JPH0696879A - Power supply unit for driving cathode discharge tube - Google Patents

Abstract

(57) [Abstract] [Purpose] The current flowing through the cathode discharge tube can be stabilized even if the discharge characteristics of the cathode discharge tube change due to temperature changes or the discharge characteristics of the individual cathode discharge tubes vary. Provided is a power supply device for driving a cathode discharge tube. A voltage control circuit 1 for controlling a voltage from the input power supply Ei, a switching circuit 2 connected to the voltage control circuit 1, and a transformer connected to the switching circuit 2 for the input power supply Ei. T, the cathode discharge tube L connected to the secondary winding side of the transformer T, and the current flowing in the cathode discharge tube L are detected to output a feedback signal, and the voltage control circuit 1 uses a reference voltage common to each circuit. A plurality of current detection circuits 3 to be input to the voltage control circuit 1 are provided for comparison with Vref.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for driving a cathode discharge tube used as a light source of a liquid crystal backlight.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram of a conventional cathode discharge tube driving power source for driving a plurality of cathode discharge tubes.

The inverter composed of the switching circuit 2 and the transformer T outputs a constant voltage V ₀ to the secondary winding of the transformer T. This constant voltage V _{0 is} passed through the ballast capacitors C ₁ , C ₂ , C _n to the cathode discharge tubes L ₁ , L ₂ ,
By applying it to L _n , it is turned on.

[0004]

However, in the above-mentioned conventional device, the discharge voltage of the cathode discharge tubes L ₁ , L ₂ , and L _n changes depending on external conditions such as the ambient temperature, so that the cathode discharge is inevitable. Currents I ₁ flowing in the tubes L ₁ , L ₂ , L _n ,
I ₂ and I _n change, so that the cathode discharge tubes L ₁ , L ₂ and L
_This causes the inconvenience that the brightness of _n changes.

Also, the cathode discharge tubes L ₁ , L ₂ , L are intentionally
_{Even when} the secondary winding voltage V ₀ of the transformer T is changed in order to change the brightness of _n, the cathode discharge tubes L ₁ , L ₂ , L
_Since the individual discharge voltage characteristics of _n vary, the currents I ₁ , I ₂ , and I _n flowing through the cathode discharge tube do not change as intended, and the variation in the luminance change among the discharge tubes also becomes large.

An object of the present invention is to provide a cathode discharge tube driving power supply device using a plurality of tubes, even when the discharge characteristics of the cathode discharge tube change due to temperature change or the like, or when the discharge characteristics of the individual cathode discharge tubes vary. An object of the present invention is to provide a power supply device for driving a cathode discharge tube, which can stabilize a current flowing through the cathode discharge tube.

[0007]

The above-described object is to provide an input power supply with a voltage control circuit for controlling the voltage from the input power supply, a switching circuit connected to the voltage control circuit, and a switching circuit therefor. The connected transformer, the cathode discharge tube connected to the secondary winding side of the transformer, and the current flowing in the cathode discharge tube are detected, and the feedback signal is supplied to the reference voltage common to each circuit by the voltage control circuit. This is achieved by including a plurality of current detection circuits which are input to the voltage control circuit for comparison.

[0008]

[Function] The change in the current flowing through the cathode discharge tube is detected by the current detection circuit, and the detected amount is fed back to the voltage control circuit. The voltage control circuit compares the reference voltage and the fed back amount common to each circuit. An output signal corresponding to the amount is input to the switching circuit to generate a voltage such that a predetermined constant current is generated in the secondary windings of each of the plurality of transformers.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit block diagram of a power source device for driving a cathode discharge tube according to an embodiment.

In a power supply device for driving a plurality of cathode discharge tubes, individual currents I flowing through the cathode discharge tubes L ₁ , L ₂ and L _n.
Current detection circuits 3 ₁ , 3 ₂ , 3 for detecting ₁ , I ₂ , I _n
n is connected in series to the cathode discharge tubes L ₁ , L ₂ and L _n to detect the amount of detection in the current detection circuits 3 ₁ , 3 ₂ and 3 _n (cathode discharge due to changes in external conditions such as temperature). Tubes L ₁ , L ₂ , L _n
The amount of change in currents I ₁ , I ₂ , and I _n ) flowing in each of the voltage control circuits 1 ₁ , 1 ₂ , and 1 _n is fed back.

The voltage control circuits 1 ₁ , 1 ₂ ,
1 _n compares the amount of feedback back with the reference voltage Vref and outputs the output voltage corresponding to the amount of feedback back to each switching circuit 2 ₁ , 2 ₂ , 2 _n and the transformers T ₁ , T ₂ , T _n.
In addition to the inverter composed of, transformers T ₁ , T ₂ ,
Voltages V ₁ , V ₂ and V _n are generated on the secondary winding side of T _{n so} that predetermined currents I ₁ , I ₂ and I _n are constant.

As described above, the cathode discharge tubes L ₁ , L ₂ , L _n
By controlling the individual currents I ₁ , I ₂ , and I _n flowing through the constant current to the cathode discharge tubes L ₁ , L ₂ , and L _n even if the discharge voltage changes due to external conditions such as temperature. Since the current can be kept constant, it is possible to configure a power source for a plurality of cathode discharge tube driving devices that maintains stable brightness.

The voltage control circuits 1 ₁ , 1 ₂ ,
The present invention is characterized in that the reference voltage Vref of 1 _{n is} the same for each cathode tube drive circuit. because,
When it is desired to change the current flowing through the cathode discharge tubes L ₁ , L ₂ and L _n to change the brightness, the reference voltage Vref is simply changed to detect the current detection circuit 3 ₁ for each cold cathode tube L ₁ , L ₂ and L _n . Three
_This is because the amount of feedback back for ₂ and 3 _n changes, so that the tube current (luminance) can be changed at the same amount or the same ratio for each tube at the same time.

[0015]

As described above, according to the present invention,
The change in the current flowing in the cathode discharge tube is detected by the current detection circuit, the detected amount is fed back to the voltage control circuit, the voltage control circuit compares the reference voltage common to each circuit and the amount of feedback, and the amount of feedback is adjusted according to this amount. The output signal is input to the switching circuit to generate a voltage such that a predetermined constant current is generated in the secondary windings of each of the plurality of transformers. Therefore, the discharge voltage of the cathode tube changes due to changes in ambient temperature. Even if it changes, the current can be controlled to be constant, and a cathode ray tube driving power source with stable brightness can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit block diagram of a power supply device for driving a cathode discharge tube according to an embodiment of the present invention.

FIG. 2 is a circuit block diagram of a power supply device for driving a cathode discharge tube according to a conventional example.

[Explanation of symbols]

Ei input power supply Vref reference voltage 1 ₁ to 1 _n voltage control circuit 2 ₁ to 2 _n switching circuit T _{1 to} T _n transformer L _{1 to} L _n cathode discharge tube 3 _{1 to} 3 _n current detection circuit

Claims (1)

[Claims] 1. A voltage control circuit for controlling a voltage from the input power source, the voltage control circuit comprising:
A switching circuit connected to the voltage control circuit and a transformer connected to the switching circuit,
A cathode discharge tube connected to the secondary winding side of the transformer,
A plurality of current detection circuits for inputting to the voltage control circuit for detecting the current flowing through the cathode discharge tube and comparing the feedback signal with the reference voltage common to each circuit in the voltage control circuit are provided. A power supply device for driving a cathode discharge tube.