JPH09138382A - Negative power source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an excellent liquid crystal display picture state without using a high precision circuit element. SOLUTION: A negative power source circuit 15 of an LCD in front of a sewing-machine inputs an alternate signal to an input terminal 15a, and outputs a negative voltage based on the alternate signal from an output terminal 15b. An adjustment switch 11 for adjusting the LCD is provided. A CPU 12 controls a frequency variable circuit 14 inputting the alternate signal to the input terminal 15a according to the operation of the adjustment switch 11. The frequency variable circuit 14 varies its frequency within the range of 1kHz-20kHz.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative power supply device that generates a negative voltage required to drive a liquid crystal display.

[0002]

2. Description of the Related Art A positive power source and a negative power source are required to drive a liquid crystal display. The positive power source uses a power source such as a microcomputer or a logic circuit, and the negative power source is separately prepared. In addition, the liquid crystal display requires a negative power source because the contrast (contrast) of the screen varies from product to product due to variations in the product itself and the parts related to the power supply, and it is also possible to adjust it to the density desired by the user. The voltage value of is configured to be variably adjustable to adjust the shading. In this case, the voltage value of the negative power supply is, for example, about -8V with a center voltage of -8V in steps of 0.2V.
It is required to be variable in the range of -10V.

As an example of such a negative power supply device, FIG.
And the configuration shown in FIG. 8 is provided. This configuration,
As shown in FIG. 7, a contrast adjustment switch 1
It is composed of a CPU 2, a voltage adjustment signal generation circuit 3, a negative power supply generation circuit 4, and a voltage adjustment circuit 5. In this case, the negative power supply generation circuit 4 is configured to input an AC signal of, for example, 20 kHz from the voltage adjustment signal generation circuit 3 to generate a negative voltage of −12 V or less, and to apply the negative voltage to the voltage adjustment circuit 5. ing.

Then, the voltage adjusting circuit 5 outputs a negative voltage which is varied in the range of about -5V to -10V and in steps of 0.2V according to the duty of the PWM signal given from the voltage adjusting signal generating circuit 3. Is configured to.
Further, the voltage adjustment signal generation circuit 3 is configured to output a PWM signal having a duty corresponding to the voltage adjustment control signal given from the CPU 2. And adjustment switch 1
As a case where a dark switch for darkening the lightness of the screen of the liquid crystal display and a light switch for lightening the lightness are provided,
When the CPU 2 receives the signal from the dark switch, it outputs a voltage adjustment control signal necessary for adjusting the voltage so that the lightness of the screen is darker than the present, and on the other hand, when the signal from the light switch is received, It is configured to output a voltage adjustment control signal necessary for adjusting the voltage so that the shading becomes lighter than that at present.

[0005]

FIG. 8 shows a specific electric circuit configuration of the negative power supply generation circuit 4 and the voltage adjustment circuit 5 having the above-described conventional configuration. As shown in FIG. 8, the negative power supply generation circuit 4 includes a Zener diode, a transistor,
It is configured by connecting circuit elements such as diodes, capacitors, and resistors as shown in the figure. Here, since each circuit element of the negative power supply generation circuit 4 has product variations, the negative voltage output from the negative power supply generation circuit 4 may vary by about ± 2 V for each product. Even if such a voltage change occurs, a voltage of -12 V or less is output.

On the other hand, the voltage adjusting circuit 5 is constituted by connecting circuit elements such as operational amplifiers, capacitors and resistors as shown in FIG. 8, and is a so-called analog circuit. The voltage adjustment circuit 5 is configured to output a negative voltage having an accurate voltage value, specifically, a negative voltage with a voltage fluctuation of 0.5 V or less. A circuit element that is small, that is, highly accurate is used. Therefore, in the above-described conventional configuration, there is a problem that the manufacturing cost of the voltage adjusting circuit 5 is increased, which in turn increases the manufacturing cost of the entire device.

Therefore, an object of the present invention is to provide a negative power supply device which has a structure in which the negative voltage can be variably adjusted, but which does not require an expensive circuit using highly accurate circuit elements and can reduce the manufacturing cost. To provide.

[0008]

The negative power supply device of the present invention comprises:
In a negative power supply device that generates a negative voltage for a liquid crystal display based on an alternating current signal, negative power supply means for generating a negative voltage according to the frequency of an input alternating current signal, and the negative power supply device so as to make the light and shade of the liquid crystal display constant. It is characterized in that it is provided with variable means for varying the frequency of the AC signal input to the power supply means.

According to the above construction, the alternating voltage signal whose frequency is varied by the varying means so as to make the light and shade of the liquid crystal display constant is given to the negative power source means. Therefore, the negative voltage output from the negative power source means is used. When the liquid crystal display is driven, the shading becomes constant. Since the negative power supply means can be configured with the same circuit configuration as the negative power supply generation circuit of the conventional configuration, the configuration corresponding to the voltage adjustment circuit of the conventional configuration can be unnecessary. Also, the variable means for varying the frequency of the AC signal supplied to the negative power source means,
For example, it is configured by a logic array, and can be configured by a circuit that is almost equivalent to the circuit configuration of the conventional voltage adjustment signal generation circuit that outputs a plurality of PWM signals with different duty. That is, the provision of the variable means does not complicate the configuration. Therefore, it is possible to eliminate the need for an expensive circuit configuration that uses highly accurate circuit elements, even though the negative voltage can be variably adjusted.

Further, in the case of the above configuration, the variable means is
It is a preferable configuration to change the frequency of the AC signal input to the negative power supply means within a predetermined range. Further, it is preferable that the varying means varies the frequency of the AC signal input to the negative power source means, based on the characteristic relating to the portion forming the negative power source means.

On the other hand, it is preferable that the liquid crystal display is arranged on the main body of the sewing machine. In the case of this configuration, since the predetermined shade is captured from the beginning, it is easy to visually recognize the screen.
In the sewing machine, even if the screen of the liquid crystal display is difficult to see, it is practically impossible to tilt the sewing machine body in which the liquid crystal display is arranged to change the angle of the screen of the liquid crystal display (in particular, During sewing, it is impossible to tilt the sewing machine body because the cloth extends from the sewing machine to the sewing machine installation surface). For this reason, it is very convenient to see the screen of the liquid crystal display from the beginning.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in which the present invention is applied to a liquid crystal display arranged on a sewing machine main body of a domestic embroidery sewing machine will be described with reference to FIGS. First, in FIG. 3, which shows the schematic overall configuration of the sewing machine, the sewing machine main body 51 is configured to integrally have an arm portion 53 above a sewing machine bed 52. Arm part 5
A needle bar 55 having a needle 54 is provided at the distal end of 3, and a presser foot 56 is provided.

On the other hand, a needle plate 57 corresponding to the needle bar 55 is provided on the upper surface of the sewing machine bed 52, and the needle plate 57 is provided.
A hook mechanism (not shown) is provided on the lower surface side of. Although not shown, the needle bar 55, the shuttle mechanism, the cloth presser 56, and the like are synchronously driven by a sewing machine motor through a drive mechanism, so that the sewing operation is executed.

The sewing machine bed 52 is provided with an embroidery frame 58 for holding the work cloth during the embroidery sewing operation, and the embroidery frame 58, and thus the work cloth, is freely movable in the horizontal direction on the sewing machine bed 52. A horizontal movement mechanism 59 is provided for the purpose. In this case, the embroidery frame 58 has a substantially rectangular frame shape, and is composed of an outer frame and an inner frame, and a work cloth is sandwiched between them to hold the work cloth stretched inside the frame. It is like this.

Although not described in detail, the horizontal moving mechanism 59 includes a moving body 60 configured to freely move the embroidery frame 58 in the Y-axis (front-back) direction by a Y-axis motor (not shown). It is configured to be freely moved in the X-axis (left and right) direction by an X-axis motor that is not provided. Thus, the work cloth held by the embroidery frame 58 is moved by the horizontal movement mechanism 59 to an arbitrary position based on the unique XY coordinate system. Such a horizontal movement mechanism 5
The needle bar 55 is driven by the drive mechanism while moving the work cloth by 9, thereby performing the embroidery sewing operation.

A start / stop key 61 is provided on the front surface of the arm portion 53 on the distal end side, and a power switch 62 is provided on the lower portion of the right side wall surface of the sewing machine main body 51.
The external ROM card 63 is detachably mounted on the upper portion of the power switch 62. In addition to the embroidery, the embroidery sewing machine of the present embodiment can of course perform various types of general practical sewing (straight stitch, zigzag stitch, bleed stitch, etc.). In this case, the cloth presser 56 can be exchanged between the illustrated embroidery sewing and the practical sewing, and the horizontal movement mechanism 59 portion includes the sewing machine bed 52.
When the embroidery sewing is not performed, this portion can be removed together with the embroidery frame 58 and replaced with a flat table for general sewing.

A liquid crystal display (hereinafter referred to as LCD) 64, which is a display means for displaying various patterns and messages on the screen, is provided on the front surface of the arm portion 53. On the LCD 64, a pattern selection screen, a confirmation screen, etc., which are necessary for the user to perform embroidery, are displayed. In this configuration, L
The CD 64 cannot adjust the screen angle. still,
The screen shown in FIG. 3 is a gray scale adjustment screen. Further, a touch panel 65 is provided on the surface of the LCD 64. As is well known, the touch panel 65 is configured by arranging transparent electrodes vertically and horizontally, can detect a position touched by a user's finger, and functions as a so-called touch switch.

In the sewing machine main body 51, a sewing machine motor (driving mechanism), an X-axis motor of a horizontal movement mechanism 59, and a Y
A control device for controlling the shaft motor, the LCD 64, the touch panel 65, etc. is provided. This control device is mainly composed of a microcomputer, and has a function of controlling the sewing machine motor (driving mechanism), the X-axis motor of the horizontal movement mechanism 59, the Y-axis motor, the LCD 64, the touch panel 65, etc. , Control program for controlling embroidery sewing operation and practical sewing operation of the sewing machine, LCD
A control program 64 for display control, a data processing program for performing various data processing such as reading and editing of embroidery data, and the like are stored.

Further, in the main body 51 of the sewing machine, an LCD 64
There is provided a negative power supply device 66 (see FIG. 1) for supplying a negative power supply to drive the negative power supply device. A specific configuration of the negative power supply device 66 will be described later. By variably adjusting the negative voltage output from the negative power supply device 66, the LCD 64
It is possible to adjust the contrast of the screen.

When it is necessary to adjust the shading of the screen of the LCD 64, the control device displays the shading adjustment screen as shown in FIG. In this case, as the adjustment switch 11 for adjusting the lightness and darkness of the LCD 64, a darkness switch 11a for darkening the lightness and a lightness switch 11b for lightening the lightness are provided, and specifically, a dark character is displayed on the screen of the LCD64. And a display figure (triangle) for the dark switch 11a,
A display figure (triangle) for the light switch 11b and light characters are displayed.

Then, in this screen state, the dark switch 11
When the user touches the display graphic for a with a finger, the control device inputs a signal that the dark switch 11a is turned on based on the detection signal from the touch panel 65, while the display graphic for the light switch 11b is touched. When touched with, the control device is configured to input a signal indicating that the light switch 11b is turned on.

Next, the specific configuration of the negative power supply device 66 is shown in FIG.
It will be described according to. FIG. 1 is a diagram showing the negative power supply device 66 in a combination of functional blocks. As shown in FIG. 1, the negative power supply device 66 includes an adjustment switch 11, a CPU 12 that constitutes a part of the control device, an EEPROM 13 that is a storage unit, a frequency variable circuit 14 that is a variable unit, and a negative unit. It is composed of a negative power supply circuit 15 which is a power supply means.

Here, the negative power supply circuit 15 has an input terminal 15
The AC signal is input to a and a negative voltage corresponding to the input AC signal is output from the output terminal 15b. In this case, when the frequency f of the input AC signal is changed within a predetermined range, for example, 1 kHz to 20 kHz, the level of the negative voltage output is -5.
It can be varied in the range of V to -10V.
The specific circuit configuration of the negative power supply circuit 15 (see FIG. 2) will be described later.

The frequency variable circuit 14 is the CPU
12 has a function of receiving a voltage adjustment control signal from 12 and varying the frequency f of the AC signal given to the negative power supply circuit 15 in the range of 1 kHz to 20 kHz according to the voltage adjustment control signal. It is composed of a digital circuit. Further, as the adjustment switch 11, a dark switch that darkens the contrast of the screen of the liquid crystal display,
A light switch is provided to lighten the light and shade.

Then, the CPU 12 uses the adjustment switch 11
When the switch signal from the dark switch 11a is input,
The negative voltage output from the negative power supply circuit 15 is adjusted so that the shade becomes darker by the set amount than before (current), for example, the voltage adjustment control signal necessary for lowering the negative voltage by 0.2 V is output. The voltage adjustment control signal is provided to the frequency variable circuit 14. As a result, the frequency variable circuit 14 generates an AC signal having a frequency that lowers the negative voltage of the negative power supply circuit 15 by 0.2 V than before,
The AC signal is supplied to the negative power supply circuit 15.

On the other hand, when the CPU 12 receives a switch signal from the light switch 11b of the adjustment switch 11, the CPU 12 adjusts the negative voltage of the negative power supply circuit 15 so that the contrast becomes lighter by a set amount than before, for example, a negative voltage. Is output by 0.2 V, and the voltage adjustment control signal is supplied to the frequency variable circuit 14. As a result, the frequency variable circuit 14 makes the negative voltage of the negative power supply circuit 15 0.
An AC signal having a frequency to be increased by 2 V is generated and the AC signal is supplied to the negative power supply circuit 15.

Therefore, in the case of the above configuration, the adjustment switch 1
When the dark switch 11a or the light switch 11b of No. 1 is operated, the frequency variable circuit 14 changes the frequency of the AC signal according to the operation, and accordingly, the negative power supply circuit 15 has a range of about -5V to -10V. It is configured to output a negative voltage that is varied in steps of 0.2V. In the initial state (when the power is turned on), the negative power supply circuit 15 has, for example, -8V.
Is configured to output a negative voltage of, and accordingly, the liquid crystal display is configured to have a constant shade (shade that a general user is satisfied).

Further, the EEPROM 13 stores a correction value for correcting the output voltage fluctuation caused by the product variation of the circuit elements constituting the negative power supply circuit 15. Specifically, at the stage of shipping from the factory (at the stage where the product is almost completed), while changing the frequency of the AC signal supplied to the negative power supply circuit 15, the frequency of the AC signal and the negative power output from the negative power supply circuit 15 are changed. Measure the voltage value and
Frequency fmax corresponding to the maximum voltage (for example, -5V),
The frequency fmin corresponding to the minimum voltage (for example, -10V) is stored in the EEPROM 13 as a correction value.
In the case of the present embodiment, the center frequency ftyp corresponding to the center voltage (for example, -8V) is also stored in the EEPROM 13.

Now, a specific structure of the negative power supply circuit 15 will be described with reference to FIG. In FIG.
The collector of the first transistor 16, which is, for example, an NPN transistor, is connected to the + 24V DC voltage terminal 17. A Zener diode 18 and a capacitor 19 having the illustrated polarities are connected in parallel between the base of the transistor 16 and the ground. Further, a resistor 2 is provided between the collector and the base of the transistor 16.
0 is connected.

The emitter of the first transistor 16 is connected to the emitter of the second transistor 21, which is a PNP transistor, for example. This second
The collector of the transistor 21 is connected to the collector of the third transistor 22, which is an NPN transistor, for example. The emitter of this third transistor 22 is connected to ground. A resistor 24 and a diode 25 of the polarity shown in the figure are connected in series between the base of the third transistor 22 and the + 5V DC voltage terminal 23. A resistor 26 is connected between the emitter of the third transistor 22 and the ground.

On the other hand, the base of the second transistor 21 is connected via a resistor 27 to the collector of a fourth transistor 28 which is, for example, an NPN transistor. Further, a resistor 29 is connected between the emitter and the base of the second transistor 21.

Further, a diode 30 having the illustrated polarity is connected between the collector of the fourth transistor 28 and the intermediate connection point between the resistor 24 and the diode 25. Further, the base of the fourth transistor 28 has a resistor 3
1 is connected to the input terminal 15a. still,
The resistor 32 is connected between the base of the fourth transistor 28 and the ground.

On the other hand, a capacitor 33 is provided between the output terminal 15b and the intermediate connection point between the collector of the second transistor 21 and the collector of the third transistor 22.
And the diodes 34 of the polarities shown in the figure are connected in series. Between the connection point between the capacitor 33 and the diode 34 and the ground, the diode 3 having the polarity shown in FIG.
5 is connected. Further, a capacitor 36 and a resistor 37 are connected in parallel between the output terminal 15b and the ground.

Now, in the above-mentioned negative power supply circuit 15,
The voltage between the base and the emitter of the first transistor 16 is VBE, the voltage between the collector and the emitter of the second transistor 21 and the third transistor 22 is VCE, the zener voltage of the zener diode 18 is Vz, and the capacitor The capacitance of 33 is C, and the forward voltage of the diodes 34 and 35 is V
F, the current supplied from the negative power supply circuit 15 is i, the input terminal 1
Assuming that the frequency of the frequency signal given to 5a is f, the voltage V at the output terminal 15b is expressed by the following equation.

V = − (Vz−VBE−2 · VCE−2 · VF−i / (2πfC)) (1) From the above formula (1), the frequency f of the AC signal applied to the input terminal 15a and the output terminal 15b. It is understood that a linear relationship (hereinafter, referred to as FV characteristic) as shown in FIG. That is, the input terminal 15
If the frequency f of the AC signal given to a is changed, the negative voltage V of a desired voltage value from the output terminal 15b, for example, -5V-
It is possible to output a negative voltage V in the range of −10V and in steps of 0.2V.

Since the circuit elements constituting the negative power supply circuit 15 have product variations, the linear relationship between the frequency f of the frequency signal and the negative voltage V, that is, The FV characteristic fluctuates.
Specifically, the inclination of the FV characteristic changes as shown in FIG. 5 due to product variation in the capacitance C of the capacitor 33.

Further, the voltage VB of the first transistor 16
E, second transistor 21 and third transistor 22
Voltage VCE, zener voltage V of zener diode 18
As shown in FIG. 6, the level of the FV characteristic fluctuates due to the product variation of the forward voltage VF of z and the diodes 34 and 35.

Therefore, the negative voltage V of the negative power supply circuit 15 varies from product to product due to the above-described fluctuation of the FV characteristic. Therefore, in order to prevent such a variation, in the present embodiment, in the EEPROM 13, the frequency fmax corresponding to the maximum voltage Vmax of the negative voltage V and the minimum voltage Vmax.
The frequency fmin corresponding to min and the center frequency ftyp corresponding to the center voltage Vtyp are stored at the time of factory shipment. By reading this stored value, the CP
U12 is F− of the negative power supply circuit 15 including the product variation.
The V characteristic (see FIG. 6) can be seen. As a result, the CPU 12 can accurately output the negative voltage V of a desired value from the negative power supply circuit 15 by applying the voltage adjustment control signal to the frequency variable circuit 14 based on the FV characteristic. That is, it is possible to accurately correct the output voltage fluctuation of the negative power supply circuit 15 due to product variations.

Specifically, when it is desired to output the center voltage as the negative voltage V, the CPU 12 gives the frequency variable circuit 14 a voltage adjustment control signal such that the frequency variable circuit 14 outputs the frequency signal having the center frequency ftyp. Good. In addition, a change voltage value (for example, 0.2
The value obtained by dividing the difference between the maximum voltage and the minimum voltage by V), that is, the number of change steps is N, and with this N, (fmax-fmi
A value obtained by dividing n), that is, (fmax-fmin) / N is calculated, and a voltage adjustment control signal for changing the frequency f by the calculated value is applied to the frequency variable circuit 14. , The negative voltage V can be changed in increments of the change voltage value.

According to this embodiment having such a configuration, the frequency f of the AC signal is changed by the frequency changing circuit 14 based on the switch signal from the adjusting switch 11, and the changed AC signal is supplied to the negative power supply circuit 15. The negative power supply circuit 15 outputs the negative voltage V variably adjusted according to the voltage adjustment command. And
Since the negative power supply circuit 15 of the present embodiment can be configured by the same circuit configuration as the negative power supply generation circuit 4 (see FIG. 8) of the conventional configuration, the voltage adjustment circuit 5 of the conventional configuration (FIG. 7 and FIG. A configuration corresponding to (see FIG. 8) can be eliminated.

In the case of the above embodiment, the negative power supply circuit 15
The frequency variable circuit 14 for varying the frequency f of the AC signal given to the circuit is composed of, for example, a logic array, and has a voltage adjustment signal generating circuit 3 (see FIG. 7) of a conventional configuration that outputs a plurality of PWM signals with different duty. ) Is a circuit of a configuration almost equivalent to the circuit configuration. Therefore, by providing the frequency variable circuit 14, the negative power supply device 6 is provided.
The circuit configuration of 6 does not become more complicated than the conventional configuration.

Therefore, in the above embodiment, although the negative voltage can be variably adjusted, an expensive circuit using highly accurate circuit elements, specifically, the voltage adjusting circuit 5 having the conventional structure (see FIG. 8) is used. ) Can be eliminated. For this reason,
In the above embodiment, the manufacturing cost can be made considerably lower than that of the conventional configuration.

Further, in the above embodiment, the EEPROM 13
The frequency fmax corresponding to the maximum voltage of the negative voltage V, and
The frequency fmin corresponding to the minimum voltage is stored at the time of factory shipment. As a result, it becomes possible to correct the output voltage fluctuation caused by the product variation of the negative power supply circuit 15 based on the stored frequencies fmax and fmin (correction values). Therefore, the negative voltage V of the negative power supply circuit 15 can be accurately variably adjusted. In particular, in the above embodiment, the frequency fmax corresponding to the maximum voltage and the frequency fmin corresponding to the minimum voltage are stored. Therefore, even when the slope of the FV characteristic changes, the output voltage fluctuation of the negative power supply circuit 15 is suppressed. It can be corrected accurately, and highly accurate control can be realized.

In the above embodiment, the frequency fmax corresponding to the maximum voltage and the frequency fmin corresponding to the minimum voltage are stored as the correction values. However, the present invention is not limited to this, and F-V The frequency values f1 and f2 at two different arbitrary points on the characteristic may be stored.

Further, in the above embodiment, the EEPROM 13
Since the center frequency ftyp corresponding to the center voltage of the negative voltage V is stored in the inside, the negative voltage V of the center voltage value based on the above center frequency ftyp is stored in the negative power supply in the initial state without calculation. It can be output from the circuit 15, which simplifies control. Further, in the case of the above-described embodiment, in the initial state, the negative voltage V of the central voltage value output from the negative power supply circuit 15 is supplied to the LCD 64, so that the screen of the LCD 64 becomes a constant shade from the beginning. Therefore, it is easy to visually recognize the screen of the LCD 64.

Here, in the sewing machine, even if the screen of the LCD 64 is difficult to see, it is practically impossible to tilt the sewing machine main body 51 in which the LCD 64 is arranged to change the angle of the screen of the LCD 64. . Especially during sewing, the cloth extends from the sewing machine to the sewing machine installation surface, etc.
It is impossible to tilt the sewing machine body 51. For this reason,
If the screen of the LCD 64 is easy to see from the beginning (when the power is turned on),
It is very convenient for the user.

Further, as in the above embodiment, the adjustment switch 11 for adjusting the lightness and darkness of the LCD 64 is softened by the LCD 6.
In the case of the configuration displayed on the screen of No. 4 (see FIG. 3), even if the predetermined shade is not captured from the time of shipment (from the beginning) of the sewing machine, it is difficult to perform even the work of adjusting the shade. Further, in such a configuration in which the light and shade adjustment is executed by software, the work of the light and shade adjustment is more troublesome than in the configuration in which the adjustment switches are individually arranged, and the adjustment is apt to be neglected. Therefore, in such a sewing machine, it is further desired that a predetermined shade is obtained from the time of shipment of the sewing machine, and the sewing machine of the above-described embodiment meets such a request.

Further, in the above embodiment, the EEPROM 13
Although the storage means is configured by the above, it is not limited to this, and may be configured by a RAM with a backup function, an EPROM, or the like.

[0049]

As is apparent from the above description, the present invention provides a negative power supply means for generating a negative voltage according to the frequency of an input AC signal, and a negative power supply means for keeping the light and shade of a liquid crystal display constant. Since the configuration is provided with the variable means for varying the frequency of the AC signal input to the device, the negative voltage can be variably adjusted, but an expensive circuit that uses highly accurate circuit elements is not required and the manufacturing cost is reduced. It has an excellent effect that it can be cheaper.

Further, it is preferable to arrange the liquid crystal display on the sewing machine main body. In the case of this configuration, since the predetermined shade is captured from the beginning, it is easy to visually recognize the screen. In particular, in the case of a sewing machine, even if it is difficult to see the screen of the liquid crystal display, it is practically impossible to tilt the sewing machine body on which the liquid crystal display is placed to change the angle of the screen of the liquid crystal display. Therefore, the fact that the screen of the liquid crystal display is easy to see is very convenient.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is an electric circuit diagram of a negative power supply circuit.

FIG. 3 is a perspective view of the entire sewing machine.

FIG. 4 is a diagram showing FV characteristics.

FIG. 5 is a diagram showing a case where the slope of the FV characteristic changes.

FIG. 6 is a diagram showing a case where the level of the FV characteristic changes.

FIG. 7 is a diagram corresponding to FIG. 1 showing a conventional configuration.

FIG. 8 is a diagram corresponding to FIG. 2;

[Explanation of symbols]

11 is an adjustment switch, 12 is a CPU, 13 is EEPRO
M (storage means), 14 is a frequency variable circuit (variable means),
Reference numeral 15 is a negative power supply circuit (negative power supply means), 16 is a first transistor, 18 is a zener diode, 21 is a second transistor, 22 is a third transistor, 28 is a fourth transistor, 33 is a capacitor, and 34 is Diode, 3
5 is a diode, 51 is a sewing machine main body, 64 is an LCD (liquid crystal display), and 66 is a negative power supply device.

Claims (4)

[Claims] 1. A negative power supply device for generating a negative voltage for a liquid crystal display based on an alternating current signal, wherein a negative power supply means for generating a negative voltage according to the frequency of an input alternating current signal and a constant shade of the liquid crystal display. As described above, the negative power source device is provided with a variable unit for varying the frequency of the AC signal input to the negative power source unit. 2. The negative power supply device according to claim 1, wherein the variable means changes the frequency of the AC signal input to the negative power supply means within a predetermined range. 3. The negative power source according to claim 1, wherein the variable means varies the frequency of an AC signal input to the negative power source means based on a characteristic relating to a portion forming the negative power source means. apparatus. 4. The negative power supply device according to claim 1, wherein the liquid crystal display is disposed on the main body of the sewing machine.