JP4409679B2 - Filament drive circuit for fluorescent display tube - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a filament driving circuit for a fluorescent display tube.
[0002]
[Prior art]
A fluorescent display tube (hereinafter referred to as VFD) is composed of a segment (anode), a grit, and a filament (cathode). Power is supplied to the filament to generate heat, thereby generating thermoelectrons. It is a display element that emits light by accelerating electrons and colliding the segment phosphors with thermionic electrons. The filament voltage applied to the VFD filament is determined by the filament length and filament diameter inside the VFD.
[0003]
[Problems to be solved by the invention]
Since the filament voltage is preferably an AC voltage, the conventional filament drive circuit has a configuration using a power transformer 20 as shown in FIG. In FIG. 4, 21 is a VFD filament. In actual products, VFD sizes vary widely, and the filament voltage also has a different value for each type of VFD. For this reason, in the conventional filament driving circuit shown in FIG. 4, it is necessary to change the type of the transformer 20 for each type of VFD, and the work such as circuit design, reliability test and parts arrangement becomes complicated. It was. Further, the conventional filament driving circuit has a problem that it is difficult to change the filament voltage unless the transformer 20 is changed.
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a filament driving circuit that does not require a transformer for each type of VFD and can easily change the filament voltage.
[0004]
[Means for Solving the Problems]
The filament driving circuit for a fluorescent display tube of the present invention has a control means (1-6) for outputting a pulse width modulation signal having a duty ratio according to setting data inputted from the outside, and a phase outputted from the control means is different. Alternately connecting the high potential side and the low potential side according to the pair of pulse width modulation signals is performed for each pulse width modulation signal to generate a pair of pulse voltages F1 and F2 having different phases , and the pair of pulses Output means (8, 9) for applying an alternating pulse voltage to the filament so that both ends of the filament are alternately connected to the high potential side by applying voltages F1, F2 to both ends of the filament of the fluorescent display tube. ).
Also, as one configuration example of the filament driving circuit for a fluorescent display tube of the present invention, the output means is configured such that when the filament voltage is turned off, the application of the pulse voltages F1 and F2 is stopped according to the pulse width modulation signal. Are connected to the low potential side.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a filament driving circuit according to an embodiment of the present invention, and FIG. 2 is a timing chart showing the operation of the filament driving circuit of FIG.
The filament driving circuit of FIG. 1 compares the binary counter 1 that counts the clock signal CLK input from the outside, the setting data D0 to D5 input from the outside, and the data DK0 to DK5 input from the binary counter 1. The comparison circuit 2 that outputs the comparison result signal COMP, the counter 3 that counts the clock signal CLK, the inverter 4 that logically inverts the output signal Tc of the counter 3, and the logical product of the comparison result signal COMP and the signal Tc. A positive voltage Vfs is applied to the AND circuit 6 that takes the logical product of the AND circuit 5 that takes the comparison result signal COMP and the signal bar Tc input from the inverter 4, and the filament 11a of the fluorescent display tube 11 (hereinafter referred to as VFD). Filament power supply 7 for supplying and pulse width modulation signal inputted from AND circuit 5 with voltage Vfs An output circuit 8 that turns on / off according to CTL1, an output circuit 9 that turns on / off the voltage Vfs according to the pulse width modulation signal CTL2 input from the AND circuit 6, a power supply voltage to the anode 11b and the grid 11c of the VFD 11 Drive power supply 10 for supplying
[0006]
The binary counter 1, the comparison circuit 2, the counter 3, the inverter 4, and the AND circuits 5 and 6 constitute control means for outputting pulse width modulation signals CTL1 and CTL2 having a duty ratio corresponding to setting data input from the outside. Yes.
Next, the operation of such a filament drive circuit will be described. The 6-bit binary counter 1 repeatedly counts an externally input clock signal CLK from 0 to 63, and outputs the count value as 6-bit digital data DK0 to DK5.
[0007]
The comparison circuit 2 compares the 6-bit digital data (setting data) D0 to D5 input from the outside with the 6-bit digital data DK0 to DK5 input from the binary counter 1, and the data DK0 to DK5 is the data D0. When it is smaller than .about.D5, the comparison result signal COMP of "H" level is output. When the data DK0 to DK5 is equal to or more than the data D0 to D5, the comparison result signal COMP of "L" level is output. As a result, a comparison result signal COMP as shown in FIG.
[0008]
The 6-bit digital data D0 to D5 is setting data for setting the duty ratio of the pulsed output voltages F1 and F2 applied to the filament 11a. By taking a value of 0 to 63, the duty ratio is set. It can be set to 0-1.
[0009]
Next, the counter 3 repeats counting the externally input clock signal CLK from 0 to 63 and finishes counting 64 times from 0 to 63 (every time the count value is reset to 0). The output signal Tc is inverted. As a result, the output signal Tc alternately repeats the “L” level and the “H” level as shown in FIG.
[0010]
The inverter 4 logically inverts the signal Tc input from the counter 3 and outputs the output signal bar Tc (FIG. 2 (c)).
The AND circuit 5 calculates the logical product of the comparison result signal COMP input from the comparison circuit 2 and the signal Tc input from the counter 3, and outputs the result of the logical product as a pulse width modulation signal CTL1.
The AND circuit 6 calculates the logical product of the comparison result signal COMP input from the comparison circuit 2 and the signal bar Tc input from the inverter 4, and outputs the result of the logical product as a pulse width modulation signal CTL2.
[0011]
The output circuits 8 and 9 turn on / off the positive DC voltage Vfs supplied from the filament power supply 7 according to the pulse width modulation signals CTL1 and CTL2, and output the pulsed output voltages F1 and F2 by this on / off control. Apply to filament 11a.
FIG. 3A is a block diagram showing the configuration of the output circuits 8 and 9, and FIG. 3B is a circuit diagram showing an example of the actual circuit configuration of the output circuits 8 and 9.
[0012]
The switch 8a constituting the output circuit 8 is turned on when the pulse width modulation signal CTL1 is at “H” level, and connects the first terminal of the filament 11a to the high potential side (voltage Vfs). When it is at the “L” level, it is turned off, and the first terminal is connected to the low potential side (ground).
Similarly, the switch 9a constituting the output circuit 9 is turned on when the pulse width modulation signal CTL2 is at “H” level, and connects the second terminal of the filament 11a to the high potential side, and the signal CTL2 becomes “L”. ”Level to turn off and connect the second terminal to the low potential side.
[0013]
In this way, pulsed output voltages F1 and F2 as shown in FIGS. 2D and 2E are applied to the filament 11a. When the switch 8a is turned on and the switch 9a is turned off, the filament current flows in the direction of the switch 8a → the filament 11a → the switch 9a → the ground. When the switch 9a is turned on and the switch 8a is turned off, the filament current flows in the direction of the switch 9a → the filament 11a → the switch 8a → the ground.
[0014]
In an actual circuit, the switch 8a includes an N channel transistor 8b and a P channel transistor 8c, and the switch 9a includes an N channel transistor 9b and a P channel transistor 9c.
As described above, in this embodiment, the filament voltage can be easily changed by setting data by using a pulse width modulation type driving circuit.
[0015]
The filament 11a has a function as a cathode (cathode) into which a cathode current flows, in addition to the function of self-heating. In the present embodiment, when the filament voltage is turned off, the output circuits 8 and 9 connect the terminal of the filament 11a to the low potential side (ground). Therefore, the filament is operated as a cathode even when the filament voltage is turned off. And the luminous efficiency can be improved.
[0016]
【The invention's effect】
According to the present invention, by providing the control means and the output means, the duty ratio of the output voltage can be easily changed by the setting data inputted from the outside, whereby the filament voltage can be easily changed. it can. As a result, there is no need to prepare a power transformer for each type of fluorescent display tube as in the prior art, and operations such as circuit design, reliability test, and parts arrangement are facilitated. In addition, since the filament voltage can be easily changed, for example, control that is impossible with a conventional circuit such as lowering the filament voltage in the power saving mode at night becomes possible. Further, since it is not necessary to use a power transformer such as a conventional filament driving circuit, the circuit can be miniaturized.
[0017]
In addition, when the output means is turned off in response to the pulse width modulation signal, the filament terminal is connected to the low potential side, so that the filament can be operated as a cathode even when the filament voltage is turned off. Can be improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a filament drive circuit according to an embodiment of the present invention.
FIG. 2 is a timing chart showing the operation of the filament drive circuit of FIG.
FIG. 3 is a block diagram illustrating a configuration of an output circuit and a circuit diagram illustrating an example of an actual circuit configuration of the output circuit.
FIG. 4 is a circuit diagram of a conventional filament driving circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Binary counter, 2 ... Comparison circuit, 3 ... Counter, 4 ... Inverter, 5, 6 ... AND circuit, 7 ... Filament power supply, 8, 9 ... Output circuit, 10 ... Drive power supply, 11 ... Fluorescent display tube, 11a ... Filament, 11b ... anode, 11c ... grid.

Claims (2)

Control means for outputting a pulse width modulation signal having a duty ratio according to setting data inputted from the outside;
According to a pair of pulse width modulation signals with different phases output from the control means, the high potential side and the low potential side are alternately connected for each pulse width modulation signal, and a pair of pulse voltages F1, F1 with different phases are connected . By generating F2 and applying the pair of pulse voltages F1 and F2 to both ends of the filament of the fluorescent display tube, the AC pulse voltage is changed to connect the both ends of the filament alternately to the high potential side. And a filament driving circuit for a fluorescent display tube. The filament drive circuit for a fluorescent display tube according to claim 1,
The output means connects the both ends of the filament to a low potential side when the filament voltage at which application of the pulse voltages F1 and F2 is stopped according to the pulse width modulation signal is turned off. Filament drive circuit.

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