator 300 and the sensor unit 100 according to a signal of a dimming operation signal It may include a power switching unit 600 for supplying.

The sensor unit 100 is installed at the entrance of a parking lot where humans frequently enter or exit an object, such as a car, and the like, and detects the entrance of a person or a car at the entrance or parking entrance.

The sensor unit 100 may be connected to the (+) and (-) terminals of the dimmer 200. The dimmer 200 may adjust the brightness of the LED module 900. The dimmer 200 may adjust the brightness according to the voltage by applying a range of voltages to the LED driving driver 910. Such a voltage range may use a voltage in the range of 0-10V, for example. The dimmer 200 may dimm the illumination by inputting a DC voltage between 0 and 10 V at an input voltage ratio of 10 V, and the connection part may be divided to have a negative (−) input part and a positive (+) input part. Can be.

The PWM signal generator 300 may generate a PWM signal for controlling dimming according to the signal sensed by the sensor unit 100. The PWM signal generator 300 may control the power level of the driving power source according to the brightness control signal of the dimmer. The PWM signal generator 300 may be configured using an inductor, a capacitor, or the like.

The PWM signal output from the PWM signal generator 300 may be input to the first photo coupler PC1. The first photo coupler PC1 may electrically insulate the PWM signal generator 300 from the output unit 400. Here, the output terminal of the first photo coupler PC1 may be configured to convert a voltage of 0V to 10V into a voltage of 0V to 3.3V.

The first photo coupler PC1 is an element for coupling an electrical signal to light, and may be configured by a property in which a light emitting diode as a light emitting unit and a photo transistor as a light receiving unit are electrically insulated from each other. When the PWM input signal is input, the light is emitted from the light emitting diode and touches the photo transistor so that the photo transistor is electrically operated. Accordingly, the PWM output signal output from the photo transistor may be output to the LED driving driver 900 through the output unit 400.

The output unit 400 may include a PWM signal inverting unit 410, a thirteenth resistor R13, and a first capacitor C1. The sensor unit 100 may be normally opened so that a contact is opened and turned on when an object is detected. Therefore, when the external dimming signal is input from the sensor unit 100, a strong dimming signal is normally input when there is no entry and exit, and when there is an entry or exit of an object, a weak dimming signal is input and the dimming adjustment is reversed. Therefore, in order to use the external dimming signal of the sensor unit 100 as an input means, it is necessary to invert and provide the input external dimming signal, and the PWM signal inverting unit 410 may serve to invert the signal. . The thirteenth resistor R13 and the first capacitor C1 may smooth and output a signal.

The LED driving driver 910 may control the brightness of the LED module 900 by supplying driving power to the LED module 900. Although not shown in the drawings, the LED driving driver 910 may include an EMI filter unit, a rectifier, a power factor corrector, and a DC / DC converter.

The EMI filter unit may remove noise of an input power source from an electromagnetic interference (EMI) filter unit. When input power is supplied from the power supply unit 100, electrical noise may be converted into a magnetic field, and electromagnetic interference (EMI) may be generated, which causes interference with other elements of the lighting control device. The EMI filter unit can remove this noise. The EMI filter portion may be configured by an inductor and / or a capacitor to remove EMI.

The rectifier serves to rectify the AC power of the power supply unit 500. The rectifier may comprise a diode. The rectifier may include a bridge rectifier, but is not limited thereto. The rectified power may be supplied to the DC-DC converter.

The PFC control unit controls the output terminal from overvoltage by controlling the on / off of the DC / DC converter switch and controls the output of the DC / DC converter as a sine wave. Accordingly, the output voltage waveform and the current waveform have the same shape and phase, so that the power factor can be improved and the constant current control function can be performed.

In order to drive the LED module 900, the DC-DC converter may increase or decrease the power and convert the power into DC power to supply the LED module 900.

The LED module 900 may include a plurality of LEDs. The LEDs of the LED module 900 may emit light according to the DC power output from the LED driving driver 900. The LED module 900 includes a plurality of LEDs connected in series, and several sets of the plurality of LEDs connected in series may be connected in parallel. The LED module 900 may include a red LED array, a green LED array, and a blue LED array, each of which may be connected in series or in parallel.

The power supply unit 500 may generate AC power. The power supply unit 500 supplies the overall input power of the lighting control device. The power supply unit 500 may serve as a supply power supply for various devices used in the power supply device. The input power input to the power supply unit 500 may be 220V commercial power. In the case of a commercial power supply of 220V, it may have a sinusoidal form that alternates periodically between -311V and +311. Since the AC power varies from country to country, the power supply unit 500 outputs an AC voltage of 100 V to 250 V, and a frequency of 50 Hz or 60 Hz may be used.

According to an embodiment, a power switch 600 may be provided to selectively supply power to a PWM signal generator operating in a dimming operation mode and a sensor unit operating in a standby mode to reduce standby power consumption.

The power supply unit 500 may supply power to the sensor unit 100, the PWM signal generator 300, and the LED driving driver 910. The power switch 600 may selectively switch the power supplied to the PWM signal generator 300 operating in the dimming operation mode and the sensor unit 100 operating in the standby mode.

The power switching unit 600 may selectively supply power by receiving a dimming operation signal. To this end, the first switch Q1 may be connected to the power switch 600. The first switch Q1 may be turned on or off by a dimming operation signal. The first switch Q1 may provide an ON signal to the power switching unit 600 in the dimming operation mode. The first switch Q1 may provide an off signal to the power switching unit 600 in the standby mode. The first switch Q1 may include a MOSFET circuit.

The power switching unit 600 may include a second photo coupler PC2 disposed between the power supply unit 500 and the PWM signal generator 300. The other side of the second photo coupler PC2 may be connected to the first switch Q1. The second photo coupler PC2 may supply or block power to the PWM signal generator 300 by an on / off operation.

The power switch 600 may include a second switch Q2. The second switch Q2 may be disposed between the power supply unit 500 and the sensing detector 700. One end of the second switch Q2 may be connected to the power supply unit 500, and the other end of the second switch Q2 may be branched between the second photo coupler PC2 and the PWM signal generator 300. The second switch Q2 may include a BJT circuit. The second switch Q2 can be turned off by the potential difference between the emitters of the base.

The first resistor R1 may be connected between the emitter and the base of the second switch Q2, and the first resistor R1 may be connected between the base and the second resistor R2 of the second switch Q2. . The third resistor R3 may be connected in series with the second resistor R2, and between the second resistor R2 and the third resistor R3 and the end of the third resistor R3 is the PWM signal generator 300. It can be connected with. When the second switch Q2 is turned on, power is supplied to the sensing detector 700. When the second switch Q2 is turned off, the power is not supplied to the sensing detector 700 and the sensor unit 100.

As shown in FIG. 2, a high signal may be provided to the first switch Q1 in the dimming operation mode. The first switch Q1 may be turned on and a current may be supplied to the second photo coupler PC2. The second photo coupler PC2 may be turned on by the supplied current. Power generated from the power supply unit 500 flows through the first line L1. Power flowing through the first line L1 flows to the second line L2 by the second photo coupler PC2. Power flowing through the second line L2 may be provided to the PWM signal generator 300 to activate the PWM signal generator 300.

On the other hand, power flows through the first node N1 between the power supply unit 500 and the second switch Q2, and also in the second node N2 between the second photo coupler PC2 and the second switch Q2. Since the same power flows, the potential difference does not occur between the base of the second switch Q2 and the emitter, so that the second switch Q2 may be turned off. As a result, power supplied to the sensor unit 100 may be cut off.

As illustrated in FIG. 3, a low signal may be provided to the first switch Q1 in the standby mode. The first switch Q1 may be turned off and current may be cut off to the second photo coupler PC2. As a result, the second photo coupler PC2 may be turned off. The power generated by the power supply unit 500 may be supplied with power through the first line L1, but the power does not flow in the second line L2 because the second photo coupler PC2 is turned off. As a result, power is not supplied to the PWM signal generator 300.

On the other hand, since power flows to the first node N1 between the power supply unit 500 and the second switch Q2, and no power flows to the second node N2, the base and the emi of the second switch Q2. The potential difference is generated between the second and second switches Q2. As a result, power may be supplied to the sensor unit 100.

According to the embodiment, power is switched according to the dimming operation mode and the standby mode, thereby effectively preventing power loss generated during the standby mode. Conventionally, the power loss by the PWM signal generator in the standby mode was about 150mW, but in the embodiment, the power loss by the PWM signal generator is about 10mW as in the standby mode, thereby minimizing the power loss.

1, the lighting control apparatus according to the embodiment may further include a sensing detector 700. The sensing detector 700 may transmit a low signal generated from the sensor unit 100 to the output unit when the movement of the object is detected in the standby mode. Conventionally, the signal is transmitted through the PWM signal generator, but in the embodiment, since power is not supplied to the PWM signal generator in the standby mode, the sensing detector 700 according to the embodiment may be provided to easily output the sensing signal.

The sensing detector 700 may include a third switch Q3 disposed between the sensor unit 100 and the first photo coupler PC1. The third switch Q3 is turned on by the high signal of the sensor unit 100 in the standby mode and may be turned off when the switch is switched to the low signal. The sensing detector 700 may include a plurality of resistors and diodes for voltage distribution.

The first diode D1 may be disposed between the PWM signal generator 300 and the (+) terminal of the dimmer 200. A third diode D3 may be disposed at the source terminal of the third switch Q3, and the third diode D3 may be connected between the PWM signal generator 300 and the first photo coupler PC1. The fourth resistor R4 may be connected to the power switch 600 at the drain terminal of the third switch Q3. A seventh resistor R7 may be connected to the gate terminal of the third switch Q3. The seventh resistor R7 may be connected between the PWM signal generator 300 and the negative terminal of the dimmer 200. A fifth resistor R5 and a sixth resistor R6 may be disposed at the gate end of the third switch Q3. The sixth resistor R6 may be disposed between the fifth resistor R5 and the gate terminal of the third switch Q3. The fifth resistor R5 may be connected to the fourth resistor R4. The second diode D2 may be connected between the fifth resistor R5 and the sixth resistor R6 between the first diode D1 and the positive terminal of the dimmer 200.

As shown in FIG. 4, since the power of 14 V is cut off in the dimming operation mode, both the second diode D2 and the third diode D3 may be turned off, and the sensing detector 700 may also be inactivated. Can be.

In the standby mode, a 14V power supply is divided by a voltage divided by the combined resistance of the fifth resistor R5, the sixth resistor R6, and the seventh resistor R7, and this voltage causes the second diode D2 to turn on. Can be. As a result, the positive and negative terminals of the dimmer 200 may be maintained at a voltage divided at 14V. In this case, the sensor unit 100 may maintain a high signal.

Since Vgs of the third switch Q3 is higher than Vth, the second diode D2 remains on and supplies current to the first photo coupler PC1 through the fourth resistor R4 and the third diode D3. Can be maintained to supply. The voltage across the first capacitor C1 of the output unit 400 may maintain a high voltage.

When an object is detected in the standby mode, the sensor unit 100 may switch from a high signal to a low signal. At this time, the positive and negative terminal voltages of the dimmer 200 may be 3V or less by the sensor unit 100. Since Vgs of the third switch Q3 is lower than Vth, the third switch Q3 is turned off and the current supplied to the first photo coupler PC1 can be cut off.

As a result, the first photo coupler PC1 may be turned off, and the input of the PWM signal inverting unit 410 may be changed from a low voltage to a high voltage. The high voltage is changed to the low voltage by the PWM signal inverting unit 410 so that a low voltage may be applied to both ends of the first capacitor C1 of the output unit 400.

In the lighting control apparatus according to the exemplary embodiment, the sensing detector has a simple structure composed of a switch and a passive element, thereby effectively outputting a low signal generated from a sensor.

1, the lighting control apparatus according to the embodiment may further include a bias current controller 800.

The bias current controller 800 may be disposed between the first photo coupler PC1 and the output unit 400. The bias current controller 800 may change the bias current supplied to the collector of the PWM inversion signal unit 410 and the first photo coupler PC1 according to the dimming operation mode or the standby mode.

If the bias current input to the first photo coupler PC1 is small, distortion of the signal may be severely generated in the dimming operation mode. If the bias current is large, the signal may not be turned off in the standby mode.

To prevent this, the bias current controller 800 according to the embodiment may control to increase the current in the dimming operation mode and reduce the current in the standby mode.

The bias current controller 800 may include a fourth switch Q4 connected to the first switch Q1. The fourth switch Q4 may be a MOSFET circuit. The gate terminal of the fourth switch Q4 may be connected to the source terminal of the first switch Q1. The drain terminal of the fourth switch Q4 may be branched and connected between the first photo coupler PC1 and the PWM signal inverting unit 410.

The fourth resistor Q4 may be connected to the tenth resistor R10 and the eleventh resistor R11 between the gate terminal and the source terminal of the fourth switch Q4. One end of the eighth resistor R8 may be connected to the tenth resistor R10, and the other end of the eighth resistor R8 may be branched between the first photo coupler PC1 and the PWM signal inverting unit 410. The ninth resistor R9 is connected to the eighth resistor R8 and may be connected between the first photo coupler PC1 and the PWM signal inverting unit 410.

As illustrated in FIG. 5, in the dimming operation mode, the first switch Q1 may be turned on by a high signal, and 3.3V may be applied to both ends of the eleventh resistor R11. Since Vsg of the fourth switch Q4 is higher than Vth, the fourth switch Q4 may be turned on. At this time, the tenth resistor R10 and the eighth resistor R8 are connected in parallel so that the combined resistance value of the two resistors is reduced. Thereby the bias current can be increased.

As illustrated in FIG. 6, in the standby mode, the first switch Q1 may be turned off by a low signal, and 0 V may be applied to both ends of the eleventh resistor R11. Since Vsg of the fourth switch Q4 is lower than Vth, the fourth switch Q4 may be turned off. In this case, the tenth resistor R10 and the eighth resistor R8 are separated, and the combined resistance of the two resistors is increased to the tenth resistor R10. This reduces the bias current.

As shown in FIG. 7, in the dimming operation mode, when the synthesis resistance increases, signal distortion occurs. Accordingly, when the bias current controller 800 according to the embodiment increases the current by decreasing the synthesis resistance during the dimming operation, the signal without distortion of the signal can be transmitted.

On the other hand, in the standby mode, when the synthesis resistance is small, the vertical width of the signal is narrowed, so that the off signal may not be generated. As a result, when the bias current controller 800 according to the embodiment decreases the current by increasing the combined resistance value in the standby mode, the on-off operation can be easily performed.

That is, the bias current control unit according to the embodiment has the effect of effectively reducing the current by increasing the synthesis resistance in the dimming operation mode and decreasing the current by increasing the synthesis resistance in the standby mode, thereby effectively transmitting the lighting control signal.

Those skilled in the art to which the present invention pertains will understand that the above-described present invention can be implemented in other specific forms without changing the technical spirit or essential features. Therefore, it is to be understood that the embodiments described above are exemplary in all respects and not restrictive.

The scope of the present invention is shown by the following claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be construed as being included in the scope of the present invention. do.

100: sensor
200: dimmer
300: PWM signal generator
600: power switch
700: sensing detector
800: bias current controller

Claims (10)

A sensor unit detecting an object;
A PWM signal generator for generating a PWM input signal according to the signal sensed by the sensor unit;
A first photo coupler to which a signal output from the PWM signal generator is input;
An output unit to which a signal output from the first photo coupler is input;
A power supply unit supplying power to the sensor unit and the PWM signal generator; And
A power switching unit for selectively supplying power to the PWM signal generator and the sensor unit according to a dimming operation signal;
And the first photo coupler electrically insulates the PWM signal generator and the output unit. The method of claim 1,
And a first switch configured to provide an on-off signal to the power switching unit according to the dimming operation signal. The method of claim 2,
The power switching unit is disposed between the power supply unit and the PWM signal generating unit, and the power switching unit is turned off to cut off power to the PWM signal generating unit when the first switch is turned off and the second photo coupler and the second And a second switch branched between the photo coupler and the PWM signal generator and disposed between the power supply unit and the sensor unit. The method of claim 3,
The second switch includes a BJT circuit, wherein the BJT circuit is turned on and off by a potential difference between a first node between the power supply unit and the BJT circuit and a second node between the second photo coupler and the PWM signal generator. Lighting control device. The method of claim 4, wherein
And the second switch is turned off when the first switch is turned on so that power of the power supply unit is applied to the PWM signal generator. The method of claim 5,
And a sensing detector configured to output a low signal generated by the sensor unit through the first photo coupler. The method of claim 6,
The sensing detector includes a third switch disposed between the sensor unit and the first photo coupler, the third switch being turned on by the high signal of the sensor unit when the first switch is turned off and turned off when being switched to the low signal. Device. The method according to any one of claims 1 to 7,
And a bias current controller configured to control the bias current of the second photo coupler by the on-off signal of the first switch. The method of claim 8,
The bias current controller increases the bias current of the photo coupler when the on signal of the first switch is received, and reduces the bias current of the first photo coupler when the off signal of the first switch is received. The method of claim 9,
The bias current controller includes a MOSFET circuit and a tenth and eleventh resistors connected in parallel between the fourth switch and the gate terminal and the source terminal of the fourth switch and the fourth switch turned on and off according to the signal of the first switch, And an eighth resistor connected in parallel with the tenth resistor between the source terminal of the third switch and the first photo coupler.

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