JPH05208516A - Driving circuit for thermal head - Google Patents

Abstract

PURPOSE:To realize low cost by controlling a thermal head, in which heat- generatig sections by respective power sources of phase A and phase B are disposed on a straight line in a manner of setting one of respective power sources of phase A and phase B at the time of connecting the other with the electric source by means of linking changeover switches. CONSTITUTION:In a thermal head, heat generating resistors 1 are formed in the straight line on a ceramic base and lead conductors are disposed at equal intervals in the direction square to the line. The lead conductors are classified into power source side lead conductors 8 and grounding side lead conductors 9 alternately for every other piece, and every other piece of power source side lead conductors 8 is connected with power source lines 2 and 3 of phase A and phase B, while the grounding side lead conductors 9 are connected with correponsing terminals of a control circuit 7. The interval of the heat resistors 1 between the conductors 8 and 9 forms one heating interval. When the power source of one phase is connected with a power source line in the thermal head, linking changeover switches 5-1 and 5-2 for grounding the power source line of counterpart phase are provided to make the system small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for a thermal head used in a thermal recording apparatus.

[0002]

2. Description of the Related Art FIG. 3 is a connection diagram showing a conventional circuit of this type. 1 is a heating resistor, 2 is an A-phase power source line, 3 is a B-phase power source line, 4 is a power source, 5 is a changeover switch, 6 Is a reverse current blocking diode, 7 is a control circuit, 8 is a power source side lead conductor, and 9 is a ground side lead conductor. Heating resistor 1 on ceramic substrate
Are formed in a straight line, and lead conductors that come into contact with and cross the heating resistor in a direction perpendicular to the straight line are arranged at equal intervals. Every other lead conductor is connected to the power supply side lead conductor 8
And the ground side lead conductor 9, and the power source side lead conductors 8 are connected to the A-phase power source line 2 and the B-phase power source line 3 every other line, and the ground side lead conductor 9 is a corresponding terminal of the control circuit 7. And is grounded (connected to the negative terminal of the power supply 5) for a predetermined time controlled by the control circuit 7. Each section of the heating resistor 1 between one power supply side lead conductor 8 and the ground side lead conductor 9 adjacent thereto forms one heating section.

The control circuit 7 shown in FIG. 3 grounds the terminal indicated by reference numeral 7-1, and the changeover switch 5 supplies the power source 4 to the A-phase power source line 2.
, The current flows through the circuit of the power supply 4, the reverse current blocking diode 6-2, the point a, the point b, and the terminal 7-1.
The ab heat generating section generates heat. When the power supply 4 is connected to the B-phase power supply line 3 while the terminal 7-1 is grounded, a current flows through the backflow prevention diode 6-3 and the heat generation section cb heats up. In addition, the voltage of the A-phase power supply line 2 passes through the power-supply-side lead conductor 8 connected to the A-phase power supply line 2 and the power-supply-side lead conductor 8 connected to the B-phase power supply line 3, and the B-phase power supply line 3 The reverse current blocking diode 6 prevents the voltage of the B-phase power supply line 3 from entering the A-phase power supply line 2.

[0004]

As described above, the drive circuit of the conventional thermal head is provided with the array of the backflow preventing diodes 6, which makes the manufacturing cost high and the array on the substrate of the thermal head. There is a problem that it occupies a large area.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a driving circuit for a thermal head which is small in size and can be manufactured at a reduced cost.

[0006]

A drive circuit for a thermal head according to the present invention does not use a backflow prevention diode,
Instead, an interlocking changeover switch is provided, and when one of the A and B phase power supply lines is connected to the power supply, the other interlocking changeover switch is controlled so that the other is grounded.
The current that is grounded from one power source side lead conductor of the A (B) phase power supply line to the B (A) phase power supply line via the heating resistor 1 is 1/2 of the normal heating current. It is easy to design so that the heat-sensitive recording paper does not change due to the heat generated by.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a connection diagram showing an embodiment of the present invention.
The same reference numerals as those in FIG. 3 denote the same or corresponding portions, and 5-1 and 5
Reference numeral -2 is an interlocking changeover switch which operates in conjunction with each other. The interlocking changeover switches 5-1 and 5-2 operate such that when the power source is connected to the power source line of one phase, the power source line of the other phase is grounded.

FIG. 2 is a connection diagram showing the current flowing in the heat generating section in the vicinity when the terminal 7-1 is grounded in FIG. 1, and corresponds to the terminal 7-1 when the power supply voltage is E and the ground voltage is 0. b
The point voltage is 0, the voltages at points a and d connected to the A-phase power supply line 2 are E, and the voltages at points c and e connected to the B-phase power supply line 3 are 0. Therefore, a current of E / R flows between a and b, and this becomes a normal heat generation current. In this heat generation section, there is heat generation corresponding to (E / R) ² R = E ² / R, but b current between -c is 0, between the d-c, at d-e current such as between the E / 2R, in part of the heating compartment by this ^{current, (E / 2R) 2 R} = E 2 / 4R Has a fever equivalent to. Since the amount of heat generated corresponding to E ² / 4R is 1/4 of the heat generated by the normal heat generating current, the printing by the heat generating section in which the normal heat generating current flows is in the normal state, and the thermal recording paper changes in other areas. It is necessary to set the values of E and R so that they do not occur, but this is easy.

In the drive circuit of the present invention, the heat-generating section of the non-printing portion is also preheated to the extent that the change does not occur on the thermal recording paper, so that the printable temperature is reached when a regular heat-generating current is passed. Also, there is an effect that the rising speed becomes faster and high-speed printing becomes possible. In addition, since a large amount of heat is generated every time in most of the heat-generating sections of the non-printed portion, there is an effect that it becomes easy to control the heat storage history.

[0010]

As described above, the drive circuit for the thermal head according to the present invention does not require the backflow prevention diode, so that the manufacturing cost can be reduced, the size can be reduced, and most of the heat generating section where printing is not performed is possible. By preheating each time, high-speed printing becomes possible, and there is an effect that the heat storage history can be easily controlled.

[Brief description of drawings]

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

FIG. 2 is a connection diagram showing voltages and currents of respective parts in FIG.

FIG. 3 is a connection diagram showing a conventional circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating resistor 2 A phase power supply line 3 B phase power supply line 4 Power supply 5-1 and 5-2 Interlocking changeover switch 7 Control circuit 8 Power supply side lead conductor 9 Ground side lead conductor

Claims (1)

[Claims] 1. A plurality of linear heating resistors that form a plurality of heating sections are formed, and a plurality of heating resistors that come into contact with and cross the heating resistors in a direction perpendicular to the linear direction of the heating resistors are formed. The lead conductors are formed at equal intervals, and this lead conductor is
A power supply side lead conductor and a ground side lead conductor are set every other line, the power supply side lead conductor is connected to one terminal of the power supply, and one or more lead conductors selected from the ground side lead conductors are selected.
Is connected to the other terminal of the power source through a control circuit, the driving circuit of the thermal head driven so as to flow the heating current to the selected heating section among the plurality of heating sections, When connecting to one terminal of the above power supply,
When the B-phase power supply line is connected to the other terminal of the power supply and the A-phase power supply line is connected to the other terminal of the power supply, the B-phase power supply line is controlled to be connected to one terminal of the power supply. A drive circuit for a thermal head, comprising: a changeover switch; and means for connecting every other one of the power source side lead conductors to the A phase power source line and the B phase power source line.