KR100679288B1 - Flat fluorescent lighting fixture of low voltage switching type - Google Patents

Abstract

A flat fluorescent lighting fixture of a low voltage switching type is provided to prevent an accident such as a fire due to a high voltage and an electric shock by forcibly breaking a driving of a PWM(Pulse Width Modulation) control unit in a protection circuit unit when a portion of lamps of a load part does not operate or is damaged. In a flat fluorescent lighting fixture of a low voltage switching type, a rectifier(15) receives an AC commercial power(10) and rectifies the power. A voltage dropping unit(20) connected with the rectifier(15) drops the rectified voltage. An inverter driving unit(25) switches the dropped DC power and drives an inverter(30). The inverter(30) transforms the dropped DC power to an AC power. A lamp(35) connected with the inverter(30) lights by the inverter(30). A PWM control unit(40) controls an output current by applying a control signal to the inverter driving unit(25). The inverter driving unit(25) comprises a first switching unit and a second switching unit outputting two switching signals mutually alternated to the inverter(30). The inverter(30) includes a DC/AC transformer which receives the signals of the first and second switching units and transforms the DC power to the AC power, a transforming unit including two transformers reversely connected to an output terminal of the DC/AC transformer, and a resonant unit consisting of a capacitor connected to a reverse phase output terminal of the transforming unit.

Description

Flat fluorescent lighting fixture of low voltage switching type

1 is a block diagram showing an example of a conventional flat fluorescent lighting device.

2 is a block diagram of a flat fluorescent lighting apparatus according to the present invention.

3 is a circuit diagram showing a configuration of an inverter driver according to the present invention.

4 is a circuit diagram showing the configuration of an inverter according to the present invention.

5 is a circuit diagram showing the configuration of a PWM control unit according to the present invention.

6 is a circuit diagram showing a configuration of a protection circuit unit according to the present invention.

<Explanation of symbols for the main parts of the drawings>

10: commercial power 15: rectifier

20: step down part 25: inverter drive part

27: first switching unit 28: second switching unit

30: inverter 31: DC / AC converter

32: transformer 33: resonator

34: current sensing unit 35: lamp

40: PWM control unit 45: Dimming unit

50: protection circuit

The present invention relates to a flat fluorescent lamp used as a backlight unit or independent lighting, and more particularly, to obtain a high voltage output compared to a low input voltage at the inverter side, while minimizing the burden on the insulation of the transformer, frequency deviation by product It relates to a low-pressure switching type flat panel lighting device to solve the problem of applying the over-voltage to the load in normal operation by the PWM control unit reacts to the load side abnormality by lowering the lamp evenly.

In general, since a liquid crystal display (LCD) does not emit light by itself, light emitting means such as a back light unit (BLU) is mounted on a rear surface of the LCD to improve visibility of the LCD. Conventionally, BLU is mainly installed cold cathode fluorescent lamp on the thickness of light guide plate, and diffused light emitted from linear light source into surface light source. BLU is being replaced by flat light emitting devices.

Among flat light emitting BLUs, flat fluorescent lamps using the field emission (emission) characteristics of cold cathode fluorescent lamps form a discharge channel between an upper plate and a lower plate, and when an electric field is emitted from a cathode disposed in the discharge channel, Electron accelerated by the light flows through the discharge space containing the inert gas and mercury, and excites the fluorescent material applied to the inner wall of the upper plate to generate visible light. In addition to the BLU, such a flat fluorescent lamp has been increasingly used as an independent lighting device.

Figure 1 shows a conventional driving device for driving such a flat fluorescent lamp. Referring to this, the conventional flat fluorescent lamp driving device is a rectifier 110 for rectifying the commercial power supply 100, the inverter driving unit 120 for driving the inverter by switching the rectified DC voltage, and the rectified DC power lamp Inverter 140 for converting to a high-voltage AC power for driving the 130, the voltage sensing unit 150 for sensing the voltage of the lamp 130, and the pulse width in accordance with the detected voltage of the voltage sensing unit 150 By controlling the control period of the inverter driving unit 120 is configured by the PWM (Pulse Width Modulation) control unit 160 to maintain the brightness of the lamp uniformly.

In the above configuration, in order to apply a high voltage to the lamp 130, a high input voltage is required at the input of the inverter 140 side, and an insulation burden is caused to the high voltage induced on the secondary side of the transformer Tr. . In addition, the inverter 140 configures a half bridge of the first FET Q1 and the second FET Q2 and amplifies the AC power switched in each FET in the transformer Tr. At this time, the resonance frequency is set by using the LC resonant circuit of the inductor (L1) and the capacitor (C1) to match the driving frequency of the product. However, due to the deviation of the inductance component of the inductor and the deviation of the capacitor, a deviation of the driving frequency occurs for each product. As a result, the load-side current is unstable for some products, causing the lamps to not emit light evenly.

Meanwhile, a flat fluorescent lamp used as a BLU drives a plurality of lamps 130 with a single inverter 140 for light weight and low power consumption of LCDs. In this case, when some of the lamps are not connected to the lamp or a failure occurs due to the burnout of the lamp electrode, the voltage detector 150 detects the low voltage of the lamp side, the PWM controller 160 is such a To compensate for the low voltage, the pulse width is widened to increase the output of the inverter. Accordingly, more than necessary overvoltage is applied to the lamps in normal operation, causing a problem that causes the lamp to fail. In addition, there is a risk that a safety accident, such as a fire caused by overheating of the components of the lamp due to the overvoltage induced on the lamp side, or an electric shock accident due to a high current shorted to the enclosure side, may occur.

The present invention has been proposed in order to solve the above problems, by minimizing the input voltage of the inverter to reduce the cost of the switching element and the insulation phase of the transformer to reduce the cost of the inverter, the LC resonance circuit configuration By eliminating the frequency deviations associated with each product, it stabilizes the load side current so that the lamp evenly emits light, and the operation of the inverter is stopped by interrupting the operation of the PWM control unit over the load side, causing fire and electric shock due to the high voltage of the output part. An object of the present invention is to provide a low-pressure switching type flat panel lighting device that can be prevented in advance.

Low pressure switching type flat fluorescent lighting apparatus of the present invention for achieving the above object is a flat type fluorescent lighting device for lighting the flat fluorescent lamp using an inverter at high frequency, rectifying unit for receiving rectified AC commercial power And a step-down part connected to the rectifier to step down the rectified voltage, an inverter drive part to switch the stepped-down DC power source to drive the inverter, an inverter to convert the step-down DC power stepped down to AC power, and A lamp connected to the inverter and turned on by the inverter, and a PWM controller for controlling an output current by applying a pulse width control signal to the inverter driver;

The inverter driving unit includes a first switching unit and a second switching unit for outputting two switching signals which are alternated to the inverter by using the stepped down DC power as a driving power source, and the inverter includes the first switching unit and the second switching unit, respectively. A DC / AC converter which receives a negative signal and converts a DC power source into an AC power source, a transformer unit comprising two transformers connected inversely to the output terminal of the DC / AC converter unit, and a capacitor connected to an antiphase output terminal of the transformer unit. Characterized in that comprises a resonator made of.

Preferably, the inverter further includes a current sensing unit for detecting a lamp side current through a pull-down resistor connected to the transformer secondary coil of the transformer, the output of the current sensing unit is transmitted to the PWM control unit of the inverter in accordance with the current variation of the lamp side Control the output.

In addition, between the current sensing unit and the PWM control unit, a protection circuit unit comprising a comparator for comparing the voltage applied to the pull-down resistor of the current sensing unit with a reference voltage, and a protection switching element for shutting off the power supply of the PWM control unit by the output of the comparator. Is connected.

In addition, a separate DC power supply and a variable resistor are connected to the input side of the PWM control unit to form a dimming unit. By arbitrarily manipulating the variable resistor of the dimming unit, a DC signal is added to or subtracted from the current feedback signal of the PWM control unit to adjust the brightness of the lamp. Is done.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings and embodiments.

2 is a block diagram of a flat fluorescent lighting apparatus according to the present invention, FIG. 3 is a circuit diagram showing a configuration of an inverter according to the present invention, FIG. 4 is a circuit diagram showing a configuration of a PWM control unit according to the present invention, and FIG. Is a circuit diagram showing a configuration of a protection circuit according to the present invention.

First, referring to the block diagram of FIG. 2, the lighting apparatus of the present invention includes a rectifier 15 for rectifying the AC commercial power supply 10, a step-down part 20 for stepping down the rectified DC power source, and a stepped low-voltage DC power source. The inverter driving unit 25 for switching the inverter to drive the inverter, the inverter 30 for converting the stepped low-voltage DC power into AC power, the lamp 35 that is turned on by the drive of the inverter 30, and the inverter driving unit 25. PWM control section 40 for applying a pulse width control signal to the. The rectifier 15 converts AC commercial power into half-wave or full-wave rectification and converts it into a DC component. The rectifier 15 includes a rectifier circuit that is commonly used. The DC power rectified by the rectifier 15 is stepped down to low pressure through the step-down part 20 and applied to the inverter driver 25. Step-down portion 20 is also composed of a commonly used DC / DC converter.

3 illustrates the inverter driver 25, and the inverter driver 25 outputs a switching signal that is alternated by using a DC power stepped down by the step-down part 20 as a driving power source. And a second switching unit 28. Each of the switching units 27 and 28 converts the DC voltage input from the step-down unit 20 by the constant voltage diodes D1 and D4 and alternately switches the switching signal Pch1 according to the pulse input from the PWM control unit 40. , Nch1, Pch2, Nch2) are output. At this time, the switching signals Pch1 and Nch1 and the switching signals Pch2 and Nch2 are outputted alternately. Each switching signal output from the inverter driver 25 is transmitted to the DC / AC converter 31 provided at the input terminal of the inverter 30. The DC / AC converter is composed of four FETs (FET1, FET2, FET3, and FET4) constituting a full-bridge circuit. As shown in FIG. 4, each switching signal is provided at each FET gate terminal. Is entered. First, the switching signals Pch1 and Nch1 of the first switching unit 27 are input to the FET1 and the FET2, and the FET1 and FET2 are triggered according to the switching signals Pch1 and Nch1 of the first switching unit 27 to form the step-down unit ( 20) Convert the low voltage DC power applied to AC component and output it. Similarly, FET3 and FET4 are triggered according to the switching signals Pch2 and Nch2 of the second switching unit 28 to convert the low-voltage DC power applied from the step-down unit 20 into an AC component and output the AC component. At this time, the first switching unit 27 and the second switching unit 28 outputs a switching signal which is alternated by the control of the PWM1 signal and the PWM2 signal of the PWM control unit 40, the DC / AC converter 31 ) Outputs an AC power source, which is boosted by the transformer unit 32.

The transformer 32 is composed of two transformers TR1 and TR2 reversely connected to the output terminal of the DC / AC converter 31. Accordingly, the outputs of the transformers TR1 and TR2 are mutually out of phase so that the potential difference between the two electrodes of the lamp 35 is twice the output of each transformer. As a result, in supplying a sufficient high voltage to generate a high electric field in the cold cathode fluorescent lamp, it is possible to minimize the burden on the insulation of the transformer. The reverse phase output terminal of the transformer unit 32 is connected to both electrodes of the lamp 35, in which the capacitor C1 is connected in parallel to both electrodes of the lamp 35 to form the resonator unit 33. The resonator 33 resonates with the secondary leakage magnetic flux of the transformer together with the load stray capacitance to supply the sine wave voltage with a fluorescent lamp.

Since the current flowing on the transformer secondary coil is the same as the current flowing on the lamp side, the current for connecting the pull-down resistors R3 and R4 to the other side of the transformer secondary coil and grounding it to detect the current on the lamp 35 side. The sensor 34 is configured. The output of the current sensing unit 34 is fed back to the PWM control unit 40, and the PWM control unit 40 controls the output of the inverter 30 in response to the current variation on the lamp 35 side. For example, when the lamp 35 side current is detected as the low current, the PWM controller 40 increases the output of the inverter 30 by widening the pulse width to compensate for this.

5 shows a circuit configuration of the PWM control unit 40, and the signal detected by the current sensing unit 34 is connected to the input pin of the IC U1 of the PWM control unit 40. The PWM controller 40 outputs pulse signals PWM1 and PWM2 that cross each other to the inverter driver 25 in response to the feedback current value of the current detector 34. At this time, the dimming unit 45 composed of a separate DC power supply (Vd) and the variable resistor (R1) is connected to the input pin of the PWM controller 40. As such, by implementing the dimming function using the PWM control unit 40, since an insulation circuit such as an auxiliary winding or a photocoupler, which is required when directly controlling the lamp side current, is not necessary, the dimming function can be implemented with a simple circuit configuration. Will be. In addition, the user may arbitrarily manipulate the variable resistor of the dimming part to add or subtract a DC signal to the current feedback signal of the PWM controller to adjust the amount of lamp current to easily adjust the brightness of the lamp.

On the other hand, the driving power source Vcc of the PWM control unit 40 is input via the protection circuit unit 50. 7 is a circuit diagram showing the configuration of the protection circuit unit 50. It consists of a pair of comparators (OP1, OP2) from the protection circuit, the reference voltage (Vref) is input to the inverting terminals of each comparator (OP1, OP2), the output of the current sensing unit 34 is connected to the non-inverting terminal do. Each of the comparators OP1 and OP2 compares the reference voltage with the output of the current sensing unit 34 to drive the switching element Q14, which interrupts the driving power of the PWM control unit 40. Since the pull-down resistors R3 and R4 of the current sensing unit 34 are connected to the transformer secondary coil, when the lamp 35 is not turned on or the lamp 35 is not connected, the voltage applied to the pull-down resistor is in a normal state. It is significantly lower than the contrast. Therefore, a very low voltage is applied to the non-inverting terminals of the comparators OP1 and OP2, and accordingly, the switching element Q14 connected to the output terminal of the comparator blocks the driving power supply Vcc from being applied to the PWM controller 40. The operation of the inverter 30 is stopped. Therefore, when the lamp fails to turn on normally due to lamp deterioration, failure, sudden impedance change, disconnection, or other factors, the output of the inverter is shut off, resulting in a fire or an electric shock due to high voltage, which is a no-load output. Will be prevented.

The present invention is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes are possible within the scope without departing from the technical spirit of the present invention. It will be apparent to those who have knowledge.

As described above, the low-voltage switching type flat fluorescent lighting device according to the present invention step-down the rectified DC power source, switching the stepped DC power source, by boosting the DC / AC converted AC component to the transformer reverse connection As a result, the burden on the rating of the switching element and the burden on the transformer insulation can be reduced, thereby significantly reducing the cost of the inverter.

In addition, by eliminating the configuration of the LC resonant circuit to match the resonant frequency, the capacitor is connected in parallel to both of the lamp side electrodes in the reverse phase output terminal of the transformer, and resonates with the secondary leakage magnetic flux of the transformer together with the load stray capacitance. It solves the frequency imbalance problem for each product due to the deviation and deviation of the capacitance component, and has an effect of improving the uniformity of light emission of the lamp by uniformly adjusting the frequency for each product.

In addition, when some lamps on the load side are not lit or broken, the protection circuit unit forcibly cuts off the driving of the PWM control unit, thereby preventing safety accidents such as fire and electric shock due to high voltage on the output side.

In addition, by providing a dimming unit using a variable resistor on the input side of the PWM control unit, there is an effect that the dimming function can be implemented by a simple circuit configuration, without the configuration of the insulating circuit involved when controlling the lamp side current.

Claims (4)

In the flat-type fluorescent lighting device for high-frequency lighting of the flat-type fluorescent lamp using an inverter, A rectifying unit for receiving and rectifying AC commercial power, a step-down unit connected to the rectifying unit to step down the rectified voltage, an inverter drive unit for driving an inverter by switching the step-down DC power source, and a direct-current power source stepped down in the step-down unit An inverter for converting to an AC power source, a lamp connected to the inverter and lit by the inverter, and a PWM control unit for controlling an output current by applying a pulse width control signal to the inverter driving unit; The inverter driving unit includes a first switching unit and a second switching unit for outputting two switching signals which are alternated to the inverter by using the stepped down DC power as a driving power source, and the inverter includes the first switching unit and the second switching unit, respectively. A DC / AC converter which receives a negative signal and converts a DC power source into an AC power source, a transformer unit comprising two transformers connected inversely to the output terminal of the DC / AC converter unit, and a capacitor connected to an antiphase output terminal of the transformer unit. Low voltage switching type flat panel fluorescent lighting device comprising a resonator made of. The method of claim 1, The inverter further includes a current sensing unit for detecting a lamp side current through a pull-down resistor connected to the transformer secondary coil of the transformer unit, the output of the current sensing unit is transmitted to the PWM control unit to control the output of the inverter in accordance with the ramp-side current change Low-voltage switching type flat fluorescent lighting device, characterized in that. The method of claim 2, Between the current sensing unit and the PWM control unit, a protection circuit unit comprising a comparator for comparing the voltage applied to the pull-down resistor of the current sensing unit with a reference voltage, and a protection switching element for shutting off the power supply of the PWM control unit by the output of the comparator. Low voltage switching type flat fluorescent lighting device, characterized in that. The method of claim 1, A separate DC power supply and a variable resistor are connected to the input side of the PWM control unit to form a dimming unit, and by adjusting the variable resistor of the dimming unit arbitrarily, a DC signal is added to or subtracted from the current feedback signal of the PWM control unit to adjust the brightness of the lamp. Low-voltage switching type flat fluorescent lighting device, characterized in that.

Images