TWI442830B - Multi lamp driving system - Google Patents

Description

Multi-lamp drive system

The invention relates to a backlight driving system, in particular to a multi-lamp driving system.

Cold cathode fluorescent lamps are often used as backlights for liquid crystal display screens. In order to drive the cold cathode fluorescent lamp to illuminate, an inverter is required to convert the DC power source into an AC power source to provide a suitable driving power source. In order to protect the cold cathode fluorescent lamp and the inverter itself, an abnormality detection and protection circuit is often provided in the inverter to detect abnormalities and take protective measures. Usually, the anomaly detection and protection circuit compares the detected signal with the set reference voltage to determine whether to protect. However, since the set reference voltage is a fixed voltage, it is easy to cause malfunction due to changes in ambient temperature and lamp parameters.

In view of this, it is necessary to provide a multi-lamp driving system that can accurately detect abnormalities and avoid malfunctions.

A multi-lamp driving system for driving a plurality of lamps, including a filter circuit, a switch circuit, a pulse width modulation controller, a protection circuit, a complex transformer, and an anomaly detection circuit. Each of the transformers includes a primary winding and a secondary winding. The primary windings of the transformers are connected in parallel to the switching circuit, and the high voltage terminals of the secondary windings of the transformers are connected to the lamps one by one. The abnormality detecting circuit is connected to the transformer and the protection circuit for detecting whether the multi-lamp driving system and the lamps are abnormal, including a signal conversion circuit, a maximum tube current obtaining circuit, a minimum tube current obtaining circuit, and a comparison circuit. A signal conversion circuit is coupled to the low voltage end of the secondary winding of the transformer for converting a current signal flowing through the lamps into a voltage signal. The highest tube current acquisition circuit is connected to the signal conversion circuit for obtaining the highest voltage signal after the lamp having the highest current in the lamps. The lowest tube current acquisition circuit is connected to the signal conversion circuit for obtaining the lowest voltage signal after the lamp having the lowest current in the lamps. The comparison circuit is connected to the highest tube current acquisition circuit and the minimum tube current acquisition circuit for comparing whether the difference between the highest voltage signal and the lowest voltage signal exceeds a preset range, and at the highest voltage signal and the lowest voltage signal When the difference exceeds the preset range, a trigger signal is generated. The protection circuit controls the pulse width modulation controller to stop outputting the pulse width modulation signal when the trigger signal is received, thereby turning off the output of the switch circuit.

Preferably, the signal conversion circuit includes a plurality of signal conversion units, which are respectively connected to the low voltage ends of the secondary windings of the transformers. Each of the signal conversion units includes a first resistor and a first capacitor, and the first resistor is connected at one end to the corresponding one. The low voltage end of the secondary winding of the transformer is grounded, and the first capacitor is connected in parallel with the first resistor.

Preferably, the highest tube current obtaining circuit comprises a plurality of first diodes, which are respectively connected to the low voltage end of the signal converting unit and the secondary windings of the transformers, and the anodes are respectively connected to the low voltage ends of the secondary windings of the corresponding transformers. The cathode is connected and outputs the highest voltage signal.

Preferably, the minimum tube current obtaining circuit comprises a plurality of second diodes, which are respectively connected to the low voltage end of the signal converting unit and the secondary windings of the transformers, and the cathodes are respectively connected to the low voltage ends of the secondary windings of the corresponding transformers. The anode is connected and receives the first reference voltage via the second resistor and outputs the lowest voltage signal.

Preferably, the comparison circuit includes a switch, a third diode, a second capacitor, and a fourth power Resistance. The switch includes a control electrode, a first electrode and a second electrode, the control electrode is connected to the anodes of the second diodes and grounded via a third resistor, and the first electrode is connected to the cathodes of the first diodes. The anode of the third diode is connected to the second electrode of the switch, and the cathode outputs the trigger signal. One end of the second capacitor is connected to the cathode of the third diode, and the other end is grounded. The fourth resistor is in parallel with the second capacitor.

Preferably, the switch is a P-type metal oxide semiconductor field effect transistor, the control is a gate, the first electrode is a source, and the second electrode is a drain.

Preferably, the comparison circuit includes a comparator, a third diode, a second capacitor, a fourth resistor, and a fifth resistor. The comparator includes a positive input terminal, a negative input terminal, and an output terminal. The positive input terminal is coupled to the cathodes of the first diodes, and the negative input terminal is coupled to the anodes of the second diodes. The anode of the third diode is connected to the output of the comparator, and the cathode outputs the trigger signal. One end of the second capacitor is connected to the cathode of the third diode, and the other end is grounded. The fourth resistor is in parallel with the second capacitor. One end of the fifth resistor is connected to the output of the comparator, and the other end receives the second reference voltage.

The multi-lamp driving system dynamically obtains the highest tube current and the minimum tube current and compares them to determine whether an abnormality occurs. Therefore, when the ambient temperature and the lamp parameters change, the maximum tube current and the minimum tube current change accordingly, It will affect the judgment of abnormal conditions and avoid the occurrence of malfunctions.

10, 20‧‧‧Multiple lamp drive system

100‧‧‧Filter circuit

110‧‧‧ pulse width modulation controller

120‧‧‧Switch circuit

130‧‧‧Anomaly detection circuit

1300‧‧‧Signal Conversion Circuit

1301‧‧‧Signal Conversion Unit

1310‧‧‧Maximum tube current acquisition circuit

1320‧‧‧Minimum tube current acquisition circuit

1330, 1330A‧‧‧ comparison circuit

1331‧‧‧ Comparator

140‧‧‧Protection circuit

T1, T2‧‧‧ transformer

L1, L2‧‧‧ lamps

Q‧‧‧ switch

R1, R2, R3, R4, R5‧‧‧ first to fifth resistors

C1, C2‧‧‧ first to second capacitor

D1, D2, D3‧‧‧ first to third diodes

Vcc1‧‧‧ first reference voltage

Vcc2‧‧‧second reference voltage

Vin‧‧‧Input power supply

1 is a schematic diagram of a multi-lamp driving system according to an embodiment of the present invention; FIG. 2 is a specific circuit diagram of a multi-lamp driving system according to an embodiment of the present invention; and FIG. 3 is a multi-lamp driving according to another embodiment of the present invention. The specific circuit diagram of the system.

1 is a schematic diagram of a multi-lamp drive system 10 in accordance with an embodiment of the present invention. In the present embodiment, the multi-lamp driving system 10 is for converting the input power source Vin into an AC power source, and driving the plurality of lamps L1 and L2 (only two are taken as an example). The input power source Vin is a DC power source. In other embodiments of the invention, the input power source Vin can also be an AC power source. The multi-lamp driving system 10 includes a filter circuit 100, a switch circuit 120, a pulse width modulation controller 110, a complex transformer T1, T2, an abnormality detecting circuit 130, and a protection circuit 140. The filter circuit 100 is used for filtering. In the present embodiment, the filter circuit 100 includes a capacitor, for example, three capacitors connected in parallel with each other. The filter circuit 100 filters and outputs a DC power signal. The switch circuit 120 is connected to the filter circuit 100 for converting the DC power signal outputted by the filter circuit 100 into a first AC power signal. In this embodiment, the first AC power signal is a square wave signal. The switching circuit 120 includes a full bridge circuit, a half bridge circuit, a push-pull circuit, and the like.

The pulse width modulation controller 110 is configured to generate a pulse width modulation signal, and the control switch circuit 120 is turned on or off to convert the DC power signal outputted by the filter circuit 100 into a first AC power signal. The protection circuit 140 is configured to protect the multi-lamp driving system 10 or the lamps L1, L2 when abnormal, and notify the pulse width modulation controller 110 to stop the pulse width modulation controller 110 from outputting the pulse width modulation signal. Switching circuit 120 stops switching, thereby turning off multi-lamp drive system 10 to avoid damage.

Each of the transformers T1, T2 includes a primary winding and a secondary winding. The primary windings of the transformers T1 and T2 are connected in parallel to the switch circuit 120. The high voltage ends of the secondary windings are connected to the lamps L1 and L2 one by one, that is, the high voltage end of the secondary winding of the transformer T1 is connected to the lamp L1, and the secondary of the transformer T2. The high voltage end of the winding is connected to the lamp tube L2. The transformers T1 and T2 are used to convert the first alternating current power signal outputted by the switch circuit 120 into the second alternating current power. Source signal. In this embodiment, the second AC power signal is a sine wave signal.

The abnormality detecting circuit 130 is connected to the transformers T1 and T2 and the protection circuit 140 for detecting whether the multi-lamp driving system 10 and the lamps L1 and L2 are abnormal, including the signal conversion circuit 1300, the highest tube current obtaining circuit 1310, and the minimum tube current. The circuit 1320 and the comparison circuit 1330 are obtained. The signal conversion circuit 1300 is connected to the low voltage end of the secondary windings of the transformers T1 and T2 for converting the power signals flowing through the lamps L1 and L2 into voltage signals. The highest tube current acquisition circuit 1310 is connected to the signal conversion circuit 1300 for obtaining the highest voltage signal after the lamp having the highest current in the lamps L1 and L2. The minimum tube current acquisition circuit 1320 is connected to the signal conversion circuit 1300 for obtaining the lowest voltage signal after the lamp having the lowest current in the lamps L1 and L2. The comparison circuit 1330 is connected to the highest tube current acquisition circuit 1310 and the lowest tube current acquisition circuit 1320 for comparing whether the difference between the highest voltage signal and the lowest voltage signal exceeds a preset range, and the difference between the highest voltage signal and the lowest voltage signal. When the preset range is exceeded, a trigger signal is generated to trigger the protection circuit 140. In the present embodiment, the preset range can be set according to actual conditions and needs, for example, 0.7V. The protection circuit 140 protects when receiving the trigger signal, and controls the pulse width modulation controller 110 to stop outputting the pulse width modulation signal, thereby turning off the output of the switch circuit 120.

The multi-lamp driving system 10 dynamically obtains the highest tube current and the minimum tube current and compares them to determine whether an abnormality has occurred, instead of the conventional fixed reference voltage comparison, and thus, the ambient temperature and the lamp L1, L2 parameters change, the highest tube Both the current and the minimum tube current change, avoiding the occurrence of malfunctions. In addition, in the safety requirement items for the multi-lamp driving system 10, such as contact current, when the lamps L1 and L2 are short-circuited, the capacitances of the lamps L1 and L2 do not participate in resonance, and the tube current signal generates a phase shift. The anomaly detection circuit 130 can detect this anomaly and trigger the protection circuit 140.

2 is a circuit diagram of a multi-lamp driving system 10 in accordance with an embodiment of the present invention. In the present embodiment, the signal conversion circuit 1300 includes a complex signal conversion unit 1301, which corresponds to the low voltage end of the secondary winding connecting the transformers T1 and T2, that is, the first signal conversion unit 1301 is connected to the transformer T1, and the second signal conversion Unit 1301 is connected to transformer T2. Each of the signal conversion units 1301 is configured to convert the current signals of the corresponding lamps L1 and L2 into voltage signals, which include a first resistor R1 and a first capacitor C1. One end of the first resistor R1 is connected to the low voltage end of the secondary winding of the corresponding transformer T1, T2, and the other end is grounded, and the first capacitor C1 is connected in parallel with the first resistor R1. The first resistor R1 is used to convert the current signals of the corresponding lamps L1 and L2 into voltage signals, and the first capacitor C1 is used to filter the voltage signals converted by the first resistor R1 to obtain a stable voltage. In this embodiment, the converted voltage signal is an alternating current signal.

The highest tube current acquisition circuit 1310 includes a plurality of first diodes D1, one to one corresponding to the low voltage terminals of the secondary windings of the signal conversion unit 1301 and the transformers T1, T2. The anodes of the first diodes D1 are respectively connected to the low voltage ends of the secondary windings of the corresponding transformers T1, T2, and the cathodes are connected and output the highest voltage signal. The first diodes D1 filter and output the highest voltage signals among the converted voltage signals of the signal conversion unit 1301 to the comparison circuit 1330.

The lowest tube current acquisition circuit 1320 includes a plurality of second diodes D2, one to one corresponding to the low voltage terminals of the secondary windings of the signal conversion unit 1301 and the transformers T1, T2. The cathodes of the second diodes D2 are respectively connected to the low voltage terminals of the secondary windings of the corresponding transformers T1, T2, and the anodes are connected and receive the first reference voltage Vcc1 via the second resistor R2 and output the lowest voltage signal to the comparison circuit 1330. In this embodiment, the highest voltage signal and the lowest voltage signal are both AC signals.

The comparison circuit 1330 includes a switch Q, a third diode D3, a third resistor R3, and a second Capacitor C2 and fourth resistor R4. The switch Q includes a control electrode, a first electrode, and a second electrode. The control electrode of the switch Q is connected to the anode of the second diode D2, that is, receives the lowest voltage signal, and is grounded via the third resistor R3. The first electrode of the switch Q is connected to the cathode of the first diode D1, that is, receives the highest voltage signal, and the second electrode is connected to the anode of the third diode D3. The cathode of the third diode D3 outputs the trigger signal to the protection circuit. One end of the second capacitor C2 is connected to the cathode of the third diode D3, and the other end is grounded. The fourth resistor R4 is connected in parallel with the second capacitor C2. The third diode D3, the second capacitor C2, and the fourth resistor R4 are used to convert the highest voltage signal of the alternating current into a direct current signal, and then output to the protection circuit 140, that is, the trigger signal is a direct current signal.

In the present embodiment, the switch Q is a P-type metal oxide semiconductor field effect transistor, and the gate is controlled to be a gate, the first electrode is a source, and the second electrode is a drain.

In the present embodiment, the parameters of the lamps L1 and L2 are the same, the parameters of the transformers T1 and T2 are the same, the parameters of the signal conversion unit 1301 are the same, the parameters of the first diode D1 are the same, and the parameters of the second diode D2 are the same. . Therefore, if the lamps L1, L2 and the multi-lamp driving system 10 have no abnormality, the currents flowing through the lamps L1 and L2 are not much different, the difference value does not reach the preset range, and the comparison circuit 1330 generates no trigger signal, and the protection circuit 140 Will not be protected.

If any of the lamps L1, L2 and the multi-lamp driving system 10 is abnormal, for example, the lamp L1 is broken, at this time, the current flowing through the lamp L1 is small. Therefore, the voltage of the voltage signal of the signal conversion unit 1301 corresponding to the lamp L1 is smaller than the voltage of the voltage signal of the signal conversion unit 1301 corresponding to the lamp L2. Moreover, since the first diode D1 has the same parameters and the cathodes are connected, the first diode corresponding to the lamp L2 is turned on, that is, the first diode D1 obtains the highest voltage signal corresponding to the highest current signal. The voltage of the first electrode of the switch Q is equal to the highest voltage signal minus the conduction voltage drop of the first diode D1.

At the same time, since the second diode D2 has the same parameters and the anodes are connected, the second diode D2 corresponding to the lamp L1 is turned on, that is, the second diode D2 obtains the lowest voltage signal corresponding to the lowest current signal. The voltage of the control electrode of the switch Q is equal to the minimum voltage signal plus the conduction voltage drop of the second diode D2. The voltage difference between the control electrode of the switch Q and the first electrode is the lowest voltage plus the conduction voltage drop of the first diode D1 and the second diode D2 minus the highest voltage, because the lowest voltage is almost zero, and the highest voltage is at least For a few volts, the switch Q is turned on. At this time, the highest voltage signal is input to the anode of the third diode D3, and is rectified and filtered by the third diode D3, the second capacitor C2, and the fourth resistor R4, and then becomes a DC-type trigger signal and is input to the protection. Circuit 140. As such, the detection circuit 130 can detect an abnormality.

3 is a circuit diagram of a multi-lamp driving system 20 in accordance with another embodiment of the present invention. The multi-lamp driving system 20 in the present embodiment is different from the multi-lamp driving system 10 in FIG. 2 in that the specific structure of the comparison circuit 1330A is different from the comparison circuit 1330, and the rest is identical, and thus will not be described herein. The comparison circuit 1330A includes a comparator 1331, a third diode D3, a second capacitor C2, a fourth resistor R4, and a fifth resistor R5. The positive input terminal of the comparator 1331 is connected to the cathode of the first diode D1, the negative input terminal is connected to the anode of the second diode D2, and the output terminal is connected to the anode of the third diode D3. One end of the fifth resistor R5 is connected to the output terminal of the comparator 1331, and the other end receives the second reference voltage. The connection relationship and effect of the third diode D3, the second capacitor C2, and the fourth resistor R4 are the same as those in FIG. 2, and will not be described in detail herein. In the present embodiment, the comparison circuit 1330A differs from the comparison circuit 1330 of FIG. 2 in that the comparator 1331 is used instead of the switch Q, but the operation principle is similar and will not be further described.

The multi-lamp driving system 10, 20 of the present invention dynamically obtains the highest tube current and the minimum tube current and compares them to determine whether an abnormality occurs, and thus, when the ambient temperature and the tube are When the L1 and L2 parameters change, the maximum tube current and the minimum tube current change, which will not affect the judgment of abnormal conditions and avoid the occurrence of malfunction.

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.

10‧‧‧Multiple lamp drive system

100‧‧‧Filter circuit

110‧‧‧ pulse width modulation controller

120‧‧‧Switch circuit

130‧‧‧Anomaly detection circuit

1300‧‧‧Signal Conversion Circuit

1310‧‧‧Maximum tube current acquisition circuit

1320‧‧‧Minimum tube current acquisition circuit

1330‧‧‧Comparative circuit

140‧‧‧Protection circuit

T1, T2‧‧‧ transformer

L1, L2‧‧‧ lamps

Claims (6)

A multi-lamp driving system for driving a plurality of lamps, comprising a filter circuit, a switching circuit, a pulse width modulation controller and a protection circuit, wherein the multi-lamp driving system further comprises: a plurality of transformers, each transformer The primary winding and the secondary winding are connected, and the primary windings of the transformers are connected in parallel to the switching circuit, the high voltage ends of the secondary windings of the transformers are connected to the lamps one by one; and the abnormality detecting circuit is connected to the transformers and The protection circuit is configured to detect whether the multi-lamp driving system and the lamps are abnormal. The abnormality detecting circuit comprises: a signal conversion circuit connecting the low-voltage end of the secondary winding of the transformer for flowing through The current signals of the lamps are converted into voltage signals; the highest tube current obtaining circuit is connected to the signal conversion circuit for obtaining the highest voltage signal after the lamp having the highest current in the lamps; the lowest tube current obtaining circuit, Connecting the signal conversion circuit for obtaining the lowest voltage signal after the lamp having the lowest current in the lamps; and comparing the circuit The maximum tube current obtaining circuit and the minimum tube current obtaining circuit are configured to compare whether a difference between the highest voltage signal and the lowest voltage signal exceeds a preset range, and a difference between the highest voltage signal and the lowest voltage signal exceeds When the preset range is set, a trigger signal is generated; wherein, when receiving the trigger signal, the protection circuit controls the pulse width modulation controller to stop outputting the pulse width modulation signal, thereby turning off the output of the switch circuit, and the signal conversion The circuit includes a plurality of signal conversion units, one-to-one corresponding to the low-voltage end of the secondary windings of the transformers, each of the signal conversion units includes a first resistor and a first capacitor, and the first resistor is connected at one end Connected to the low voltage end of the secondary winding of the corresponding transformer, and the other end is grounded, and the first capacitor is connected in parallel with the first resistor. The multi-lamp driving system of claim 1, wherein the highest tube current obtaining circuit comprises a plurality of first diodes, and the low voltages of the signal winding units and the secondary windings of the transformers are connected one by one. The anode and the anode are respectively connected to the low voltage end of the secondary winding of the corresponding transformer, and the cathode is connected and outputs the highest voltage signal. The multi-lamp driving system of claim 2, wherein the minimum tube current obtaining circuit comprises a plurality of second diodes, and the low voltages of the signal winding units and the secondary windings of the transformers are connected one by one. The cathode is respectively connected to the low voltage end of the secondary winding of the corresponding transformer, and the anode is connected and receives the first reference voltage via the second resistor and outputs the lowest voltage signal. The multi-lamp driving system of claim 3, wherein the comparison circuit comprises: a switch comprising a control electrode, a first electrode and a second electrode, the control electrode connecting the anodes of the second diodes and Grounded via a third resistor, the first electrode is connected to the cathode of the first diode; the third diode, the anode of the third diode is connected to the second electrode of the switch, and the cathode outputs the trigger signal; The second capacitor has one end connected to the cathode of the third diode and the other end grounded; and a fourth resistor connected in parallel with the second capacitor. The multi-lamp driving system of claim 4, wherein the switch is a P-type metal oxide semiconductor field effect transistor, the control is a gate, the first electrode is a source, and the second electrode is a germanium. pole. The multi-lamp driving system of claim 3, wherein the comparison circuit comprises: a comparator comprising a positive input terminal, a negative input terminal and an output terminal, wherein the positive input terminal is connected to the first diodes a cathode, the negative input terminal is connected to the anode of the second diode; the third diode, the anode of the third diode is connected to the output end of the comparator, and the cathode outputs the cathode a second capacitor having one end connected to the cathode of the third diode and the other end being grounded; a fourth resistor connected in parallel with the second capacitor; and a fifth resistor having one end connected to the output of the comparator and the other end receiving Second reference voltage.