JP2837926B2 - Heating element drive circuit device - Google Patents

Description

The present invention relates to a heating element driving circuit device (driver IC) for a thermal head.

(B) Conventional technology The driver IC mounted on a thermal head detects a voltage drop when the circuit power supply voltage falls below a specified value, such as when a large current flows due to a circuit abnormality. It has a function to forcibly interrupt output. By providing this function, it is possible to prevent the thermal head from running away due to an abnormal drop in the circuit power supply voltage and being destroyed. As shown in FIG. 4, this type of conventional output stop function is provided when the circuit power supply voltage V _DD falls from 5 V to a specified value of 4 V or less.
The How in regardless output voltage drop period t _x has been stopped.

(C) Problems to be Solved by the Invention In the above-mentioned conventional driver IC, the output stop function is activated regardless of the voltage drop period. Due to the variation according to the variation, the OF is also affected by the V _DD variation (GND variation) generated by the normal energizing operation of the thermal head.
There was F. Therefore, although the V _DD variation (GND fluctuation) occurring usually about operation defines the upper limit of the specified value of the IC so as not to react, when considering the IC production capacity such as a specified value and V _DD fluctuates There was a problem that a sufficient margin could not be obtained between them.

The present invention has been made in view of the above problems, and provides a heating element drive circuit device in which an output stop function does not work at a voltage drop of about a normal operation without concern for variations in ICs. It is intended to be.

(D) Means and Action for Solving the Problems A heating element drive circuit device of the present invention is a circuit device mounted on a thermal head and driving a plurality of heating elements, wherein a supplied power supply voltage has a predetermined value. A voltage drop detecting means for detecting that the voltage has dropped below, and a timer means for measuring that the voltage drop state has continued for a predetermined time, and a predetermined time serving as a reference for stopping the drive output to the heat generating element is supplied to the heat generating element. Is set to be longer than the voltage drop time at the time of normal energization, and the drive output to the heating element is stopped when the voltage drop state measured by the timer means continues for the predetermined time.

In this heating element drive circuit device, when the supplied power supply voltage drops below a predetermined value, the voltage drop detection means detects this. However, the output is not stopped immediately upon detection of the voltage drop. The timer means measures that the voltage drop state has continued for a predetermined time or more, and the drive output to the heating element is stopped. Therefore, even if the power supply voltage falls to a predetermined value or less when the normal heating element is energized, the drive output is not stopped because the duration is short.

(E) Embodiment FIG. 1 is a block diagram showing an internal circuit configuration of a driver IC of a thermal head showing an embodiment of the present invention.
In FIG. 1, a driver IC 1 is provided with a shift register 2 for taking in data inputted from a DIN terminal in accordance with a clock pulse inputted from a CLK terminal, and simultaneously taking in the data taken in the shift register 2 by the input of a latch signal LA. Latch circuit 3 for latching, power supply voltage V applied from _VDD terminal
_DD is the specified value the voltage drop detection circuit 4 for detecting that drops below typically outputs a predetermined high signal, when a voltage drop is detected, outputs a low signal at a predetermined delay time t _x A delay circuit (timer) 5, a gate circuit 6 that receives the output of the latch circuit 3, the strobe signal STR, and the output of the delay circuit 5 as inputs, and a drive output to the heating resistor element 8 in response to the output of the gate circuit 6. A drive circuit 7 is provided.
In this embodiment, the heating resistance element 8 includes 8 ₋₁ , 8 ₋₂ ,
.., 8 to ₆₄ dots, and the shift register 2, the latch circuit 3, the gate circuit 6, and the drive circuit 7
The same number is provided for each. However, the actual number of dots of the thermal head is even larger, and the driver IC
Are also juxtaposed.

In the circuit of this embodiment, when the power supply voltage V _DD is supplied to a specified value or more, a high signal is input from the delay circuit 5 to the gate circuit 6. When print data is input in this state, the print data is serially taken into the shift register 2, and
Each cell 2 ₋₁ , 2 ₋₂ , 2 of the shift register 2 is output by the latch signal LA.
_-3 ,..., _2-64 "1""0" bit data
Each cell 3 _-1, 3 _-2, 3 _-3, ..., are simultaneously latched in the 3 _-64. When the strobe signal STR is input, “1”
Circuit 6 corresponding to the cell of the latch circuit 3 that stores
The inputs of the individual gates are aligned at “1”, and the corresponding drive circuit 7
Operates to energize and drive the corresponding heating resistor element. The voltage drop time during normal energization of the heating resistor 8 is
When t _1, Yes is set to t ₁ <t _x, hence the delay circuit 5 also decreases the power supply voltage is below the specified value (see FIG. 3) by energization does not output a low signal, thus driving the output Will not be stopped.

Next, abnormality occurs in the circuit, for example, as shown in FIG. 3, only t ₂ hours in a relationship of t _x <t _2, when the power supply voltage V _DD falls below a specified value, the delay circuit 5, the voltage after detecting a voltage drop in the drop detection circuit 4, a low over time t _x. Therefore, one input to the gate circuit 6 becomes low, the drive circuit 7 is not all turned on, and the drive output to the heating resistor 8 is stopped.

As another embodiment, a power supply voltage V _DD is taken in instead of the voltage drop detection circuit 4 and the delay circuit 5 in FIG. 1, and a CPU or a gate array having a comparison function and a timekeeping function is shown in FIG. The process of the flow may be executed. In this process, first, the acquired power supply voltage V _DD and the specified value V
_T is compared (step ST1), and if V _DD > V _T , the operation continues as it is (NO in step ST1) (step ST2). However, V if _DD ≦ V _T, the timer is started t _x (step ST3), while continuing the judgment of the subsequent "or V _DD ≦ V _T", if the voltage drop is followed is, as it is a timer t _x
Since clocking of is made, at step ST5, the timer t _x is determined whether the time is up, until the time is up, step
Steps ST4 and ST5 are repeated. As t ₁ of FIG. 3, when the voltage drop at the time of energization, until the timer t _x is the time is up, the power supply voltage V _DD is larger than the prescribed value V _T, the determination in step ST4 but becomes NO, returns to step ST3, the re-start and reset the timer T _x. Therefore, in this case, the output is not stopped.

However, in the case of the voltage drop at the time of abnormality in FIG. 3, t ₂ > t _x
So, to turn OFF the output at the time of the timer t _x (step ST6).

Now, for example, when the detection specified value of the driver IC is 3.5V ± 1V and the _VDD fluctuation (GND fluctuation) in the thermal head is 5 ± 0.6V
When there is, in the worst case, _VDD becomes 4.4V, so the specified value of the IC becomes 3.5 + 1 = 4.5V or less, and the output is turned off. For this reason, in the conventional case, it was necessary to suppress the variation width from 3.5 + 1 V to 3.5 ± 0.8. However, in the present invention, the voltage drops during energization, and even if the voltage falls below the specified value, the voltage drops for a predetermined time or more. If it does not continue, the output will not be turned off, so there is no need to use nerves for the variation width of the IC.

(F) Effects of the Invention According to the present invention, when a decrease in the power supply voltage is detected,
Turns off the output when the voltage drops for more than a predetermined time
Therefore, it is possible to prevent a printing error caused by erroneously turning off the output during energization in normal printing. Further, it is not necessary to suppress the variation in the detection voltage (specified value) of the IC strictly, so that there is no need to use a high-priced IC and the cost of the thermal head can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an internal circuit function of a driver IC of a thermal head showing one embodiment of the present invention, FIG. 2 is a flowchart for explaining another embodiment, and FIG.
FIG. 4 is a time chart for explaining the operation of the conventional driver IC, and FIG. 4 is a time chart for explaining the operation of the conventional driver IC. 1: Driver IC, 4: Voltage drop detection circuit, 5: Delay circuit, 7: Drive circuit, 8: Heating resistance element.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 2/355 B41J 29/38 B41J 29/46 G06F 3/12

Claims (1)

(57) [Claims] 1. A heating element drive circuit device mounted on a thermal head and driving a plurality of heating elements, comprising: a voltage drop detecting means for detecting that a supplied power supply voltage has dropped below a predetermined value; Timer means for measuring that the voltage drop state has continued for a predetermined time, and setting a predetermined time serving as a reference for stopping the drive output to the heating element to be longer than the voltage drop time when the heating element is normally energized, The heating element drive circuit device, wherein the drive output to the heating element is stopped when the voltage drop state measured by the means continues for the predetermined time.