JP3396646B2 - Fluorescent display tube drive circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bias applying system in a fluorescent display tube driving circuit.

[0002]

2. Description of the Related Art FIG. 3 shows a DC drive circuit for a fluorescent display tube.
A conventional example of a / DC converter is shown. Input terminal 1 has a flat
Smoothing capacitor 2, pulse width control circuit 3, transformer 1
Next winding N ₁ Are connected. Input terminal 1 has a predetermined input
Force voltage Vin is applied and primary winding N₁ Connected to the other end of
The switching transistor 5 is added to the pulse width control circuit 3.
It is driven to perform on / off operation. Primary winding of transformer 4
N₁ The electromotive voltage generated from the diode 6 and the capacitor 7
DC voltage V obtained by rectifying and smoothing with₀₁Is not shown fluorescent display
It becomes the anode voltage of the tube and the grid voltage. Transformer 4
Secondary winding N₂ AC voltage V obtained from₀₃Of the fluorescent display tube
Applied to the filament. DC voltage V₀₁The two resistance
The voltage divided by 8 and 9 is fed back to the pulse width control circuit 3.
It

A bias voltage is applied to the grid of the fluorescent display tube.
As shown in this figure, the resistance 10 and the
DC voltage V₀₁Voltage divided by 2nd
Winding N ₂ Mark the filament through the center tap 12 of
It is known how to add. At this time, the filament
Pressure or AC voltage V₀₃Is the Zener than the ground level
It is biased to a value higher by the voltage of the ion 11.

[0004]

The duty of the AC voltage V ₀₃ is uniquely determined by the ratio of the input voltage Vin and the DC voltage V ₀₁ in its operation. Then, as the ratio between the input voltage Vin and the DC voltage V ₀₁ is opened, the duty becomes 1:
It goes away from 1, ie 50%. When the filament is lit by using the AC voltage V ₀₃ having such a waveform, a sufficient cutoff bias voltage is not applied to the grid even when the lit display is erased by the display erasing signal. For this reason, the lit display cannot be completely erased, and the non-selected anode of the fluorescent display tube sometimes causes a thin light-emission phenomenon.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a fluorescent display tube drive circuit which does not cause a leakage light emission phenomenon.

[0006]

A fluorescent display tube driving circuit of the present invention comprises a transformer having a primary winding and a secondary winding,
AC voltage supplied to the filament from the secondary winding ,
In a fluorescent display tube drive circuit that obtains a DC voltage to be supplied to a battery and a grid, a series circuit of a first coil and a second coil is connected in parallel to a secondary winding, and the first coil and the second coil are connected. The respective inductance values of the above are distributed at a ratio according to the duty of the AC voltage, and
DC voltage is obtained at the connection point between the second coil and the second coil
A feature is that a bias voltage is applied.

[0007]

DETAILED DESCRIPTION FIG. 1 shows one embodiment of a fluorescent display tube drive circuit of the present invention, the circuit of a conventional example of FIG. 3, via
The only difference is how to add the voltage . That is, the two coils 13 and 14 connected in series are connected to the secondary winding N _{2 of the} transformer 4.
And a voltage obtained by dividing the DC voltage V ₀₁ by the resistor 10 and the Zener diode 11 is applied to the connection point of these two coils 13 and 14.

The values of the inductances of the two coils 13 and 14 are made to be values distributed at a ratio according to the duty of the AC voltage V ₀₃ . For example, AC voltage V
_When the duty of ₀₃ is 70%, the inductance ratio between the coil 13 and the coil 14 is set to 7: 3, and when the duty of 80% is set to 8: 2. By doing so, the potential gradients from the physical center of the display effective length of the fluorescent display tube to one end and the other end become equal, so that the leakage light emission phenomenon of the fluorescent display tube does not occur.

FIG. 2 shows an embodiment in which a single-turn coil 20 with a tap is used in place of the two coils 13 and 14. The coil 20 is divided into two winding parts 21 and 22 with a tap 25 as a boundary, and a bias voltage is applied to the tap 25 as in the embodiment of FIG. Winding part 21,
The respective numbers of turns a and b of 22 are values distributed in a ratio according to the duty of the AC voltage V ₀₃ .

[0010] Note that the coil 13 and winding portions 21 and 22 connected in parallel to the secondary winding N _2, than the secondary winding N ₂ is to choose those large enough inductance. In this way, the inductance of the coils 13 and 14 and the winding portions 21 and 22 does not significantly affect the inductance of the secondary winding N ₂ , and does not affect the operating conditions of the entire fluorescent display tube drive circuit.

[0011]

According to the present invention, since the bias application point can be set at an optimum position according to the duty of the filament voltage, there is an effect that the occurrence of the leakage light emission phenomenon of the fluorescent display tube can be prevented.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a fluorescent display tube driving circuit of the present invention.

FIG. 2 is a circuit diagram of a main part of a fluorescent display tube drive circuit showing another embodiment of the present invention.

FIG. 3 is a circuit diagram showing an example of a conventional fluorescent display tube drive circuit.

[Explanation of symbols]

N ₂ Secondary winding 4 Transformer 13, 14 Coil 21, 22 Winding section

Claims (2)

(57) [Claims] 1. An AC voltage supplied from a secondary winding to a filament , comprising a transformer having a primary winding and a secondary winding.
When the anode, the fluorescent display driving circuit for obtaining a DC voltage supplied to the grid, the series circuit of the first coil and the second coil are connected in parallel to said secondary winding, said first coil and said while the value allocated at a ratio corresponding to each value of inductance of the second coil to the duty of the AC voltage, by which is obtained by the DC voltage to the connection point of the first coil and said second coil
A fluorescent display tube drive circuit characterized in that an ass voltage is applied. 2. A first winding portion and a second winding portion divided by a tap.
2. A fluorescent display tube drive circuit according to claim 1, further comprising a single-winding coil having a winding portion, wherein the first coil comprises a first winding portion, and the second coil comprises a second winding portion. .