JPH01146292A - Power source circuit for driving fluorescent lamp - Google Patents

Abstract

PURPOSE:To make the starting of a fluorescent lamp easy and secure even in the case ambient temperature lowers or in the case an input power source voltage lowers by employing a voltage changeover circuit for supplying a voltage higher than that of a steady state to a fluorescent circuit only for a certain period of time measured with a timer circuit. CONSTITUTION:A timer circuit 16 for measuring a certain period of time from a detection time point by detecting the turning on of an input power source voltage and a voltage changeover circuit 14 for supplying a voltage higher than that of a steady state to a fluorescent lamp circuit only for a certain period of time measured with the circuit 16 are provided. Namely the fluorescent lamp is started with a voltage of an amplitude larger than that of the voltage for a steady state and the lamp is lighted at the steady-state voltage at the time of lighting. This makes it possible to start the fluorescent lamp easily and securely without increasing electric power at the time of lighting even in the case the input power source voltage lowers or in the case ambient temperature lowers.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a power supply circuit E for driving a fluorescent lamp used in a backlight of a liquid crystal television or the like.

BACKGROUND OF THE INVENTION In recent years, fluorescent lamps have been used as backlights for liquid crystal televisions, and their driving circuits and driving methods have been studied from various angles.

An example of a conventional power supply circuit for driving a fluorescent lamp will be described below with reference to the drawings.

FIG. 3 is a block diagram of a conventional power supply circuit for driving a fluorescent lamp. In FIG. 3f, 1 is a DC voltage power source such as a dry battery, and its voltage value is Vi.

This DC voltage power source 1 is connected to a fluorescent lamp drive circuit 4 via a power switch 2 and a fluorescent lamp power switch 3, and a fluorescent lamp 5 is turned on by its output. Further, the DC voltage power supply 1 is connected to the DC-DC converter circuit 6I via the power switch 2.
The liquid crystal television circuit 7 is operated by its output.

The operation of the fluorescent lamp drive power supply circuit configured as above will be described below.

4(a) and 4(b) are voltage waveform diagrams of various parts of the fluorescent lamp driving voltage circuit shown in FIG. 3. Figure 4(a)
.

In (b), voltage waveforms E and F are the waveforms at the third output of the fluorescent lamp power switch and the output of the fluorescent lamp drive circuit 4, respectively. Now, when the power switch 2 and the fluorescent lamp power switch 3 are turned on at time t=to, the voltage applied to the fluorescent lamp drive circuit 4 becomes t < to, as shown in voltage waveform E in FIG. 4(a). 0, t≧to
becomes Vi. The fluorescent lamp drive circuit 4 inputs the voltage shown in FIG. 4(a) and generates an alternating voltage as shown in FIG. 4(b). This AC voltage starts the fluorescent lamp 5 and
lights up.

Problems to be Solved by the Invention However, in the conventional configuration as described above, when the voltage value Vi of the DC voltage power source 1 decreases due to a decrease in the capacity of the dry battery, the output voltage F from the fluorescent lamp drive circuit 4 decreases. The amplitude of the signal decreases, making it difficult for the fluorescent lamp 5 to start.Furthermore, when the ambient temperature becomes low, the fluorescent lamp 5 also becomes difficult to start.
It had the problem of becoming thick.

The present invention solves the above-mentioned conventional problems, and provides a power supply circuit for driving a fluorescent lamp that can reliably start the fluorescent lamp even when the voltage of the input DC voltage power supply decreases or the ambient temperature decreases. The purpose is to provide

Means for Solving the Problems In order to solve the above problems, the power supply circuit for driving a fluorescent lamp of the present invention includes a timer circuit that detects the application of input power supply voltage and measures a certain period of time from the time of said detection. and a voltage switching circuit that supplies a voltage higher than the steady voltage to the fluorescent lamp drive circuit E for a certain period of time measured by the timer circuit.

Operation With the above configuration, the application of the input power supply voltage is detected by the timer circuit I, and the voltage switching circuit supplies a voltage higher than the steady voltage to the fluorescent lamp drive circuit for a certain period of time measured from the time of this detection. Therefore, when a fluorescent lamp is started, it is started with a voltage higher than the steady voltage with a large amplitude, and when it is turned on, it is lit with a steady voltage with a small amplitude, so if the input power supply voltage drops or the ambient temperature is low. If it becomes 1
Also, the fluorescent lamp can be easily and reliably started once without increasing the electric power when the lamp is turned on.

EXAMPLE Hereinafter, a first example of the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of a source circuit for driving a fluorescent lamp showing an embodiment of the present invention. In FIG. 1, reference numeral 11 denotes a non-DC voltage power source such as a dry battery that outputs an input power source voltage, and the voltage value of the DC power source voltage as a steady voltage is defined as Vi. The DC voltage power source 11 is connected via a power switch 12 and a fluorescent lamp power switch 13 to a terminal 15 of a power source voltage changeover switch 14 as a voltage changeover circuit and to a timer circuit 16, respectively. In addition, the DC voltage power source 11 is connected to a power switch 12.
6 connected to the DC-DC converter circuit 17 via
Further, the DC-DC converter circuit 17 is connected to the liquid crystal television set circuit 181 and also to the terminal 19 of the power supply voltage changeover switch 14. The common terminal 20 of the power supply voltage changeover switch 14 is switched between the terminal 15 side and the terminal 19 side E depending on the output voltage of the timer circuit 16.

Further, a common terminal 20 of the power supply voltage changeover switch 14 is connected to a fluorescent lamp drive circuit 21 to drive a fluorescent lamp 22.

The operation of the fluorescent lamp driving power supply circuit configured as described above will be explained below.

FIG. 2 is a voltage waveform diagram of each part of the fluorescent lamp drive power supply circuit shown in FIG. 1. In FIGS. 2(a) to (d), voltage waveforms A, B, C, and D are the voltage waveforms at the output section of the fluorescent lamp power switch 13 in FIG. 1, respectively, and the voltage waveforms at the output section of the timer circuit 16. B shows the voltage waveform C1 at the output section of the power supply voltage changeover switch 14 and the voltage waveform at the output section of the fluorescent lamp drive circuit 21. Now, if the power switch 12 and the fluorescent lamp power switch 13 are turned on at time 1 = 1o, the output voltage of the fluorescent lamp power switch 13 will be 1 (0 at 1o) as shown in the voltage waveform Af in Fig. 2(a). .t≧to, then Vi.

The timer circuit 16 detects the rising edge of the voltage waveform A, rises up, and waits for a certain period of time Δ as shown in FIG. 2(b) after 1=1. Outputs voltage waveform B that falls at . The power supply voltage changeover switch 14 is switched by the output voltage waveform B of the timer circuit 16, and the voltage waveform C shown in FIG. The voltage vH is higher than the DC power supply voltage Vi generated by the circuit 17, and when the voltage waveform B of the output voltage of the timer circuit 16 is low, the DC power supply voltage Vi becomes a steady voltage. In other words, Fig. 2 (
As shown in c), the output voltage of the power supply voltage changeover switch 14 for the fluorescent lamp drive circuit is 0° t<to and t0≦t.
< t, te vH, t≧t, the voltage waveform C changes as Vi(7). The fluorescent lamp drive circuit 21 receives this output voltage as an input and generates an AC voltage waveform as shown in FIG. 2(d)f. This alternating voltage activates the fluorescent lamp 22, which then turns on. In this way, the amplitude of the AC voltage waveform increases only during the period Δt after the power is turned on, and after that it becomes a small amplitude of the steady voltage.
When the fluorescent lamp 22 is started, it is driven with a large amplitude, and when the fluorescent lamp 22 is turned on thereafter, it is driven with a small amplitude.

Note: The DC-DC converter circuit 17 is shown in FIG. 2(d)l.
This shows t. It is constantly operated with the liquid crystal television set circuit 18 using large amplitude voltages at −1 and +.

As described above, according to this embodiment, even when the voltage of the input DC power source such as a dry battery drops or the ambient temperature drops, it is possible to easily start up the fluorescent lamp, and to turn on the fluorescent lamp. It can also prevent an increase in power consumption.

Effects of the Invention As described above, according to the present invention, there is provided a timer circuit that detects the application of an input power supply voltage and measures a certain period of time from the detection point, and a fluorescent lamp that operates for a certain period of time measured by the timer circuit. By having a voltage switching circuit that supplies a voltage higher than the steady voltage to the circuit, the fluorescent lamp can be started with a high voltage with a large amplitude when starting up, and can be driven with a steady voltage with a small amplitude when it is lit. Even when the input power supply voltage drops, such as when the ambient temperature drops, it is possible to easily and reliably start the fluorescent lamps, and to prevent an increase in power consumption when lighting the fluorescent lamps. It is something.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a power supply circuit for driving a fluorescent lamp showing an embodiment of the present invention, FIG. 2 is a voltage waveform diagram of each part of the power supply circuit for driving a fluorescent lamp shown in FIG. FIG. 4 is a block diagram of a power supply circuit for driving a fluorescent lamp. FIG. 4 is a voltage waveform diagram of each part of the power supply circuit for driving a fluorescent lamp shown in FIG. 11...DC voltage power supply (input power supply voltage), 14...
Power supply voltage selection switch, 15, 19...terminal, 16
...Timer circuit, 20...Common terminal, 21...
Fluorescent lamp drive circuit.

Claims (1)

[Claims] 1. A timer circuit that detects the application of input power supply voltage and measures a certain period of time from the detection point, and supplies a voltage higher than the steady voltage to the fluorescent lamp drive circuit for the certain period of time measured by the timer circuit. A power supply circuit for driving a fluorescent lamp having a voltage switching circuit.