JP3028046B2 - Power supply circuit for fluorescent display tube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit for a fluorescent display tube, and more particularly to a power supply circuit suitable for a fluorescent display module.

[0002]

2. Description of the Related Art A fluorescent display tube (hereinafter, referred to as "VFD").
Has features such as bright and easy to see, high degree of freedom of display, and high reliability. It is used in various fields, but the design of the drive circuit and power supply necessary to drive VFD For example, such a method requires a considerable amount of time and specialized knowledge, and it is troublesome to use the VFD as a part of the system in a short period of time. Therefore, in order to solve this problem, the VFD itself and peripheral circuits such as a drive circuit and a power supply circuit for the VFD are compactly packed, and a simple interface and a power supply are simply prepared without a troublesome design when used. A VFD module that can be used in a PFD is practically used.

[0003] Such a VFD module is configured to operate by receiving power required for its operation from a device in which the module is incorporated. The VFD module has a built-in logic circuit for storing and editing data to be displayed transferred from an external device and generating a signal for driving the VFD. There is no problem when the power is 5 (V) and the power of 5 (V) is supplied from an external device. However, for example, in a POS system or the like, the influence of a voltage drop (line drop) in routing the power supply line inside the system 12 or 24 to reduce the number of lines of the power supply line itself.
In some cases, a single power supply voltage of about (V) is supplied to each device in the system. In such a case, the VFD module may have 12 or 24
Since only the DC voltage of (V) is supplied, in order to obtain a DC voltage of 5 (V) to be supplied to the built-in logic circuit, 12 V is supplied inside the VFD module.
Alternatively, a circuit for stepping down 24 (V) to 5 (V) has been provided.

FIG. 2 shows a configuration example of such a conventional VFD module. In FIG. 2, reference numeral 1 denotes a VFD module to which a data signal, a control signal such as a read / write control signal and a selection signal, and a power supply voltage are supplied from an external device. Here, it is assumed that, for example, only 24 (V) is supplied as the power supply voltage. Reference numeral 10 denotes a microcomputer for performing input / output of data with an external device, storage / editing of display data, and other controls required for driving the VFD. Reference numeral 20 denotes a drive circuit including an anode drive circuit and a grid drive circuit, and a VF based on a signal output from the microcomputer 10.
This is a drive circuit for dynamically or statically driving D. The microcomputer 10 and the drive circuit 20 usually have an operating voltage of 5
This is a logic circuit requiring (V). Although the example in which the microcomputer 10 and the drive circuit 20 are separately provided has been described here, an ASIC in which these are integrally configured may be used.

[0005] Reference numeral 30 denotes a fluorescent display tube (VFD), for example, a plurality of strip-shaped anode electrodes in which a phosphor is adhered inside an envelope, and a plurality of anode electrodes provided in a direction intersecting the anode electrodes. A grid electrode is provided, and desired image information can be displayed by applying a display signal to the grid electrode while sequentially scanning the anode electrode. Reference numeral 40 denotes a DC / DC converter, which receives a 24 (V) DC voltage supplied from an external device as an input, and
It outputs an anode voltage Eb, a grid voltage Ec, and an AC filament voltage Ef supplied to D.
Reference numeral 50 denotes a power supply circuit composed of a switching regulator or the like, which receives a 24 (V) DC voltage supplied from an external device as an input and supplies a logic circuit, that is, a 5 (V) power supply for the microcomputer 10 and the drive circuit 20. It outputs a voltage.

FIG. 3 shows a configuration example of a power supply circuit portion in the VFD module thus configured. In this figure, the drive circuit 20, terminals are provided to which the voltage Eb and Ec is supplied, the terminals to the grid electrode driving transistor Tr ₁ and the anode electrode driving transistor Tr ₂ source - scan is connected to I have. A lighting control signal supplied from the microcomputer 10 shown in FIG. 2 is supplied to the gates of both the driving transistors Tr ₁ and Tr ₂ via a buffer circuit (not shown). The drains of both driving transistors Tr ₁ and Tr ₂ are connected to the grid and anode of VFD 30, respectively, and the pull-down resistors Rpd ₁ and Rp
through d ₂ is connected to the ground GND. In this figure, the VFD 30 is simplified and described.
Actually, as described above, a plurality of anode electrodes and grid electrodes of the VFD 30 are provided, and a plurality of grid electrode driving transistors Tr ₁ and a plurality of anode electrode driving transistors Tr ₂ are provided. It is driven sequentially in order.

Further, DC / DC converter 40, an oscillation circuit 41, a transformer T, a diode D, resistors R, an oscillation type DC / DC converter with a zener diode ZD and a smoothing capacitor C _1, is supplied from the external device For example, a DC voltage of 24 (V) is input. The oscillation circuit 41 provided on the primary winding side of the transformer T
An AC voltage is generated in the secondary windings Ns ₁ and Ns ₂ of the transformer T. An AC voltage generated at both ends of the _first secondary winding Ns1 having the center tap CT is supplied to the filament of the VFD 30 as a filament voltage Ef. The AC voltage generated in the second secondary winding Ns ₂ is a diode D
And supplied to the drive circuit 20 as the anode voltage Eb of the VFD 30 and the grid voltage Ec.

A Zener diode ZD is connected between the center tap CT of the secondary winding Ns ₁ of the transformer T and the ground GND, and a Zener diode ZD is connected between the center tap CT and the output side of the diode D. The resistor R is connected.
Zener voltage Vz of the Zener diode ZD is set to the cut-off bias voltage Ek, via a pull-down resistor Rpd ₁ and Rpd ₂ of the driver circuit 20, VF
D30 of which is applied to the anode and grid, thereby, the driving transistor Tr ₁ and Tr ₂ are in the off, are made so as not to be an emission leak VFD30. The value of the cutoff bias voltage Ek is determined according to the magnitude of the filament voltage Ef. In the case of a VFD having a normal magnitude,
The voltage is higher than 5 (V).

In the VFD power supply circuit thus configured, a lighting control signal is applied to the gates of the grid electrode driving transistor Tr ₁ and the anode electrode driving transistor Tr ₂ , respectively, and the anode of the VFD 30 and the grid are connected to the anode. When the voltage Eb and the grid voltage Ec are supplied, the VFD 30 turns on. VFD
When 30 is turned on, the anode current ib and grid current ic flows through the anode and grid VFD30, is the sum of both current Ik = ib + ic zener from the center tap CT of the secondary winding Ns ₁ of the transformer T It will flow to the diode ZD. As a result, a Zener voltage Vz is generated in the Zener diode ZD. As described above, it is applied to the anode electrode and the grid electrode of the VFD through the pull-down resistor Rpd ₁ and Rpd ₂ as the cutoff bias voltage Ek, reverse biased with respect to the filament to the anode electrode and the grid electrode is not driven Since a voltage is applied, leakage light emission can be prevented.

The resistor R is provided to prevent the current Ik from flowing to the Zener diode ZD when neither the anode electrode nor the grid electrode is driven, and to prevent Ek from being generated. This is a resistor provided to allow a bias current of about 1 to 3 mA to flow through ZD.

[0011]

As described above, VF
D30 is when in the on state, a current Ik flows to the Zener diode ZD through the center tap CT of the secondary winding Ns ₁ of the transformer T from the filament. This current Ik depends on the size of the fluorescent display tube,
Approximately 100 (mA), so that power consumption of P = Ik × Ek occurs in the Zener diode ZD. However, since this power consumption does not contribute to the emission of the fluorescent display tube VFD at all, it is useless power consumption. As the power consumption in the VFD module increases, the use of a Zener diode ZD large enough to withstand the power consumption is required. Is required, which may cause a problem in mounting. Further, the phosphor has a temperature quenching characteristic, that is, a characteristic that the luminance decreases as the temperature rises, and there is a problem that the luminance of the VFD 30 decreases due to the heat generated by the power consumption. These points cannot be ignored especially in a VFD module in which the VFD and its peripheral circuits are compactly integrated.

Furthermore, since the conventional VFD module is configured as described above, the DC voltage supplied from the device in which the VFD module is built is 12 or 24.
In the case of (V), it is necessary to provide a power supply circuit for generating a power supply voltage of 5 (V) for the logic circuit inside the VFD module.

Accordingly, the present invention provides a fluorescent display (VF)
D) It is an object of the present invention to provide a power supply circuit for a fluorescent display tube that can effectively use power that has been wasted in a power supply circuit for D). It is another object of the present invention to provide a power supply circuit for a fluorescent display tube in which a small zener diode for generating a cutoff bias can be used and heat generation in the zener diode is small.

[0014]

In order to achieve the above object, a power supply circuit for a fluorescent display tube according to the present invention is connected between a center tap of a filament winding for supplying a filament voltage to the fluorescent display tube and ground. A cut-off bias voltage generation circuit including a Zener diode, a logic circuit power supply voltage generation circuit that generates a power supply voltage to be supplied to a logic circuit by using a DC voltage generated in the Zener diode in the cut-off bias voltage generation circuit. Is provided.

Further, the power supply circuit for a fluorescent display tube of the present invention comprises:
In the cutoff bias voltage generation circuit, the zener diodes are formed as a plurality of zener diodes connected in series, and the logic circuit power supply voltage generation circuit is configured to output the zener diodes among the plurality of zener diodes connected in series. A DC voltage generated at both ends of a Zener diode connected to the ground side is supplied to the logic circuit as a power supply voltage. Still further, in the power supply circuit for a fluorescent display tube according to the present invention, the power supply voltage generation circuit for a logic circuit is configured as a switching regulator to which a voltage generated at both ends of the zener diode is input and an output of which is supplied to the logic circuit. Is what it is.

[0016]

According to the present invention thus constructed, VF
Since the current flowing through the Zener diode for generating the cutoff bias voltage at the time of lighting D can be supplied to the logic circuit as a power source, the power that has been wasted in the conventional Zener diode can be effectively used. As a result, a small Zener diode can be used.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a power supply circuit for a fluorescent display tube according to the present invention will be described with reference to FIG. In this figure, T is a transformer, which is the same as the transformer T shown in FIG. In this figure, only the secondary side of the transformer T is shown. Ns ₁ is the secondary winding of the transformer T,
CT is the center tap secondary winding Ns _1, AC voltage Ef generated in the secondary winding Ns ₁ is applied to the filaments of VFD30 not shown. Also, Ns
₂ the secondary winding of the transformer T, D a diode, C ₁ is a smoothing capacitor, the secondary winding Ns ₂ of the transformer T by the rectification circuit comprising the diode D and a smoothing capacitor C ₁ Metropolitan By rectifying the generated AC voltage, VF
When the D30 is turned on, an anode voltage Eb and a grid voltage Ec supplied to the anode and the grid of the VFD 30 are generated. The anode voltage Eb and the grid voltage Ec are supplied to the drive circuit 20.

R is a resistor, ZD ₁ and ZD ₂ are Zener diodes, and C ₂ is a capacitor. In this embodiment of the invention, first and second zener diodes ZD ₁ and ZD ₂ connected in series between the center tap CT of the secondary winding Ns ₁ of the transformer T and ground,
A cutoff bias voltage Ek of VFD 30 is generated. That is, the cut-off bias voltage Ek is a voltage of the sum of the Zener voltage Vz ₂ of Zener Zener voltage of diode ZD ₁ Vz ₁ and a Zener diode ZD _2.

A voltage generated across the second Zener diode ZD ₂ is supplied as a power supply voltage to a logic unit including the microcomputer 10 and the drive circuit 20. That is, the Zener voltage Vz ₂ as a Zener diode ZD ₂ is with the existing 5 (V), to generate a DC voltage of 5 (V) is supplied to the logic unit comprising a microcomputer 10 and a driving circuit 20. It has been done. Current Ik flowing from the center tap CT of the secondary winding Ns ₁ to the Zener diode ZD _1, when the normal size of the VFD, since several 10 to 100 (mA) degree, the microcomputer 10 and a drive circuit 2
A current of about several tens to 100 (mA) can be passed through the logic part composed of zero. Usually, low power consumption CMOS circuits are often used for these circuits, and therefore, with this configuration, they can be sufficiently used as a power supply of a logic circuit.

The resistor R is a Zener diode ZD ₁
And a capacitor for flowing a predetermined bias current through ZD ₂ , and a capacitor C ₂ is a smoothing capacitor for absorbing a ripple contained in a current Ik flowing through the center tap CT of the secondary winding Ns _1. It is.

FIG. 1B shows a second embodiment of the present invention capable of supplying a larger power to a logic circuit. In this figure, a transformer T, a secondary winding N of the transformer T
s ₁ and Ns ₂ , the center tap C of the secondary winding Ns ₁
T, diode D, smoothing capacitor C ₁ , and resistor R
Each of them is the same as that shown in FIG. ZD is a Zener diode for generating a cut-off bias voltage Ek, 5 is a power supply circuit including a switching regulator, etc., and receives a voltage generated at both ends of the Zener diode ZD and stabilizes 5 (V). To output the applied DC voltage.

In the embodiment shown in FIG. 1B, the cutoff bias voltage Ek generated by the Zener diode ZD is used as it is as the input voltage of the power supply circuit 5, and the power supply circuit 5 uses the cutoff bias voltage Ek for the logic section. Of 5
(V), the power input to the power supply circuit 5 is equal to the cutoff bias voltage Ek × current I
k, so that a larger DC power can be supplied to the logic section than in the first embodiment shown in FIG.

When the power is turned on, the filament voltage Ef of the VFD 30, the anode voltage Eb, and the grid voltage Ec rise before the power supply voltage of the logic circuit. May occur. This, for example, the secondary winding of the resistor R and the Zener diode ZD or ZD ₁ at the connection point between the transformer T N
Leave inserting the switching circuit between the center tap CT of s _1, that after detecting that rises the power supply voltage for the logic circuit providing a rising sequence circuit configured to turn on the switch circuit Can be avoided.

[0024]

According to the present invention, the power wasted in the cut-off bias voltage generating circuit can be effectively used as the power supply for the logic circuit, so that the power consumption in the fluorescent display tube (VFD) module is reduced. The power can be reduced. Further, heat generation in the Zener diode for generating the cutoff bias voltage can be avoided, and the Zener diode for generating the cutoff bias can be reduced in size.

[Brief description of the drawings]

FIG. 1 is a diagram showing first and second embodiments of a power supply circuit for a fluorescent display tube (VFD) of the present invention.

FIG. 2 is a diagram showing a conventional fluorescent display tube (VFD) module.

FIG. 3 is a diagram showing a conventional power supply circuit for a fluorescent display tube (VFD).

[Explanation of symbols]

1 fluorescent display (VFD) modules 5,50 power supply circuit 10 microcomputer 20 driving circuit 30 fluorescent display (VFD) 40 DC / DC converter 41 the oscillation circuit C _1, C ₂ capacitors D diodes R, Rpd _1, Rpd ₂ resistors T transformer Tr ₁ , Tr ₂ transistor ZD, ZD ₁ , ZD ₂ Zener diode

Claims (3)

(57) [Claims] 1. One end is grounded and the other end is connected via a rectifying element to a fluorescent lamp.
A first winding for supplying the anode voltage of the light display tube, and a second winding for supplying the filament voltage of the fluorescent display tube
Lines and the resistance lines of the anode voltage side Zener diode
Ground, connect the connection point between the resistor and the Zener diode and the filament.
Cut off the fluorescent display tube by connecting the midpoint
A bias voltage generating circuit for applying a voltage, and the Zener die forming the bias voltage generating circuit.
The DC voltage generated at the terminal of the ode is connected to the fluorescent display tube.
A power supply circuit for a fluorescent display tube, which is supplied as a power supply for a driving logic circuit. A bias voltage generating circuit;
At least two or more diodes in series.
Of the zener diodes connected in series,
Terminal voltage of Zener diode connected to ground side
2. The power supply circuit for a fluorescent display tube according to claim 1 , wherein the power supply is a voltage source of the logic circuit. 3. A switch for controlling the terminal voltage of the Zener diode.
Supply to the switching power supply circuit,
Therefore, the supply voltage to the logic circuit is formed.
The power supply circuit for a fluorescent display tube according to claim 1, wherein