KR950008983Y1 - Printer head overheat protect driving circuit - Google Patents

Abstract

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Description

Overheat prevention drive circuit of thermal print head

1 is a circuit diagram of the present invention.

2 is a comparison diagram of the control unit output a, the thermal recording head temperature b, the Schmitt trigger circuit output c, and the actual recording characteristic d of the inventive design.

3 is a curve diagram of the thermistor characteristic a and Schmitt trigger circuit characteristic b used in the present invention.

4 is a conventional circuit diagram.

5 is a circuit diagram using a conventional sensor.

6 is a waveform diagram of FIG.

7 is a waveform diagram of FIG.

* Explanation of symbols for main parts of the drawings

1: Oagate 2: Control part

3: Schmitt trigger circuit 4: Thermal printer head

5: Thermistor 8: Temperature sensing circuit

TR1-TR3: Transistor R1-R5: Resistor

D1: Zener Diode

The present invention relates to a thermal printer head driving circuit, and more particularly, to a protection circuit against malfunction and head failure due to overheating during high speed printing.

In the conventional thermal printhead driving circuit, the base of the transistor TR1 is connected to the control unit 2 through the inverter gate I1, the collector is grounded through the thermal printhead 4, and the emitter is configured by applying power. Alternatively, the reference voltage V _REF is set at the (+) input terminal of the comparator 6 and connected to the (−) input terminal of the comparator 6 through the sensor 7 from the thermal recording head 4, and the output terminal is connected to the control unit ( 2) and the collector is grounded through the thermal recording head 4 to the base of the transistor TR1 via the inverter gate I11, and the emitter is configured by applying power.

Such a driving circuit has the output waveforms and temperature graphs of the driving circuit shown in FIGS. 4 and 5 as shown in FIGS. 6 and 7. (2) and the transistor TR1 is driven by the output pulse of the inverter gate I1 to drive the thermal print head 4, and the long pulse (printed in FIG. 6 a) of the printing pulse is output from the controller 2. This pulse signal is inverted through the inverter gate I1 to control the transistor TR1 on / off.

When the transistor TR1 is turned on, the thermal print head 4 is normally driven within the saturation temperature T _s (b degree in FIG. 6) but with a short waveform pulse (c degree in FIG. 6), that is, printing. When a high-speed pulse is output, the thermal print head 4 is driven even when it is out of the saturation temperature T _s (d degrees in FIG. 6). In some cases, a malfunction of the print and the thermal print head 4 may be damaged. .

The circuit shown in FIG. 5 detects the heat generation temperature of the thermal print head 4 from the sensor 7 and applies it to the comparator 6 in which the reference voltage V _{REF has} already been set and outputs the control unit 2. The output pulses of the control unit 2 such as a and c in FIG. 7 are inverted through the inverter gate I11 to drive the transistor TR1 and the thermal printhead 4, which is why the sensor 7 and a comparator (6) is a current supply controlled by be no thermal damage to the transistor (TR1) caused by temperature characteristics, but in the thermal printing head 4 is provided above the saturation temperature (T _S) in the existing heat remaining The operation of the thermal print head 4 remains intact, and a color printer, which requires a multi-gradition method, has a problem such as simply passing a desired density.

The present invention has been devised to solve such a conventional problem and will be described in detail by the accompanying drawings as follows.

The temperature sensing circuit 8 is connected to the input terminal Vi of the Schmit Trigger circuit 3, and the output terminal Vo controls the pulse of the control unit 2 so that the output of the Schmit Trigger circuit 3 is combined with the output of the control unit 2. It is connected to the input terminal of 1) and the output terminal of the OR gate 1 is connected to the base of the transistor TR1 through the inverter gate I1, the power supply voltage Vcc1 is connected to the emitter, and the collector is connected to the thermal print head 4. Grounded through.

Here, the Schmitt trigger circuit 3 is composed of transistors TR2 and TR3 and resistors R3-R5, and the temperature sensing circuit 8 is composed of thermistor 5, zener diode D1, and resistors R1 and R2. The input terminal Vi of the Schmitt trigger circuit 3 is the base of the transistor TR3, the output terminal Vo is the collector of the transistor TR2, and the output terminal of the temperature sensing circuit 8 is the voltage output terminal of the thermistor 5.

The operation and effects of the present invention configured as described above are as follows.

The thermistor 5 of the thermal printhead temperature sensing circuit 8 senses the temperature change generated by the current flow in the thermal printhead 4 to generate the input voltage of the Schmitt trigger circuit 3. 4) If the temperature increases due to a large current flow, the input voltage of the Schmitt trigger circuit 3 also increases due to the temperature (T) -resistance (R _T ) characteristic of the thermistor 5 as shown in FIG. When the current flows slightly and the temperature decreases, the input voltage of the Schmitt trigger circuit 3 also decreases.

Accordingly, the Schmitt trigger circuit 3 in which the input voltage is adjusted by the thermistor 5 alternates between two stable states as shown in FIG. 3B. FIG. 2B shows the thermal printer as shown in the waveform. When the head 4 reaches the saturation temperature T _S , the output of the Schmitt trigger circuit 3 becomes “Voh” so that the data pulse of the controller 2 (FIG. 2 a in FIG. 2) is no longer thermally sensitive. The transistor TR1 is turned off to prevent the transfer to the print head 4 and the driving of the thermal print head 4 is prevented, and the thermal print head 4 is below the print start temperature T _P. When the output of the Schmitt trigger circuit 3 is " low " (VoL), the output state is enabled and the transistor TR1 is turned on in accordance with the data pulse of the control unit 2, and the thermal print head 4 is normally driven. Let's go.

Therefore, the present invention operates in the same way as the conventional printing at the normal speed, and in addition to the effect of preventing thermal damage of the thermal print head which occurs during the high speed printing, the hysteresis phenomenon of the Schmitt trigger circuit is prevented. The saturation temperature (T _S ) and residual temperature of thermal print heads are identified, and the printing enable signal is properly controlled, which is a phenomenon that occurs during high-speed printing, that is, the thermal print head is a saturation temperature (T _S ) due to residual heat. It is possible to solve the problem that is printed when not to be printed while remaining between the print start temperature (T _P ).

Claims (1)

The temperature sensing circuit 8 which senses the temperature generated from the thermosensitive printhead 4 and outputs a voltage corresponding thereto, and checks the lower and upper limits of the voltage output from the temperature sensing circuit 8 to maintain a stable state. A Schmitt trigger circuit 3 for outputting a pulse signal, a controller 2 which recognizes an output pulse signal of the Schmitt trigger circuit 3 and outputs a print pulse signal according thereto, and a print pulse signal of the controller 2 And an orifice (1) for controlling the thermal print head (4) through the inverter gate (I1) by logically combining the output pulses of the Schmitt trigger circuit (3).