TWI407836B - Protection circuit and lamp driving device employing the same - Google Patents

Abstract

A discharge lamp driving device, comprises a power stage circuit, a transformer circuit, a control circuit, a feedback circuit and a lamp protection circuit. The lamp protection circuit includes a current sensing circuit, a referrence voltage selecting circuit, a comparing circuit and a protection signal outputting circuit. The current sensing circuit is used for respectively sensing current flowing through the lamps, and converting the current signals to voltage signals. The referrence voltage selecting circuit is connected to the current sensing circuit for choosing a maximal voltage as a reference voltage signal. The comparing circuit is connected to the current sensing circuit and the comparing circuit for comparing the referrence voltage signal with the voltage signals to output a plurality of comparing signals. The protection signal outputting circuit is connected between the comparing circuit and the control circuit, for selecting a maximal comparing signal as the protection signal. The control circuit is connected to the comparing circuit for controlling the output of the power stage circuit according to the protection signal.

Description

Protection circuit and lamp driving device using same

The present invention relates to a lamp driving device, and more particularly to a lamp driving device having a protection circuit.

At present, it is widely practiced to provide at least two sets of lamps in the lighting circuit of many devices (such as liquid crystal displays) to meet the lighting requirements. In order to protect the at least two groups of lamps when they are open or short-circuited, they are not damaged by the ultra-high voltage generated in the lighting circuit, and the open circuit protection circuit and the short-circuit protection circuit are respectively provided in the lighting circuit for protection.

Please refer to the schematic diagram of the lamp driving device 10 shown in FIG. 1 . The lamp driving device 10 includes a lamp protection circuit 103 . The lamp protection circuit 103 includes an open circuit protection circuit 1032 and a short circuit protection circuit 1033 . When the first lamp L1 or the second lamp L2 is open, the current sensing unit 1031 transmits the respectively sensed flow through the first current sensing unit 1031A and the second current sensing unit 1031B to the open circuit protection circuit 1032. The current signal of the first lamp L1 and the second lamp L2, and the open circuit protection circuit 1032 sends an open circuit protection signal to the control circuit 101 according to the current signals, and the control circuit 101 controls the output according to the open circuit protection signal. The signal controls the output of the power conversion circuit 100 to protect the lamps L1 and L2.

Similarly, when the first lamp L1 or the second lamp L2 is short-circuited, the current sensing unit 1031 transmits the respectively sensed to the open circuit protection circuit 1032 through the first current sensing unit 1031A and the second current sensing unit 1031B. a current signal flowing through the first lamp L1 and the second lamp L2, the short circuit protection circuit 1033 sends a short circuit protection signal to the control circuit 101 according to the current signals, and the control circuit 101 outputs another according to the short circuit protection signal. A control signal controls the power conversion circuit 100 to output an AC signal to protect the lamps L1 and L2.

This method protects the lamp according to its open and short circuit conditions when the lamp is in operation. However, the open circuit protection circuit and the short circuit protection circuit are independent single lines, and generally adopt a resistor voltage division to drive the crystal field effect transistor, and need to work separately. Moreover, one of the protection lines is easily affected by the high voltage of the other lamp, and the protection function cannot be accurately realized.

In view of the above, it is desirable to provide a lamp driving device that can simultaneously detect the current flowing through the plurality of lamps through a protection circuit to simultaneously achieve open and short circuit protection of the lamp.

A lamp driving device for driving a plurality of lamps to protect the lamps when an abnormality occurs, including a power conversion circuit, a transformer circuit, a control circuit, a feedback circuit, a control circuit, and a protection circuit. The protection circuit includes a current sensing circuit, a reference voltage selection circuit, a comparison circuit, and a protection signal output circuit. The current sensing circuit includes a plurality of current sensing units for respectively sensing current flowing through each of the lamps and converting the sensed currents into voltage signals. A reference voltage selection circuit is connected to the current sensing circuit for setting a maximum value of the voltage signal signals to a reference power Pressure. The comparison circuit includes a plurality of comparison units connected to the current sensing circuit and the reference voltage selection circuit for comparing the reference voltage with the voltage signals divided by the voltage signals, and outputting the plurality of comparison signals. The protection signal output circuit is connected to the comparison circuit for selecting the largest of the comparison signals for output as a protection signal. The control circuit is connected to the protection signal output circuit for outputting a control signal according to the protection signal, and controlling the power conversion circuit to be turned off.

The lamp driving device of the invention adopts a total current feedback mode, uses a plurality of comparison units, takes the maximum voltage value of the plurality of lamp currents as a reference voltage, and flows the reference voltage and the double lamp tube through the sensing resistor The voltage is compared to detect whether the lighting circuit is open or shorted, so that the lamp opening and short circuit protection can be realized by using one set of lines.

10, 20‧‧‧Light tube drive

100, 200‧‧‧ power conversion circuit

101, 201‧‧‧ control circuit

102, 202‧‧ ‧ feedback circuit

103‧‧‧Light tube protection circuit

203‧‧‧Protection circuit

1031, 2031‧‧‧ current sensing circuit

1031A, 2031A‧‧‧First current sensing unit

1031B, 2031B‧‧‧second current sensing unit

1032‧‧‧Open circuit protection circuit

1033‧‧‧Short circuit protection circuit

2032‧‧‧reference voltage selection circuit

2033‧‧‧Comparative circuit

2033A‧‧‧ first comparison unit

2033B‧‧‧Second comparison unit

2034‧‧‧protection signal output circuit

204‧‧‧Transformer circuit

R1, R2, R3, R4, R5, R6‧‧‧ resistors

D1, D2, D3, D4‧‧‧ diodes

U1, U2‧‧‧ comparator

L1‧‧‧first lamp

L2‧‧‧Second lamp

1 is a schematic view of a lamp driving device shown in the prior art; FIG. 2 is a schematic view of a lamp driving device of the present invention; and FIG. 3 is a specific circuit diagram of the protection circuit 203 of FIG.

Fig. 2 is a circuit function block diagram of a lamp driving device 20 according to an embodiment of the present invention. The lamp driving device 20 includes a power conversion circuit 200, a control circuit 201, a feedback circuit 202, a protection circuit 203, and a transformer circuit 204 for driving a plurality of lamps. For the sake of simplicity, in the present embodiment, only the first The lamp L1 and the second lamp L2 are shown. The power conversion circuit 200 is configured to convert the received external signal into an AC signal. The voltage conversion circuit 204 is connected to the power conversion circuit 200 for converting the alternating current signal into electrical signals that can drive the lamps L1 and L2. Wherein, the electrical signal is a sine wave signal .

In the present embodiment, the protection circuit 203 includes a current sensing circuit 2031, a reference voltage selection circuit 2032, a comparison circuit 2033, and a protection signal output circuit 2034. The current sensing circuit 2031 includes a plurality of current sensing units correspondingly connected to the plurality of lamps for sensing current flowing through the lamps. In the present embodiment, the current sensing circuit 2031 includes a first current sensing unit 2031A and a second current sensing unit 2031B for sensing current flowing through the first lamp L1 and the second lamp L2, respectively. The sensed current is converted into a voltage signal. In detail, the first current sensing unit 2031A is connected to the first lamp L1 for sensing the current flowing through the first lamp L1, converting the sensed current into the first voltage signal V1, and The first voltage signal V1 is divided to obtain a first divided voltage signal V11. The second current sensing unit 2031B is connected to the second lamp L2 for sensing the current flowing through the second lamp L2, converting the sensed current into the second voltage signal V2, and the second voltage signal V2 The voltage division is performed to obtain a second divided voltage signal V21. In this embodiment, only two lamps are taken as an example. In other embodiments, the number of the lamps may be two or more. Accordingly, the number of the current sensing units may be correspondingly increased.

The reference voltage selection circuit 2032 is connected to the current sensing circuit 2031 for comparing the first voltage signal V1 and the second voltage signal V2, and selecting the maximum value as the reference voltage signal Vref.

The comparison circuit 2033 is connected to the current sensing circuit 2031 and the reference voltage selection circuit 2032, and includes a plurality of comparison units corresponding to the current sensing units. In the present embodiment, the comparison circuit 2033 includes a first comparison unit 2033A and a second comparison unit 2033B. The first comparison unit 2033A is connected to the first current sensing unit 2031A. The reference voltage selection circuit 2032 is configured to receive the first divided voltage signal V11 and the reference voltage signal Vref, and compare the first divided voltage signal V11 with the reference voltage signal Vref to output the first comparison signal. The second comparison unit 2033B is connected to the second current sensing unit 2031B and the reference voltage selection circuit 1302 for receiving the second divided voltage signal V21 and the reference voltage signal Vref, and the second divided voltage signal V21 and the reference voltage signal Vref A comparison is made to output a second comparison signal. In this embodiment, only two lamps are taken as an example. In other embodiments, if the number of the lamps increases, the number of the current sensing unit and the comparison unit may also increase accordingly, and details are not described herein again.

The protection signal output circuit 2034 is connected to the comparison circuit 2033 for selecting the largest of the plurality of comparison signals output by the plurality of comparison units. In this embodiment, the larger one of the first comparison signal and the second comparison signal is selected. Used as a protection signal output.

The control circuit 201 is connected between the power conversion circuit 200 and the protection signal output circuit 2034 of the protection circuit 203 for outputting a control signal to the power conversion circuit 200 according to the protection signal to control the output of the power conversion circuit 200, thereby protecting the plurality of lamps. Tubes L1 and L2.

The feedback circuit 202 is connected between the control circuit 201 and the current sensing circuit 2031 for feeding back the total current flowing through the first lamp L1 and the second lamp L2 to the control circuit 201. At the same time, the control circuit 201 also controls the output of the power conversion circuit 200 based on the feedback current.

FIG. 3 is a specific circuit diagram of an embodiment of FIG. 2 of the present invention. In this embodiment, the first A current sensing unit 2031A is connected to the first lamp L1 for sensing the current flowing through the first lamp and converting the current signal into the first voltage signal V1. The second current sensing unit 2031B is connected to the second lamp L2 for sensing the current flowing through the second lamp and converting the current signal into the second voltage signal V2. The first current sensing unit 2031A includes a voltage dividing circuit composed of a first resistor R1 and a second resistor R2 connected in series between the first lamp L1 and the ground for using the first voltage signal V1. The voltage division is performed to obtain the first divided voltage signal V11. The first voltage signal V1 is outputted by the common node of the first lamp L1 and the first resistor R1, and the first voltage dividing voltage signal V11 is outputted by the common node of the first resistor R1 and the second resistor R2.

The second current sensing unit 2031B includes a voltage dividing circuit composed of a third resistor R3 and a fourth resistor R4 connected in series between the second lamp L2 and the ground for dividing the second voltage signal V2. , thereby obtaining a second divided voltage signal V21. The second voltage signal V2 is outputted by the common node of the second lamp L2 and the fourth resistor R4, and the second voltage dividing voltage signal V21 is outputted by the common node of the third resistor R3 and the fourth resistor R4. In the present embodiment, the resistance values of the first resistor R1 and the fourth resistor R4 are the same, and the resistance values of the second resistor R2 and the third resistor R3 are the same.

The reference voltage selection circuit 2032 includes a first diode D1, a second diode D2, and a fifth resistor R5 and a sixth resistor R6. The anode of the first diode D1 is electrically connected to the first current sensing unit 2031A, that is, connected between the first resistor R1 and the first lamp L1 for receiving the first voltage signal V1. The anode of the second diode D2 is electrically connected to the second current sensing unit 2031B, that is, connected between the fourth resistor R4 and the second lamp L2 for receiving the second voltage signal V2. The fifth resistor R5 and the sixth resistor R6 are sequentially connected in series between the cathode of the first diode D1 and the second diode D2 and the ground for The voltages transmitted by the first diode D1 and the second diode D2 are divided to output a reference voltage signal Vref. The reference voltage signal Vref is outputted at a common node of the fifth resistor R5 and the sixth resistor R6. In the embodiment, the resistance of the fifth resistor R5 is greater than the resistance of the sixth resistor R6, and may be smaller than the resistance of the first resistor R1 to the fourth resistor. In other embodiments, the number and resistance of the resistors can be flexibly set according to the requirements of the actual circuit, and are not limited by the embodiments.

The comparison circuit 2033 is connected to the reference voltage selection circuit 2032 and the current sensing circuit 2031, and includes a first comparison unit 2033A and a second comparison unit 2033B. In the present embodiment, the first comparison unit 2033A includes a first comparator U1 having a first input connected to the reference voltage selection circuit 2032 for receiving the reference voltage signal Vref and a second input coupled to the first current sensing unit 2031A. The first divided voltage signal V11 is received, and the output end is used for outputting the first comparison signal. The second comparison unit 2033B includes a second comparator U2, the first input terminal is connected to the reference voltage selection circuit 2032 to receive the reference voltage signal Vref, and the second input terminal is connected to the second current sensing unit 2031B to receive the second voltage divider. The voltage signal V21 has an output for outputting the second comparison signal. In this embodiment, the first input end of the comparator is a positive input terminal, and the second input end is a negative input terminal. In other embodiments, the first input of the comparators can be a negative input and the second input can be a positive input.

The protection signal output circuit 2034 is connected to the comparison circuit 2033, and includes a third diode D3 and a fourth diode D4 for selecting the larger one of the first comparison signal and the second comparison signal to be output as a protection signal to the control circuit. 201. The anode of the third diode D3 is connected to the output end of the first comparator U1 to receive the first comparison signal. The anode of the fourth diode D4 is connected to the output end of the second comparator U2 to receive the second comparison signal . The cathode of the third diode D3 is connected to the cathode of the fourth diode D4 to select the larger of the first comparison signal or the second comparison signal as the protection signal output.

The embodiment is described in the case of only two lamps. In other embodiments, if the number of the lamps increases, the number of the current sensing unit and the comparison unit may increase correspondingly. Narration.

For example, when the protection signal is a high voltage signal, the control circuit 201 outputs a control signal to control the power conversion circuit 200 to be turned off. Therefore, in the embodiment, the resistance values of the first resistor R1 and the fourth resistor R4 are both set to 806 kilo ohms, and the resistance values of the second resistor R2 and the third resistor R3 are both set to 1200 kilo ohms, and the fifth resistor R5 The resistance is set to 73.2 kilo ohms, and the resistance of the sixth resistor R6 is set to 30.1 kilo ohms.

In this embodiment, the first input end of each comparator is set as the positive input end, and the second input end is set as the negative input end. In other embodiments, the first input of the comparators can be set as a negative input and the second input can be set as a positive input.

When the first lamp L1 and the second lamp L2 are both normally working, the current flowing through the two lamps is equal, and the first voltage signal V1 is the same as the second voltage signal V2, which is 12 volts. The first divided voltage signal V11 is the same as the second divided voltage signal V21, and each is about 4.82 volts, and the comparison voltage Vref is about 3.49 volts. At this time, the voltages of the positive input terminals of the first comparator U1 and the second comparator U2 transmitted to the comparison circuit 2033 are both 3.39 volts, and the voltages transmitted to the negative terminals of the first comparator U1 and the second comparator U2 are both 4.82. Volt, that is, the input voltage signal of the positive input terminal of the first comparator U1 and the second comparator U2 is smaller than the input voltage of the negative input terminal, and the first comparison is Both the U1 and the output of the second comparator U2 output a low voltage signal. At this time, the third diode D3 and the fourth diode D4 are also unable to output a high voltage signal, so the control circuit 201 will not issue a control signal to turn off the power conversion circuit 200. Thereby, the lamp driving device 20 operates normally.

When the lamp is in an abnormal state of open circuit or short circuit, the current flowing through the lamps is unbalanced, and the protection circuit 203 will protect the lamp according to the imbalance. In this embodiment, when the current flowing through the first lamp L1 and the second lamp L2 is different by 2 mA, correspondingly, when the first voltage signal V1 and the second voltage signal V2 are different by 4 volts, the protection circuit 203 will control to turn off the power conversion circuit 200 to protect the lamps. For example, if the first lamp L1 is short-circuited and the second lamp L2 is not short-circuited, the current flowing through the first lamp L1 will be greater than the current flowing through the second lamp L2. For example, in the embodiment, when the first voltage signal V1 is 18 volts, the second voltage signal is 6 volts.

At this time, the reference voltage selection circuit 201 selects the first voltage signal V1 as a reference voltage, and outputs the first voltage signal V1 to the positive input terminals of the first comparator U1 and the second comparator U2. In this embodiment, only the first voltage signal V1 is transmitted through the first diode D1 to the fifth resistor R5 and the sixth resistor R6, and is divided into reference voltage signals by the fifth resistor R5 and the sixth resistor R6. Vref is output to the comparison circuit 2033. At this time, the reference voltage signal Vref is about 5.24 volts.

In the comparison circuit 2033, the reference voltage signal Vref is output to the positive input terminals of the first comparator U1 and the second comparator U2, and the first current sensing unit 2031A transmits the first divided voltage signal V11 to the first comparator U1. The second current sensing unit 2031B transmits the second divided voltage signal V21 to the negative input of the second comparator U2. Into the end. At this time, the first divided voltage signal V11 is about 7.25 volts, and the second divided voltage is about 2.41 volts.

In the first comparing unit 2033A, the first comparator U1 compares the reference voltage signal Vref with the first divided voltage signal V11 to output a first comparison signal. That is, the input voltage signal of the positive input terminal of the first comparator U1 is smaller than the voltage signal input by the negative input terminal. Therefore, the first comparison signal output by the first comparator U1 is a low voltage signal. In the second comparison unit 2033B, the second comparator U2 compares the reference voltage signal Vref with the second divided voltage signal V21 to output a second comparison signal. That is, the input voltage signal of the positive input terminal of the second comparator U1 is greater than the voltage signal input by the negative input terminal. Therefore, the second comparison signal output by the second comparator U1 is a high voltage signal.

In the protection signal output circuit 2034, since the first comparison signal is a low voltage signal and the second comparison signal is a high voltage signal, only the high voltage signal is transmitted as a protection signal through the cathode of the fourth diode D4 to the control. Circuit 201. Therefore, the control circuit 201 sends a control signal according to the protection signal, that is, the high voltage signal, to control the power conversion circuit 200 to be turned off.

Similarly, when the first lamp L1 is open circuit and the second lamp L2 is short-circuited or normally operated, the current flowing through the first lamp L1 is less than the current flowing through the second lamp L2, and the first voltage signal V1 is smaller than the first The second voltage signal V2, so that the reference voltage selection circuit 2032 selects the second voltage signal V2 as the reference voltage, and outputs the second voltage signal V2 to the positive input terminals of the first comparator U1 and the second comparator U2. The first current sensing unit 2031A transmits the first divided voltage signal V11 to the negative input terminal of the first comparator U1. At this time, the first comparison signal output by the first comparator U1 is a high voltage signal. Similarly The second current sensing unit 2031B transmits the second divided voltage signal V21 to the negative input terminal of the second comparator U2. At this time, the second comparison signal output by the second comparator U2 is a low voltage signal.

In the protection signal output circuit 2034, the third diode D3 receives the high voltage signal output by the first comparator U1; the fourth diode D4 receives the low voltage signal output by the second comparator U2, and only the The high voltage signal is transmitted as a protection signal through the cathode of the third diode D3. Therefore, the control circuit 201 sends a control signal according to the high voltage signal to control the power conversion circuit 200 to be turned off.

Similarly, in other embodiments, the first lamp L1 and the second lamp L2 may be respectively in a short circuit, an open circuit or a normal working state, but within the scope of the present invention, the state changes of the lamps may be The working principle of the circuit disclosed above is implemented, and thus the present invention does not enumerate the various situations.

The invention provides a protection circuit in the lamp driving device to sense the current flowing through the different lamps, so that the abnormal state of the current flowing through the lamps can be detected in time when the lamp is in an abnormal state of being disconnected or short-circuited, and The abnormal current is converted into a voltage signal and compared by a comparison circuit, and the operation of the lamp driving device can be controlled in time according to the comparison results to protect the lamps and corresponding components from damage.

In summary, the present invention complies with the requirements of the invention patent and submits a patent application according to law. The above description is only the preferred embodiment of the present invention, and equivalent modifications or variations made by those skilled in the art of the present invention should be included in the following claims.

20‧‧‧Light tube drive

200‧‧‧Power conversion circuit

201‧‧‧Control circuit

202‧‧‧Return circuit

203‧‧‧Protection circuit

2031‧‧‧ Current sensing circuit

2031A‧‧‧First Current Sensing Unit

2031B‧‧‧Second current sensing unit

2032‧‧‧reference voltage selection circuit

2033‧‧‧Comparative circuit

2033A‧‧‧ first comparison unit

2033B‧‧‧Second comparison unit

2034‧‧‧protection signal output circuit

204‧‧‧Transformer circuit

L1, L2‧‧‧ lamps

Claims (12)

A lamp driving device for driving a plurality of lamps, the lamp driving device comprising: a power conversion circuit for converting the received external power signal into an alternating current signal; and a transformer circuit connected to the power conversion circuit Converting the alternating current signal into an electrical signal capable of driving the light pipes; and a protection circuit connected to the light pipes for outputting a protection signal when the lamps are abnormal, comprising: a current sensing circuit, and the The lamps are connected to sense current flowing through the lamps and convert the current signals into voltage signals; a reference voltage selection circuit is connected to the current sensing circuit for performing the voltage signals Comparing and selecting the maximum voltage signal as the reference voltage signal; the comparison circuit is connected to the reference voltage selection circuit and the current sensing circuit for comparing the reference voltage signal and the voltage signals to output a plurality of comparison signals; And a protection signal output circuit connected to the comparison circuit for selecting the largest of the comparison signals for use as a protection signal output; Circuit connected to the protection signal output circuit between the power conversion circuit for such protection signal output control signal to control the output of the power conversion circuit. The lamp driving device of claim 1, wherein the current sensing circuit further comprises a plurality of current sensing units, each of the current sensing units being connected to one of the lamps for sensing flow The current through the lamp and convert the current into a voltage signal number. The lamp driving device of claim 2, wherein each current sensing unit comprises a plurality of resistors serially connected between the lamp and the ground for dividing the voltage signal and outputting Divided voltage signal. The lamp driving device of claim 3, wherein the reference voltage selection circuit comprises: a plurality of diodes, and an anode of each of the diodes is connected to a current sensing unit for receiving the voltage signal And a plurality of resistors connected in series between the cathode common junction of the diodes and the ground; wherein the common node of the resistors outputs the reference voltage. The lamp driving device of claim 4, wherein the reference voltage selection circuit is configured to select the largest of the voltage signals through the diodes. The lamp driving device of claim 4, wherein the comparing circuit comprises a plurality of comparing units, each comparing unit comprises a comparator, wherein the first input end is electrically connected to the reference voltage selecting circuit, The two input terminals are respectively connected to the current sensing units, and are configured to output a plurality of comparison signals according to the reference voltage and the divided voltage signals. The lamp driving device of claim 6, wherein the protection signal output circuit comprises a plurality of diodes, and an anode of each of the diodes is connected to an output of one of the comparison units for The comparison signal outputted by the comparison unit is received; wherein the cathodes of the diodes are connected to one point for selecting the largest one of the comparison signals to be output as the protection signal. A protection circuit that outputs a protection signal when an abnormality occurs in one of the plurality of input AC signals, which includes: a plurality of current sensing units for sensing the plurality of alternating current signals and converting the alternating current signals into voltage signals; and a reference voltage selecting circuit connected to the current sensing units for comparing the voltage signals The maximum voltage signal is selected as the reference voltage signal; the comparison unit is connected to the reference voltage selection circuit and the current sensing unit for comparing the reference voltage signal and the voltage signals to output a plurality of comparison signals; and protecting The signal output circuit is connected to the comparison unit for selecting the largest of the comparison signals to be output as the protection signal. The protection circuit of claim 8, wherein the plurality of current sensing units each comprise a plurality of resistors connected in series between the lamp and the ground for dividing the voltage signals and outputting Divided voltage signal. The protection circuit of claim 9, wherein the reference voltage selection circuit comprises: a plurality of diodes, wherein the anode of each of the diodes is connected to a current sensing unit for receiving the voltage signal; A plurality of resistors are connected in series between the cathode common junction of the diodes and the ground; wherein the common node of the resistors outputs the reference voltage. The protection circuit of claim 10, wherein the comparison units each comprise a plurality of comparators, wherein the first input end of each comparison unit is electrically connected to the reference voltage selection circuit, and the second input ends are respectively connected The current sensing unit is configured to output a plurality of comparison signals according to the reference voltage and the divided voltage signal. The protection circuit of claim 11, wherein the protection signal output circuit further comprises: a plurality of diodes, wherein the anode of each of the diodes is connected to an output of one of the comparison units for receiving a comparison signal output by the comparison unit; wherein the cathodes of the diodes are connected to one point , for selecting the largest one of the output comparison signals to output as the protection signal.