JPH02232686A - Power source device for fluorescent display tube - Google Patents

Abstract

PURPOSE:To obtain a stable voltage for display erasure with simple and inexpensive circuit constitution by superposing a voltage, obtained by rectifying the output of 2nd secondary winding on a half-wave basis and smoothing it, upon a reference voltage in a negative direction. CONSTITUTION:A power source transformer 21 for a control circuit is equipped with primary winding to which a commercial AC power source is connected, 1st secondary winding S1, and the 2nd secondary winding S2. The output of the 2nd secondary winding S2 is applied to a heater 273 through a resistance R4 connected in series with the heater 273 of a fluorescent display tube 27. The voltage VP for display erasure which is applied to the anode 217 and grid 272 of the fluorescent display tube is obtained by superposing the voltage VD, obtained by rectifying the output of the 2nd secondary winding S2 on a half- wave basis and smoothing it, upon the reference voltage VD. A voltage VP applied to the heater 273 is made less in amplitude than the voltage across the 2nd secondary winding S2 by a resistance R4, so the voltage VP for display erasure is lower than the heater voltage. Consequently, the stable voltage for display erasure is obtained with the simple and inexpensive circuit constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a power supply device for a fluorescent display tube, and particularly for home appliances such as a microwave oven, an electronic jar rice cooker, etc. equipped with a fluorescent display tube as a display means. Regarding a power supply device for a fluorescent display tube suitable for the product.

(Prior Art) FIG. 5 shows a circuit of an example of a conventional power supply device for a fluorescent display tube. A commercial AC power source is connected to the primary winding of the control circuit NR transformer 1. The secondary side of the power transformer 1 includes a first secondary winding SI and a second secondary winding S2. The output of the first secondary winding S, is connected to four diodes D,
-D, is rectified by a bridge type full-wave rectifier circuit 2, and smoothed by a capacitor 3. As a result, a DC voltage ■ is obtained. Stabilization circuit 4 and capacitor 5
A stabilized DC voltage vD is obtained from the DC voltage V, and the DC voltage VD is supplied to the power supply terminal of the microcomputer 6.

The micro combinator 6 has a built-in display register and the like for controlling the display state of the fluorescent display tube 7. The display state of the fluorescent display tube 7 is controlled according to the contents of the display register. In FIG. 5, two switches SW and S
W2 schematically indicates the function of the display register. The fluorescent display tube 7 is in a non-display state when the switches SW and SW2 are open;
And when SW2 is closed, it is in the display state.

The output of the second secondary winding S2 is half-wave rectified by a diode D5 and applied to the heater 73 of the fluorescent display tube 7. A voltage doubler rectifier circuit 8 constituted by diodes D6 and D7 and capacitors C2 and C is further connected to the second secondary winding S2.

The voltage obtained by the voltage doubler rectifier circuit 8 is voltage ■. The anode 7l of the fluorescent display tube 7 and the grid 7
The display erasing voltage V, which is applied to 2, is obtained.

A timing detection circuit 9 consisting of a diode DI1 and a resistor R is connected between the secondary winding S and the anode of the diode D1. A node P, which is a connection point between the diode D of the timing detection circuit 9 and the resistor R3, is connected to the microcomputer 6 at tMH. has been done. By referring to the voltage at the node P, the microcomputer 6 is able to bring the fluorescent display tube 7 into a display state every half cycle of the commercial AC power supply.

FIG. 6 schematically shows the waveforms of the N source voltage vD1, heater voltage vE, and display erasing voltage V of the microcombinator 6 in the conventional power supply device described above.

(Problems to be Solved by the Invention) As home appliances such as microwave ovens and electronic rice cookers become more sophisticated, they are increasingly being equipped with various data display means. Fluorescent display tubes that display multiple digits are widely used as data display means in such home appliances.

A fluorescent display tube is equipped with an anode serving as a display body, a heater that emits electrons to the anode, and a grid that controls the amount of electrons reaching the anode.In the case of a multi-digit fluorescent display tube, The heaters are usually installed in common from the most significant digit to the least significant digit, and external terminals leading to the heaters are led out from both ends of the multi-digit fluorescent display tube. Therefore, the voltage drop across the heater is often so large that it cannot be ignored compared to the voltage between the heater anodes. For this reason, a problem has arisen in that the circuit for obtaining stable heater voltage and display erasing voltage becomes quite complex and expensive as shown in FIG.

The present invention was made in view of the current situation, and
The object is to provide a power supply device for a fluorescent display tube that is capable of obtaining a stable display erasing voltage using a relatively simple and inexpensive circuit.

(Means for Solving the Problems) A power supply device for a fluorescent display tube according to the present invention has first and second power supplies.
a power transformer having a secondary winding; a DC power source means for obtaining a stabilized DC voltage from the output of the first secondary winding;
means for applying a reference voltage based on the DC voltage of a predetermined portion within the DC power supply means to the output of the second secondary winding;
means having a resistor connected in series with the heater of the fluorescent display tube and applying an output of the second secondary winding to the heater via the resistor; and an output of the second secondary winding. means for obtaining a display erasing voltage to be applied to the grid and anode of the fluorescent display tube by superimposing a voltage obtained by half-wave rectification and smoothing on the reference voltage in a negative direction; operated by power supply means and comprising means for controlling the voltage applied to the grid and the anode, thereby achieving the above object.

(Function) A DC voltage stabilized by the DC power supply means is obtained from the output of the ml secondary winding of the power transformer.

A reference voltage based on the DC voltage of a predetermined portion within the DC power supply means is used as a reference potential for the output of the second secondary winding of the power transformer.

The second secondary winding output is applied to the heater of the fluorescent display tube through a resistor connected in series with the heater. The display erasing voltage applied to the anode and grid of the fluorescent display tube is obtained by superimposing a voltage obtained by half-wave rectifying and smoothing the second secondary @ line output on the reference voltage.

Since the voltage applied to the heater has an amplitude smaller than the voltage across the second secondary winding due to the resistance, the display erasing voltage is always lower than the heater voltage, and display erasing is reliably performed.

(Example) The invention will now be described with reference to examples.

FIG. 1 shows a circuit diagram of a first embodiment of the present invention.

The control circuit 14-source transformer 21 has a primary winding to which a commercial AC power source is connected, a first secondary winding S, and a second secondary winding S! Equipped with IS2.

A bridge type full-wave rectifier circuit 22 consisting of diodes D, to D4 is connected to the first secondary winding 11 S +.

The output of the rectifier circuit 22 is smoothed by the capacitor 23, so that the DC voltage V. is obtained. Rectifier circuit 2
A stabilizing circuit 24 and a capacitor 25 are connected to the downstream of the capacitor 2 and the capacitor 23, and a stabilized DC voltage vI is obtained by them. The stabilized DC voltage VD is supplied to the power terminal of the microcomputer 26.

The microcombi 26 has a built-in display register and the like for controlling the display state of the fluorescent display tube 27.

The microcombinator 26 generates signals for controlling the anode 271 and grid 272 of the fluorescent display tube 27 according to the contents of the display register. In FIG. 1, this control mechanism is schematically illustrated by two switches sw and sw2.

A timing detection circuit 29 including a diode D and a resistor R is connected between the anodes of the diodes of the rectifier circuit 22 and the first secondary winding S. A node P, which is a connection point between the diode D● and the resistor R3, is connected to the micro combinator 26. By referring to the voltage of the node P, the micro combinator 26
Commercial exchange 71! The fluorescent display tube 27 can be controlled so that display is performed every half cycle of [, thereby suppressing display unevenness.

One terminal of the second secondary winding S2 is connected to the heater 273 of the fluorescent display tube 27 via a resistor R4. Therefore, the voltage vF obtained by subtracting the voltage drop due to the resistor R4 from the voltage appearing across the secondary @R52 is applied to the heater 273. Heater voltage VF can be adjusted by the value of resistor R4.

A diode D is further connected to the terminal of the second secondary winding gAS2 so that the cathode becomes 82 ml of the secondary winding. The 7 nodes of the diode D6 are connected to the anode 27 of the fluorescent display tube 27 via resistors R and R2, respectively.
1 and grid 272. Diode D
A capacitor C5 is connected between a node R on the anode side of the secondary winding S2 and a node S on the other terminal side of the secondary winding S2. The output of the secondary winding s2 is half-wave rectified by a diode D6 and smoothed by a capacitor C5.

A diode D5 is connected between a node T and a node R in the IL source circuit connected to the first secondary winding S, so that the anode is on the 7th node R side. There is.

Therefore, even if the capacitor C is not provided, the voltage at the node R is the lower of the voltage at one terminal of the secondary winding s2 to which the diode D6 is connected and the voltage v at the node T. The voltage is the sum of the forward voltage drop of diode D or D6.

Node S is connected to node U in the circuit connected to the first secondary winding S, and therefore the voltage at node U is
, serves as a reference for the voltage in the circuit connected to the second secondary winding. Anode 271 and grid 2 of fluorescent display tube 27
The display erasing voltage vP applied to the capacitor 72 is obtained by superimposing the voltage across the capacitor cs on the voltage VD.

The operation of this embodiment will be explained with reference to FIG.

A heater voltage V adjusted by a resistor R4 is applied to the heater 273 of the fluorescent display tube 27. Heater voltage vF
As shown in FIG. 2, V changes periodically around the reference voltage VD. By applying the voltage, the temperature of the heater 273 increases and electrons are emitted.

The display erasing voltage 2 is the voltage 2 as can be seen from the voltage of the diode D6. will be lower than Also, the heater voltage V
, is determined by the voltage drop caused by the resistor R4 in the secondary winding S.
2, the display erasing voltage V, is lower than the heater voltage V, even during the period when the heater voltage V, is lower than the voltage V,.

In this way, the display erasing voltage V, is always the heater voltage V,
This ensures that the display on the fluorescent display tube 27 is erased. The broken line in Figure 2 shows the waveform of voltage V when capacitor C is not installed, but as can be seen from this waveform, if capacitor C5 is installed Even if there is no voltage V
, is always lower than the voltage V,.

In this embodiment, during the half cycle when the heater voltage vF is at a high level, the switch SW of the microcomputer 26 is
, and SW2 are closed, and the potentials of the anode 27l and the grid 272 rise to the ground potential, which is sufficiently higher than the potential of the heater 273. Therefore, the heater 2 is connected to the anode 271.
The electrons from 73 arrive, and the fluorescent substance on node 7 emits light, producing a display.

FIG. 3 shows a circuit diagram of a second embodiment of the invention.

The configuration of this embodiment is the same as that of the first embodiment except for the circuit connected to the second secondary winding IIS2, so corresponding parts are given the same reference numerals as in FIG. Their explanation will be omitted.

Among the circuits connected to the second secondary winding S2, the portion for applying voltage to the heater 273 of the fluorescent display tube 27 is the same as that in the first embodiment.

One terminal of the second secondary winding vaS2 is connected to the second
A diode D6 is connected to the secondary winding S2 side. Nodes R and 2 on the anode side of diode D8
A capacitor C5 is connected between the second winding S2 and the node S on the other terminal side. Node S is connected to a node T in the power supply circuit connected to the first secondary winding S,. The voltage V, therefore serves as a reference for the voltage in the circuit connected to the secondary winding S2. The output of the second secondary winding S2 is half-wave rectified by the diode D6, and the capacitor CG
smoothed by By superimposing the voltage across the capacitor C5 on the voltage V, a display erasing voltage V, is obtained. In addition, the /- node S is connected to the node U connected to the microcombi coater 26, and the capacitor C
It is also possible to obtain the display erasing voltage V by superimposing the voltage across the voltage VD on the voltage VD.

In this embodiment, the circuit connected to the second secondary winding S2 requires only one resistor, one diode, and one capacitor, and the circuit configuration is even simpler than in the first embodiment. be.

FIG. 4 shows voltage waveforms at various parts in this embodiment. As is clear from FIG. 4, in this embodiment as well, the display erasing voltage (2) is always kept lower than the heater voltage (V). Therefore, when the switches SW and SW2 are open, the display can be erased reliably. Incidentally, the broken line in FIG. 4 indicates the display erasing voltage V in the case where the capacitor C6 is not provided.

(Effects of the Invention) According to the present invention, a stable display erasing voltage can be obtained with a circuit configuration that is simpler and cheaper than the conventional one, and the fluorescent display tube can be stably operated. A power supply is provided for.

4. Figure 1 is a circuit diagram of the first embodiment of the present invention, and Figure 2 is a circuit diagram of the first embodiment of the present invention.
Figure 3 is a circuit diagram of the second embodiment of the present invention, and Figure 4 is a voltage waveform of each part in the second embodiment. Figure 5 showing the outline of
The figure is a circuit diagram of a conventional example, and FIG. 6 is a diagram schematically showing voltage waveforms at various parts in the conventional example.

DESCRIPTION OF SYMBOLS 21... Control power supply transformer, 26... Micro-combiner converter, 27... Fluorescent display tube, 271... Anode of fluorescent display tube, 272... Grid of fluorescent display tube,
273... Fluorescent display tube heater, D,, D2, D3
, D4, D6, D6...Diode, R4...Resistor, C,, C4, C5...Capacitor, S,...Secondary winding of the first winding, S2...Second secondary winding.

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Claims (1)

[Claims] 1. A power supply device for a fluorescent display tube, which comprises a power transformer having first and second secondary windings, and stabilization from the output of the first secondary winding. DC power supply means for obtaining a DC voltage of the second secondary winding; means for applying a reference voltage based on the DC voltage of a predetermined portion within the DC power supply means to the output of the second secondary winding; has a resistor connected in series with the heater,
means for applying the output of the second secondary winding to the heater via the resistor; and a voltage obtained by half-wave rectifying and smoothing the output of the second secondary winding to the reference voltage. means for obtaining a display erasing voltage to be applied to the grid and anode of the fluorescent display tube by superimposing the voltage in a negative direction; and a voltage operated by the DC power supply means and applied to the grid and the anode. A power supply device for a fluorescent display tube, comprising means for controlling.