JP4268029B2 - Fluorescent display power supply circuit - Google Patents

Description

  The present invention relates to a power supply circuit attached to a fluorescent display device.

  In a fluorescent display device, electrons emitted from a cathode collide with a phosphor coated on the anode in a vacuum vessel (envelope) at least one of which is transparent to cause the phosphor to emit light, thereby forming a desired pattern. An electron tube to be displayed. In general, this fluorescent display device is most often used in a three-pole structure having a grid for controlling the action of electrons.

[Conventional example 1]
FIG. 9 is a block diagram showing a conventional general fluorescent display tube and a circuit attached to the fluorescent display tube (see Patent Document 1). In the figure, 1 is a fluorescent display tube, and 100 is a power supply circuit attached to the fluorescent display tube 1. The fluorescent display tube 1 includes an anode 5 composed of a plurality of anode electrodes 4 coated with a phosphor 3 in an envelope 2 that has been evacuated, a cathode 6 disposed on the upper surface of the anode 5, and an anode 5. And a grid 7 arranged between the cathode 6 and the cathode 6 for controlling electrons emitted from the cathode 6. The anode 5 is formed on the anode substrate 8.

  Here, the cathode 6 is a filament coated with an electron emission material, and is connected to an AC power supply 10 through a transformer 9 with a center tap and grounded (GND) through the center tap of the transformer 9. Thereby, an AC filament voltage Ef is applied between the cathodes 6 (between the terminals F1 and F2).

  Grid 7 is formed in a mesh shape and receives supply of DC voltage VDD2 from booster circuit 11. Each anode electrode 4 is connected to a drive circuit 12. The drive circuit 12 is also supplied with the DC voltage VDD2 from the booster circuit 11. The booster circuit 11 boosts the input voltage Vi (DC voltage) to produce an anode / grid DC voltage VDD2. The drive circuit 12 controls on / off of the positive voltage applied to each anode electrode 4 based on the input display data.

[Conventional example 2]
FIG. 10 is a block diagram showing a power supply circuit that generates the anode / grid DC voltage VDD2 and pulse-drives the filament, and FIG. 11 is a waveform diagram showing the operation of the power supply circuit of FIG. 10 (see Patent Document 2). In this power supply circuit 100, reference numeral 20 denotes a logic power supply, which generates a DC power supply VCC from an input voltage (DC voltage) Vi. Reference numeral 21 is a reference oscillator, which generates a reference clock signal as shown in FIG. Reference numeral 22 denotes a divide-by-2 circuit that generates an external clock signal as shown in FIG. 11B in which the frequency of the reference clock signal is halved.

  A filament driver 23 switches the input voltage Vi and outputs differential pulse voltages P1 and P2 that are complementary to each other from the output terminals OUT1 and OUT2 (FIGS. 11C and 11D). Differential pulse voltages P 1 and P 2 from the filament driver 23 are applied to the filament 6. Thereby, an alternating filament voltage Ef is applied between the filaments 6 (between the terminals F1 and F2). A booster circuit 24 boosts and rectifies the differential pulse voltages P1 and P2 output from the filament driver 23, and outputs the rectified voltage as an anode / grid DC voltage VDD2.

[Cutoff voltage]
In the fluorescent display tube, if the filament potential is lower than the extinguishing level of the anode potential, there is a possibility that leakage light emission occurs. That is, the filament potential needs to be higher than the extinguishing level of the anode potential, and this filament potential is called a cut-off voltage.

  In FIG. 9, the average voltage (filament F1 terminal side average voltage) between one end of the filament 6 and GND is equal to the average voltage (filament F2 terminal side average voltage) between the other end of the filament 6 and GND, The average voltage of the filament 6 is the cut-off voltage. This cut-off voltage can be adjusted by the value of the resistor RC1 connected between the center tap of the transformer 9 and GND.

  In FIG. 10, the average voltage between the one end of the filament 6 and the output terminal OUT1 of the filament driver 23 (filament F1 terminal side average voltage) and the average voltage between the other end of the filament 6 and the output terminal OUT2 of the filament driver 23. It is equal to (filament F2 terminal side average voltage), and the average voltage of the filament 6 is the cut-off voltage. This cut-off voltage can be adjusted by the values of the resistor RC2 connected between F1 and OUT1 and the resistor RC3 connected between F2 and OUT2.

JP 2002-260565 A JP 2003-29711 A

In the circuit of the conventional example 1 (FIG. 9), the cutoff voltage can be adjusted by the resistor RC1, but this cutoff voltage is made smaller than the average voltage between the terminals F1, F2 and the center tap of the transformer 9. The degree of freedom in setting the cut-off voltage was low.
In the circuit of the conventional example 2 (FIG. 10), the resistors RC2 and RC3 for adjusting the cut-off voltage are connected in series with the filament 6, so that the input voltage Vi is reduced by the voltage drop at the resistors RC2 and RC3. All could not be used as a voltage to the filament 6. In addition, the power consumed by the resistors RC2 and RC3 is large, and the power consumed by the filament 6 is added to the power to increase the power. The filament driver 23 must be rated and sized to withstand the power. However, there was a problem that the cost increased.

  The present invention has been made to solve such a problem, and the object of the present invention is to provide a high degree of freedom in setting a cut-off voltage, low power consumption, and all input voltages to the filament. Another object of the present invention is to provide a power supply circuit for a fluorescent display device that can be used as a power supply.

  In order to achieve such an object, the present invention provides a first switching element and a second switching element connected in series between a DC voltage input line and a ground line, and a resistance and a reverse flow connected in series with each other. A series connection circuit comprising a prevention element and a constant voltage element and connected in parallel to the first switching element; a first capacitor connected between an input terminal and an output terminal of the constant voltage element; and a constant voltage A first terminal connected to a connection point between the input terminal of the element and the first capacitor; a second capacitor connected between the second terminal and the ground line; a first switching element; And a control means for alternately turning on / off the two switching elements, the first switching element is connected as a DC voltage input line side with respect to the second switching element, and the backflow prevention element is connected to the constant voltage element. DC power Connect as the input line side, is obtained so as to connect the cathode between a first terminal and a second terminal.

According to the present invention, when the first switching element is turned off and the second switching element is turned on, the resistor, the backflow prevention element, and the constant voltage element are connected from the DC voltage (Vi) input line through the series connection circuit. A current flows to the ground line, and the charging voltage (Vc1) of the first capacitor connected in parallel to the constant voltage element becomes equal to the constant voltage (VF) generated at both ends of the constant voltage element. The voltage between the lines becomes Vc1. Next, when the first switching element is turned on and the second switching element is turned off, the DC voltage Vi through the first switching element is added to the charging voltage Vc1 of the first capacitor, and the first terminal And the ground line is Vi + Vc1. On the other hand, the voltage between the second terminal and the ground line becomes Vi · Don + Vc1 when the on-duty of the first switching element is Don due to charging / discharging of the second capacitor via the filament. Thereby, a rectangular wave voltage (AC filament voltage) having a voltage width Vi is applied to the cathode (filament) connected between the first terminal and the second terminal. In this case, the cut-off voltage is Vi · Don + Vc1, and the cut-off voltage can be arbitrarily set by Don and Vc1. The effective voltage ef applied to the cathode is ef = Vi · [(1−Don) · Don) ^1/2 ], and can be arbitrarily set within the range of ef ≦ 0.5 Vi by Don.

According to the present invention, the cut-off voltage becomes Vi · Don + Vc1, and the cut-off voltage can be arbitrarily set by Don and Vc1, and the degree of freedom in setting the cut-off voltage is increased.
In addition, a rectangular wave voltage having a voltage width Vi is applied to the filament, and all the DC voltage (input voltage) Vi can be used as the voltage to the filament.
In addition, since there is no resistance in the supply path to the filament of the input voltage Vi, there is no power consumption at this resistance, resulting in low power consumption.

[Embodiment 1]
Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing a main part of an embodiment of a power supply circuit according to the present invention.

  The power supply circuit 300 includes a control circuit 13, a booster circuit 14, and a cut-off circuit 15, and has an input terminal Pin, an output terminal Pout, and filament terminals F1 and F2. A DC voltage (input voltage) Vi is applied to the input terminal Pin. An anode / grid DC voltage VDD2 is output from the output terminal Pout. A cathode (filament) 6 of the fluorescent display tube 1 is connected between the filament terminals F1 and F2.

  The cut-off circuit 15 includes a first switch SW1, a second switch SW2, a resistor R, diodes D1 and D2, and capacitors C1 and C2. The switch SW1 and the switch SW2 are connected in series between the input line L1 of the DC voltage Vi and the ground line L2 (GND). In this series connection, the switch SW1 is on the input line L1 side of the DC voltage Vi, and the switch SW2 is on the ground line L2 side. In addition, a series connection circuit of a resistor R, a diode D2, and a diode D1 is connected in parallel to the switch SW1.

  In the cut-off circuit 15, the diode D1 is used as a constant voltage element, and the diode D2 is used as a backflow prevention element. The diode D2 is provided on the input line L1 side of the DC voltage Vi with respect to the diode D1. That is, the anode of the diode D2 is connected to the input line L1 of the power supply voltage Vi through the resistor R, the cathode of the diode D2 is connected to the anode of the diode D1, and the cathode of the diode D1 is the connection point between the switch SW1 and the switch SW2. It is connected to the. The resistor R is used as a resistor for setting a forward current flowing through the diodes D1 and D2.

  The capacitor C1 is connected in parallel with the diode D1. That is, one end of the capacitor C1 is connected to the anode of the diode D1 (input terminal of the constant voltage element), and the other end of the capacitor C1 is connected to the cathode of the diode D1 (output terminal of the constant voltage element). A filament terminal F1 is connected to a connection point PA with the capacitor C1. The capacitor C2 is connected between the filament terminal F2 and the ground line L2.

  The control circuit 13 uses the DC voltage Vi as an operating power supply, and periodically turns on / off the switches SW1 and SW2 of the cutoff circuit 15 in opposite directions. That is, the operation of “turning off the switch SW2 when the switch SW1 is turned on and turning on the switch SW2 when the switch SW1 is turned off” is repeated periodically. The booster circuit 14 boosts the DC voltage Vi to generate an anode / grid DC voltage VDD2.

  In the control circuit 13, the switching cycle T and the duty ratio (on duty, off duty) when the switch SW1 and the switch SW2 are periodically turned on / off in opposite directions can be adjusted. The switching period T is defined as t on when the switch SW1 is on (= time when the switch SW2 is off) and toff when the switch SW1 is off (= time when the switch SW2 is on). , T = ton + Toff. The on-duty Don of the switch SW1 is expressed as Don = ton / T. The off duty Doff of the switch SW1 is expressed as Doff = toff / T = (T-ton) / T = 1-Don.

[Filament voltage]
[Waveform between F1 and GND]
FIG. 2 shows voltage waveforms (waveforms between F1 and GND) appearing at the filament terminal F1 by the on / off control of the switches SW1 and SW2 of the control circuit 13.

  When the switch SW1 is turned off and the switch SW2 is turned on, a current flows through the path of the resistor R, the diode D2, the diode D1, and the switch SW2, and the charging voltage Vc1 of the capacitor C1 becomes equal to the forward voltage VF of the diode D1. Therefore, during the period of toff, the voltage between F1 and GND is Vc1 = VF.

  When the switch SW1 is turned on and the switch SW2 is turned off, the DC voltage Vi through the switch SW1 is added to the charging voltage Vc1 of the capacitor C1, and the potential at the connection point PA becomes Vi + Vc1. Therefore, during the period t on, the voltage between F1 and GND is Vi + Vc1. In this case, the potential at the connection point PA becomes higher than Vi, but no current flows into the input line L1 due to the backflow prevention by the diode D2.

[Waveform between F2 and GND]
FIG. 3 shows a voltage waveform (waveform between F2 and GND) appearing at the filament terminal F2 by the on / off control of the switches SW1 and SW2 of the control circuit 13.

When the switch SW1 is turned on and the switch SW2 is turned off, the DC voltage Vi through the switch SW1 is added to the charging voltage Vc1 of the capacitor C1, and the potential at the connection point PA becomes Vi + Vc1. As a result, a current If1 flows through the filament 6, and the capacitor C2 is charged by this current (charging current) If1.
When the switch SW1 is turned off and the switch SW2 is turned on, the potential at the connection point PA is returned to Vc1, so that the discharge current If2 from the capacitor C2 flows through the filament 6.

  The current If1 · Don charged by the switch SW1 and charging the capacitor C2 is equal to the current If2 · Doff discharged from the capacitor C2 by turning on the switch SW2. If If1 · Don> If2 · Doff, Vc2 increases but If2 increases, resulting in a decrease in Vc2. If If1 · Don <If2 · Doff, Vc2 decreases but If1 increases, resulting in an increase in Vc2. Eventually, Vc2 tries to maintain a constant value, so If1 · Don = If2 · Doff.

  If1 · Don = If2 · Doff, (Vi + Vc1−Vc2) · Don = (Vc2−Vc1) · (1−Don). Don−Vc1 + Vc1 · Don, and Vi · Don = Vc2−Vc1. Therefore, Vc2 = Vi · Don + Vc1, and the voltage between F2 and GND is Vc2 = Vi · Don + Vc1 in both the toff period and the ton period.

[Waveform between F1-F2]
The voltage waveform between the filament terminals F1 and F2 (the waveform between F1 and F2) is a voltage waveform as shown in FIG. 4 when the voltage Vc2 = Vi · Don + Vc1 applied to the filament terminal F2 is used as a reference. That is, the voltage applied to both ends of the filament 6 is a rectangular wave voltage (AC filament voltage) having a voltage width of Vi by the on / off control of the switches SW1 and SW2 by the control circuit 13.

[Effective value of filament voltage]
If the effective voltage applied to both ends of the filament 6 when the switch SW1 is on and the switch SW2 is off is ef1, it is obtained as ef1 = (Vi + Vc1−Vc2) · Don ^1/2 . Substituting Vc2 = Vi · Don + Vc1 into this equation,
ef1 = (Vi + Vc1-Vi.Don-Vc1) .Don ^1/2
= Vi ・ (1-Don) ・ Don ^1/2・ ・ ・ ・ (1)
It becomes.

If the effective voltage applied to both ends of the filament 6 when the switch SW1 is off and the switch SW2 is on is ef2, ef2 = (Vc2-Vc1) .Doff1 / ² = (Vc2-Vc1). (1-Don ) ^Calculated as ^1/2 . Substituting Vc2 = Vi · Don + Vc1 into this equation,
ef2 = (Vi · Don + Vc1−Vc1) · (1−Don) ^1/2
= Vi ・ Don ・ (1-Don) ^1/2・ ・ ・ ・ (2)
It becomes.

The effective value ef of the filament voltage applied to both ends of the filament 6 is obtained as ef = (ef1 ² + ef2 ² ) ^1/2 . If both sides of this equation are squared, ef ² = [Vi · (1-Don) · Don ^1/2 ] ² + [Vi · Don · (1-Don) ^1/2 ] ² = Vi ² · (1 (Don) ² · Don + Vi ² · Don ² · (1−Don) = Vi ² · (1−Don) · Don · [(1−Don) + Don] = Vi ² · (1−Don) · Don From this equation, the effective value ef of the filament voltage applied to both ends of the filament 6 is
ef = Vi. [(1-Don) .Don] ^1/2 ... (3)
It becomes.

  In the above equation (3), the condition that the effective value ef of the filament voltage becomes maximum is when Don = 0.5, and the effective value ef of the filament voltage at this time is ef = 0.5 Vi. As can be seen, in the present embodiment, the effective value ef of the filament voltage can be arbitrarily set in the range of ef ≦ 0.5 Vi by the on-duty Don of the switch SW1.

[Cutoff voltage]
In this power supply circuit 300, the average voltage (filament F1 terminal side average voltage) VF1 of the filament terminal F1 is:
VF1 = (Vi + Vc1) .Don + Vc1. (1-Don)
= Vi · Don + Vc1 (4)
The average voltage (filament F2 terminal side average voltage) VF2 of the filament terminal F2 is
VF2 = Vc2
= Vi · Don + Vc1 (5)
Therefore, the cut-off voltage is the same at the filament terminals F1 and F2. As can be seen from the equations (4) and (5), the cut-off voltage can be arbitrarily set by the charging voltage Vc1 of the capacitor C1, that is, the forward voltage VF of the diode D1 and the on-duty Don of the switch SW1. .

In this embodiment, since the cutoff voltage is Vi · Don + Vc1 as described above, the cutoff voltage could not be made smaller than the average voltage between the filament terminal and the center tap of the transformer. Compared to Example 1, it becomes possible to set the cut-off voltage low, and the degree of freedom of the cut-off voltage increases.
In the present embodiment, since a rectangular wave voltage having a voltage width Vi is applied to the filament 6, the entire input voltage Vi is used as the voltage to the filament 6. Further, since there is no resistance in the supply path to the filament 6 of the input voltage Vi, there is no power consumption at this resistance, and the power consumption is low. As a result, the voltage rating, current rating, and power consumption capacity of the circuit components can be reduced, and the size and cost of the components can be reduced.

[Embodiment 2]
FIG. 5 shows an application example of the power supply circuit 300 shown in FIG. In the power supply circuit 300 ′, the third switch SW3 and the fourth switch SW4 are connected in series between the input line L1 of the DC voltage Vi and the ground line L2. In this series connection circuit, the switch SW3 is on the input line L1 side of the DC voltage Vi, and the switch SW4 is on the ground line L2 side. A capacitor C2 is connected between the connection point of the switches SW3 and SW4 and the filament terminal F2.

  In addition, the switch SW1 and the switch SW4 are a first switch pair, the switch SW2 and the switch SW3 are a second switch pair, and the control device 13 ′ controls the first switch pair (SW1, SW4) and the second switch pair. The switch pair (SW2, SW3) is periodically turned on / off alternately in the opposite direction.

  That is, the control device 13 ′ sets “when the first switch pair (SW 1, SW 4) is simultaneously turned on, the second switch pair (SW 2, SW 3) is simultaneously turned off and the first switch pair (SW 1, SW 4). ) Are turned on at the same time, the second switch pair (SW2, SW3) is turned on simultaneously "is repeated periodically.

  6, 7, and 8 show waveforms between F2 and GND, waveforms between F2 and GND, and waveforms between F1 and F2 corresponding to FIGS. 2, 3, and 4. As can be seen from these waveforms, also in the second embodiment, a rectangular wave voltage (alternating filament voltage) is applied to the filament 6 as in the first embodiment. However, in this case, the voltage width of the rectangular wave voltage applied to the filament 6 is 2 · Vi.

In the second embodiment, when the on / off duty ratio of the first switch pair (SW1, SW4) and the second switch pair (SW2, SW3) are the same, Vc1 = Vc2. The average voltages VF1 and VF2 of the filament terminals F1 and F2 are VF1 = VF2 = Vi · Don + Vc1. The effective value ef of the filament voltage is ef = (2 · Don) ^1/2 .

  In the first and second embodiments described above, switching elements such as transistors and FETs are used as the switches SW1 to SW4. In the series connection circuit of the resistor R, the diode D2, and the diode D1 connected to the first switch SW1, the resistor R may be provided between the diodes D1 and D2, and the connection point between the switches SW1 and SW2 It may be provided between the diode D1. Further, although the diode D1 is used as a constant voltage element and the diode D2 is used as a backflow prevention element, these elements are not limited to the diode.

It is a circuit diagram which shows the principal part of one Embodiment (Embodiment 1) of the power supply circuit which concerns on this invention. It is a figure which shows the voltage waveform (waveform between F1-GND) which appears in the terminal F1 for filaments in Embodiment 1. FIG. It is a figure which shows the voltage waveform (waveform between F2-GND) which appears in the terminal F2 for filaments in Embodiment 1. FIG. It is a figure which shows the voltage waveform (waveform between F1-F2) between the terminals F1-F2 for filaments in Embodiment 1. FIG. It is a circuit diagram which shows the principal part of other embodiment (Embodiment 2) of the power supply circuit which concerns on this invention. It is a figure which shows the voltage waveform (waveform between F1-GND) which appears in the terminal F1 for filaments in Embodiment 2. FIG. It is a figure which shows the voltage waveform (waveform between F2-GND) which appears in the terminal F2 for filaments in Embodiment 2. FIG. It is a figure which shows the voltage waveform (waveform between F1-F2) between the terminals F1-F2 for filaments in Embodiment 2. FIG. It is a block diagram which shows the conventional general fluorescent display tube and the circuit attached to this fluorescent display tube. It is a block diagram which shows the conventional power supply circuit which makes the DC voltage for anodes / grids, and drives a filament pulse. It is a wave form diagram which shows operation | movement of this power supply circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fluorescent display tube, 2 ... Envelope, 3 ... Phosphor, 4 ... Anode electrode, 5 ... Anode, 6 ... Cathode (filament), 7 ... Grid, 8 ... Anode substrate, 12 ... Drive circuit, 13, 13 '... Control circuit, 14 ... Boost circuit, 15, 15' ... Cutoff circuit, L1 ... Input line, L2 (GND) ... Ground line, SW1 ... First switch, SW2 ... Second switch, SW3 ... Third Switch, SW4 ... fourth switch, R ... resistor, D1 ... diode (backflow prevention element), D2 ... diode (constant voltage element), C1, C2 ... capacitor, Pin ... input terminal, Pout ... output terminal, F1, F2 ... Filament terminal, 300, 300 '... Power supply circuit.

Claims (2)

The fluorescent display device includes a cathode that emits electrons, an anode that receives electrons emitted from the cathode, and a grid that is disposed between the cathode and the anode and controls electrons emitted from the cathode. A fluorescent display device power supply circuit,
First and second switching elements connected in series between a DC voltage input line and a ground line;
A series connection circuit comprising a resistor, a backflow prevention element and a constant voltage element connected in series with each other, and connected in parallel to the first switching element;
A first capacitor connected between an input end and an output end of the constant voltage element;
A first terminal connected to a connection point between the input terminal of the constant voltage element and the first capacitor;
A second capacitor connected between a second terminal and the ground line;
Control means for alternately turning on and off the first switching element and the second switching element;
The first switching element is connected as an input line side of the DC voltage with respect to the second switching element,
The backflow prevention element is connected as an input line side of the DC voltage from the constant voltage element,
A power supply circuit for a fluorescent display device, wherein the cathode is connected between the first terminal and the second terminal. The fluorescent display device includes a cathode that emits electrons, an anode that receives electrons emitted from the cathode, and a grid that is disposed between the cathode and the anode and controls electrons emitted from the cathode. A fluorescent display device power supply circuit,
First and second switching elements connected in series between a DC voltage input line and a ground line;
A third and a fourth switching element connected in series between the DC voltage input line and the ground line;
A series connection circuit comprising a resistor, a backflow prevention element and a constant voltage element connected in series with each other, and connected in parallel to the first switching element;
A first capacitor connected between an input end and an output end of the constant voltage element;
A first terminal connected to a connection point between the input terminal of the constant voltage element and the first capacitor;
A second capacitor connected between a connection point between the third switching element and the fourth switching element and a second terminal;
The first switching element and the fourth switching element serve as a first switching element pair, and the second switching element and the third switching element serve as a second switching element pair. Control means for alternately turning on and off the switching element pair and the second switching element pair,
The first switching element is connected as an input line side of the DC voltage with respect to the second switching element,
The third switching element is connected as an input line side of the DC voltage with respect to the fourth switching element,
The backflow prevention element is connected to the input line side of the DC voltage from the constant voltage element,
A power supply circuit for a fluorescent display device, wherein the cathode is connected between the first terminal and the second terminal.

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