JP5090328B2 - Fluorescent display tube power circuit device - Google Patents

Description

  The present invention relates to a power supply circuit device for a fluorescent display tube that generates a filament voltage and an acceleration voltage of the fluorescent display tube.

  The fluorescent display tube is fixed to a filament that emits thermoelectrons when a filament voltage is applied, a plurality of anodes to which a phosphor layer formed in a predetermined display pattern is fixed, and the plurality of anodes A plurality of grids for accelerating the thermoelectrons in the phosphor layer, and the phosphor layer on the anode to which the acceleration voltage is similarly applied within the selected range of the grid to which the DC acceleration voltage, that is, the display voltage is applied The phosphor is caused to emit light in a predetermined pattern by being caused to collide with thermionic electrons. The filament voltage requires a low voltage of, for example, several VAC to several tens of volts, and the acceleration voltage requires a relatively high voltage of, for example, about 30 to 70 VDC.

By the way, in order to obtain the filament voltage and the acceleration voltage, generally, separate AC power supply and DC power supply are required, but a power supply circuit device that shares a part has been proposed. For example, the power supply circuit device of the fluorescent display tube described in Patent Document 1 is this. According to this, a pair of differential pulse voltage signals with different phases (complementary) are generated by turning on / off the DC input voltage, and the AC voltage between the pair of differential pulse voltage signals is used as the filament voltage. Simultaneously with the output, the voltage doubler circuit can be used to boost the filament voltage to a relatively high DC voltage and output it as an acceleration voltage.
JP 2003-029711 A

  By the way, in the above-mentioned conventional fluorescent display tube power supply circuit device, since the output filament voltage and acceleration voltage cannot be directly controlled, a constant voltage circuit for stabilizing the DC input voltage is provided, and a stable DC input is provided. The filament voltage and accelerating voltage output are stabilized by using the voltage. For this reason, power consumption by the constant voltage circuit is relatively large, and sufficient efficiency cannot be obtained.

  The present invention has been made against the background of the above circumstances, and an object thereof is to provide a power supply circuit device for a fluorescent display tube with low power consumption.

The gist of the invention according to claim 1 for achieving the above object is that: (a) a pair of pulse voltage signals having different phases are generated from a DC input voltage input from a DC power supply; a switching circuit for outputting a differential voltage between the voltage pulse signal as a filament voltage of the fluorescent display tube to light displayed on the fluorescent display tube by half-wave voltage doubler rectifying the differential voltage between the pair of pulse voltage signal And a booster circuit that generates and outputs an acceleration voltage for the fluorescent display tube, and (b) inputs a potential difference value between the DC input voltage and the lowest value of the pair of pulse voltage signals. By feeding back to the side, the lowest value of the pair of pulse voltage signals is controlled so that the potential difference between the DC input voltage and the lowest value of the pair of pulse voltage signals becomes a constant value. And a filament voltage control circuit for stabilizing the filament voltage by controlling the back.

The gist of the invention according to claim 2 is that, in the invention according to claim 1, (c) between the line indicating the lowest value of the pair of pulse voltage signals and the ground level in the switching circuit. It is coupled to the ground level in a floating state via a capacitive element, and (d) further includes a power feedback circuit that boosts the terminal voltage of the capacitive element and feeds it back to the DC input voltage side.

According to the power supply circuit device for a fluorescent display tube of the first aspect of the invention, the filament voltage control circuit feeds back the value of the potential difference between the DC input voltage and the lowest value of the pair of pulse voltage signals to the input side. The minimum value of the pair of pulse voltage signals is controlled by the feedback control so that the potential difference between the DC input voltage and the minimum value of the pair of pulse voltage signals, that is, the amplitude value of the filament voltage becomes a constant value. with voltage is stabilized, an acceleration voltage thereof filament voltage is obtained by being allowed to half-wave voltage doubler rectification is also stabilized. Thus, since the filament voltage and the acceleration voltage can be stabilized without using a constant voltage circuit, the power consumption caused by the constant voltage circuit is unnecessary, and a power supply circuit device for a fluorescent display tube with low power consumption can be obtained. .

According to the power supply circuit device for a fluorescent display tube of the invention according to claim 2, the line between the line indicating the lowest value of the pair of pulse voltage signals and the ground in the switching circuit is grounded via a capacitive element ( GND) is coupled in a floating state, and is fed back by the filament voltage control circuit so that the potential difference between the DC input voltage and the lowest value of the pair of pulse voltage signals, that is, the amplitude value of the filament voltage is constant. When controlled, since any grid of the fluorescent display tube is set to the ground level when it is off, the voltage is lowered with respect to the filament, so that a sufficient cut-off voltage is formed. In addition, since a power period circuit for increasing the terminal voltage of the capacitive element and converting it to the input voltage is provided, the power consumption is lower than when a cutoff voltage is formed using a resistor. Less and higher efficiency is obtained.

  Hereinafter, an image display apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an example in which an image display apparatus 10 according to an embodiment of the present invention includes a typical fluorescent display tube 12 that performs image display by simple matrix driving. In FIG. 1, a fluorescent display tube 12 functions as an image display, and a plurality of linear cathodes (electron sources stretched by a pair of anchors 14 connected to filament terminals F1 and F2) Filament) K, a plurality of grids Gn connected to a plurality of grid lead wires 16, and a plurality of anodes connected to a plurality of anode lead wires 18, for example, a pair of glass plates via spacers It is provided in a vacuum container (not shown) constituted by being coupled together. In FIG. 2, a glass substrate 20 which is one of a pair of glass plates is provided with a large number of dot-like light emitting elements 22 made of phosphor layers formed on a large number of anode electrode patterns on one surface. A plurality of vertical grids Gn with a predetermined gap are fixed on the light emitting element 22 to the glass substrate 20, and a cathode with a predetermined gap is crossed on the grids Gn. It is erected. The glass substrate 20 has an anode terminal A1a connected to a plurality of light emitting elements 22 arranged at a predetermined interval among the light emitting elements 22 arranged in the horizontal direction, for example, a plurality of anode terminals A1a shown in FIG. An anode terminal A1b connected to a plurality of devices shown in FIG. 2B, an anode terminal A1c connected to a plurality of devices shown in FIG. 2C, and the like are provided for each horizontal row of the light emitting elements 22. Among the light emitting elements 22 positioned under the grid Gn to which the control voltage is applied, the one to which the acceleration (anode) voltage is applied emits light. In the fluorescent display tube 12 that functions as the image display, one light emitting element 22 functions as one display pixel.

  Returning to FIG. 1, the electronic control unit 26 is a so-called microcomputer having a CPU, a RAM, a ROM, and an input / output I / F. BK (Blanking) signal for processing the signal and prohibiting display of a small time interval at the switching timing of the display control cycle, light emission time (pulse width) corresponding to the multi-level luminance gradation represented by the display data D For example, a GCP (grayscale control pulse) signal, a LAT (latch) signal, and a plurality of grids Gn indicating timing pulses that gradually decrease from “35” to “0” with time. Control (acceleration) at a preset frequency and application time Grid signal that performs grid scan to apply voltage sequentially and periodically To output. The display data D is data indicating the luminance gradation of one pixel in an image memory of one frame in which an image to be displayed on the fluorescent display tube 12 is stored, and is supplied for each light emitting element 22 in a time division manner.

  The display drive control circuit 30 is provided for each of the anode terminals A1a, A1b, A1c, etc., and is controlled by the GCP signal, the LAT (latch) signal, the frequency set in advance for the plurality of grids Gn and the application time ( Acceleration) Based on a grid signal or the like that performs grid scanning in which voltages are sequentially and periodically applied, the multi-tone luminance is displayed on the light emitting element 22, and a driver (transistor) and the driver are driven. And an IC control circuit (driver IC) for control.

  The image display device 10 uses a filament voltage Ef applied to the filament terminals F1 and F2 of AC number V to several tens of volts and an acceleration voltage (display voltage) VBB, which is a source voltage of the grid voltage and anode voltage, as a direct current. A power supply circuit device 40 that generates from a DC input voltage Vi supplied from the power supply 38 is further provided. As shown in FIG. 1, the DC power source 38 is a device that outputs a DC voltage Vi of about 24V from a commercial AC voltage, for example. The power supply circuit device 40 generates a pair of first pulse voltage signal F1 and a second pulse voltage signal F2 that are complementary to each other from the DC input voltage Vi input from the DC power supply 38, and have a pair of these. A switching circuit 42 that outputs a differential voltage (F1-F2) between the first pulse voltage signal F1 and the second pulse voltage signal F2 as the filament voltage Ef of the fluorescent display tube, and the pair of the first pulse voltage signal F1 and the first pulse voltage signal F1 A booster circuit 44 for generating and outputting an acceleration voltage VBB for lighting and displaying on the fluorescent display tube 12 by rectifying the differential voltage (F1-F2), that is, the filament voltage Ef, between the two pulse voltage signals F2; The potential difference (Vi-Vk) between the DC input voltage Vi and the lowest value Vk of the first pulse voltage signal F1 and the second pulse voltage signal F2, that is, the filament A filament voltage control circuit 46 to stabilize the filament voltage Ef by feedback control so that the amplitude of the pressure Ef is a constant value, a.

  In the power supply circuit device 40, between the line L1 indicating the minimum value Vk of the filament voltage Ef in the switching circuit 42 and the ground GND, the ground GND is connected via a capacitor C5 made of, for example, an electrolytic capacitor functioning as a capacitive element. The power feedback circuit 46 is further coupled to the level in a floating state, and boosts the positive terminal voltage Vk of the capacitor C5 and feeds it back to the input line L2 of the DC input voltage Vi.

  For example, as shown in FIG. 3, the switching circuit 42 includes four switching transistors arranged in an H shape and driven by four kinds of drive pulses P1, P2, N1, and N2 output from the electronic control unit 26 (see FIG. 3). Power MOS FET) It is composed of an H bridge circuit including TR1, TR2, TR3, TR4. The four types of drive pulses P1, P2, N1, and N2 are those shown in FIG. 4 and all have the same period T, but the phases of the drive pulses P1 and P2 are 180 degrees different between them. N1 and N2 are 180 degrees out of phase with each other and the duty ratio D (= t / T) is ½. The duty ratio D does not necessarily have to be 1/2, but is used to make the cutoff as low as possible. The switching transistors TR1 and TR2 are Pch power MOS FETs (for example, 4V drive enhancement type), and TR3 and TR4 are Nch power MOS FETs. The switching transistors TR1 and TR3 and TR2 and TR4 provided in series are provided with a slight time difference in the ON operation so as not to be simultaneously turned on. Since the switching transistors TR1 and TR2 and TR3 and TR4 are the same operation, only the operation is reversed, the operation of the switching transistors TR1 and TR3 for generating the first pulse voltage signal F1 will be described below. To do.

  In FIG. 3, when drive pulses P1 and N1 are input via the buffers ICa and ICc, the coupling capacitors C1 and C3 are charged with voltages through the Zener diodes ZD1 and ZD3. The resistors R1 and R3 are for discharging the gate when the drive pulses P1 and N1 are stopped (low level) to turn off the switching transistors TR1 and TR3. Zener diodes ZD1 and ZD3 enable charging of coupling capacitors C1 and C3 and prevention of overcharging. If the drive pulse P1 is at a low level (eg, 0V), the switching transistor TR1 is turned on. If the drive pulse P1 is at a high level (eg, 5V), the switching transistor TR1 is turned off. If the driving pulse N1 is at a high level (for example, 5V), the switching transistor TR3 is turned on. If the driving pulse P1 is at a low level (for example, 0V), the switching transistor TR3 is turned off. Therefore, when the drive pulses P1 and N1 are input as shown in FIG. 4, the first pulse voltage signal F1 output from the first filament terminal has a pulse waveform in response to the on / off states of the switching transistors TR1 and TR3. Is done. Similarly, when the drive pulses P2 and N2 are input as shown in FIG. 4, the second pulse voltage signal F2 output from the second filament terminal is a pulse waveform in response to the on / off states of the switching transistors TR2 and TR4. It is said. A voltage between the first filament terminal and the second filament terminal, that is, a filament voltage (AC) Ef (= F1−) which is a differential voltage between the first pulse voltage signal F1 and the second pulse voltage signal F2. F2) is generated as shown in FIG.

  Returning to FIG. 3, the booster circuit 44 is composed of a double rectifier circuit including rectifier diodes D1, D2, D3 and charging capacitors Co1, Co2, Co3. In this case, the charging voltages Vco1, Vco2, and Vco3 of the charging capacitors Co1, Co2, and Co3 are Vi-Vk. Therefore, if the number of the rectifier diodes and the charging capacitors is n, it is doubled according to the following general formula. A desired acceleration voltage VBB which is a rectified output voltage can be obtained.

VBB = ((Vi−Vk) × n) + Vk

  In the fluorescent display tube 12, the grid-anode voltage ebc applied to the grid Gn and the anode terminals A1a, A1b, A1c, etc. via the grid driver and the anode driver is the difference voltage between the acceleration voltage VBB and the average value Ek of the filament voltage. (VBB-Ek). Here, when the duty ratio of the first pulse voltage signal F1 and the second pulse voltage signal F2 is D, the filament voltage Ek is expressed by Ek = Vk + (Vi−Vk) × D. The anode voltage ebc is expressed by the following formula. In this equation, if n and D are constants, the grid-anode voltage ebc becomes (constant) × (constant value) by controlling so that (Vi−Vk) is constant. Regardless of the variation of Vi, it is stabilized at a constant value. At the same time, the filament voltage Ef becomes Ef = (Vi−Vk) × √ (2 × D) = (constant) × (constant value), so that the filament voltage Ef is stabilized to a constant value regardless of the fluctuation of the power supply voltage Vi. Is shown. For example, a value of about ½ is used as the duty ratio D.

ebc = (VBB-Ek)
= N * Vi- (n-1) Vk- [Vk + (Vi-Vk) * D]
= (N-D) x (Vi-Vk)

  Since (Vi -Vk) is the amplitude of the first pulse voltage signal F1 and the second pulse voltage signal F2, as shown in FIG. 4, the amplitude voltage (Vi -Vk) is the boost circuit 44. , The grid anode voltage ebc, which is a value obtained by subtracting D (Vi−Vk) from n times (Vi−Vk), is controlled to be constant. It can also be said that the grid anode voltage ebc is also stabilized at a constant value.

  The filament voltage control circuit 46 has a potential difference (Vi-Vk) between the DC input voltage Vi and the lowest value Vk of the first pulse voltage signal F1 and the second pulse voltage signal F2, that is, the amplitude of these voltage signals becomes a constant value. In order to stabilize the filament voltage Ef, which is the relative voltage of these voltage signals, to a constant value by feedback control as described above, for example, a configuration as shown in FIG. In FIG. 5, a Zener voltage Vz is generated in the Zener diode ZD5, and the first comparator IC1 has a divided voltage (Vi-Vz) * (Ri2 / (Ri1 + Ri2)) divided by resistors Ri1 and Ri2. Is compared with the divided voltage Vk × (Rk2 / (Rk1 + Rk2)) of the lowest value Vk of the first pulse voltage signal F1 and the second pulse voltage signal F2, and a signal indicating the potential difference DS is output. As shown in FIG. 6, the second comparator IC2 compares the potential difference DS with the triangular wave signal TS changing from the electronic control unit 26 and changing at a constant period T, and performs switching indicating the potential difference (= DS−TS). The signal SS is output to the switching transistor TR5. The switching transistor TR5 is turned on when the switching signal SS is a positive value, that is, the potential difference DS exceeds the triangular wave signal TS, and is turned off when the switching signal SS becomes a negative value. The switching transistor TR5 is inserted in a circuit for discharging the charging voltage of the charging capacitor C6, which is always charged by the lowest value Vk of the first pulse voltage signal F1 and the second pulse voltage signal F2, via the boost coil CL. The induced electromotive force generated in the booster coil CL when the discharge current to the ground GND is cut off by the switching transistor TR5 is led to the line L2 that leads the DC input voltage Vi through the rectifier diode D4, and the capacitor C5 is charged. The returned power is returned. For this reason, the filament voltage control circuit 46 also functions as a power feedback circuit.

  Further, in the filament voltage control circuit 46, the first pulse voltage signal F1 and the second pulse voltage signal F1 and the second pulse voltage signal F1 are set so that the potential difference DS becomes zero, in other words, the potential difference (Vi−Vk) becomes a constant zener voltage Vz. The minimum value Vk of the pulse voltage signal F2 is controlled. That is, the voltage value Vk is controlled so that the divided voltage (Vi−Vz) × (Ri2 / (Ri1 + Ri2)) compared with the first comparator IC1 is equal to the divided voltage Vk × (Rk2 / (Rk1 + Rk2)). If Ri1 = Rk1 and Ri2 = Rk2, then (Vi-Vz) = Vk and (Vi-Vk) = Vz (constant value). In FIG. 5, first, when the DC input voltage Vi decreases, (Vi−Vk) <Vz and the on-duty of the switching transistor TR5 (the ratio of the t section in the on state) increases, and the discharge current increases. Since Vk is lowered to Vk ′ (<Vk), (Vi−Vk ′) = Vz (constant value). On the other hand, when the DC input voltage Vi increases, (Vi-Vk)> Vz and the off-duty (off-state ratio) of the switching transistor TR5 increases, the discharge current decreases, and Vk becomes Vk "(> Vk). ), (Vi−Vk ″) = Vz (constant value). That is, in the filament voltage control circuit 46, when the duty ratio is D = t / T, the switching transistor TR5 is set such that Vk = (1-D) × Vi and D = (Vi−Vk) / Vi. The on-duty (ratio of t section in the on state) is controlled to regulate Vk.

  FIG. 7 shows an example of the waveform of the filament voltage Ef obtained by the voltage control operation of the filament voltage control circuit 46 when the duty ratio D is ½, and the amplitude voltage (Vi−Vk) is the boost circuit 44. The grid anode voltage ebc (= n (Vi-Vk) obtained by subtracting half (Vi-Vk) / 2 of the amplitude voltage from n (Vi-Vk) of n times obtained by double rectification by n. )-(Vi -Vk) / 2).

  As described above, according to the present embodiment, the filament voltage control circuit 46 causes the potential difference (Vi−Vk) between the DC input voltage Vi and the minimum value Vk of the pair of first pulse voltage signal F1 and second pulse voltage signal F2. ) That is, feedback control is performed so that the amplitude values of the first pulse voltage signal F1 and the second pulse voltage signal F2 become a constant value Vz, so that the filament voltage Ef (= F1-F2) is stabilized and the amplitude is The voltage (Vi−Vk) is doubled rectified n times by the booster circuit 44, so that the grid anode voltage ebc which is a value obtained by subtracting (Vi−Vk) / 2 from n times (Vi−Vk). Since it is controlled to be constant, the grid / anode voltage ebc is stabilized at a constant value. Thus, since the filament voltage Ef and the grid anode voltage ebc are stabilized without using a constant voltage circuit, the power consumption due to the constant voltage circuit becomes unnecessary, and the power source of the fluorescent display tube 12 with low power consumption. A circuit device 40 is obtained.

  Further, according to the power supply circuit device 40 of the present embodiment, the level between the line L1 indicating the lowest voltage value Vk in the switching circuit 42 and the ground GND is grounded (GND) level via the smoothing capacitor C5 (capacitance element). Are connected in a floating state by the filament voltage control circuit 46, and the potential difference (Vi -Vk) between the DC input voltage Vi and the lowest value Vk of the pair of first pulse voltage signal F1 and second pulse voltage signal F2, ie, When feedback control is performed so that the respective amplitude values of the first pulse voltage signal F1 and the second pulse voltage signal F2 become constant values, any grid of the fluorescent display tube 12 is set to the ground (GND) level when it is off. As a result, a low voltage is applied to the filament, so that a sufficient cut-off voltage is formed. Further, a resistor is further provided with a power feedback circuit (a part of the filament voltage control circuit 46) that boosts the positive terminal voltage Vk of the smoothing capacitor C5 and feeds it back to the DC input voltage Vi side. As compared with the case where the cut-off voltage is formed using the power consumption, the power consumption is reduced, and higher efficiency can be obtained.

  As mentioned above, although this invention was demonstrated in detail with reference to drawings, this invention can be implemented also in another aspect.

  For example, in the filament voltage control circuit 46 of the above-described embodiment, the minimum value Vk of the pair of first pulse voltage signal F1 and second pulse voltage signal F2 is such that (Vi−Vk) = Vz (constant value). Even though the minimum value Vk of the pair of first pulse voltage signal F1 and second pulse voltage signal F2 is controlled so that (VBB-Vk) = (constant value), the filament voltage Ef and the grid are controlled. -The anode voltage ebc is stabilized. In this case, (VBB−Vk) = [n × Vi− (n−1) Vk] −Vk = n × Vi−n × Vk = n (Vi−Vk), so that (Vi−Vk) = (constant). Value) is substantially the same.

  In addition, the booster circuit provided in the filament voltage control circuit 46 of the above-described embodiment uses the induced electromotive force generated by intermittently passing the current of the booster coil CL, but instead of that, A circuit configuration similar to that of the booster circuit 44 using a diode and a capacitor may be employed.

  Further, in the switching circuit 42, the booster circuit 44, and the filament voltage control circuit 46 shown in FIG. 5 described above, a noise removal circuit, a power saving circuit, a signal smoothing circuit, and the like may be provided as necessary. .

  Further, in FIG. 5 described above, a shunt regulator or the like may be used instead of the Zener diode ZD5.

  The above description is only an example of the present invention, and the present invention can be variously modified without departing from the gist thereof.

1 is a diagram schematically illustrating a configuration of an image display device including a power supply circuit device according to an embodiment of the present invention. It is a figure explaining the structure in the fluorescent display tube with which the image display apparatus of the Example of FIG. 1 was equipped. FIG. 2 is a circuit diagram illustrating in detail a configuration example of a switching circuit and a booster circuit included in the power supply circuit device of the embodiment of FIG. 1. 2 is a time chart for explaining in detail the operation of the switching circuit provided in the power supply circuit device of the embodiment of FIG. 1; It is a circuit diagram explaining in detail the example of a structure of the filament voltage control circuit with which the power supply circuit apparatus of the Example of FIG. 1 was equipped. It is a time chart explaining the action | operation of the filament voltage control circuit with which the power supply circuit apparatus of the Example of FIG. 1 was equipped. It is a figure which shows an example of the filament voltage waveform obtained by the action | operation of the filament voltage control circuit of FIG. 1, and a booster circuit, the grid anode voltage ebc obtained by the double voltage rectification of the amplitude value (Vi-Vk), etc.

Explanation of symbols

12: Fluorescent display tube 38: DC power supply 40: Power supply circuit device 42: Switching circuit 44: Booster circuit 46: Filament voltage control circuit (power feedback circuit)
C5: Capacitor (capacitance element)

Claims (2)

A switching circuit that generates a pair of pulse voltage signals having different phases from a DC input voltage input from a DC power source, and outputs a differential voltage between the pair of pulse voltage signals as a filament voltage of a fluorescent display tube; in the power supply circuit device of a fluorescent display tube and a booster circuit for generating and outputting an acceleration voltage for lighting the display on the fluorescent display tube by half-wave voltage doubler rectifying the differential voltage between the pair of pulse voltage signal There,
By feeding back the value of the potential difference between the DC input voltage and the lowest value of the pair of pulse voltage signals to the input side, the lowest value of the pair of pulse voltage signals is controlled, and the DC input voltage and the pair of pulses are controlled. A power supply circuit device for a fluorescent display tube, comprising: a filament voltage control circuit that stabilizes the filament voltage by performing feedback control so that a potential difference from a minimum value of the voltage signal becomes a constant value. Between the switching circuit, the line indicating the lowest value of the pair of pulse voltage signals and the ground level are coupled in a floating state to the ground level via a capacitive element,
2. The fluorescent display tube power supply circuit device according to claim 1, further comprising a power feedback circuit that boosts the terminal voltage of the capacitive element and feeds it back to the DC input voltage side.

Images