JP2000308363A - Multi-channel inverter - Google Patents

Abstract

(57) [Problem] An object of the present invention is to provide a multi-channel inverter capable of simultaneously lighting a plurality of discharge tubes without causing flicker, and further reducing the overall shape and weight. is there. In addition, the discharge tube can be easily turned on by the inverter. SOLUTION: There are provided a plurality of resonance power supply circuits RS1 to RS4 each including a boost transformer, a resonance capacitor, and a switching transistor, and the transistors are driven near the resonance frequency of the resonance power supply circuit, and all the inverters 10 to 13 are driven at the same timing. To operate the resonance power supply circuits RS1 to RS1.
A plurality of discharge tubes DS1 on the secondary side of the step-up transformer of RS4
DS4 is lit with a high frequency voltage of the same frequency. When the inverter is started, it is driven for a short time at a frequency lower than the resonance frequency in consideration of the ease of lighting of the discharge tube. When the discharge tubes are abnormal, the lighting of all the discharge tubes is stopped by using the output of the OR circuit A of the abnormal signal of each discharge tube.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-channel inverter capable of simultaneously lighting a plurality of discharge tubes.

[0002]

2. Description of the Related Art A discharge tube such as a cold cathode fluorescent lamp is generally used as a backlight of a liquid crystal display device. However, as a measure to increase the size of the display device and increase the brightness, a plurality of discharge tubes are used. There is an increasing demand for lighting at the same time. When lighting multiple discharge tubes close to each other and lighting them at the same time, if there is a difference in the frequency of the high-frequency voltage used for lighting each discharge tube, the tube wall capacity of the discharge tube, the capacity of the cable supplying the high-frequency voltage to the discharge tubes, Interference due to electromagnetic coupling of a transformer or the like occurs, which causes flicker in the brightness of the discharge tube. As a countermeasure against this flicker, measures such as physically increasing the distance between the discharge tubes and the distance of the high-frequency voltage generation circuit and newly providing a shield to prevent interference have been taken. With the increasing demand for smaller, thinner, and lighter lighting circuits for tubes, such physical measures have become impossible.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a multi-channel inverter capable of simultaneously lighting a plurality of discharge tubes without causing flickering, and reducing the overall size and weight. is there. In addition, it is easy to start lighting of the discharge tube, and at the same time, if any one of the plurality of discharge tubes has an abnormality such as breakage, an accident due to a high lighting voltage of the discharge tube may cause an accident. An object of the present invention is to provide a multi-channel inverter capable of preventing occurrence.

[0004]

According to the present invention, there is provided a boosting transformer having a discharge tube connectable to a secondary winding, a primary winding of the boosting transformer, a resonance capacitor connected to the primary winding, and a switching transistor. In a multi-channel inverter having a plurality of resonance power supply circuits, the characteristics of the same type of circuit elements forming each resonance power supply circuit are made substantially the same between the resonance power supply circuits, so that the resonance frequency of each resonance power supply circuit is substantially The switching transistors of each resonance power supply circuit are driven in synchronization with a signal having a frequency near the resonance frequency obtained by using an oscillation circuit provided separately from the resonance power supply circuit.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The multi-channel inverter of the present invention focuses on the fact that a difference in the frequency of a high-frequency voltage for lighting a discharge tube affects interference, and uses the high-frequency inverter for lighting a plurality of discharge tubes. The voltage is at the same frequency. In addition, since the resonance frequency of the resonance power supply circuit is low before the discharge tube is turned on, the lighting performance can be improved by starting the resonance power supply circuit at this low frequency, and at the same time, one of the plurality of discharge tubes is damaged. In the case where an abnormality occurs, the lighting of all the discharge tubes is stopped to prevent the occurrence of an accident caused by the high voltage.

[0006]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing an embodiment of a multi-channel inverter according to the present invention.
The multi-channel inverter shown in FIG. 1 includes four inverters 10, 1 each comprising a resonance power supply circuit including a step-up transformer.
1, 12, and 13. Inverter 10
Is connected between the discharge tube DT1 and the current detection circuit I between both ends of the secondary winding.
D1 is connected in series with a step-up transformer T1, a primary winding of the step-up transformer T1, a resonance capacitor C1, a choke coil L1, a switching transistor Q11, and a push-pull resonance power supply circuit RS1 formed of a switching transistor Q12. . The switching transistors Q11 and Q12 are N-channel MO
It is an S transistor.

The resonance capacitor C1 of the resonance power supply circuit RS1
Is connected between both ends of a primary winding of a step-up transformer T1, and both ends of the primary winding are connected to drains of a switching transistor Q11 and a transistor Q12, respectively. The sources of the transistors Q11 and Q12 are grounded. The transistors Q11 and Q12
Has a normal output terminal Q and a complementary output terminal Q _{BAR of} an oscillation circuit OSC provided separately from the resonance power supply circuit RS1.
Connect. Then, pulse voltages V _Q and V _QBAR having a duty ratio of 50% and phases different from each other by 180 ° are applied to the gate from the normal output terminal Q and the complementary output terminal Q _BAR .
The intermediate tap P1 of the primary winding is connected to a DC voltage source E1 via a choke coil L1.

An inverter 11 is a resonance power supply circuit RS2 including a step-up transformer T2 and a choke coil L2 connected to an intermediate tap P2 of the primary winding of the step-up transformer T2. An inverter 12 is an intermediate part of the step-up transformer T3 and the primary winding of the step-up transformer T3. Resonant power supply circuit RS3 including choke coil L3 connected to tap P3, inverter 13 includes boost transformer T4, and resonant power supply circuit RS4 including choke coil L4 connected to intermediate tap P4 of the primary winding of the primary winding of boost transformer T4.
And the same circuit element as the inverter 10,
Each of them is configured in substantially the same manner as the inverter 10. The characteristics of circuit elements such as the step-up transformers, choke coils, and resonance capacitors that constitute the inverters 11, 12, and 13 are substantially the same as the characteristics of the same type of circuit elements of the inverter 10, and the resonance of each resonance power supply circuit The frequencies are almost the same. In the oscillation circuit OSC, 5 is a control terminal for performing an oscillation operation and its stop, 6 is a synchronization input terminal,
_OS is an oscillation capacitor. Oscillation circuit OSC is duty ratio at the frequency for driving the switching transistor of each resonant power supply circuit is 50%, the pulse voltage V _Q having phases different from each other by 180 °, to generate the V _{QB AR.} Note that the oscillation circuit O
In the SC, the operation state and its stop state are controlled by an on / off signal applied to a control terminal 5, and pulse voltages V _Q , V _QBAR are applied to a synchronization input terminal 6 by a synchronization signal applied from a microcomputer or the like as necessary. Can also be set. Immediately after the oscillation circuit OSC starts operating in _{response to} the ON signal, the frequency of the pulse voltages V _Q and V _QBAR is sufficiently lower than the resonance frequency when the discharge tube of the resonance power supply circuit is turned on, and eventually stabilizes near the resonance frequency. Is adjusted by the control circuit CNT. The power supply voltage of the oscillation circuit OSC is supplied from a common DC voltage source E1 via a switch SW. The switch SW is normally conducting.

A push-pull resonance power supply circuit RS1, R
The resonance frequencies of S2, RS3, and RS4 are determined by a function of the product of the operating inductance of the primary winding of the step-up transformer and the capacitance of the resonance capacitor connected to the primary winding. Are substantially the same because the characteristics of the circuit elements are substantially the same. CP
1, CP2, CP3 and CP4 are comparators, and the non-inverting input terminals are connected to a common reference voltage source E2.
The inverting input terminals of the comparators CP1, CP2, CP3, and CP4 are respectively connected to the output terminals 1, 2, 3, and 4 of each current detection circuit, and the output side of each comparator is connected to the input side of the OR circuit A. .

Next, the operation of the multi-channel inverter thus configured will be described with reference to FIG. FIG.
Shows voltage waveform diagrams at the time of stable operation of the inverters 10 and 11 as representatives of four inverters.
V _Q is a pulse voltage applied from the normal output terminal _Q of the oscillation circuit OSC to the gates of the switching transistors Q11 and Q21, and V _QBAR is a complementary output terminal Q of the oscillation circuit OSC.
_The pulse voltage applied from _BAR to the gates of the switching transistors Q12 and Q22, V _Q11 and V _Q12 are the drain voltages of the switching transistors Q11 and Q12,
V _Q21 and V _Q22 are switching transistors Q21,
This is the drain voltage of Q22. The frequencies of the pulse voltages V _Q and V _QBAR that drive the switching transistors Q11 and Q12 are frequencies near the resonance frequency of the resonance power supply circuit when the discharge tube is turned on. The resonance frequency is
It is determined by the function of the product of the operating inductance of the step-up transformer connected to the discharge tube and the capacitance of the capacitor connected to the primary winding, but the characteristics of the same type of circuit elements in each resonance power supply circuit are made substantially the same. Therefore, the resonance frequency of each resonance power supply circuit, that is, the resonance frequency of each inverter is almost the same. In FIG. 2, the resonance frequency of the resonance power supply circuit RS1 of the inverter 10 is slightly lower than the average resonance frequency of the four resonance power supply circuits.
An example is shown in which the resonance frequency of one resonance power supply circuit RS2 is slightly higher than the average resonance frequency.

At time t1, the pulse of the oscillation circuit OSC
Voltage V_Q Are the transistors Q11 and Q2
1 gate, pulse voltage V_QBARIs the transistor Q12 and
And the gate of the transistor Q22.
The transistors Q11, Q12, Q21 and Q22 are driven.
Pulse voltage V_Q The transistor Q11 driven by
The transistor Q21 conducts and the drain voltage V_Q11 , V
_Q21 Becomes 0 and the pulse voltage V_QBARDriven by a transformer
The transistor Q12 and the transistor Q22 are shut off and drained.
In voltage V_Q12 , V _Q22 Is from 0 to the frequency of the resonant power supply circuit
And rises in the form of a half-wave sine wave according to.

The transistor Q1 which rises at time t1
2. The drain voltage V of Q22_Q12 , V _Q22 Is the time t
2, ie, drop near half wavelength of resonance frequency of resonance power supply circuit
It becomes almost 0. Note that the resonance power supply circuit RS1 and the resonance power supply
The resonance frequency of the source circuit RS2 is slightly shifted, and the time t
2, the drain voltage V_Q12 Before it reaches 0 completely
Rain voltage V _Q22 Is already 0. At time t2
Is the pulse voltage V_Q , V_QBARIs inverted from that at time t1
Transistor Q11 and transistor Q1
2 are added to the respective gates. Therefore, Transis
Q11 is cut off and its drain voltage V_Q11 Is half-wave
It rises like a sine wave. Transistor Q12 conducts,
Drain voltage V_Q12 Becomes 0. From time t2 to time t3
Between the drain voltage V_Q11 Is between time t1 and time t2
Collector voltage V_Q12 Stand up in the same way as
Immediately before the transistor Q11 falls and becomes 0 at time t3, the transistor Q11
Is forcibly set to 0 by conduction. Inverter 1
0, the push-pull of the resonance power supply circuit RS1
Type excitation operation completes a cycle, and the same circulation continues thereafter in the oscillation circuit O
Pulse voltage V from SC_Q , V_QBARTo continue. I
Also in the inverter 11, the transistors Q21 and Q22 are
Being driven separately in synchronization with the separate excitation operation of the barter 10
The separate excitation operation similar to that of the inverter 10 is continued.

[0013] Push-pull operation in synthesized transistors Q11, the drain voltage V _{Q1 1} of Q12, V _Q12 secondary side of the step-up transformer T1, the same transistors Q21,2
The drain voltages V _Q21 and V _Q22 are boosted on the secondary side of the step-up transformer T2 and appear as continuous sinusoidal waveforms, thereby lighting the discharge tube. The operation of the inverters 10 and 11 has been described with reference to FIG.
As is clear from FIG. 1, the oscillation circuit OS
The pulse voltage V _Q from C transistors Q11, like the transistor Q21 transistors Q31,41, pulse voltage V _Qbar is also applied to the gate of the transistor Q12, Q22 and likewise transistors Q32, Q42. Also, as described above, the resonance power supply circuits RS1, RS2, RS
3. The resonance frequency of RS4 is almost the same. Therefore, in the inverters 10, 11, 12, and 13, the oscillation circuit O
The separate excitation operation is performed at the same frequency in synchronization with the pulse voltages V _Q and V _QBAR from the SC. As in the example of FIG. 2, the frequencies of the pulse voltages V _Q and V _QBAR of the oscillation circuit OSC are near the resonance frequency of the resonance power supply circuit, and do not always completely match the resonance frequencies of the resonance power supply circuits. The resonance frequency of the resonance power supply circuit RS1 is slightly lower than the pulse voltages V _Q and V _QBAR , and the resonance frequency of the resonance power supply circuit RS2 is the pulse voltage V
_{Although the} case where the voltage is slightly higher than _Q and V _QBAR is shown, the sine wave on the secondary side of the step-up transformers T1 and T2 is slightly distorted and cannot be practically used. Also, the pulse voltage V
_Since the frequencies of _Q and V _QBAR may move due to the temperature drift of the oscillation circuit OSC or the like, a signal from a microcomputer or the like may be input to the synchronization input terminal 6 of the oscillation circuit OSC and fixed.

In this manner, the multi-channel interface of the present invention
The inverter operates at the same frequency synchronized by each inverter.
Multiple discharge tubes are synchronized on the same cycle based on their operation.
It is lit at a high frequency voltage of the wave number. In addition, multi-channel
The efficiency of the inverter is determined by the pulse voltage V of the oscillation circuit OSC._Q ,
V _QBARFrequency and resonance power supply circuit RS1, RS2, RS
3. Most efficient when the resonance frequency of RS4 is completely the same
Is good. Pulse voltage V_Q , V_QBARFrequency and resonance power times
± 1 of resonance frequency of roads RS1, RS2, RS3, RS4
If within 0%, the secondary of the step-up transformer of each inverter
Side sine wave at the same frequency with slightly different distortion
And does not cause a practical problem. Of course, no flicker
The purpose of obtaining a multi-channel inverter can be sufficiently achieved
You. Further, the oscillation circuit OSC outputs the ON signal of the control terminal 5.
Resonant power supply circuits RS1, RS2, R for a short time immediately after input
S3, more than the resonance frequency when the discharge tube of RS4 is turned on
An internal control circuit CNT is used to oscillate at a low frequency.
Has been adjusted. Therefore, the pulse of the oscillation circuit OSC
Voltage V_Q , V_QBARImmediately after the start of the oscillation operation
Resonant power supply circuit RS1, RS2, RS when discharge tube is lit
3. The frequency becomes sufficiently lower than the resonance frequency of RS4.
I have. This is the discharge connected to the secondary side of the step-up transformer.
Before lighting the tube, the secondary side of the transformer is equivalently open
Therefore, the operating inductance of the transformer is substantially large.
The resonance frequency of the resonant power supply circuit including the transformer is low.
It is based on what you are doing. This allows
From near the resonant frequency when the discharge tube is lit
Drive, a resonant sine wave is generated on the secondary side of the transformer.
Inadequate discharge and lighting of the discharge tube
Can be avoided. That is, before the discharge tube is lit,
Resonance power supply circuit RS1, RS2, RS3, RS4
A frequency close to the vibration frequency to facilitate lighting of the discharge tube.
Things.

Next, an operation in the case where the current stops flowing due to an accident such as breakage of one of the four discharge tubes or the current becomes lower than a set level will be described. For example, discharge tube D
When the current of T1 becomes equal to or less than the set level, the output generated at the output terminal 1 of the current detection circuit ID1 decreases, and the output of the comparator CP1 is inverted. And O
When the output of the R circuit A is inverted, the switch SW is turned off, and the power supply voltage supplied to the oscillation circuit OSC is cut off. This means that the driving of the switching transistors of all the resonance power supply circuits is stopped, and the resonance power supply circuits RS1, RS2, RS3, and RS4 stop operating, so that all the discharge tubes are not turned on. The method of stopping the operation is merely an example. Further, the resonance power supply circuit may be a circuit different from the push-pull type. Of course, it is not necessary to limit the number of inverters to four, and a desired number of inverters can be combined.

[0016]

As described above, in the multi-channel inverter of the present invention, each inverter operates at the same frequency on the basis of a signal having a frequency near the resonance frequency of the resonance power supply circuit obtained by using the oscillation circuit. Are lit with the same high frequency voltage synchronized. Since there is no difference in the frequency of the high-frequency voltage for lighting the discharge tube, flicker can be eliminated without using physical means such as increasing the interval between the discharge tubes. Needless to say, there is no need to newly add a shield for preventing interference. These contribute to miniaturization, thinning, and weight reduction of the multi-channel inverter. Further, the lighting performance that facilitates starting of the inverter, that is, lighting at the start of lighting of the discharge tube is also improved. Further, when the discharge tube is abnormal, lighting of all the discharge tubes can be stopped, so that occurrence of an accident due to high voltage can be prevented. The multi-channel inverter of the present invention has such excellent effects and is a very practical invention.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a multi-channel inverter according to the present invention.

FIG. 2 is a voltage waveform diagram of FIG.

[Explanation of symbols]

 FF1 flip-flop circuit DT1 discharge tube ID1 current detection circuit OSC oscillation circuit RS1 resonance circuit 10 inverter

Claims (5)

[Claims] 1. A step-up transformer having a discharge tube connectable to a secondary winding, a primary winding of the step-up transformer, and a plurality of resonance power supply circuits formed by using a resonance capacitor and a switching transistor connected to the primary winding. In a multi-channel inverter, the resonance frequency of each resonance power supply circuit is made substantially the same by making the characteristics of the same type of circuit elements forming each resonance power supply circuit substantially the same between the resonance power supply circuits. A multi-channel inverter, wherein the switching transistor of the circuit is driven in synchronization with a signal having a frequency near the resonance frequency obtained by using an oscillation circuit provided separately from the resonance power supply circuit. 2. A step-up transformer having a discharge tube connectable to a secondary winding, a primary winding of the step-up transformer, a resonance capacitor connected to the primary winding, and a pair of switching transistors. In a multi-channel inverter having a plurality of push-pull type resonant power supply circuits in which an intermediate tap is connected to a DC voltage source via a choke coil and both ends of a primary winding are connected to the switching transistor, the same forms each resonant power supply circuit. By making the characteristics of the circuit elements of the types substantially the same between the resonance power circuits, the resonance frequency of each resonance power circuit is made substantially the same, and a pair of switching transistors of each resonance power circuit are separately provided from the resonance power circuit. A pair of signals having frequencies near the resonance frequency and different in phase by 180 ° from each other obtained by using the provided oscillation circuit. Multichannel inverter, characterized in that synchronously driven. 3. The method according to claim 1, wherein the frequency of the signal obtained by using the oscillation circuit is within ± 10% of the resonance frequency of the resonance power supply circuit when the discharge tube is lit while the discharge tube is lit. 3. The multi-channel inverter according to claim 2, wherein: 4. The frequency of a signal obtained by using the oscillation circuit is sufficiently lower than the resonance frequency of the resonance power supply circuit when the discharge tube is turned on before the discharge tube is turned on when the inverter is started. 3. The multi-channel inverter according to claim 1, wherein after the lamp is turned on, the discharge tube shifts to within ± 10% of the resonance frequency of the resonance power supply circuit at the time of lighting and stabilizes. 5. A current detection circuit is connected to the secondary winding of the step-up transformer, and when the current level of at least one current detection circuit falls below a predetermined level, the driving of the switching transistors of all the resonance circuits is stopped. The multi-channel inverter according to any one of claims 1, 2, 3, and 4, wherein