KR920003091Y1 - A small fluorescent lamp lighting power equipment of liquid crystal tv - Google Patents

Abstract

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Description

Power supply unit for small fluorescent lamp lighting of LCD TVs

1 is a conventional voltage source converter circuit.

2 is a voltage and current waveform diagram according to a conventional switching operation.

3 is a voltage and current waveform diagram of switching according to a load in the conventional self-oscillation drive.

4 is a conventional current source converter circuit.

5 is a voltage and current waveform diagram applied to a switching element to light up the fluorescent lamp of FIG.

6 is a circuit diagram of a resonance current source inverter of the present invention.

7 is a switching current and voltage waveform diagram according to the present invention.

8 is an equivalent circuit diagram of the current source inverter of the present invention.

* Explanation of symbols for main parts of the drawings

T: Transformer TR ₁ , TR ₂ , Q ₁ , Q ₂ : Switching Transistor

R _L : load resistance C, C _S : condenser

R _S , R _B , R _D : Resistor L _R , Ldc: Coil

The present invention relates to a power supply device for lighting a small fluorescent lamp of a liquid crystal TV, and more particularly, to minimize the power consumption and even after the fluorescent lamp is turned on, the small size of a liquid crystal TV that can continuously light it without generating noise The present invention relates to a power supply device for lighting a fluorescent lamp.

Conventionally, the first degree of the bar, said transistor (TR ₁₎ came to by lighting a push-pull compact fluorescent lamp of a liquid crystal TV with (push-pull) operation symmetrically connected to each other a pair of transistors, such a characteristic as shown in ( When TR ₂ ) switches on its own vibration, the switching voltage and current waveform as shown in FIG. 2 are transmitted to the load RL through the transformer T.

As such, when the switching operation is performed by the vibration of the transistor, a high voltage for lighting a fluorescent lamp can be obtained using a transformer, but the saturation characteristic of the transformer is used, resulting in high power consumption.

That is, when any one of the transistors is turned on by the self-vibration of the transistors TR ₁ and TR ₂ , a current is applied to the primary coil L ₁ of the transformer T and the magnetic flux from the coil L ₁ . (Magnetic Flux) occurs.

After a certain period of time, the primary coil L ₁ becomes saturated and the maximum current flows, but the base current of the transistor TR ₁ decreases relatively due to the increase of the collector current. The transistor TR ₁ , which has been turned on until now, is turned off.

Thereafter, another transistor TR ₂ is turned on momentarily so that a primary current L ₁ of the transformer T flows in a driving current in the opposite direction unlike before, and eventually, the primary coil L ₁ flows into the primary coil L ₁ . The flowing current flows through the oscillating current so that the high voltage is induced in the secondary coil L ₂ having a relatively high number of turns, and the fluorescent lamp is turned on.

As described above, the switching operation is repeated based on the saturation characteristic of the transformer, so that a high voltage can be generated in the secondary coil L ₂ of the transformer. However, this operation uses the saturation characteristic of the transformer, which consumes a lot of power. Will be.

2a and 2b are waveform diagrams of switching voltages and currents according to on / off operation of transistors TR ₁ and TR ₂ , and FIGS. 3a and 3b are loads RL when the transformer T is driven. The voltage and current waveforms supplied thereto are shown.

4 shows a conventional current source converter circuit, in which a power supply voltage Vs is applied to the primary side coil L ₁ of the transformer T through the coil Ldc, and the transistor TR ₁ is driven by the driving circuit. When the switching operation is a high voltage is induced in the secondary coil (L ₂ ) of the transformer (T), the voltage and current across the transistors are as shown in Figures 5a and 5b. However, the current source converter also uses the saturation property of the transformer when switching, so not only the power loss in the transformer is large, but also the switching operation occurs in a saturated state in which the maximum current flows. Because of its large size and high noise, there was a problem that it was not suitable for use in small liquid crystal TVs.

Therefore, the present invention was devised to solve the above problems, and an object of the present invention is to provide a fluorescent lamp lighting power supply that can remove the influence of noise and prevent the loss of power.

The present invention for achieving the above object is that each base end of the transistors (Q ₁ , Q ₂ ) are interconnected via a first inductor (L _R ) and their collector ends are the primary coils of the transformer (T) L ₁ ) is connected to each other via a capacitor (Cs) to the secondary coil (L ₂ ) of the transformer via a medium, the middle tap terminal of each of the first inductor and the primary coil is a resistor (Rs) Interconnected by each collector terminal of the transistor, a capacitor constituting the primary coil and the LC resonance circuit is connected, and a second inductor (Ldc) is connected between the power supply terminal and the middle tap terminal of the primary coil Characterized in that.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

6 is an embodiment of the present invention, when a voltage is applied from the power supply terminal to the bases of the switching transistors Q ₁ and Q ₂ through the coil Ldc, the switching operation occurs alternately by self vibration and thus high frequency. The property is formed.

That is, when the transistor Q ₁ is switched on first, current flows through the collector stage, and the collector current gradually increases as time passes and becomes saturated, but the bias current flowing in the base stage is relatively Gradually decreasing, at some point the transistor Q ₁ is turned off. As described above, immediately after the transistor Q ₁ is turned off, another transistor Q ₂ is turned on so that current flows to the collector side, and the collector current gradually increases with time as described above. As the current flowing in gradually decreases, the transistor Q ₂ is turned off and the previous transistor Q ₁ is soon turned on. .

7a and 7b show the current Is ₁ and voltage Vs ₁ characteristics that appear during the switching operation of the transistor Q ₁ , but the same characteristics occur when the other transistor Q ₂ performs the switching operation. will be.

This can be equivalently interpreted as shown in FIG.

That is, in FIG. 8, the second inductor Ldc suppresses the flow of overcurrent when the transistors Q ₁ and Q ₂ are turned on, thereby acting as a constant current source Io, and also 1 of the transformer T. The secondary coil L ₁ and the capacitor C constitute an LC resonance circuit.

Therefore, when the high frequency according to the switching of the transistors Q ₁ and Q ₂ coincides with the resonance frequency, the maximum current flows in the LC resonant circuit, which induces the maximum voltage in the secondary coil of the transformer T, thereby providing a fluorescent lamp. The second inductor Ldc acts as a constant current source that prevents overcurrent from flowing to the collector stage and conducts a constant current when the transistors Q ₁ and Q ₂ conduct. .

In the above, the fluorescent lamp becomes the load R and the transformer T acts as an inductance.

Accordingly, in FIG. 8, the current Io flowing through the second inductor Ldc becomes Io = I ₁ -I ₂ , and the voltage Vc charged in the capacitor C is equal to Vc = V ₁ + V ₂ .

In other words, Where L is the magnetic inductance and M is the mutual inductance.

In addition, since the voltage (V _R ) applied to the fluorescent lamp is V _R = -RI ₃ , V _R + VI ₃ = 0 Or the current I ₂ flowing in the capacitor C So if you sum up the above equations, to be.

Meanwhile, an initial oscillation operation is performed when a DC input voltage is applied through the coil Ldc and the resistor Rs of FIG. 6, and when one transistor Q ₁ is switched, the other transistor Q ₂ It is turned off because a reverse voltage is applied to the base end.

At this time, the current Io flowing through the coil Ldc is to be.

In addition, the self-oscillation operation is as follows.

When the sinusoidal voltage is applied across the transformer T by the start operation, the transistors Q ₁ and Q ₂ can be switched.

That is, when the capacitor charging potential Vc is Vc> 0, the switching voltage VBES1 between the base and the emitter of the transistor Q becomes a positive (+) voltage greater than 0, and the transistor Q ₁ is turned on. The current Isd flowing in the primary coil of the transformer T having a turns ratio n: 1 is Flows as

In addition, since the high voltage is required when the fluorescent lamp is turned on, and a low operating voltage is required after the lamp is turned on, the output waveform of the transformer is maintained before the fluorescent lamp is turned on by installing the fluorescent lamp in series with the capacitor Cs as shown in FIG. Once the fluorescent lamp is turned on and turned on, the voltage across the fluorescent lamp can be appropriately selected using the voltage drop across the capacitor Cs.

In this way, the resonant current flows through the transformer T using the LC resonant circuit, thereby reducing power consumption, and by allowing the constant current to flow through the second inductor, any one of the transistors Q ₁ and Q ₂ switches. Even if it is turned off, it is possible to suppress the occurrence of switching stress to prevent the occurrence of switching stress.

As described above, the present invention can effectively remove noise by suppressing switching stress and provide a small resonant current source power supply suitable for economy by reducing power loss as much as possible.

Claims (3)

In a device for supplying power by connecting a switching element to a transformer connected to a load, each base terminal of the transistors Q ₁ and Q ₂ is interconnected via a first inductor LB and the collector terminals thereof are transformers. A load is connected to the secondary side coil L ₂ of the transformer T by a capacitor Cs while being interconnected through the primary side coil L ₁ of the T, and the first inductor LB. And the primary coil L ₁ are interconnected by a resistor Rs, and form an Lc resonance circuit together with the primary coil L ₁ between the respective collector ends of the transistors Q ₁ and Q ₂ . A condenser C is connected and a second inductor Ldc is connected between the power supply terminal E and the contacts of the primary coil L ₁ and the resistor Rs. Device. The driving operation of the switching element is a current type flowing in the coil (Ldc) Power supply device for a small fluorescent lamp lighting of the liquid crystal TV, characterized in that made to satisfy. The self-oscillating operation of the switching element is characterized in that the drive current I _SD after starting Power supply device for a small fluorescent lamp lighting of the liquid crystal TV characterized in that made to satisfy.