JPH05242989A - Dimming circuit for hot-cathode fluorescent tube - Google Patents

Abstract

PURPOSE:To save power by intermittently applying the current heating filaments synchronously with dimming duty pulses. CONSTITUTION:The discharge voltage of a discharge applied voltage generating circuit 24 is turned on or off synchronously with filament heating timing pulses, and the time-wise total sum of the light generated by a hot-cathode fluorescent tube 10 is changed for dimming. When the applied voltage by the generating circuit 24 is turned off, filaments 12, 14 are not heated, and the temperature is lowered. When the applied voltage is turned on, the temperature rises, and the fluorescent lamp 10 is returned to the dischargeable state. When the discharge voltage from the generating circuit 24 is applied to the filaments 12, 14, the discharge is continued. When these periodic actions are performed synchronously with dimming duty pulses and filament heating timing pulses, the fluorescent tube 10 is continuously lighted. The filaments 12, 14 are intermittently heated, and power can be saved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a dimming circuit for dimming a hot cathode fluorescent tube.

[0002]

2. Description of the Related Art Conventionally, a hot-cathode fluorescent tube has been provided behind a liquid crystal display unit such as a small liquid crystal television and used as a light source for a backlight of this liquid crystal display unit.
Then, it is required to reduce the power consumption of this type of hot cathode fluorescent tube. In the dimming technique of the hot cathode fluorescent tube, the voltage applied between both filaments is turned on / off while the filaments provided at both ends of the fluorescent tube are always heated. When the applied voltage is turned on, the brightness according to the on time can be obtained. In this case, electric power for constantly heating both filaments must be constantly applied to both filaments.

[0003]

However, in the above-described conventional dimming technique, if both filaments are not constantly heated by constantly supplying electric power for heating the filaments, the filaments will not be lit for the following reason. That is, when the hot cathode fluorescent tube is turned on, both filaments are first set to 800
While being heated to about 1000 ° C. and sufficient thermoelectrons are emitted from the filament, a discharge applied voltage is applied to both filaments to start discharge. After that, both filaments are heated by the discharge current, the discharge state continues, and the lighting continues. However, if the voltage applied to both filaments continues to be turned on / off, the heating temperature due to the discharge current will gradually drop, and eventually thermionic emission will not be sufficiently carried out, and the discharge will also stop and the lighting will stop.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a hot cathode which can be used as a backlight source for a small liquid crystal television, for example, by which the hot cathode fluorescent tube can be constantly turned on and power consumption can be saved. The purpose is to resist the dimming circuit of the fluorescent tube.

[0005]

According to the present invention, the above object is to provide a filament heating circuit for applying an electric current to the filament in order to heat the filament, and a filament at the time when the filament heats and emits a predetermined thermoelectron. A discharge applied voltage generating circuit for applying a discharge voltage to the above, while turning on and off the discharge applied voltage, and turning off the applied voltage until the filament temperature falls to the lower limit value of the temperature required for discharge. This is achieved by a hot cathode fluorescent tube dimming circuit having a control means for outputting a filament heating current from the filament heating circuit. Here, the control means is the dimming duty pulse generation circuit 30 in the embodiment of FIG.

[0006]

According to the above construction, the control means turns on / off the discharge applied voltage, and after the applied voltage is turned off, until the temperature of the filament falls to the lower limit value of the temperature required for discharge. A filament heating current is output to the filament by the heating circuit.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings. The examples described below are
Since it is a preferred specific example of the present invention, various technically preferable limitations are attached, but the scope of the present invention is, unless otherwise stated to limit the present invention, in the following description.
It is not limited to these modes.

FIG. 1 shows a hot cathode tube 10 according to the present invention having one electrode 16 and the other electrode 18. One electrode 16 is provided with a filament 12 and the other electrode 1
8 is provided with a filament 14. Filament circuit 20 is connected to filaments 12 and 14. The filament heating circuit 20 applies an electric current to the filaments 12 and 14 in order to heat the filaments 12 and 14.

The discharge applied voltage generating circuit 24 is connected to the filaments 12 and 14. The discharge applied voltage generating circuit 24 detects the filaments 12 and 14 when the filaments 12 and 14 are heated and predetermined thermoelectrons are emitted.
A voltage for discharge is applied to.

The dimming duty pulse generation circuit 30 includes
Discharge applied voltage generation circuit 24 and filament heating circuit 2
It is connected to 0. The dimming duty pulse generation circuit 30 turns on / off the discharge applied voltage, and
It serves as a control means for outputting a heating current from the filament heating circuit 20 until the applied voltage is turned off and the temperature of the filaments 12, 14 falls to the lower limit value (L in FIG. 2) required for discharge. Fulfill

The power source 36 is connected to the discharge applied voltage generating circuit 24 and the filament heating circuit 20.

This embodiment is constructed as described above,
Next, the operation will be described. Please refer to the time chart of FIG. FIG. 2 shows the initial lighting of the hot-cathode fluorescent tube 10 and the light control of the duty. First, as shown in (a), an output current is applied to the filaments 12 and 14 by the filament heating circuit 20, and the filament 1
Heat 2,14. As a result, the filaments 12 and 14 rise in temperature to 800 to 1000 ° C as shown in (b). The filaments 12 and 14 emit sufficient thermoelectrons. At this point, the discharge applied voltage generating circuit 24
As shown in (c), a discharge voltage is applied between the filaments 12 and 14. As a result, the hot cathode fluorescent tube starts initial lighting. Then, the filaments 12 and 14 are continuously heated by this discharge current. This is the initial lighting,
After this, the next dimming is performed.

As this dimming method, a method generally called pulse dimming (duty: dimming) is adopted. That is, the discharge voltage of the discharge applied voltage generating circuit 24 is turned on / off in synchronization with the filament heating timing pulses P1, P2 ... Shown in (d) of FIG. The dimming is performed by changing the temporal total sum of the light.

At this time, when the voltage applied by the discharge applied voltage generating circuit 24 is turned off at time t1 in (c), the filaments 12 and 14 cannot be heated, and (b).
As shown in, the temperature of the filaments 12, 14 decreases.
Before the filament temperature is lowered to the lower limit value L required for discharge, the filament heating circuit 20 outputs the filament heating output current in synchronization with the filament heating timing pulse P1 as shown in (a).
It outputs to 14 and raises the temperature of filaments 12 and 14, and it returns to the state which can be discharged. At this time (that is, t2
(At the point of time), the discharge voltage is again applied from the discharge voltage application generating circuit 24 to the filaments 12 and 14, so that the discharge continues.

Such a periodic operation is performed by a dimming duty pulse and a filament heating timing pulse P.
1, P2 ... Can be performed in synchronization with each other, so that the hot cathode fluorescent tube 10 can continue to be lit. Thus, the filament heating circuit 20 is supplied with a signal synchronized with the dimming duty pulse and the filament heating timing pulse to intermittently heat the filament, so that power saving can be achieved.

[0016]

As described above, according to the present invention, since the current for heating the filament is intermittently applied in synchronization with the duty pulse for dimming, the conventional type for constantly outputting the current for heating the filament. It is possible to significantly reduce power consumption as compared with the above. Therefore, it is possible to provide a hot cathode fluorescent tube suitable for use as a light source for a backlight of a small liquid crystal television or the like.

[Brief description of drawings]

FIG. 1 is a block diagram showing a preferred embodiment of a dimming circuit for a hot cathode fluorescent tube according to the present invention.

FIG. 2 is a diagram showing waveforms in the embodiment of FIG.

[Explanation of symbols]

 10 Hot Cathode Fluorescent Tube 12 Filament 14 Filament 20 Filament Heating Circuit 24 Discharge Applied Voltage Generation Circuit 30 Dimming Duty Pulse Generation Circuit 36 Power Supply

Claims (1)

[Claims] 1. A filament heating circuit for applying a current to the filament to heat the filament, and a discharge applied voltage generating circuit for applying a discharge voltage to the filament when the filament heats and emits predetermined thermoelectrons. A control means for turning on and off the discharge applied voltage and for outputting the filament heating current from the filament heating circuit until the applied voltage is turned off and the filament temperature falls to the lower limit of the temperature required for discharge. A hot-cathode fluorescent tube light control circuit comprising: