JPS59146873A - Driving circuit for thermal printing head - Google Patents

Abstract

PURPOSE:To provide the titled circuit enabling to simplify the construction of a thermal printer and to enhance print quality by eliminating afterimages generated in printing space, wherein a strobe function is added to a switching circuit constituting the driving circuit. CONSTITUTION:Each of the driving circuits 61, 62...6N the number of which is equal to the number of rows or digit places of a pattern to be printed is switched by a switching circuit in accordance with input signals impressed on input terminals 81, 82...8N. To the switching circuit, a strobe circuit 14 for conditioning the timing of a switching action on the basis of a strobe signal impressed on a strobe input terminal 12 is added. Accordingly, the timing of driving the thermal printing head 40 is regulated on the basis of the strobe signal impressed on the terminal 12 provided in common, so that a disturbance in a printed pattern due to an irregularity in the input signals can be eliminated.

Description

[Detailed Description of the Invention] The present invention relates to a drive circuit for a thermal printer head,
In particular, it relates to one with a strobe function added.

1 and 2 show printing patterns of a thermal printer. In the printing pattern shown in Fig. 1, the printing dots 2 are arranged in 7 rows and 5 columns, in this case, the diagonal dots 2A are the printed parts, the white dots 2B are the blank parts, and the numbers 4 are formed. In addition, the printing pattern shown in Figure 2 shows numbers constituting one digit, and by selectively printing each segment (4A, 4B, 4C, 4D, 4E, 4F, 4G), a predetermined character can be printed. Form.

When forming these printing patterns, several channels of drive circuits are installed to drive the thermal printer head, and based on predetermined drive inputs, one
Print columns or single digit segments or dots.

However, in such a printing operation, if the timing at which the drive signals end is irregular, there is a risk that an afterimage of the first column will be printed in the blank space between the first (second) column's printing and the second column's printing. There is.

Furthermore, even when printing is performed one digit at a time, as in the printing pattern shown in FIG. 1, there is a risk that such afterimage printing may occur.

For this reason, conventionally, a control circuit is installed upstream of the drive circuit of the thermal printer head to cancel the drive signal at regular intervals in order to remove such afterimage printing. Such a control circuit has the drawback of complicating the structure of the device and making it expensive.

This invention provides a drive circuit for a thermal printer head that adds a strobe function to the switching circuit that constitutes the drive circuit, simplifies the configuration of a thermal printer, and improves print quality by eliminating afterimages that occur in the print space. The purpose is to provide

The present invention includes a switching circuit that performs a switching operation based on an input signal and causes a drive current to flow through the thermal printer head, and a strobe circuit that (3) adjusts the timing of the switching operation of the switching circuit based on a strobe input. Features.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 3 shows an embodiment of the thermal printer head drive circuit of the present invention. The thermal printer is provided with a plurality of channels of drive circuits 61, 62, . Each drive circuit 61, 62...6N is a switching circuit that performs a switching operation according to an input signal provided to an input terminal 8I82...8N provided individually, and the timing of the switching operation is provided to a strobe input terminal 12. It is constructed by adding a strobe circuit 14 that performs adjustment based on a strobe signal.

In each of the drive circuits 61, 62, . A drive voltage Vcc is applied to the base of the transistor 16 from the power supply terminal 18 via a resistor 20, and the resistor 2
The input terminals 81, 82, . . . , 8N are formed for each drive circuit 61, 62, . Also,
The collector of this transistor 16 is connected to the base of a transistor 2B, which is a second switching element, via a resistor 24 and a diode 26, and is also connected to a reference potential point (GND) via the resistor 24 and a resistor 30. has been done. The transistor 28 has a resistor 3 at its collector and emitter between the power supply terminal 1 and the reference potential point.
2.34, and the emitter of this transistor 28 is connected to the base of an output transistor 36. The emitter of this output transistor 36 is connected to a reference potential point, and the collector of this transistor 36 is formed with output terminals 381, 382 . . . 38N, respectively, and these terminals 38+, 382 . A thermal printer head (5) 40 is connected between them.

A transistor 42 constituting the strobe circuit 14 is provided on the input side of the transistor 28 as the second switching element. In this embodiment, a transistor 42 is connected in parallel between the terminals of the resistor 30, and the strobe input terminal 12 is formed at the base of the transistor 42.

The operation will be explained based on the above configuration. In FIG. 4, A indicates an input signal pulse applied to the input terminals 81, 82, . . . , 8N, and B indicates a strobe signal pulse applied to the strobe input terminal 12. In the case of this embodiment, if the printing pattern of the thermal printer head 40 is set as shown in FIG. 1, each drive circuit 61, 62...6N corresponds to a column, and Codes 1 to 8 indicate column numbers. The strobe input terminal 12 receives a high (H) level at regular time intervals.
Since a low (L) level pulse is applied, the transistor 36 performs a switching operation as shown in FIG. 4(6)C in response to this strobe signal pulse. To explain this operation in detail, for example, when the input terminal 81 becomes L level, the transistor 16 becomes conductive, and when the L transistor 42 is non-conductive, the transistor 28 is connected from the transistor 16 via the resistor 24 and the diode 26. Current flows through the base of transistor 28, and transistor 28 becomes conductive. As a result, the transistor 36 becomes conductive, and at this time, a drive current is applied to heads in a predetermined column of the thermal printer head 40. In this case, the strobe circuit 14 has a strobe input terminal 1.
Since the strobe signal pulse shown in FIG. 4B is applied from 2, the transistor 42 performs a switching operation in response to this pulse.

As a result, the switching operations of the transistors 2B and 36 are regulated by the switching operations of the transistor 42, and the intervals between the driving currents flowing to the thermal printer head 40 are controlled to be constant.

In this way, each drive circuit 61, 62...6N is (7
) The drive timing of the thermal printer head 40 is regulated based on a strobe signal given from a commonly formed strobe input terminal 12. It is possible to reliably eliminate after-image printing within a space that is not specified. Furthermore, as is clear from the embodiment, the strobe circuit 14 is installed in each of the drive circuits 61, 62, . . . , 6N. In particular, a strobe signal can be applied from a common strobe terminal to the strobe circuit 14 provided in each drive circuit, and all channels can be controlled simultaneously.

Each of the drive circuits 6I, 62, . . . , 6N described above can be constructed from one integrated circuit, but the switching transistor 42 constituting the strobe circuit 14 provided in each drive circuit is connected to the substrate PNP of the integrated circuit. It can be composed of a type transistor.

FIG. 5 shows an embodiment composed of such a substrate PNP transistor (8). That is, an epitaxial layer 46 of the opposite conductivity type is formed on the surface layer of a semiconductor substrate (substrate) 44 of one conductivity type formed of silicon or the like, and this epitaxial layer 46 is a separate layer of the same conductivity type as the semiconductor substrate 44. A region 48 is formed and divided. An emitter 50 and a base 52 are formed at regular intervals on the upper surface of the epitaxial layer 46, and an epitaxial layer 46 is formed on the surface layer of the isolation region 48.
A collector 54 is formed that extends over the area. These emitter 50, base 52, and collector 54 constitute a substrate PNP type vertical transistor, and electrodes 56, 58, and 60 formed on each are provided with wiring for configuring a drive circuit 61.

According to such a substrate PNP type transistor, the current of the transistor 16 can be absorbed by a small strobe signal current compared to a PNP type lateral transistor, improving the reliability of the switching operation and eliminating blank spaces (which should not be printed). 9) It is possible to reliably prevent afterimage printing on the area.

Moreover, according to such a configuration, when configured with an integrated circuit, the chip area can be used efficiently.

As explained above, according to the present invention, since the strobe function is added inside the drive circuit, the configuration can be simplified, and the strobe circuits of each channel can be commonly controlled. Simplification and reliability of operation can be improved, afterimage printing within an interval that should not be printed can be reliably prevented, and furthermore, the cost of the thermal printer can be reduced.

[Brief explanation of the drawing]

1 and 2 are explanatory diagrams showing the printing pattern of the thermal printer head, FIG. 3 is a circuit diagram showing an embodiment of the thermal printer head drive circuit of the present invention, and FIG. 4 is an explanation showing its operation timing. FIG. 5 is an explanatory diagram showing a specific example of a transistor forming a strobe circuit. 61.62...6N...drive circuit, 14...(1
0) - Strobe circuit. (11)

Claims (1)

[Claims] (1) A switching circuit that performs a switching operation based on an input signal and causes a drive current to flow through a thermal printer head, and a strobe circuit that adjusts the timing of the switching operation of the switching circuit based on a strobe input. A drive circuit for a thermal printer head, characterized by: (2) The switching circuit includes a first switching element that performs a switching operation in response to the input signal, and a second switching element that performs a switching operation in response to the switching operation of this switching element,
Claim 1, characterized in that the strobe circuit is constructed by installing a substrate PNP type transistor capable of absorbing the switching current from the first switching element at the input part of the second switching element. The described thermal printer head drive circuit. (1)