JPH0722192A - Fluorescent lamp dimming device - Google Patents

Abstract

PURPOSE:To nullify flickers. CONSTITUTION:Pulses of a frequency (250Hz-25kHz) according to the dim signal are given by a frequency modulation circuit 12, supplied to a filament incandescent drive circuit 17, divided into halves, and supplied to the end filaments of a fluorescent lamp 14 as + or -5V pulse voltage of 100% duty. The output pulses of the frequency modulation circuit 12 are also supplied to a lamp impression voltage drive circuit 13, and in response thereto, 40-mus wide positive and negative pulses in triangular form are emitted alternately and impressed on the two ends of the fluorescent lamp 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to, for example, a backlight of a liquid crystal display, and the amount of light emitted from a fluorescent lamp is adjusted by changing the frequency of a lighting applied voltage, that is, by frequency modulation. Regarding dimmers.

[0002]

2. Description of the Related Art FIG. 2A shows a conventional fluorescent lamp dimmer. The dimming signal from the input terminal 11 is supplied to the frequency modulation circuit 12, the frequency modulation circuit 12 outputs a signal having a frequency corresponding to the dimming signal, and this signal is supplied to the fluorescent lamp applied voltage drive circuit 13, Positive and negative triangular pulse voltages from the drive circuit 13 are applied as a lighting voltage across the fluorescent lamp 14. On the other hand, the filament red heat driving circuit 15 applies a filament red heat voltage having a constant frequency to each filament at both ends of the fluorescent lamp 14 to red heat them.

A pulse of, for example, 250 Hz to 25 kHz is output from the frequency modulation circuit 12 according to the dimming signal, and a pulse of 25 kHz (having a period of 40 μm) is used for maximum brightness.
2B (a) is output, and this is alternately applied to the fluorescent lamp 14 as positive and negative triangular pulse voltages by the fluorescent lamp applied voltage drive circuit 13. For example, when the pulse width is 40 μs, the driving voltage is as shown in FIG. 2C, and the frequency is ½, which is 12.5 kHz.
As shown in FIG. 2B (b), the filament red-hot voltage from the filament red-hot driving circuit 15 is a rectangular pulse voltage that repeats positive and negative with the same pulse width and the same amplitude, and its frequency f ₁ is constant. It is 41 kHz.

In order to reduce the brightness of the fluorescent lamp 14, for example, the output frequency of the frequency modulation circuit 12 is set to 500.1 Hz as shown in FIG. 2C (a), and each pulse thereof is set as shown in FIG. 2C (c). Then, positive and negative triangular pulse voltages having a pulse width of 40 μs are applied to the fluorescent lamp 14. At this time, as shown in FIG. 2C (b), the filament incandescent voltage has a frequency of 41 kHz in this example, positive and negative square pulse voltages with the same amplitude, the same width and 100% duty are alternately taken, and the dimming state is obtained. It has a constant waveform voltage regardless of.

A pulse of lighting applied voltage to the fluorescent lamp 14.
Fixed width, 40μs in the above example, frequency 125H
Fluorescent lamp by changing in the range of z ~ 12.5 kHz
The effective voltage applied to 14 changes at a ratio of 1: 100,
It is possible to obtain a dimming ratio comparable to this. Fluorescent light is inside
When the brightness is below (1/10 of the maximum brightness), the discharge is
The filament becomes red hot and stable because it becomes unstable
Supports discharge. Filament red heat voltage frequency f
₁And the frequency f of the fluorescent lamp applied voltage₂60 Hz or less
At the bottom, the brightness fluctuates at the difference frequency, and
It looks like flicker to the eyes. From this point,
For example, the fluorescent lamp applied voltage frequency f ₂Is the highest 1
Frequency of filament incandescent voltage at 2.5 kHz
f₁Was selected to be 41 kHz.

[0006]

The filament red heat voltage frequency f ₁ is selected to be considerably higher than the fluorescent lamp applied voltage frequency f ₂ as described above to prevent flicker, but in reality, dimming is performed. Depending on the condition, it was not so large, but flicker sometimes occurred. As a result of pursuing this problem, it was found that when the difference between the harmonic wave nf _{2 of} the fluorescent lamp applied voltage frequency f ₂ and the filament incandescent voltage frequency f ₁ becomes low, the beat causes flicker. For example, in the case of the above numerical example, f ₂ = 500.1 Hz
In the case of f ₁ −nf ₂ = 41 kHz−82 × 500.1H
Since z = 8.2 Hz, flickers of 8.2 Hz occur.

[0007]

According to the present invention, the filament incandescent voltage has the same frequency as the fluorescent lamp applied voltage,
Moreover, the effective voltage of the filament incandescent voltage is constant over the entire dimming range.

[0008]

FIG. 1A shows an embodiment of the present invention, in which parts corresponding to those in FIG. 2A are designated by the same reference numerals. In the present invention, the output of the frequency modulation circuit 12 is the filament red heat driving circuit 1
7 is also branched and supplied, and the filament red heat driving circuit 17 outputs a filament red heat voltage having a constant effective voltage in the entire dimming range at the same frequency as the fluorescent lamp applied voltage, and the fluorescent lamp 1
4 to both filaments. In the filament red heat driving circuit 17, for example, the output pulse of the frequency modulation circuit 12 is input to the toggle flip flop so that the frequency is halved, the frequency is synchronized with the fluorescent lamp applied voltage, and the positive pulse of the same pulse width and the same amplitude is used. , Negative pulses are contacted and taken alternately, that is, positive with 100% duty with the same pulse width and same amplitude,
Negative pulses appear alternately and are supplied to the filament of the fluorescent lamp 14 as a filament glowing voltage.

For example, from the frequency modulation circuit 12 to FIG.
When a 25 kHz pulse as shown in (a) is output, the filament red heat driving circuit 17 outputs the pulse shown in FIG. 1B (b).
, + 5V and -5 for each input pulse
The filament red heat voltage that alternately takes V and V is output.
As shown in FIG. 1B (c), the fluorescent lamp applied voltage drive circuit 13 outputs a pulse width of 40 for each input pulse as in the conventional case.
A positive triangular pulse of μs and a negative triangular pulse are alternately output.

When the output of the frequency modulation circuit 12 is 500 Hz as shown in FIG. 1C (a), the filament red heat driving circuit 17 outputs 2 m of +5 V as shown in FIG. 1C (b).
s and 2 ms of −5 V are alternately output adjacent to each other. As shown in FIG. 1C (c), the fluorescent lamp applied voltage drive circuit 13 outputs positive and negative triangular pulse voltages with a pulse width of 40 μs of 2 ms. Is output alternately for each.

As described above, in the present invention, the frequency f ₁ of the filament incandescent voltage is the same as the frequency f ₂ of the fluorescent lamp applied voltage, and regardless of the fluorescent lamp applied voltage frequency f ₂ , that is, the entire dimming ratio range. In, a positive or negative voltage having the same absolute value is supplied to the filament of the fluorescent lamp 14, that is, the filament can always be sufficiently red-heated without changing the effective value of the filament red-hot voltage. Therefore, flicker does not occur even if the dimming ratio is changed, and stable discharge is performed. The filament incandescent voltage has the same amplitude and a duty of the same width is 1
It is assumed that the positive pulse and the negative pulse of 00% are adjacent to each other and alternately appear, but the pulse widths may not be the same.
In short, even if the fluorescent lamp applied voltage frequency f ₂ is changed, that is, the frequency f ₁ (= f ₂ ) of the filament incandescent voltage is changed, a constant effective voltage is always required.

[0012]

As described above, according to the present invention, the flicker does not occur at all because the filament red heat voltage frequency always matches the fluorescent lamp applied voltage frequency regardless of the dimming ratio. Moreover, since the effective value of the filament incandescent voltage is constant over the entire dimming ratio range, stable discharge can be obtained even in the region of medium brightness or less.

[Brief description of drawings]

FIG. 1A is a block diagram showing an embodiment of the present invention, FIG.
C is a diagram showing an example of output waveforms of the frequency modulation circuit 12, the filament red heat drive circuit 17, and the fluorescent lamp applied voltage drive circuit 13 at high brightness and medium brightness, respectively.

FIG. 2A is a block diagram showing a conventional fluorescent light dimmer,
3B and 3C are diagrams showing respective output waveform examples of the frequency modulation circuit 12, the filament red heat driving circuit 15, and the fluorescent lamp applied voltage driving circuit 13 at high luminance and medium luminance, respectively.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display area H05B 41/39 9032-3K

Claims (1)

[Claims] 1. A fluorescent light dimmer in which a filament of a fluorescent lamp is red-heated with an alternating voltage and the frequency of a voltage applied to the fluorescent lamp is changed to adjust light. A fluorescent light dimmer, wherein the filament red glow voltage has the same frequency, and the effective voltage of the filament red glow voltage is constant over the entire dimming range.