JPH0615244B2 - Driving circuit for thermal printer head - Google Patents

Description

The present invention relates to a drive circuit for a thermal printer head,
In particular, it relates to a device with a strobe function added.

FIG. 1 and FIG. 2 show print patterns of the thermal printer. In the print pattern shown in FIG. 1, print dots 2 are arranged in 7 rows and 5 columns. In this case, the shaded dots 2A indicate the print portion, the white dots 2B indicate the blank portion, and the numeral 4 is formed. Has been done. In addition, the print pattern shown in FIG. 2 shows a numeral forming one digit, and a predetermined character is formed by selectively printing each segment 4A, 4B, 4C, 4D, 4E, 4F, 4G. To do.
When forming these print patterns, a drive circuit of several channels is installed to drive the thermal printer head, and each character is constructed based on a predetermined drive input.
Print columns or 1-digit segments or dots.

However, in such a printing operation, if the timings at which the drive signals end are not uniform, the afterimage of the first column may be printed in a blank portion in the interval between the printing of the first column and the printing of the second column. Further, even when printing is performed digit by digit like the print pattern shown in FIG. 1, such afterimage printing may occur.

For this reason, conventionally, a control circuit for releasing the drive signal at a constant interval is installed in the preceding stage of the drive circuit of the thermal printer head in order to remove such afterimage printing. Such a control circuit has a drawback that it complicates the structure of the apparatus and makes it expensive.

In view of this, the present invention provides a drive circuit for a thermal printer head in which a strobe function is added to a switching circuit forming a drive circuit to simplify the configuration of a thermal printer and prevent afterimage printing in a print interval. To aim.

That is, in the thermal printer head drive circuit according to the present invention, the collector side is grounded through the first and second resistors forming a series circuit, the first transistor that receives an input signal representing the print pattern at the base and switches, and the sub transistor. The second device is formed of a straight PNP transistor.
A second transistor, which is connected in parallel to the resistor, receives a strobe signal at the base, conducts current, and draws a current from the first transistor side through the first resistor; and the first and second resistors. When the base is connected to the intermediate connection point of the first transistor via the diode, the first transistor is conductive, and the second transistor is in the cutoff state, the conductive current of the first transistor is supplied to the base. The third transistor, which is turned off when the second transistor is turned on, is connected in series to the power supply terminal through the thermal print head to form a Darlington connection with the third transistor. When the third transistor is conducting, the conducting current of the third transistor is applied to the base to conduct the current, thereby drawing in the current, Characterized by comprising a fourth transistor flowing the drive current to the multi printer head.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 3 shows an embodiment of a drive circuit for a thermal printer head according to the present invention. The thermal printer is provided with drive circuits 6 ₁ , 6 ₂ ... 6 _N for supplying a drive current to each channel corresponding to a print head having a print pattern row or digit number. Each of the drive circuits 6 ₁ , 6 ₂ ... 6 _N has a switching circuit that performs a switching operation according to an input signal provided to an individually provided input terminal 8 ₁ , 8 ₂ ... 8 _N, and the timing of the switching operation. Is formed by adding a strobe circuit 14 for adjusting the signal on the basis of the strobe signal applied to the strobe input terminal 12.

In each of the drive circuits 6 ₁ , 6 _2, ... 6 _N , a power supply terminal 18 to which the drive voltage Vcc is applied is formed via a diode 19 at the emitter of the transistor 16 as a switching element. The drive voltage Vcc is applied to the base from the power supply terminal 18 via the resistor 20, and the drive circuits 6 ₁ , 6 via the resistor 22.
Input terminals 8 ₁ , 8 ₂ ... 8 _N are formed for every ₂ ... 6 _N. That is, a transistor 16 which receives an input signal representing a print pattern at its base and switches it, and a diode 19 which is connected in series to its emitter side serve as an original signal for driving the thermal printer head 40 in response to the input signal. A constant current source that generates a constant current is configured.

The base of a third transistor 28 as a switching element is connected to the collector of the transistor 16 via a first resistor 24 and a diode 26, and a reference is also provided via a resistor 24 and a second resistor 30. It is connected to a potential point (GND). The transistor 28 is connected to the collector and the emitter between the power supply terminal 18 and the reference potential point via resistors 32 and 34, respectively, and the emitter of the transistor 28 is connected to the base of an output transistor 36 as a fourth transistor. ing. The emitter of the output transistor 36 is connected to the reference potential point, and the collector of the transistor 36 has an output terminal 38.
_{1, 38} 2 ··· _{38 N} are respectively formed, between these output terminals _{38 1, 38} 2 ··· _{38 N} and a power supply terminal 18, the thermal printer head 40 is connected.

A second transistor 42 that constitutes the strobe circuit 14 is provided on the input side of the transistor 28. In this embodiment, the 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 described based on the above configuration. In FIG. 4, A indicates an input signal pulse applied to the input terminals 8 ₁ , 8 ₂ ... 8 _N , and B indicates a strobe signal pulse applied to the strobe input terminal 12. In the case of this embodiment, the print pattern of the thermal printer head 40 is
If the configuration shown in FIG. 1 is set, each drive circuit 6 ₁ , 6 _2, ... 6 _N corresponds to a column, and the symbols 1 to 8 shown in FIG. 4 indicate column numbers. There is. Since a high (H) level pulse and a low (L) level pulse are applied to the strobe input terminal 12 at regular time intervals, the transistor 36, as shown in FIG. 4C, corresponds to the strobe signal pulse. Performs switching operation. To explain this operation in detail, for example, the input terminal 8 ₁ becomes L level, the transistor 16 becomes conductive, when the transistor 42 is in a non-conductive state, the transistor 28 from the transistor 16 via a resistor 24 and a diode 26
A current flows through the base of the transistor and the transistor 28 becomes conductive. As a result, the transistor 36 becomes conductive,
At this time, a drive current is applied to the heads of the predetermined row of the thermal printer head 40. In this case, the strobe circuit 14 receives the strobe signal pulse shown in FIG.
2 operates in response to this pulse. As a result, the switching operation of the transistors 28 and 36 is controlled by the switching operation of the transistor 42, and the interval of the drive current flowing through the thermal printer head 40 is controlled to be constant.

As described above, the drive circuits 6 ₁ , 6 _2, ... 6 _N regulate the drive timing of the thermal printer head 40 based on the strobe signal provided from the strobe input terminal 12 formed in common. Disturbance of the print pattern due to misalignment, that is, afterimage printing in the interval where printing should not be performed can be reliably eliminated. Further, as is clear from the embodiment, the strobe circuit 14 is individually installed in each of the drive circuits 6 ₁ , 6 _2, ... 6 _N , and the strobe circuit 14 is different from the case where the conventional drive circuit is installed. Can be simplified. In particular, the strobe circuit 14 provided in each drive circuit can be supplied with a strobe signal from a common strobe terminal, and all channels can be controlled simultaneously.

Each of the drive circuits 6 ₁ , 6 ₂ ... 6 _N described above can be configured by one integrated circuit. However, the switching transistor 42 that configures the strobe circuit 14 provided in each drive circuit is integrated in the integrated circuit. The substrate PNP type transistor can be used.

FIG. 5 shows an embodiment constituted by such a substrate PNP type transistor. That is, a semiconductor substrate (substrate) 4 of one conductivity type formed of silicon or the like
4, an epitaxial layer 46 of opposite conductivity type is formed on the surface layer of the semiconductor substrate 44.
An isolation region 48 having the same conductivity type as that of is formed and partitioned. An emitter 50 is formed on the upper surface of the epitaxial layer 46.
And a base 52 are formed at regular intervals, and a collector 54 extending to the epitaxial layer 46 is formed on the surface layer of the isolation region 48. These emitters 50, a substrate PNP type vertical type transistor by the base 52 and collector 54 are configured, the electrode 56, 58, 60 formed in each been subjected wiring for constituting the drive circuit 6 _1.

According to such a substrate PNP type transistor, the current of the transistor 16 can be absorbed by a slight strobe signal current as compared with the PNP type lateral transistor, the switching operation is enhanced in reliability, and a blank portion which should not be printed. It is possible to reliably prevent the afterimage printing on the. Further, according to such a configuration, the chip area can be efficiently used when the integrated circuit is used.

As described above, according to the present invention, when the input signal representing the print pattern arrives, the current representing the input signal is generated through the first transistor, and the current is supplied to the third and fourth Darlington connections. Since the current is amplified by the transistor of No. 3, the heating current for the thermal printer head can be made large, and the leakage current when the third and fourth transistors are off due to the Darlington connection can be cut off by the diode. It is possible to reliably prevent the afterimage printing that occurs within the printing interval to improve the printing quality, and the second transistor that is conductive when it receives the strobe signal is the first transistor.
Is connected in series via the first resistor and in parallel to the second resistor forming a series circuit with the first resistor. Therefore, when the second transistor is conductive, The current can be drawn from the transistor side of the transistor through the first resistor to flow to the substrate side, and the circuit connected to the substrate side can be configured with a drive element such as a CMOS circuit having a small drive capacity. Since the second transistor is a substrate PNP transistor, it is possible to realize an IC circuit having a minimum configuration and a minimum area and good characteristics.

[Brief description of drawings]

1 and 2 are explanatory views showing a print pattern of a thermal printer head, FIG. 3 is a circuit diagram showing an embodiment of a thermal printer head drive circuit of the present invention, and FIG. 4 is an explanation showing its operation timing. 5 and 5 are explanatory views showing a concrete embodiment of the transistor forming the strobe circuit. 6 ₁ , 6 ₂ ... 6 _N ... Driving circuit 14 ... Strobe circuit 16 ... First transistor 19 ... First diode 24 ... First resistance 26 ... Second diode 28 ... Third transistor 30 ... Second resistance 36 ... Fourth transistor 40 ... Thermal printer head 42 ... Second transistor

Claims (1)

[Claims] 1. A first side and a second side whose collector side forms a series circuit.
Connected to the second resistor in parallel with the first transistor, which is grounded through the resistor and is switched by receiving the input signal representing the print pattern at the base, and the substrate PNP transistor, and outputs the strobe signal to the base. A second transistor that receives and conducts, and draws a current from the first transistor side through the first resistor, and a base is connected via a diode to an intermediate connection point between the first and second resistors. When the first transistor is conducting and the second transistor is in a cutoff state, the conduction current of the first transistor is supplied to the base to conduct the current, and the second transistor conducts. , A third transistor which is turned off, and a third transistor connected in series to a power supply terminal via a thermal print head. And a Darlington connection with a transistor, and when the third transistor is conducting, the conducting current of the third transistor is applied to the base to conduct the current so that a current is drawn and the drive current is passed to the thermal printer head. 4. A drive circuit for a thermal printer head, comprising: a transistor of 4;