JPS5838558Y2 - Fluorescent display tube power supply circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a power supply circuit for a fluorescent display tube that uses a power transformer to supply power to the plate, grid, and filament of the fluorescent display tube, and is particularly applicable to digital watches, electronic desktop calculators, etc. It is most suitable for use in the power supply circuit of fluorescent display tubes.

FIG. 1 shows a power supply circuit for a fluorescent display tube of a conventional digital watch.

In FIG. 1, a power transformer 1 includes a primary winding 2, a secondary winding 3 for plates and grids, and a secondary winding 4 for filaments.

The intermediate tap 4a of the filament secondary winding 4 is connected to the ground potential side terminal of the blade and grid secondary winding 3.

By supplying a 100 V AC power source 5 to both ends of the primary winding 2 of the power transformer 1, for example, an AC voltage of 10 cm is applied to the secondary winding 3, and an AC voltage of 4 cm is applied to the secondary winding 4. induced.

The induced voltage of 10 V in the secondary winding 3 is supplied to a voltage doubler rectifier circuit consisting of a capacitor 6.9 and a diode 7.8.
Blades 13a, 13b of the fluorescent display tube 12...
. . . and a DC voltage VB of approximately 20 V for the grid 14.
is formed.

This DC voltage (18) is supplied to a drive circuit 10 for driving the fluorescent display tube 12 and a grid 14 for accelerating the fluorescent display tube 12.

Further, the induced voltage Vf (4V) of the secondary winding 4 is supplied to the filament 15 of the fluorescent display tube 12, so that the filament 15 is heated.

In this way, by selectively supplying the DC voltage VB to the plurality of plates H3a, 13b, . . . of the fluorescent display tube 12 by the drive circuit 10, necessary time display is performed.

However, in the power supply circuit shown in FIG. 1, the power transformer 1 must be provided with a secondary winding 3 for the plate and grid and a secondary winding 4 for the filament separately.

For this reason, the cost of the power transformer 1 becomes high, and the number of terminals and their holding parts increases, making the power supply l/lance 1 as a whole.
The disadvantage was that the shape of the

The present invention has been made in view of the above-mentioned problems, and is configured to supply the alternating current voltage induced in the secondary winding of the power transformer to the filament, and the plate and grid are A rectifier circuit is provided that rectifies and boosts the AC voltage induced in the secondary winding so as to supply a DC voltage larger than the AC voltage supplied to the filament.

With this configuration, a voltage for supplying power to the plate and grid of the fluorescent display tube and a voltage for supplying power to the filament can be generated from one secondary winding of the power transformer, respectively. The power transformer can be made smaller and cheaper.

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

FIG. 2 is a circuit diagram showing an embodiment in which the present invention is applied to a power supply circuit for a fluorescent display tube of a digital watch.

Note that the same parts as in FIG. 1 are given the same reference numerals.

In FIG. 2, the power transformer 1 includes one primary winding 2 and one secondary winding 16.

A DC voltage VB for the plate and grid of the fluorescent display tube 12 and an AC voltage Vf for the filament are obtained from this common secondary winding 16, respectively.

When an AC power source 5 of 100 V is supplied to the primary winding 2 of the power transformer 1, an AC induced voltage of, for example, 10 cm is obtained from the secondary winding 16.

This induced voltage is supplied to a voltage doubler rectifier circuit consisting of a capacitor 6.9 and a diode 7.8 as in FIG.
The voltage is boosted to approximately 20V DC voltage (18).

This DC voltage VB is supplied to a drive circuit 10 for driving the fluorescent display tube 12 and to the grid 14 of the fluorescent display tube 12.

Also, one end of the secondary winding 16 is connected to a ground line 1 for the current return path.
8, and this ground line 18 is connected to the drive circuit 1
Connected to the 0 ground terminal.

The drive circuit 10 includes, for example, a digital clock circuit including a crystal oscillator and a counter, and a decoder that converts the time signal of the digital clock circuit into a time display signal.
This LSI is equipped with a switch circuit that selectively applies a voltage 8 to a plurality of plays H3a, 13b, . . . of the fluorescent display tube 12 based on this time display signal.

Therefore, the output terminals 11a, llb, . . . of the drive circuit 10
A switch signal whose high level is ■8 is obtained from .
13b... is supplied.

The fluorescent display tube 12 is capable of displaying one digit by, for example, seven Japanese-shaped segments, and seven plates 131 to 13g correspond to the seven segments, respectively.

There are then four such plates representing hours and minutes.

Further, the grid 14 is for accelerating the electrons emitted from the filament 15, and its potential may be approximately the same as that of the plates 133 to 13g.

The filament 15 is a heating electrode having a predetermined resistance value, and an alternating current voltage of, for example, 4 cm is applied to both ends of the filament 15.

Then, electrons are emitted from the heated filament 15, and the emitted electrons collide with the plates 131 to 13g to emit fluorescence.

The plates 13a to 13g are equipped with the drive circuit 16.
Since the DC voltage (18) is selectively supplied by the switch circuit, a predetermined display is performed by colliding and emitting fluorescence as described above.

The induced voltage (IOV) of the secondary winding 16 , which has been stepped down by the resistor 17 , is supplied to both ends of the filament 15 .

That is, when the resistance value of the resistor 17 is R and the resistance value of the filament 15 is r, the voltage is reduced by the resistor R, and the remaining voltage is applied to both ends of the filament 15.

In this embodiment, the resistance R is reduced by approximately 6 cm, and the remaining 4 cm is supplied to the filament.

Therefore, R>r.

And the current flowing through the filament is becomes.

In this case, the resistance value r of the filament differs slightly from one fluorescent display tube to another.

However, since this change in resistance value is very small relative to R, the current i in the filament 15 can be considered to be approximately constant for each fluorescent display tube.

That is, as described above, by supplying power to the filament 15 from the relatively high voltage secondary winding 16 via the resistor 17 having a higher resistance value than the filament 15, the filament 15 can be heated with a substantially constant current.

Therefore, even if the resistance value r of the filament 15 varies, the brightness of the display of each fluorescent display tube can be made uniform.

Next, FIG. 3 shows another embodiment of a power supply circuit for a fluorescent display tube.

In FIG. 3, the induced voltage in the secondary winding 16 is set to approximately 4 V, and this is directly supplied to the filament 15.

and the plate 13a of the fluorescent display tube 12. 13b...
. . . and the grid 14 are supplied with a DC voltage 8 of approximately 20 V formed by a quintuple voltage rectifier circuit made up of diodes 21 to 25 and capacitors 26 to 30.

Therefore, in this case as well, the secondary winding that feeds power to the plate and the grid and the secondary winding that feeds power to the filament can be used in common.

Although the present invention has been described above based on the above-mentioned embodiments, various modifications are possible based on the technical idea of the present invention.

For example, in FIG. 2, the secondary winding 16 may be provided with a center tap to form a power source for the filament.

Further, the resistor 17 shown in FIG. 2 may be inserted between the ground line 18 and the filament 15.

As described above, the present invention provides step-up rectifier means for increasing the voltage supplied to the plates and grids compared to the voltage supplied to the filament of the fluorescent display tube, and a common secondary winding of the power transformer is provided. Power was supplied from the wire to the plate, grid, and filament.

Thus, from one secondary winding of the power transformer a voltage can be created for feeding the plates and grids of the fluorescent display tube and a voltage for feeding the filament,
The power transformer can be made smaller and cheaper.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a power supply circuit of a fluorescent display tube of a conventional digital watch, and Fig. 2 is a circuit diagram showing an embodiment in which the present invention is applied to a power supply circuit of a fluorescent display tube of a digital watch.
FIG. 3 is a circuit diagram similar to FIG. 2 showing another embodiment of the present invention. In addition, in the symbols used in the drawings, 1 is a power transformer, 2 is a primary winding, 3 is a secondary winding for plates and grids, 4 is a secondary winding for filaments, 10 is a drive circuit,
12 is a fluorescent display tube, 13 is a plate, 14 is a grid,
15 is a filament, 16 is a secondary winding, and 17 is a resistor.

Claims (1)

[Scope of utility model registration request] In a power supply circuit for a fluorescent display tube for supplying power to a plate, a grid, and a filament of a fluorescent display tube using a power transformer, the AC voltage induced in the secondary winding of the power transformer is supplied to the filament. In addition, the plate and the grid are provided with a rectifier circuit that rectifies and boosts the AC voltage induced in the secondary winding so as to supply a DC voltage larger than the AC voltage supplied to the filament. The power supply circuit for the fluorescent display tube.