KR100728439B1 - Open lamp protection circuit - Google Patents

Abstract

An open lamp protection circuit is provided to reduce manufacturing cost and error by detecting an open state of a lamp and simplifying the open lamp protection circuit. An open lamp protection circuit includes a transistor(51), a detection terminal(52), and a plurality of transformers(53). The plurality of transformers(53) provides an inverting voltage to a lamp used in a backlight. A forward-inverse signal generation unit sums forward signals outputted from the in-phase transformers(53) having the same polarity among the plurality of transformers(53) and inverse signals outputted from the inverse phase transformers(53) having opposite polarity among the plurality of transformers(53). The forward-inverse signal generation unit outputs a forward-inverse signal at each of feedback channels of each lamp. By inputting a predetermined detection voltage to a collector of the transistor(51) and inputting the forward-inverse signal to a base, the transistor(51) is switched off when the forward-inverse signal is a zero level, and the transistor(51) is switched on when the forward-inverse signal is not a zero level. The detection terminal(52) outputs a detection voltage by switching off the transistor(51) when the forward-inverse signal inputted to the base is the zero level by connecting an emitter of the transistor(51) to a detection voltage node.

Description

Open lamp protection circuit

1 is a circuit diagram of a conventional open lamp protection circuit.

2 is a block diagram of an open lamp protection circuit according to an exemplary embodiment of the present invention.

3 is a diagram illustrating waveforms of an input signal and an output signal of an in-phase transformer.

4 is a diagram illustrating waveforms of an input signal and an output signal of a reverse phase transformer.

5 is a circuit diagram of an open lamp protection circuit according to an embodiment of the present invention.

6 is a diagram illustrating a waveform of a forward signal, a reverse signal, and a reverse signal when the lamp is normally driven.

7 is a diagram illustrating a waveform of a forward signal, a reverse signal, and a reverse signal when the lamp is open.

* Description of the symbols for the main parts of the drawings *

50: PWM IC 51: transistor

52: detection voltage 53: transformer

54: lamp

The present invention relates to an open lamp protection circuit which simplifies the circuit by reducing the number of components.

In a liquid crystal panel such as a TFT-LCD panel, a lamp driving circuit for driving a lamp is used to light a lamp of a back light and to stabilize the lighting of the lamp. The lamp driving circuit is a lamp failure, an input voltage error, or the like. As a result, an open state of the lamp may be generated, and an open lamp protection circuit is provided to detect the open state of the lamp.

1 is a circuit diagram of a conventional Open Lamp Protection circuit implemented in a lamp.

Referring to FIG. 1, the open lamp protection circuit includes a plurality of primary transistors 11 each receiving a plurality of feedback signal input terminals 15 inputted to respective channels of lamps and the signals of the feedback signal input terminal 15 based on the plurality of primary transistors 11. And a secondary transistor 12 for providing an open lamp detection signal to the PWM IC 10. In addition, each channel is provided with a diode for preventing reverse current and a capacitor for high frequency filtering.

The operation of the open lamp protection circuit will be described below. In the normal operation of the lamps (not shown in FIG. 1), a predetermined signal is input to the base of each primary transistor 11. Therefore, in the normal operation of the lamps, each primary transistor 11 is turned on to be in a conducting state, and Vcc1 14 flows through the primary transistors 11. As a result, under normal operation of the lamps, the secondary transistor 12 is turned off because the voltage of Vcc1 14 flows through the primary transistors 11 without being input to the base of the secondary transistor 12. The Vcc2 voltage 13 is applied to the detection stage comp of the PWM IC 10 as it is.

On the other hand, when any one of the lamps is open, since no signal of the corresponding channel is input, no voltage is applied to the base of the primary transistor 11. Therefore, the primary transistor of the feedback channel is turned off. As a result, when any one of the primary transistors 11 is turned off as described above, the secondary transistor 12 remains turned on because the Vcc1 voltage 14 is input to the base of the secondary transistor 12. Done. In the turn-on state of the secondary transistor 12, since the Vcc2 voltage 13 is electrically connected to the secondary transistor 12 and grounded, 0V voltage is applied to the detection terminal of the PWM IC 10, and 0V as described above. The PWM IC 10 determines that at least one of the lamps is opened by receiving a voltage to maintain the IC shot down state.

As described above, the conventional open lamp protection circuit requires a large number of components, such as a large number of primary transistors, one secondary transistor, a capacitor, and resistors in order to detect the operation state of the lamps, which is an open lamp. In manufacturing the protection circuit, it was a cause of raising the manufacturing cost. In addition, there is a problem that the probability of malfunction due to defective parts due to a plurality of parts is increased. Therefore, in order to reduce the manufacturing cost of the open lamp protection circuit and reduce the probability of failure, the components of the open lamp protection circuit must be reduced.

The present invention has been proposed to solve the above problems, in order to simplify the circuit by reducing the number of components used in the open lamp protection circuit in order to reduce the manufacturing cost of the open lamp protection circuit and reduce the probability of failure. do.

In order to achieve the above object, the present invention provides a plurality of transformers for providing an inverting voltage to a lamp used for a backlight, and a positive signal output from an in-phase transformer having the same polarity direction among the transformers and a reversed phase in which the polarity directions of the transformers are opposite to each other. A forward and backward signal generator for outputting a forward and backward signal, which is obtained by summing up the reverse signals output from the transformer, for each feedback channel of each lamp, and a predetermined detection voltage node are input to the collector, Connected to the transistor that is turned on when the forward and reverse signal is at zero level, and the emitter and the detection voltage node of the transistor, and is turned off by the transistor when the forward and reverse signal input to the base is at zero level. And a detection stage for outputting a detection voltage.

In addition, the positive signal and the reverse signal is output on a predetermined DC voltage, the absolute value of the output signal of the positive signal and the reverse signal is the same when the lamp is in normal operation, the phase is inverted 180 degrees.

Hereinafter, the detailed description of the preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following description of the reference numerals to the components of the drawings it should be noted that the same reference numerals as possible even if displayed on different drawings.

2 is a block diagram of an open lamp protection circuit according to an exemplary embodiment of the present invention.

The open lamp protection circuit according to the present invention includes one transistor 21 and a reverse signal generator 22 so that the reverse signal generated in all feedback channels is input through the base of the transistor 21. In FIG. 2, only three feedback channels in the forward and backward signal generator 22 are illustrated, and a plurality of feedback channels may exist according to the number of ramps.

The forward and backward signals are signals generated by adding up the forward signals output from transformers having the same polarity and the reverse signals output from transformers having different polarities. The positive signal and the reverse signal are input from a transformer (not shown in FIG. 2) for supplying an inverter voltage. Hereinafter, the positive signal and the reverse signal will be briefly described. 3 and 4 briefly illustrate examples of generating the positive signal and the reverse signal, respectively. FIG. 3 illustrates a transformer (hereinafter, referred to as a 'phase transformer') having a polarity at the same position due to the same winding direction wound around the primary coil and the secondary coil, and the primary coil of the in-phase transformer. The secondary coils have polarities in the same direction, so that the input signal input to both ends of the primary coil of the in-phase transformer and the output signal of the secondary coil have the same in-phase. Therefore, the output signal of the secondary coil generated by the input signal input to the primary coil of the in-phase transformer having the same polarity direction has a positive signal having the same phase as the input signal.

On the contrary, FIG. 4 illustrates a transformer having different polarities due to winding directions wound around the primary coil and the secondary coil (hereinafter, referred to as 'reverse transformer'), and the primary coil of the reverse phase transformer and The secondary coils have polarities in opposite directions, so that an input signal input at both ends of the primary coil of the reverse phase transformer and an output signal output at both ends of the secondary coil have a phase reversed by 180 degrees. Therefore, the output signal of the secondary coil generated by the input signal input to the primary coil of the reverse phase transformer having a different polarity direction has a reverse signal having a phase inverted with the input signal.

A forward signal and an inverse signal are input to each of the feedback channels as described above, and are connected as one node, and are input to the base of the transistor 21 as a summation signal. Therefore, the transistor is turned on / off according to the level value of the forward / reverse signal of each feedback channel to detect whether the lamp is open. When the operation of the open lamp protection circuit according to the present invention will be described in more detail, when the lamps are all in normal operation, all the normal and normal signals generated by the normalized signal generator 22 become zero level, The signal is input to the base of the transistor 21. When zero level is input to the base of the transistor, the corresponding transistor 21 is turned off so that a predetermined detection voltage 23 (Vin; 5V) signal is applied to the detection terminal of the PWM IC. Not normal operation.

On the other hand, when any one of the lamps are opened and the lamps operate abnormally, the forward and backward signals output from the forward and backward signal generator 22 are not at the zero level (for example, +1 level and -1 level). As described above, the transistor 21 receiving the non-zero reverse signal is turned on so that the detection voltage 23 is connected to ground. Accordingly, 0 V is applied to the detection terminal of the PWM IC 20, and the PWM IC 20 which receives the 0 V input determines that at least one of the lamps is open to maintain the IC shot down state.

As a result, the forward and backward signals output from the forward and backward signal generator 22 are the sum of the forward and reverse signals for each channel, and the forward signals are input from the in-phase transformer among the transformers supplying the inverter voltage to the lamps. The signal is input from a reverse phase transformer among the transformers that supply the inverter voltage to the lamp.

Therefore, when the lamp is operated normally without opening the lamp, since the positive signal and the reverse signal have the magnitude and the phase is inverted by 180 degrees, the summation signal has the zero level as described above, while the lamp is open and abnormally operated. In this case, the magnitude of the forward signal or the reverse signal becomes small or is not twisted without causing an accurate 180 degree inversion to have a non-zero level.

5 is a circuit diagram of an open lamp protection circuit according to an embodiment of the present invention.

Referring to FIG. 5, the lamp is provided with a transformer 53 which provides an inverting voltage (only two transformers are shown in FIG. 5 as an example), and the transformer 53 has an in-phase transformer 53a having the same polarity. 53c) and reverse phase transformers 53b and 53d having polarities in directions different from each other. The forward signal input nodes 56a and 56b in the reverse signal generator are connected to the output terminal nodes of the in-phase transformers 53a and 53c, and the reverse signal input nodes 56b and 57b are output node nodes of the reverse phase transformers 53b and 53c. Connected with

Therefore, the in-phase transformers 53a and 53c having the forward polarity output the positive signal of the in-phase, and the reverse-phase transformers 53b and 53d having the reverse polarity output the reverse signal of the reverse phase. The positive signal and the reverse signal are input to the positive signal input nodes 56a and 56b and the reverse signal input nodes 57a and 57b, respectively. As a result, two signals (a positive signal and an inverse signal) in opposite phases can be obtained from the in-phase transformers 53a and 53c and the reverse phase transformers 53b and 53d. 58) to generate an inverse signal that is a summation signal. Each of the normal and negative signals generated in this way is input to the base of the transistor 51 as one feedback channel signal.

Meanwhile, before connecting the positive signal output from the in-phase transformers 53a and 53c and the reverse signal output from the reverse phase transformers 53b and 53d to one node point 58, the positive signal and the reverse signal are respectively connected to a diode. Pass it through. This is to pass each of the forward and reverse signals output from the in-phase and reverse phase transformers to the diode to pass only forward current.

On the other hand, in the open lamp protection circuit of Figure 5 it can be seen that the R-C filter for input noise filtering is provided in the detection terminal of the PWM IC and the base of the transistor, respectively.

The operation of the lamp when the lamp operates normally under the above-described input structure and when the lamp is opened will be described.

First, when the lamp 54 is normally operated together with the waveform graph of FIG. 6, when the lamp 54 is normally operated instead of being opened, the in-phase transformers 53a and 53c and the inverse transformers 53b and 53d are operated. The positive signal 61 and the inverted signal 61 outputted from the N-type signal have a phase inversion of each other 180 degrees. Since the ramp operates normally, only the positive signal 61 and the reverse signal 62 are inverted by 180 degrees, and the absolute magnitude of the positive signal 61 has the same value. Therefore, the forward and backward signals 63 obtained by adding the forward and reverse signals have a zero level.

As a result, when the lamp is normally operated and the zero level is input to the base of the transistor 51, the transistor 51 is turned off so that the 5 V detection voltage 52 is applied to the detection terminal 55 of the PWM IC 50. The PWM IC 50 determines that the lamp is operating normally rather than open.

On the other hand, when the lamp 54 is not in normal operation and looks open with the waveform graph of FIG. 7, when the lamp 54 is not normally operated, the forward signal 71 and the reverse signal 72 are warped or When the magnitudes of the positive and reverse signals are different from each other, the forward and reverse signals 73, which are the summation signals thereof, do not have a zero level but have a constant level (for example, +1 level and -1 level). Since the transistor receiving the forward / reverse signal having a predetermined value other than the zero level to the base is turned on, the detection voltage Vin is conducted to the ground through the transistor, and finally, the detection terminal of the PWM IC is applied with 0 V, and 0 V input. The received PWM IC determines that at least one of the lamps is open.

6 and 7 show a state in which a predetermined DC voltage (eg, a 10V DC voltage) is applied. This is because a diode provided at the reverse signal input terminal does not pass a negative voltage in the diode which limits the reverse current so that a predetermined DC voltage is applied to the positive signal and the reverse signal of the transformer. Thus, although the normal and reverse signal is shown as a 10V DC component in FIG. 6 when the lamp is normally driven, since it is the same as the DC voltage 10 [V] preloaded on the forward and reverse signals, the forward and reverse signal of FIG. 6 results in zero level. It can be seen that. However, in FIG. 6, the DC voltage terminals carried on the positive signal and the reverse signal are not shown for simplicity of the circuit diagram.

In the foregoing description of the present invention, specific embodiments have been described, but various modifications may be made without departing from the scope of the present invention. Therefore, the patent scope of the present invention is not to be determined by the above-described embodiment, and the claims will be apparent not only in the claims but also in the equivalent ranges.

As described above, the present invention can detect the open state of the lamp by using the normal and reverse signal, thereby simplifying the open lamp protection circuit by reducing the number of components used in the open lamp protection circuit. By simplifying the open lamp protection circuit, it is possible to reduce manufacturing costs and reduce the probability of defects.

Claims (8)

A number of transformers that provide an inverting voltage to the lamp used for the backlight; A forward and reverse signal outputted for each feedback channel of each lamp by outputting a forward and output signal for each feedback channel of the lamps by adding the positive signal output from the in-phase transformer having the same polarity direction among the transformers and the reverse signal output from the reverse phase transformer having the opposite polarity direction among the transformers. Generation part, A predetermined detection voltage node is input to a collector and the forward / reverse signal is input to a base, whereby the transistor is turned off when the forward / reverse signal is at zero level; A detection stage that is connected to the emitter of the transistor and the detection voltage node so that the detection voltage is output by turning off the transistor when the forward signal input to the base is at the zero level Open lamp protection circuit provided with. The open lamp protection circuit of claim 1, wherein the positive signal and the reverse signal are output by being loaded on a predetermined DC voltage. The open lamp protection circuit of claim 1, wherein the absolute value of the output signal of the positive signal and the reverse signal is substantially the same and the phase is inverted by 180 degrees when the lamp is in normal operation. The open lamp protection circuit according to claim 1, wherein an output value of any one of the forward signal and the reverse signal is distorted or reduced in size when the lamp is opened. 2. The open lamp protection circuit according to claim 1, wherein the detection voltage is determined to be a lamp open state when the detection voltage is input to the detection terminal without conducting the transistor. The open lamp protection circuit of claim 1, wherein each feedback channel of the forward and backward signal generator is provided with a diode passing only forward current. The open lamp protection circuit of claim 1, wherein an input node of the detection stage is provided with an RC filter for filtering input noise. The open lamp protection circuit of claim 1, wherein the base of the transistor comprises an RC filter for filtering input noise.

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