JPH0611801Y2 - Thermal head drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] In a two-power-source thermal printer using an AC adapter or a battery, the print density also changes when the power supply voltage of the drive circuit changes. Therefore, the width of the pulse signal is automatically switched according to the level of the power supply voltage to stabilize the print density in the dual power supply type printer.

[Industrial application field]

The present invention relates to a dual-power-source thermal printer using an AC adapter or a battery, and more particularly to a thermal head driving device for stabilizing print density.

Thermal printers are widely used as output devices in various electronic devices such as simple word processors. Particularly, thermal printers used in portable devices are configured to be driven by an AC adapter or a battery.

When such a two-power-source thermal printer is driven by an AC adapter, the battery is usually charged in parallel with the driving of the thermal printer. Therefore, the power supply voltage when driven by the AC adapter is set higher than the power supply voltage when driven by the battery, and there is a difference in print density between when the AC adapter is used and when the battery is used. Occurs.

However, when printing with a thermal printer, it is desirable that there is no difference in print density. Therefore, research on a method for stabilizing the print density in a dual power supply type printer is underway.

[Conventional technology]

FIG. 2 is a block diagram showing a conventional thermal head driving device, and FIG. 3 is a timing chart showing its operation.

In FIG. 2, a conventional thermal head driving device has a monostable multivibrator (hereinafter referred to as monomulti) 1 that has external resistors 11 and 12 and an external capacitor 13 and generates a pulse signal, and an external device. A data latch circuit 2 for temporarily storing the print data input from the printer and converting the width of the print data by the pulse signal, and a driver for applying a voltage to the thermal head 4 based on the signals sequentially output from the data latch circuit 2. And circuit 3.
The variable external resistor 11 is a resistor for adjusting the print density.

When the trigger signal is input to the monomulti 1 as shown in FIG. 3, the monomulti 1 generates a pulse signal having a constant pulse width and inputs the pulse signal to the data latch circuit. When the clock signal is input to the data latch circuit, if there is print data, the pulse signal is transformed by the clock signal and becomes a print pulse and is output from the data latch circuit. However, if there is no print data, no print pulse is output. A voltage is applied to the thermal head from the driver circuit based on the print pulse. A number of resistance heating elements are formed on the thermal head,
By selecting a resistance heating element corresponding to the print data and applying a voltage thereto, the resistance heating element generates heat and the opposing dye is colored.

[Problems to be solved by the invention]

The print density in a thermal printer is proportional to the product of the voltage applied to the resistance heating element and its time. Therefore, in order to stabilize the print density, when the voltage applied to the resistance heating element changes, the time for applying the voltage must also be changed to make the product constant. In the two-power-source thermal printer, the voltage applied to the resistance heating element, that is, the power supply voltage is different when driven by an AC adapter and when driven by a battery. However, in the conventional thermal head driving device, the time for applying the voltage, that is, the period of the pulse signal generated in the monomulti 1 is constant. Therefore, there is a problem that a difference in print density occurs when the power source is switched.

[Means for solving problems]

FIG. 1 is a block diagram showing a thermal head driving device according to the present invention. Note that the same object is denoted by the same symbol throughout the drawings.

The problems described above include a mono-multi 1 that has an external resistor and an external capacitor to generate a pulse signal, a data latch circuit 2 that converts the width of input print data by the pulse signal, and a data latch circuit 2 sequentially. A driver circuit 3 for applying a voltage to the thermal head 4 based on the output signal, and a plurality of resistors 51, 52, a diode 53,
The automatic selection resistance circuit 5 including the voltage level detection circuit 54 and the voltage level detection circuit 54 serves as an external resistance of the monomulti 1 and is solved by the thermal head driving device of the present invention.

[Action]

In FIG. 1, by incorporating an automatic selection resistance circuit 5 as an external resistance of the monomulti 1, the thermal density of the dual power supply system driven by an AC adapter or a battery can reduce the print density generated when the power supply is switched. The difference can be eliminated.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to FIG.

In the figure, there are multiple automatic selection resistor circuits 5 (two in the figure).
Resistors 51 and 52, diode 53, and voltage level detection circuit 5
The voltage level detection circuit 54 includes a reference voltage generator 55 that generates a reference voltage Vs, and an input circuit 56 that inputs a comparison voltage Vd obtained by dividing the power supply voltage V.

In the automatic selection resistance circuit 5, the comparison voltage Vd when the power supply voltage V is divided by the input circuit 56 is added to the voltage level detection circuit 54, and the reference voltage Vs from the reference voltage generator 55 is added to the other input side. .

In this case, if the comparison voltage Vd and the reference voltage Vs are set so that “Vd> Vs” is satisfied when the power supply voltage from the AC adapter higher than the power supply voltage of the battery is used, the voltage level detection circuit 54 The output 57 of the resistor becomes high level and the resistance 51,5
Since 2 can be regarded as a circuit equivalently connected in parallel, the resistance value between the output terminals 58 and 59 becomes a combined resistance value of the resistors 51 and 52, and the value can be reduced.

On the other hand, when driving with the power supply voltage from the battery, “Vd <V
If the comparison voltage Vd and the reference voltage Vs are set so as to be “s”, the output section 57 of the voltage level detection circuit 54 becomes a low level and the resistors 51 and 52 are equivalently connected in series. As can be seen, since a diode 53 is connected in series with the resistor 52, no current flows through the resistor 52, and as a result, the resistance value between the output terminals 58 and 59 is the resistance value of the resistor 51 only. The value can be increased.

Therefore, by setting the reference voltage Vs between the output voltage of the AC adapter and the output voltage of the battery, the resistance between the output terminals will be small when the AC adapter is connected to the power supply, and between the output terminals when the battery is connected to the power supply. The resistance value of can be increased.

The thermal head driving device according to the present invention has an external resistor and an external capacitor 13 to generate a pulse signal, a mono-multi 1 for temporarily storing print data input from an external device, and a width thereof for the pulse. The data latch circuit 2 includes a data latch circuit 2 for converting a signal, and a driver circuit 3 for applying a voltage to the thermal head 4 based on a signal sequentially output from the data latch circuit 2. An automatic selection resistance circuit 5 is incorporated.

As described above, when the AC adapter is connected to the power supply, the automatic selection resistance circuit 5 can reduce the resistance value between the output terminals, and can connect the battery to the power supply to increase the resistance value between the output terminals. Therefore, the pulse signal generated by the mono-multi 1 having the automatic selection resistor circuit 5 as an external resistor is not
When the C adapter is connected, the cycle is short, and when the battery is connected, the cycle is long. By making the resistance value of the resistor 51 adjustable, the cycle of the pulse signal can be finely adjusted.

The print density in a thermal printer is proportional to the product of the voltage applied to the resistance heating element and its time. Therefore, by incorporating an automatic selection resistance circuit as the external resistance of the mono-multi, it is possible to eliminate the difference in print density that occurs when the power supply is switched in a two-power-source thermal printer driven by an AC adapter or a battery. it can.

[Effect of device]

As described above, according to the present invention, it is possible to provide a thermal head driving device for stabilizing the print density in a dual power source type thermal printer.

[Brief description of drawings]

FIG. 1 is a block diagram showing a thermal head driving device according to the present invention, FIG. 2 is a block diagram showing a conventional thermal head driving device, and FIG. 3 is a timing chart showing its operation.
In the figure, 1 is a mono-multi, 2 is a data latch circuit, 3 is a driver circuit, 4 is a thermal head, 5 is an automatic selection resistance circuit, 51 and 52 are resistors, 53 is a diode, 54 is a voltage level detection circuit, and 55 is a reference. A voltage generator, 56 is an input circuit, 57 is an output unit, and 58 and 59 are output terminals.

Claims (1)

[Scope of utility model registration request] 1. A thermal head driving device for a thermal printer using an AC adapter or a battery as a power source for driving, which is a mono-multi having an external resistor and an external capacitor connected in series to generate a pulse signal. (1), a data latch circuit (2) for converting the width of the input print data by the pulse signal, and a predetermined value for the thermal head (4) based on the signal sequentially output from the data latch circuit (2) The external resistance of the thermal head driving device comprising a driver circuit (3) for applying the voltage of, a voltage level detection circuit (54) for detecting the difference between the external power supply voltage and a predetermined reference voltage, The voltage level detection circuit (54) so that the resistance value for the monomulti (1) can be changed corresponding to the voltage difference detected by the voltage level detection circuit (54).
A plurality of resistors (51, 52) and a diode (53) connected to
A thermal head drive device comprising an automatic selection resistance circuit (5) consisting of