JP4864393B2 - Driving circuit and driving method for fluorescent display tube - Google Patents

Description

  The present invention relates to a drive circuit for a fluorescent display tube adopting a filament pulse drive system.

A driving circuit for a fluorescent display tube adopting a conventional filament pulse driving method will be described with reference to FIGS. Parts common to FIGS. 3 and 4 use the same reference numerals.
First, FIG. 3 will be described. Note that the filament pulse driving method shown in FIG.
In FIG. 3, 1 is a control circuit and 3 is a fluorescent display tube. The fluorescent display tube 3 includes a filament F that emits thermoelectrons, grids G1 to Gn that control electrons emitted from the filament F, and anode electrodes A1 to Am that are coated with phosphors. The phosphors of the anode electrodes A1 to Am are excited by the electrons emitted from the filament F and emit light. The filament power supply voltage (input voltage) HV of the control circuit 1 is applied to the filament F through the conductor 21, and the grid power supply voltage (input voltage) HV of the control circuit 1 is applied to the grids G1 to Gn through the conductor 23. The anode power supply voltage (input voltage) HV of the control circuit 1 is applied to the anode electrodes A <b> 1 to Am through the conductive wire 24. Here, the filament power supply voltage, the grid power supply voltage, and the anode power supply voltage are set to the same voltage.

  In the drive circuit of FIG. 3, when the control voltage Vc is applied from the control circuit 1 to the transistor Tr1 by the conducting wire 22, the transistor Tr1 is turned on, the input voltage HV is applied to the filament F, and the control voltage Vc is stopped. The transistor Tr1 is turned off and the input voltage HV is not applied to the filament F. That is, when the transistor Tr1 is controlled to be turned on / off by the control voltage Vc of the control circuit 1, the input voltage HV is chopped to generate a DC pulse voltage (filament pulse voltage having a predetermined pulse width), and the transistor Tr1 is turned on. During the period, a pulsed input voltage HV is applied to the filament F. Filament current flows through the filament F during the period Th during which the input voltage HV is applied, and the filament F is heated.

  By the way, when a filament is driven with an alternating voltage, a fluorescent display tube generally applies a cutoff bias voltage to the filament in order to prevent so-called leakage light emission, in which an anode electrode other than the selected anode electrode emits light. Even in a drive circuit adopting a filament pulse drive system as shown in FIG. 3, a cut-off bias voltage may be required depending on the structure of the fluorescent display tube. For example, in the case of a graphic type fluorescent display tube in which a grid and an anode electrode are arranged in a matrix, the intersection of the selected anode electrode and the selected grid electrode emits light, but the intersection of both electrodes is the anode electrode. If is selected, leaking light may be emitted even if the grid is not selected. In addition, a fluorescent display tube having a so-called rib grid formed by forming an insulating material layer on the anode substrate and forming a grid on the insulating material layer or a fluorescent display tube of a type that applies a high voltage to the anode electrode emits light. Sometimes. In order to prevent the leakage light emission, it is necessary to apply a cutoff bias voltage to the filament.

For the generation of the cut-off bias voltage, a cut-off bias voltage generating circuit using a Zener diode has been proposed (see, for example, Non-Patent Document 1).
FIG. 4 shows an example of a drive circuit in which a cut-off bias voltage generation circuit composed of a Zener diode is added to the drive circuit of FIG.
4A shows a drive circuit, and FIG. 4B shows voltage waveforms at various points in the drive circuit of FIG. 4A.
In the drive circuit of FIG. 4A, a Zener diode ZD is connected to the negative side of the filament F, and a cutoff bias voltage Ek is generated by the Zener diode ZD. A resistor R is connected between the conductor 21 and the Zener diode ZD, but the resistance value is large and can be ignored.
4B-1 shows the voltage waveform Ef1 at the end A of the filament F on the transistor Tr1 side, and FIG. 1B-2 shows the voltage waveform Ef2 at the end B of the filament F on the Zener diode ZD side. FIG. 1B-3 shows voltage waveforms Vg of the grids G1 to Gn, respectively. In FIG. 1 (b-1) to FIG. 1 (b-3), the input voltage HV = 24V and the cutoff bias voltage Ek = 5V are set.

An input voltage HV (24 V) is applied to the filament F during the on-period Th1 of the transistor Tr1, but a cutoff bias voltage Ek (5 V) is also applied. Accordingly, the filament peak voltage (filament effective voltage) Efp (HV-Ek) contributing to the filament current (current for heating the filament F) is 19V.
The grids G1 to Gn are scanned during a period Th2 where the input voltage HV is not applied to the filament F (between the periods Th1 and Th1), and grid power supply voltages Vg1 to Vgn (24V) of the input voltage HV are sequentially applied. The Since the cut-off bias voltage Ek (5V) is applied to the grids G1 to Gn in addition to the input voltage HV (24V), the effective voltage (effective grid voltage) ec as the control voltage is 19V (HV-Ek). become.

JP 2004-294727 A Edited by Shoichi Matsumoto, “Electronic Display”, first edition, third printing, Ohm Co., Ltd., July 25, 1999, p. 169

In the case of the driving circuit employing the filament pulse driving method of FIG. 4A, the filament F flows in the filament F during the period Th1 in which the transistor Tr1 is turned on and the input voltage HV is applied. The filament current also flows through the Zener diode ZD at the same time. Accordingly, reactive power is generated in the Zener diode ZD during the period Th1.
In view of the generation of reactive power, the present invention relates to the power consumption (reactive power) of a cutoff bias voltage generation circuit such as a Zener diode during heating of a filament in a fluorescent display tube driving circuit adopting a filament pulse driving system. The purpose is to reduce.

In order to achieve the object of the present invention, the drive circuit for the fluorescent display tube according to claim 1 is connected in series with the filament on the negative side of the filament, and has a cutoff bias voltage for preventing leakage light emission applied to the filament. For a short circuit for short-circuiting the cutoff bias voltage generating circuit in a fluorescent display tube driving circuit having a cutoff bias voltage generating circuit for generating and adopting a filament pulse driving system that drives a filament for electron emission by a filament pulse voltage A switching element and a control circuit for the short-circuit switching element, and the control circuit controls the short-circuit switching element to short-circuit the cutoff bias voltage generation circuit during a period in which the filament pulse voltage is applied to the filament. Features.
According to a second aspect of the present invention, there is provided the fluorescent display tube driving circuit according to the first aspect, further comprising a chopping switching element for chopping a filament power supply voltage to generate the filament pulse voltage. It is characterized by.
The fluorescent display tube drive circuit according to claim 3 is the fluorescent display tube drive circuit according to claim 1 or 2, wherein the cut-off bias voltage generation circuit is constituted by a Zener diode. Features.
5. A method for driving a fluorescent display tube according to claim 4, wherein a filament power supply for supplying a cutoff bias voltage and a filament current for preventing leakage light emission generated by a cutoff bias voltage generating circuit connected in series with the filament on the negative side of the filament is provided. In a fluorescent light emitting tube driving method in which a voltage is applied to a filament to drive a fluorescent light emitting tube, a cut-off bias voltage generation circuit is short-circuited and a filament power supply voltage is applied to the filament without applying a cut-off bias voltage to the anode. In the first period during which no anode power supply voltage is applied and the anode is not allowed to emit light, the cutoff bias voltage generation circuit is not short-circuited, the cutoff bias voltage is applied to the filament, and the filament power supply voltage is not applied to the anode to the anode. the power supply voltage is applied and a second period for emitting an anode, repeated alternately And wherein the door.
According to a fifth aspect of the present invention, there is provided the fluorescent display tube driving method according to the fourth aspect, wherein the filament power supply voltage is a filament pulse voltage.

  The drive circuit of the fluorescent display tube of the present invention short-circuits the cutoff bias voltage generation circuit such as the Zener diode ZD during the period when the filament current flows, and reduces the power consumption (reactive power) of the cutoff bias voltage generation circuit. Can be reduced. Further, since the power consumption of the cut-off bias voltage generating circuit is small, it is not necessary to provide a heat dissipation means in a circuit element such as the Zener diode ZD of the cut-off bias voltage generating circuit. Therefore, a circuit element such as a small Zener diode ZD can be used.

The drive circuit for the fluorescent display tube of the present invention has a cutoff bias voltage of 0 V during the period in which the filament current is flowing. Therefore, the filament peak voltage (filament effective voltage) contributing to the filament current can be increased accordingly. . Therefore, high luminance can be achieved by the same input voltage (filament power supply voltage (cathode voltage)), or the same luminance can be achieved by low input voltage (filament effective voltage).
The drive circuit for the fluorescent display tube of the present invention has a small duty ratio at the time of application of the input voltage (filament power supply voltage (cathode voltage)) (at the time of application of the filament pulse voltage). Brightness increases.

  A driving circuit for a fluorescent display tube employing a filament pulse driving system according to an embodiment of the present invention will be described with reference to FIGS. In addition, the same code | symbol is used for the part common to FIG. 1, FIG.

FIG. 1 shows a driving circuit of a fluorescent display tube and voltage waveforms at various points.
FIG. 1A shows a drive circuit, and FIG. 1B shows voltage waveforms at various points in the drive circuit of FIG.
First, in FIG. 1A, 1 is a control circuit and 3 is a fluorescent display tube. The fluorescent display tube 3 includes a filament (cathode) F that emits thermoelectrons, grids G1 to Gn that control electrons emitted from the filament F, and anode electrodes (anodes) A1 to Am that are coated with phosphors. ing. The phosphors of the anode electrodes A1 to Am are excited by the electrons emitted from the filament F and emit light.

  ZD is a Zener diode for a cut-off bias voltage generation circuit, Tr1 is a transistor of a chopping switching element, Tr2 is a transistor of a short-circuit switching element of the cut-off bias voltage generation circuit, and R is a resistor. The resistance value of the resistor R is large and can be ignored. The zener diode ZD is connected to the negative side of the filament F, and generates a cutoff bias voltage Ek and applies it to the filament F. The transistors Tr1 and Tr2 are ON / OFF controlled by the control voltages (control signals) Vc1 and Vc2 of the control circuit 1. The transistor Tr1 chops the input voltage HV applied to the filament F, and the transistor Tr2 Performs a short circuit and a short circuit release of the Zener diode ZD.

  A filament power supply voltage (cathode voltage) [input voltage] HV of the control circuit 1 is applied to the filament F through the conductive wire 21, and a grid power supply voltage (input voltage) HV of the control circuit 1 is applied to the grid G <b> 1 to Gn through the conductive wire 23. The anode power supply voltage (input voltage) HV of the control circuit 1 is applied to the anode electrodes A1 to Am by the conductive wire 24. Here, the filament power supply voltage, the grid power supply voltage, and the anode power supply voltage are set to the same input voltage HV.

Next, voltage waveforms in FIGS. 1B-1 to 1B-3 will be described.
1B-1 shows the voltage waveform Ef1 at the end of the filament F on the transistor Tr1 side, and FIG. 1B-2 shows the voltage waveform Ef2 at the end B of the filament F on the Zener diode ZD side. FIG. 1B-3 shows the voltage waveforms Vg of the grids G1 to Gn, respectively. In FIG. 1 (b-1) to FIG. 1 (b-3), the input voltage HV = 24V and the cutoff bias voltage Ek = 5V are set.
Filament current flows through the filament F during a period (first period) Th1 during which the input voltage HV is applied (described later).
The grids G1 to Gn are scanned during a period (second period) Th2 (between periods Th1 and Th1) in which the input voltage HV is not applied to the filament F, and the grid power supply voltages Vg1 to Vgn (24 V) of the input voltage HV. Are sequentially applied.
The anode power supply voltage (24V) of the input voltage HV is applied to the selected electrodes of the anode electrodes A1 to Am during the period Th2 when the input voltage HV is not applied to the filament F. The crossed portion of the grid electrodes thus emitted emits light.

  In the drive circuit of FIG. 1A, when the control voltage Vc1 is applied from the control circuit 1 to the transistor Tr1 by the conducting wire 221, the transistor Tr1 is turned on, the input voltage HV is applied to the filament F, and the control voltage Vc1 is stopped. The transistor Tr1 is turned off and the input voltage HV is not applied to the filament F. That is, when the transistor Tr1 is controlled to be turned on / off by the control voltage Vc1 of the control circuit 1, the input voltage HV is chopped to generate a DC pulse voltage (filament pulse voltage with a pulse width Th1), and the period in which the transistor Tr1 is on. A pulsed input voltage HV is applied to the filament F during Th1. Filament current flows through the filament F during the period Th1 during which the input voltage HV is applied, and the filament F is heated. During the period Th2 when the input voltage HV is not applied, the filament current does not flow, but the filament F emits thermoelectrons during the preheating. Note that when a filament current flows through the filament F, an emission luminance gradient occurs due to a filament potential gradient (the potential at both ends of the filament varies depending on the voltage drop of the filament), thereby reducing the image quality. The grid electrode is turned off to stop the electron emission of the filament F. When a filament current flows through the filament F, the filament current also flows through the Zener diode ZD, and a cut-off bias voltage Ek is generated.

  When the transistor Tr1 is turned on and the control voltage Vc2 is applied to the transistor Tr2 by the conducting wire 222 from the control circuit 1 during the period Th1 in which the input voltage HV is applied to the filament F (filament pulse voltage is applied), The transistor Tr2 is turned on to short-circuit the Zener diode ZD. When the Zener diode ZD is short-circuited, the cutoff bias voltage Ek becomes 0V.

In the drive circuit of FIG. 1A, when the transistor Tr1 is turned on and the input voltage HV (24V) is applied to the filament F, the filament current flows to heat the filament F. At this time, the Zener diode ZD Is short-circuited by the transistor Tr2, the filament current flows through the transistor Tr2 and does not flow through the Zener diode ZD. Then, the cutoff bias voltage Ek becomes 0V.
Accordingly, the filament peak voltage (filament effective voltage) Eppp contributing to heating of the filament F is Efppp = input voltage HV = 24V. That is, in the drive circuit of FIG. 1A, the cutoff bias voltage Ek is 0 V during the period Th1 in which the filament current flows in the filament F, so that the filament peak voltage Efp can be increased accordingly, and the zener diode The power (reactive power) consumed by ZD can be reduced.
On the other hand, since the cut-off bias voltage Ek (5 V) is applied to the grids G1 to Gn in addition to the input voltage HV (24 V), the effective voltage (effective grid voltage) ec as the control voltage is 19 V (HV-Ek). )become.

Next, referring to FIG. 2, the reactive power when the filament current flows through the filament F in the drive circuit of FIG. For comparison, FIG. 2 also shows reactive power and the like of the drive circuit in FIG.
2A shows a filament-related portion of the drive circuit of FIG. 1A, and FIG. 2B shows numerical values such as voltages at various points in the drive circuit of FIG. 2A.

  In FIG. 2B, the input voltage (filament power supply voltage) HV is 24 V in both FIGS. 1 and 4, the cut-off bias voltage Ek is 5 V in both FIGS. 1 and 4, and the filament peak voltage that contributes to heating of the filament ( Filament effective voltage) Efp is 19V in FIG. 4 and 24V in FIG. The duty ratio of the application time (pulse width of the filament pulse voltage) Th1 of the input voltage HV is 1/40 in FIG. 4 and 1/64 in FIG. The filament current when the input voltage HV is applied is 633 mA in FIG. 4, 800 mA in FIG. 1, and the invalid voltage when the input voltage HV is applied is 5 V in FIG. 4, and 0.3 V in FIG. The reactive power when the input voltage HV is applied is 3167 mW in FIG. 4 and 240 mW in FIG. 1. The average reactive power based on the duty ratio is 79.2 mW (3167 mW / 40) in FIG. 4, 3.75 mW (240 mW / 64) in FIG. 1, and the lighting period duty ratio is 39/40 in FIG. 4 and 63 in FIG. / 64.

  As described above, since the average reactive power is 79.2 mW in FIG. 4 and 3.75 mW in FIG. 1, the average reactive power in FIG. 1 is about 5% of the average reactive power in FIG. To reduce. The reactive power when the input voltage HV is applied is 3167 mW in FIG. 4, whereas it is 240 mW in FIG. 1. Therefore, the reactive power when the input voltage HV is applied in FIG. It can be reduced to about 1 / min. Therefore, the drive circuit of FIG. 1 can reduce power consumption, and the Zener diode ZD can reduce power consumption. Therefore, it is not necessary to provide a heat dissipating means, and a small-sized one can be used.

In the drive circuit of FIG. 1, when the input voltage HV is applied to the filament F, the cut-off bias voltage Ek becomes 0 V. Therefore, even when a high cut-off bias voltage Ek is required, the fluorescent display tube is driven with a filament pulse. be able to. In the drive circuit of FIG. 1, the cutoff bias voltage Ek is 0V as described above. Therefore, when the same input voltage HV, that is, the same filament power supply voltage is seen, the brightness is higher than that in the case where the cutoff bias voltage Ek cannot be 0V. The input voltage HV can be made lower than when the cutoff bias voltage Ek cannot be reduced to 0V for the same luminance.
The duty ratio when the input voltage HV is applied is (1/40) in FIG. 4, whereas (1/64) in FIG. 1, so that the lighting period duty ratio is higher in FIG. Greater than 4, thus increasing the brightness.

In the above embodiment, the example in which the cutoff bias voltage generating circuit is configured by the Zener diode ZD has been described. However, a constant voltage element or a constant voltage circuit other than the Zener diode may be used. Moreover, although the said Example demonstrated the example which uses transistor Tr1, Tr2 as a switching element, switching elements other than a transistor may be sufficient.
In the above-described embodiment, the fluorescent display tube has been described. However, in addition to the fluorescent display tube, a fluorescent tube such as a print head arc tube or a flat CRT may be used.

1 shows a drive circuit for a fluorescent display tube according to an embodiment of the present invention. Numerical values such as voltages at various points in the drive circuit of FIGS. 1 and 4 are shown. A driving circuit of a fluorescent display tube adopting a conventional filament pulse driving system is shown. FIG. 3 shows a drive circuit to which a cutoff bias voltage generation circuit using a Zener diode is added.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control circuit 3 Fluorescent display tube Ek Cut-off bias voltage Ef1, Ef2 A, B part voltage Efppp Filament peak voltage ec Grid effective voltage HV Input voltage (filament power supply voltage, grid power supply voltage, anode power supply voltage)
ZD Zener diode

Claims (5)

A filament that is connected in series with the filament on the negative side of the filament, has a cutoff bias voltage generation circuit that generates a cutoff bias voltage for preventing leakage light emission applied to the filament, and drives the filament for electron emission by the filament pulse voltage A driving circuit for a fluorescent display tube adopting a pulse driving method, comprising: a short-circuit switching element for short-circuiting a cutoff bias voltage generation circuit; and a control circuit for the short-circuit switching element. A drive circuit for a fluorescent display tube, characterized in that the cut-off bias voltage generation circuit is short-circuited while the filament pulse voltage is applied to the filament.   2. The drive circuit for a fluorescent display tube according to claim 1, further comprising a chopping switching element for chopping a filament power supply voltage to generate the filament pulse voltage.   3. The fluorescent display tube driving circuit according to claim 1, wherein the cutoff bias voltage generating circuit is constituted by a Zener diode. Fluorescence that drives a fluorescent tube by applying a cutoff bias voltage for preventing leakage light emission generated by a cutoff bias voltage generation circuit connected in series with the filament on the negative side of the filament and a filament power supply voltage for passing the filament current to the filament In the arc tube driving method, the cut-off bias voltage generation circuit is short-circuited , the filament power supply voltage is applied without applying the cut-off bias voltage to the filament , and the anode power supply voltage is not applied to the anode without causing the anode to emit light. a first time period, the cut-off bias voltage generating circuit is a second period in which the light emitting anode by applying an anode power supply voltage to the anode without applying the filament power supply voltage is applied to the cut-off bias voltage to the filament without shorting And the method for driving the fluorescent light-emitting tube, which are alternately repeated. 5. The method of driving a fluorescent light emitting tube according to claim 4, wherein the filament power supply voltage is a filament pulse voltage.

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