JP2001052891A - Separate excitation type inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of flicker in plural cold cathode-ray tubes, and to enable the separate dimming by providing an inverter transformer provided with a primary coil having the push-pull structure, two switching elements for controlling ON-OFF of both ends of the primary coil, and a clock signal generating circuit for supplying the clock signal having a different phase to these switching elements. SOLUTION: A single clock signal (i), a clock signal e1 having an opposite phase, and a PWM signal (g) to be generated by a PWM signal generating circuit 6 are input to an AND gate 9, and the single clock signal (i), an in-phase clock signal f1, and the PWM signal (g) are input to an AND gate 10. During the time when the signal (g) is High, switching elements 11, 12 are driven for push-pull by the signal output from the gates 9, 10 so as to perform the PAM dimming of the driving signal Z1 of a cold cathode tube 16 (a cold cathode-ray tube 17 is similarly dimmed). Similar operation is performed to AND gates 19, 20 except for the input of a clock signal f2 having the same phase with the single clock signal (i) to the later.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separately-excited inverter, and more particularly to a separately-excited inverter used for a cold-cathode tube and the like and capable of easily dimming, a parallel output inverter used for a multi-light cold-cathode tube and the like, and an independent inverter. And a parallel output inverter whose output can be adjusted.

[0002]

2. Description of the Related Art Generally, a backlight is used as a light source in a liquid crystal display panel (LCD), and a plurality of cold cathode tubes are used when high luminance is required.

When a plurality of CCFLs are turned on, a beat is generated due to a difference in the lighting frequency between the CCFLs. When the lighting frequencies are close to each other, they are visually recognized as flickering. In order to prevent such flickering, it is necessary to synchronize the lighting frequency of each cold-cathode tube. In a conventional inverter for a multi-light cold-cathode tube, a self-excited inverter as shown in FIG. A method of using a plurality of outputs of the transformer 101 and a method of using a common oscillation circuit on the primary side of the inverter transformer have been adopted. FIG.
In the separately-excited inverter 102, a driving pulse is generated by a driving pulse generating circuit, and a switching element connected to one end of a primary winding is turned on / off.

Generally, a DC / DC converter is used in order to prevent the luminance of the cold-cathode tube from fluctuating due to fluctuations in the primary-side power supply. The oscillation frequency of the DC / DC converter is usually three to four times the frequency of about 60 kHz, which is the oscillation frequency of the inverter transformer, in order to prevent flicker due to interference with the inverter transformer.

[0005]

However, the conventional cold-cathode tube inverter has the following problems. In other words, in the self-excited inverter, the oscillation frequency may fluctuate due to the characteristics of the components, and a beat may occur in the brightness of the illuminated LCD. In addition, in a method in which a plurality of outputs of the self-excited inverter transformer are used to light a plurality of cold cathode tubes, the output capacity of the inverter transformer
There is a problem that the number of cold cathode tubes is limited. Further, in the method of sharing the oscillation circuit on the primary side of the inverter transformer, there is a problem that the power capacity of the switching element, for example, the transistor increases, and the switching element becomes large.

Further, in the above-described method for synchronizing the lighting frequencies of the respective cold-cathode tubes and preventing flicker, it is not possible to independently control the light of each of the cold-cathode tubes. Also,
In a separately-excited inverter driven by a driving pulse, the switching element is connected to only one of the primary windings of the inverter transformer. Therefore, it is sufficient if the winding ratio between the primary side and the secondary side of the inverter transformer is not increased. There is a disadvantage that an output voltage on the secondary side cannot be obtained and the inverter transformer becomes expensive. In addition, in the separately-excited inverter 102 shown in FIG. 4, when the cold-cathode tube is turned on, the resonance frequency and the driving pulse frequency of the inverter transformer are shifted due to the variation of the components, and the output, for example, the tube current fluctuates. There is a problem that the power conversion efficiency is reduced.

[0007] DC / DC used in the inverter
The oscillation frequency of the converter is 200 kHz to 300 kHz
Switching loss in the DC / DC converter is large. Further, when the oscillation frequency of the DC / DC converter is lowered, a beat is generated due to interference with the oscillation frequency of the inverter transformer, and there is a problem that the cold cathode fluorescent lamp flickers.

The present invention has been made to solve at least one of the problems existing in the prior art, and is capable of reducing the cost and performing dimming of a cold cathode tube as a load with a simple configuration. A separately-excited inverter and a multi-lamp cold-cathode tube inverter capable of dimming each cold-cathode tube independently while synchronizing the lighting frequencies of a plurality of cold-cathode tubes to prevent flicker, and DC / D
It is an object of the present invention to provide a highly efficient inverter in which the frequency of a C converter is reduced.

[0009]

A first other example of the inverter according to the present invention comprises an inverter transformer having a primary winding of a push-pull configuration, and both ends of the primary winding are turned on.
It has two switching elements to be turned off, and a clock signal generating circuit for supplying clock signals of opposite phases to the two switching elements.

An inverter transformer having a primary winding of a push-pull configuration, and both ends of the primary winding are ON-O
A plurality of separately-excited inverters each including two switching elements for performing FF control and a clock signal generation circuit for supplying clock signals having phases opposite to each other to the two switching elements are provided. The clock signal of the circuit is shared.

In addition, one PW is connected to the separately-excited inverter.
An M signal generating circuit and two AND gates are provided, and two switching elements of the separately-excited inverter are connected so as to be controlled by an AND output of a clock signal of the clock signal generating circuit and a PWM signal of the PWM signal generating circuit. It was done.

Each of the separately-excited inverters is provided with one PWM signal generating circuit and two AND gates.
The clock signal of the clock signal generation circuit and the PWM signal
It is connected so as to be controlled by AND output with a PWM signal of a signal generation circuit.

Further, an output voltage of a DC / DC converter is used as an input power supply supplied to the primary winding of the inverter transformer, and the DC / DC converter is synchronized with an oscillation frequency of the clock signal generation circuit. It is a thing.

Further, after the power is turned on, the DC / DC signal is output until the output transmission of the clock signal generation circuit is stabilized.
It has a delay circuit for delaying the output of the DC converter.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 shows an inverter circuit for a cold cathode fluorescent lamp according to an embodiment of the present invention. Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 14, 15, 24 and 25 are inverter transformers, 1
Reference numerals 1, 12, 21, and 22 are switching elements formed of FETs that push-pull drive the inverter transformer.
The single clock signal i generated by the clock signal generation circuit 4 whose frequency can be adjusted is
One is sent to the AND gate 9 via the inverter gate 8 and the other is sent directly to the AND gate 10 in order to push-pull drive 1, 12, 21, 22. The same applies to the inverter gate 18 and AND gates 19 and 20. When the clock signal generation circuit 4 has the opposite phase output, the inverter gates 8 and 18 can be omitted. PWM signals for controlling the switching elements 11, 12, 21, and 22 and controlling the dimming of the cold-cathode tubes 16, 17, 26, and 27 are generated by the PWM signal generation circuits 5 and 6, and
It is sent to gates 9, 10, 19 and 20. The primary power supply 1 is connected to the middle point of each inverter transformer via the coils 13 and 23, the DC / DC converter 3, and the power switch 2. Although power supply lines to other electronic circuits are omitted, a power supply voltage is applied in conjunction with the power switch 2. Clock signal generating circuit 4 and delay circuit 7 are connected to DC / DC converter 3.

In the above configuration, the AND gate 9 has a clock signal e having a phase opposite to that of the single clock signal i.
(El) and PWM generated by the PWM signal generation circuit 5
The M signal g is input. The AND gate 10 has a clock signal f (f1) in phase with the single clock signal i and a PWM signal.
The PWM signal g generated by the signal generation circuit 5 is input.

Therefore, while the PWM signal g is High,
The switching elements 11 and 12 connected to both ends of the primary winding of the inverter transformer 14 are push-pull driven by the signals a and b output from the AND gates 9 and 10, respectively, and as shown in FIG. The drive signal Z1 of the cathode tube 16 is subjected to PWM dimming. The cold cathode tube 17 is also 1
PWM dimming is similarly performed by the inverter transformer 15 sharing the next winding.

The AND gate 19 receives the clock signal e (e2) having a phase opposite to that of the single clock signal i and the PWM signal h generated by the PWM signal generating circuit 6. AN
The D gate 20 receives the clock signal f (f2) having the same phase as the single clock signal i and the PWM signal h generated by the PWM signal generation circuit 6.

Therefore, while the PWM signal h is High,
The switching elements 21 and 22 connected to both ends of the primary winding of the inverter transformer 24 are push-pull driven by the signals c and d output from the AND gates 19 and 20, respectively, and as shown in FIG. The drive signal Z3 of the cathode tube 26 is subjected to PWM dimming. The cold-cathode tube 27 is similarly PWM-dimmed.

Here, the PWM signal generation circuits 5 and 6 perform PWM modulation independently of each other. The pulse repetition frequency of both of them is synchronized with one as a master and the other as a slave, or the clock of the clock signal generation circuit 4 is controlled. It is desirable to synchronize the signals with a common clock signal that counts the signals. This can prevent flicker due to interference between the PWM signals g and h.

As described above, as shown in FIG. 2, the drive signal Z1 for the cold cathode tube 16 and the drive signal Z3 for the cold cathode tube 26
Operate in synchronization with a single clock signal, and therefore also operate in synchronization with each other. Further, since the cold-cathode tubes 16 and 26 are dimmed by different PWM signals, each of them is independently dimmed. Also, the frequency of a single clock signal is
The tube current is monitored by the tube ammeters 28 and 38, and is adjusted to a predetermined frequency by a variable resistor or a variable capacitor connected to the clock signal generation circuit 4. As a result, it is possible to prevent a change in output and a decrease in power conversion efficiency due to a difference between the frequency of the single clock signal and the resonance frequency of the inverter transformer.

As described above, according to the present invention, since the primary winding of the inverter transformer has the push-pull configuration, the winding ratio of the primary winding to the secondary winding is not the push-pull configuration. Can be set smaller than.
Further, since the dimming means uses an AND output of the clock signal e (or the clock signal f) and the PWM signal, dimming of the cold-cathode tube can be easily performed. Furthermore, the operation of a plurality of cold-cathode tubes can be synchronized to prevent dimming while preventing flickering, and the difference between the resonant frequency of the inverter transformer and the frequency of a single clock signal due to the variation in parts can be found. Output fluctuations and a decrease in power conversion efficiency.

Embodiment 2 The DC / DC converter 3 shown in FIG. 1 supplies a constant DC voltage to the inverter transformers 14, 15, 24, 25 even if the power supply voltage fluctuates, so that the cold cathode tubes 16, 17, 26, 27
Are provided so that the luminance of the image is stable. That is, the input end of the DC / DC converter 3 is connected to the power supply 1 via the power switch 2, and the output end is connected to the coil 1.
The inverters 3 and 23 are connected to the respective middle points of the primary windings of the respective inverter transformers. A clock signal for controlling the oscillation of the DC / DC converter 3 is supplied from a connection line from a clock signal generation circuit 4. For the oscillation of the DC / DC converter 3, switching elements 11, 12, 2
By using the same clock signal as the single clock signal generated by the clock signal generating circuit 4 for driving the inverters 1 and 22, the inverter transformer and the DC / DC converter 3 operate synchronously, and no beat is generated. Tube flicker does not occur. Here, the clock signal for synchronizing the DC / DC converter 3 and the inverter circuit is supplied from the clock signal generation circuit 4 of the inverter circuit to the DC / DC converter, but is supplied from the DC / DC converter to the inverter circuit. You may.

As described above, according to the present invention, since the DC / DC converter 3 oscillates at the same low frequency as the inverter transformer, no beat occurs and the cold cathode fluorescent lamp 1
The flickers of 6, 17, 26 and 27 can be eliminated.

Embodiment 3 The delay circuit 7 shown in FIG. 1 can be constituted by an integrator circuit using a resistor and a capacitor or a preset counter for counting a fixed number of clock signals.
Connected to F control terminal. The delay circuit 7 delays the output of the DC / DC converter 3 for a fixed time after the power switch 2 is turned on, and outputs the output. Here, the clock signal generation circuit 4, the inverter gates 8, 18, the AND gates 9, 10, 19, 20 and the PWM signal generation circuit 5,
6 is supplied with power in conjunction with the power switch 2 without passing through the DC / DC converter 3. The power switch 2 is turned on, the clock signal generation circuit 4 oscillates stably, and A
After the outputs of the ND gates 9, 10, 19 and 20 are turned on,
Until the output becomes stable, the output of the DC / DC converter is delayed. After stable oscillation, the output of the DC / DC converter gradually rises in a ramp shape.

As described above, the AND gates 9, 1
0, 19, and 20 all become High when the output is indeterminate immediately after the power is turned on, and even if the switching elements 11, 12, 21, and 22 connected to the primary winding of the inverter transformer are continuously turned on, the output is excessive. Inrush current can be prevented by preventing current from flowing and raising the output of the switching element in a ramp shape.

[0027]

The separately excited inverter according to claim 1 of the present invention comprises an inverter transformer having a primary winding of a push-pull configuration, and two switching elements for controlling both ends of the primary winding on and off. And a clock signal generating circuit for supplying clock signals of opposite phases to the two switching elements, so that the oscillation frequency is not restricted by the resonance frequency of the inverter transformer.
Can be set freely. Further, since the primary winding of the inverter transformer has a push-pull configuration, the winding ratio of the primary winding to the secondary winding can be reduced, and the cost of the inverter can be reduced.

A separately excited inverter according to a second aspect of the present invention includes an inverter transformer having a primary winding of a push-pull configuration, two switching elements for controlling both ends of the primary winding on and off, A plurality of separately-excited inverters having a clock signal generation circuit for supplying clock signals of opposite phases to the two switching elements are provided, and each separately-excited inverter shares the clock signal of the clock signal generation circuit. Therefore, all the separately-excited inverters operate synchronously, and flickering of a plurality of cold cathode tubes can be prevented. In addition, one of the inverter transformers
Since the next winding has a push-pull configuration, the cost of the inverter can be reduced.

According to a third aspect of the present invention, the separately-excited inverter includes one PWM signal generation circuit and two AND gates, and the two switching elements of the separately-excited inverter are connected to the clock signal generation circuit. Circuit clock signal and PWM of said PWM signal generating circuit
Because it was connected to control by signal and AND output,
The oscillation frequency and the output can be adjusted independently and freely.

A separately excited inverter according to claim 4 of the present invention drives a switching element by sending a clock signal and a PWM signal to a switching element connected to a primary winding of an inverter transformer via an AND gate. With this configuration, it is possible to adjust the output such as dimming of the CCFL with a simple configuration, and independently control each CCFL while synchronizing the drive signals of multiple CCFLs to prevent flicker. Can be dimmed.

A separately excited inverter according to claim 5 of the present invention uses an output voltage of a DC / DC converter as an input power supply supplied to the primary winding of the inverter transformer. Since the oscillation frequency of the clock signal generation circuit is synchronized, the oscillation frequency of the DC / DC converter is set to the same low frequency as the inverter transformer while preventing the occurrence of beat, thereby reducing the switching loss of the DC / DC converter. Can be smaller.

A separately excited inverter according to a sixth aspect of the present invention is an inverter for separately excited cold cathode tubes, wherein
Even when the switching element connected to the primary winding of the inverter transformer is continuously ON at N, overcurrent can be prevented, and inrush current can be prevented by soft start.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a circuit configuration according to an embodiment of the present invention.

FIG. 2 is a diagram showing signal waveforms at various parts in FIG.

FIG. 3 is a circuit diagram showing a circuit configuration of a conventional self-excited inverter for a cold cathode tube.

FIG. 4 is a circuit diagram showing a circuit configuration of a conventional separately-excited inverter.

[Explanation of symbols]

 Reference Signs List 1 power supply 2 power switch 3 DC / DC converter 4 clock signal generation circuit 5, 6 PWM signal generation circuit 7 delay circuit 8, 18 inverter gate 9, 10, 19, 20 AND gate 11, 12, 21, 22 switching element 13, 23 Inductor 14, 15, 24, 25 Inverter transformer 16, 17, 26, 27 Cold cathode tube 28, 38 Tube ammeter

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hisaharu Oura 997 Miyoshi, Nishigoshi-cho, Kikuchi-gun, Kumamoto Prefecture Inside Advanced Display Co., Ltd. (72) Inventor Masanori Kageyama 2-3-2 Marunouchi 2-chome, Chiyoda-ku, Tokyo Inside Electric Co., Ltd. (72) Inventor Nobuyuki Ichinomiya 1-7 Yukitani Otsuka-cho, Ota-ku, Tokyo Alps Electric Co., Ltd. F-term (reference) 3K072 AA01 AA19 AB01 BA05 BC03 CB04 DA02 GA02 GB14 GC04 HA03 HA06 HA10 3K098 CC23 CC41 CC62 DD22 DD37 EE14 EE31

Claims (6)

[Claims] 1. An inverter transformer having a primary winding having a push-pull configuration, and both ends of said primary winding being ON-OFF.
A separately-excited inverter having two switching elements to be controlled and a clock signal generating circuit for supplying clock signals having opposite phases to the two switching elements. 2. An inverter transformer having a primary winding having a push-pull configuration, and both ends of said primary winding being ON-OFF.
A plurality of separately-excited inverters each including two switching elements to be controlled and a clock signal generation circuit for supplying clock signals having phases opposite to each other to the two switching elements, wherein each separately-excited inverter includes the clock signal generation circuit. Separately-excited inverter sharing the same clock signal. 3. The externally-excited inverter includes one PWM signal generation circuit and two AND gates, and two switching elements of the externally-excited inverter are connected to the clock signal of the clock signal generation circuit and the PWM signal generation circuit. 2. The self-excited inverter according to claim 1, wherein the inverter is connected so as to be controlled by an AND output with a PWM signal. 4. Each of the separately-excited inverters has one
Comprising two PWM signal generation circuits and two AND gates,
3. The separately-excited inverter according to claim 2, wherein each of the switching elements of the separately-excited inverter is connected to be controlled by an AND output of a clock signal of the clock signal generation circuit and a PWM signal of the PWM signal generation circuit. 5. An output voltage of a DC / DC converter is used as an input power supplied to the primary winding of the inverter transformer, and the DC / DC converter is synchronized with an oscillation frequency of the clock signal generation circuit. 5. The separately-excited inverter according to claim 1, 2, 3, or 4. 6. The DC / DC converter until the output transmission of the clock signal generation circuit is stabilized after the power is turned on.
6. The separately-excited inverter according to claim 5, further comprising a delay circuit for delaying an output of the converter.