JPS591804Y2 - Heat generating head drive circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a heat-generating head drive circuit that is capable of correcting variations in resistance values of heat-generating resistors.

A heat-generating head is a device in which heat-generating resistors are arranged in a matrix or in a row on a substrate using thick-film or thin-film technology.A current is passed through the heat-generating resistors to generate heat, and recording is performed by bringing the heat-sensitive recording paper into contact with the heat-generating surface. It is.

However, since a large number of heat generating resistive elements are used, variations in resistance occur between the elements due to manufacturing.

Generally, there is a variation of around 20%, and when the same current is passed through such heating elements, the amount of heat generated differs, resulting in variation in print density.

However, reducing the variation increases the cost of the heat generating head.

The purpose of the present invention is to provide a heat generating head drive circuit that can control the amount of heat generated to be constant in order to obtain the same printing density even if the resistance value of the resistor varies.
A first transistor for supplying current to a plurality of heat generating resistors arranged on the substrate is connected, and the first transistor is connected to a reference voltage created by a Zener diode at the connection point of the heat generating resistors and the voltage of the heat generating resistors is connected. It is distantly related to a heating head drive circuit characterized in that a second transistor is connected so as to compare the voltages at both ends, operate when the reference voltage is low, and shunt the current to the heating resistor.

Hereinafter, the present invention will be explained in detail based on examples.

FIG. 1 is a diagram showing the principle of the present invention. In the figure, Q
1 is a transistor for supplying current to the heating resistive element Rx, Q2 is a transistor for voltage comparison, ZD is a Zener diode, Vl and v2 are power supplies, and R1 and R2 are bias resistors.

To explain the operation, the power supply V1 is connected via the bias resistor R2.
Since a voltage is applied between the base and emitter of the transistor, the transistor Q1 is turned on, the resistor R2 and the transistor Q1 form a constant current source, and current is supplied from the power source 2 to the heating resistor Rx, which generates heat.

Here, the collector of transistor Q1 and the heating resistance element Rx
Since the base of the transistor Q2 is connected to the connection point of and the zener diode ZD is connected to the emitter of the transistor Q2, the resistance value of the heating resistor Rx is high and the voltage at point a is the reference voltage created by the zener diode ZD. When the voltage becomes higher, transistor Q2 turns on.

When the 1H transistor Q2 is turned on, the current flowing through the transistor Q1 to the heat generating resistor Rx is shunted to the transistor Q2, so that the amount of heat generated becomes the reference value.

FIG. 2 is a diagram showing, in terms of deviation values, changes in the amount of heat generated with respect to changes in the resistance value of the heating resistive element Rx when the circuit according to the present invention is used.

The deviation value is shown with 1 (W) as the standard (0).

In the figure, curve 1 has a resistance value R1 of 100Ω and a resistance R2
When R1 is 83.3Ω, curve 2 shows resistance R1 as 109Ω.
．． 54Ω, and the case where the resistance R2 is 84 and 56Ω is shown.

As is clear from the figure, for example, when the reference resistance value of the heating resistor Rx is set to 100Ω, even if the actual resistance value deviates by 40% and becomes 60Ω, the amount of heat generated changes by only 5%, and the printing There is almost no difference in concentration.

Next, an application example of the present invention will be explained with reference to FIG.

In FIG. 3, a case will be explained in which heating resistive elements are arranged in a matrix on a substrate. Before that, Madnox driving will be explained with reference to FIG. 4.

As shown in the figure, power supply lines X1 to X4. Y1
~ Y6 is arranged, and heating resistive elements R10 and R1 are placed at the intersection.
2.R construction...R46 is connected to a diode for preventing wraparound.

Driving is performed by selecting one feed line in the Y direction and one in the X direction and applying a pulse to each of them.

Next, a detailed explanation will be given using FIG. 3.

FIG. 3 shows the heating resistor elements R10 and R2□ of FIG. 4 extracted.

In the figure, transistors Q1a, Qlb, transistors Q2a, Q2b, bias resistors R,a, Rlb,
R2a.

R2b are transistors Q1. Q2 performs the same function as bias resistors R1 and R2.

Diode D1. D□'5 D2 , D2 '9 D3
5 D3' is a diode for preventing wraparound.

The transistor Q3 and the Zener diode ZD1 constitute a constant voltage power supply corresponding to the power supply ■1 in FIG. 1, and the diodes D1. Transistor Q1a via D1'.

Apply a bias voltage to Qlb.

Also, the circuit formed by the resistors R5, R6, the zener diode ZD2, and the transistor Q6, and the circuit formed by the resistors R7, R8, the zener diode ZD3, and the transistor Q7 will become clear from the explanations given later, but It performs the same function as the inner diode ZD and power supply V2.

To explain the operation, when a negative pulse is applied to the Y direction terminal SY1 and a positive pulse is applied to the X direction terminal SX1, a positive pulse is applied to the transistor Q4 via the inverting circuit IN1, so the transistor Q4 is turned on. As a result, transistor Q3 turns on, and transistors 1 to Q
Current flows from No. 3 to transistor Q4 via diode D1 and resistor R4, causing the potential at one point to drop, and when the potential at one point where the bias voltage is applied to transistor Q5 drops, Qta turns on. .

When the transistor Q1a is turned on, a current flows through the path of resistor R2a-1 - transistor Q1a - heating resistance element R1□ - diode n - transistor Q5.
generates a fever.

At this time, transistor Q5 is on and resistor R
5 and Zener diode ZD2, transistor Q6 is biased with a constant voltage and turned on.

As a result, a current is supplied to the resistor R6 via the transistor Q5, and a constant voltage is generated across the resistor R6.

Furthermore, when a negative pulse is applied to the Y-direction terminal SY2 and a positive pulse is applied to the X-direction terminal SX2, the transistor Q4'
turns on when a positive pulse is applied from the inverter circuit IN2, which also turns on the transistor Q3, so a current flows through the diode D1' and turns on the transistor Q1b.

In addition, since the transistor Q5' is also turned on, the heating resistor R22 generates heat, current is supplied to the zener diode ZD3 and the resistor R7, a constant voltage is supplied between the pace emitter of the transistor Q, and the transistor Q7 is turned on. Therefore, a constant voltage is generated across the resistor R6.

Note that one power source is provided for each column to apply to the heating resistor.

Transistor Q2a to keep the amount of heat constant.

Q2b, diode D3. D3', resistance R1a, R,
The circuit consisting of b operates.

For example, terminal SX1. When a pulse is applied to SYl,
Transistor Q5. Q6 turns on and performs the operation described above to supply current to resistor R6.

Since the voltage generated across resistor R6 is a constant voltage, a constant voltage is applied to the emitter of transistor Q2a.

Here, when the resistance value of the heating resistor element R1□ is high, the voltage at the ¥1 point becomes higher than the emitter voltage of the transistor Q2a, and the transistor Q2a is turned on.

Therefore, the current flowing through the transistor Q1a is shunted to the transistor Q2a, and the amount of heat generated becomes the reference value.

The same thing is done for the heating resistor element R2□.

As is clear from the above, according to the present invention, even if the resistance value of the heating resistor varies, the supplied current can be controlled, so that variations in print density can be eliminated.

Although the case where the heat generating resistive elements are arranged in a matrix has been described above, the present invention can also be applied to a case where the heat generating resistive elements are arranged in a line.

[Brief explanation of drawings]

Figure 1 is a diagram showing the principle of the present invention, Figure 2 is a diagram showing changes in heat generation amount with respect to changes in the resistance value of the heating resistor element, Figure 3 is a diagram showing an application example of the present invention, and Figure 4 is a matrix. FIG. 3 is a diagram for explaining driving. In the figure, Ql and Q2 are transistors, R1 and R2 are bias resistors, Rx is a heating resistance element, ZD is a Zener diode, 1. v2 is a power supply.

Claims (1)

[Scope of utility model registration request] In a heat generating head drive circuit that is connected to a constant current source and includes a heat generating resistor that generates heat with the current from the constant current source, a Zener diode is used as a reference at the connection point between the constant current source and the heat generating resistor. Connect the output end of a reference voltage circuit that creates a voltage via a resistor, compare the voltage across the heating resistor at the connection point with the reference voltage, and if the reference voltage is lower, the heating resistor A heat-generating head drive circuit characterized by providing a transistor so as to shunt current to the body.