JPH08278762A - Power circuit for fluorescent display tube - Google Patents

Abstract

PURPOSE: To reduce power consumption and heat generation in a power circuit for a vacuum fluorescent display(VFD). CONSTITUTION: Voltages applied to the anode and the grid of the VFD is generated by rectifying the voltage generated on a secondary winding wire Ns2 of a transformer T of a DC/DC converter by a diode D. Further, the cut-off bias voltage of the VFD is generated by Zener diodes ZD1 and ZD2 or the Zener diode ZD inserted between the central tap CT and the ground GND of the secondary winding wire Ns1 of the transformer T. Then, the voltave generated on the Zener diode ZD2 or the Zener diode ZD is supplied to logic circuits such as a microcomputer and a drive circuit as a supply voltage as it is or through the power circuit.

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 is particularly suitable for application to a fluorescent display tube module.

[0002]

2. Description of the Related Art 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, and is used in various fields, but the design of the drive circuit and power supply necessary to drive the VFD. Etc. required a considerable amount of time and specialized knowledge, and there were some things that were troublesome to use the VFD as a part of the system in a short period of time. Therefore, in order to solve this, the VFD itself and peripheral circuits such as the drive circuit and the power supply circuit for the VFD are compactly integrated, and a simple interface and a power supply are prepared without a troublesome design when using. The VFD module that can be used in the above is put to practical use.

Such a VFD module is constructed so as to be operated by receiving a supply of electric power necessary 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 to generate a signal for driving the VFD. Normally, the operating voltage of the logic circuit is It is 5 (V), and there is no problem when the power of 5 (V) is supplied from an external device, but in a POS system, for example, the influence of a voltage drop (line drop) in routing the power supply line inside the system. 12 or 24 in order to reduce the number of power lines and the number of power lines themselves.
It may be configured to supply a single power supply voltage of about (V) to each device inside the system. In such cases, the VFD module must have 12 or 24
Since only the direct current voltage of (V) is supplied, the internal voltage of the VFD module is 12 in order to obtain the direct current voltage of 5 (V) for supplying to the built-in logic circuit.
Alternatively, a circuit is provided for stepping down 24 (V) to 5 (V).

FIG. 2 shows an example of the configuration of such a conventional VFD module. In FIG. 2, reference numeral 1 is a VFD module, to which control signals such as data signals, read / write control signals and selection signals, and power supply voltage are supplied from an external device. Here, for example, only 24 (V) is supplied as the power supply voltage. Reference numeral 10 denotes a microcomputer, which performs input / output of data with an external device, storage / editing of display data, and other control necessary for driving the VFD. Reference numeral 20 is a drive circuit composed of an anode drive circuit and a grid drive circuit, and based on a signal output from the microcomputer 10, VF
It is a drive circuit for dynamically driving or statically driving D. Then, the microcomputer 10 and the drive circuit 20 usually operate at an operating voltage of 5
It is a logic circuit that requires (V). Although the example in which the microcomputer 10 and the drive circuit 20 are separately provided is shown here, an ASIC in which these are integrated may be used in some cases.

A fluorescent display tube (VFD) 30 includes, for example, a plurality of strip-shaped anode electrodes each having a fluorescent material coated on the inside of an envelope, and a plurality of strip-shaped anode electrodes arranged in a direction intersecting with 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 DC voltage of 24 (V) supplied from an external device as an input and
The anode voltage Eb supplied to D, the grid voltage Ec, and the AC filament voltage Ef are output.
Reference numeral 50 denotes a power supply circuit including a switching regulator and the like, which receives a DC voltage of 24 (V) supplied from an external device as an input, and which is a logic circuit, that is, a power supply of 5 (V) for the microcomputer 10 and the drive circuit 20. It outputs a voltage.

FIG. 3 shows an example of the configuration of the power supply circuit portion in the VFD module configured as described above. In the figure, the drive circuit 20 is provided with terminals to which the voltages Eb and Ec are supplied, and the sources of the grid electrode driving transistor Tr ₁ and the anode electrode driving transistor Tr ₂ are connected to the terminals. There is. A lighting control signal supplied from the microcomputer 10 shown in FIG. 2 is supplied to the gates of both drive 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 the VFD 30, respectively, and the pull-down resistors Rpd ₁ and Rp are connected.
It is connected to the ground GND via d ₂ . Although the VFD 30 is simplified in this figure,
Actually, a plurality of anode electrodes and grid electrodes of the VFD 30 are provided as described above, and a plurality of grid electrode driving transistors Tr ₁ and a plurality of anode electrode driving transistors Tr ₂ are provided respectively, and a predetermined number of them are provided. It is driven in order.

The DC / DC converter 40 is an oscillation type DC / DC converter having an oscillation circuit 41, a transformer T, a diode D, a resistor R, a zener diode ZD and a smoothing capacitor C ₁ and is supplied from an external device. For example, a DC voltage of 24 (V) is input. With the oscillation circuit 41 provided on the primary winding side of the transformer T,
An alternating voltage is generated in the secondary windings Ns ₁ and Ns ₂ of the transformer T. The AC voltage generated across the _first secondary winding Ns ₁ having the center tap CT is supplied to the filament of the VFD 30 as the filament voltage Ef. The alternating voltage generated in the second secondary winding Ns ₂ is the diode D
Is rectified by and is 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 between the center tap CT and the output side of the diode D. The resistor R is connected.
The Zener voltage Vz of the Zener diode ZD is set as the cutoff bias voltage Ek, and the VF is passed through the pull-down resistors Rpd ₁ and Rpd ₂ of the driver circuit 20.
The voltage is applied to the anode and grid of D30, so that the VFD 30 does not leak and emit light when the driving transistors Tr ₁ and Tr ₂ are off. The value of the cutoff bias voltage Ek is determined according to the magnitude of the filament voltage Ef, but in the case of a normal VFD,
The voltage is higher than 5 (V).

In the VFD power supply circuit configured as described above, 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 anode. When the voltage Eb and the grid voltage Ec are supplied, the VFD 30 lights up. VFD
When 30 is turned on, the anode current ib and the grid current ic flow in the anode and the grid of the VFD 30, and the current Ik = ib + ic which is the sum of the two flows from the center tap CT of the secondary winding Ns ₁ of the transformer T to the zener. It will flow to the diode ZD. As a result, the Zener voltage Vz is generated in the Zener diode ZD. As described above, this is applied as the cutoff bias voltage Ek to the anode electrode and the grid electrode of the VFD through the pull-down resistors Rpd ₁ and Rpd ₂ , and the anode electrode and the grid electrode that are not driven are reverse-biased with respect to the filament. Since a voltage is applied, leakage light emission can be prevented.

The resistor R is a Zener diode in order to prevent the current Ik from flowing through the Zener diode ZD and the Ek from not occurring when neither the anode electrode nor the grid electrode is driven. It is a resistor provided to flow a bias current of about 1 to 3 mA to ZD.

[0011]

As mentioned above, the VF
When D30 is in a lighting state, a current Ik flows from the filament to the Zener diode ZD through the center tap CT of the secondary winding Ns ₁ of the transformer T. This current Ik depends on the size of the fluorescent display tube, but is several tens.
The magnitude is about 100 (mA), which causes power consumption of P = Ik × Ek in the Zener diode ZD. However, this power consumption is useless because it does not contribute to the light emission of the fluorescent display tube VFD at all, and the power consumption in the VFD module increases, and it is necessary to use the Zener diode ZD having a size that can withstand this. Was required, which could be a problem in implementation. Further, the phosphor has a temperature extinction characteristic, that is, the characteristic that the brightness decreases as the temperature rises, and there is a problem that the brightness of the VFD 30 decreases due to the heat generated by the power consumption. These points cannot be ignored especially in the VFD module in which the VFD and its peripheral circuits are compactly integrated.

Further, since the conventional VFD module is constructed as described above, the DC voltage supplied from the device incorporating the VFD module is 12 or 24.
When it was (V), it was necessary to provide a power supply circuit for generating a power supply voltage of 5 (V) for the logic circuit inside the VFD module.

Therefore, the present invention provides a fluorescent display tube (VF).
An object of the present invention is to provide a fluorescent display tube power supply circuit that can effectively use the electric power wasted in the D) power supply circuit. It is another object of the present invention to provide a power supply circuit for a fluorescent display tube which can use a small-sized Zener diode for generating a cutoff bias and which generates little heat in the Zener diode.

[0014]

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

Further, the power supply circuit for a fluorescent display tube of the present invention comprises:
The Zener diode in the cut-off bias voltage generating circuit is a plurality of Zener diodes connected in series, the power supply voltage generating circuit for the logic circuit, among the plurality of Zener diodes connected in series The DC voltage generated across the Zener diode connected to the ground side is supplied to the logic circuit as a power supply voltage. Furthermore, in the fluorescent display power supply circuit of the present invention, the logic circuit power supply voltage generation circuit is a switching regulator in which a voltage generated across the Zener diode is input and the output is supplied to the logic circuit. There is something.

[0016]

In the present invention thus constructed, the 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 wasted in the conventional Zener diode can be effectively used. As a result, it becomes possible to use a small Zener diode.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a fluorescent display tube power supply circuit of 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 is a secondary winding of the transformer T, D is a diode, C ₁ is a smoothing capacitor, and the secondary winding Ns ₂ of the transformer T is connected to the secondary winding Ns ₂ by a rectifying circuit composed of the diode D and the smoothing capacitor C _1. By rectifying the generated AC voltage, VF
When the D30 is turned on, the anode voltage Eb and the 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, the 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.

The voltage generated across the second Zener diode ZD ₂ is supplied as a power supply voltage to the logic section including the microcomputer 10 and the drive circuit 20. That is, a Zener diode ZD ₂ having a Zener voltage Vz ₂ of 5 (V) is used to generate a DC voltage of 5 (V) to be supplied to the logic section including the microcomputer 10 and the drive circuit 20. Has been done. The current Ik flowing from the center tap CT of the secondary winding Ns ₁ to the Zener diode ZD ₁ is about several tens to 100 (mA) in the case of a normal VFD, and therefore the microcomputer 10 and the drive circuit. Two
It is possible to pass a current of about several tens to 100 (mA) to the logic section consisting of 0. Usually, CMOS circuits with low power consumption are often used for these circuits, and thus this configuration can be sufficiently used as a power supply for a logic circuit.

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

A second embodiment of the present invention capable of supplying a large amount of power to a logic circuit is shown in FIG. 1 (b). In this figure, the transformer T and the 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 are
Both are the same as those shown in FIG. Further, ZD is a Zener diode for generating a cutoff bias voltage Ek, 5 is a power supply circuit including a switching regulator, and the voltage generated at both ends of the Zener diode ZD is input to stabilize 5 (V). It outputs the generated 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 is used for the logic section. Of 5
Since the power supply voltage of (V) is generated, the power input to the power supply circuit 5 is cutoff bias voltage Ek × current I.
Therefore, compared with the first embodiment shown in FIG. 1A, a larger DC power can be supplied to the logic section.

When the power is turned on, the filament voltage Ef, the anode voltage Eb, and the grid voltage Ec of the VFD 30 rise earlier than the power supply voltage of the logic circuit, so that erroneous light emission occurs momentarily. May occur. This is, for example, the connection point of the resistor R and the Zener diode ZD or ZD _{1 and} the secondary winding N of the transformer T.
A switch circuit is inserted between the center tap CT of s ₁ and a rising sequence circuit configured to turn on the switch circuit after detecting that the power supply voltage for the logic circuit has risen is provided. Can be avoided by

[0024]

According to the present invention, the power wasted in the cut-off bias voltage generating circuit can be effectively used as the power source of the logic circuit, and therefore the power consumption in the fluorescent display tube (VFD) module is improved. 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 downsized.

[Brief description of 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 Tube (VFD) Module 5, 50 Power Supply Circuit 10 Microcomputer 20 Driving Circuit 30 Fluorescent Display Tube (VFD) 40 DC / DC Converter 41 Oscillation Circuit C ₁ , C ₂ Capacitor D Diode R, Rpd ₁ , Rpd ₂ Resistance T transformer Tr ₁ , Tr ₂ transistor ZD, ZD ₁ , ZD ₂ Zener diode

Claims (3)

[Claims] 1. A cutoff bias voltage generating circuit comprising a Zener diode connected between a center tap of a filament winding for supplying a filament voltage to a fluorescent display tube and ground, and the cutoff bias voltage generating circuit. A power supply circuit for a fluorescent display tube, which uses a DC voltage generated in a Zener diode to generate a power supply voltage to be supplied to a logic circuit for driving the fluorescent display tube. . 2. The Zener diode in the cut-off bias voltage generating circuit comprises a plurality of Zener diodes connected in series, and the power supply voltage generating circuit for logic circuit includes a plurality of Zener diodes connected in series. 2. The power supply for a fluorescent display tube according to claim 1, wherein a DC voltage generated across both of the Zener diodes connected to the ground side among the Zener diodes is supplied to the logic circuit as a power supply voltage. circuit. 3. The power supply voltage generation circuit for logic circuit is a switching regulator to which a voltage generated across the Zener diode is input and whose output is supplied to the logic circuit. A power supply circuit for the fluorescent display tube described.