JPS621018A - Thermal print head - Google Patents

Abstract

PURPOSE:To avoid the damage by burning of a heating resistor by utilizing the Zener voltage branched from a power supply for heating resistor via a Zener diode to the power supply of a driving IC. CONSTITUTION:The input voltage given from a heater power supply VH is branched to a heating resistor R1 and a Zener diode Zd. The constant voltage VZd is extracted out of a Zener diode Zd as the power supply VDD for driving IC and then supplied to a logic circuit part Lo. As a result, the holding energy of the corresponding power supply VH is small even in the unstable areas caused by the switch ON and OFF modes. This avoids the damage by burning of the register R1.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a thermal print head incorporated in a printer mechanism such as a facsimile machine, word processor, or electronic typewriter, particularly a thermal print head in which a driving IC is mounted on the same substrate. The present invention relates to a circuit configuration of a power source for a driving IC and a power source for a heat generating resistor in the present invention.

(Prior Art) FIG. 3 shows a basic circuit diagram of a conventional thermal print head equipped with a driving IC (1). In the figure, the driving IC (1) is composed of a logic circuit portion Lo and a switching transistor St, and a heating resistor R1 for printing on thermal recording paper or thermal ribbon is connected to the switching transistor St. There is. The logic circuit section Lo is connected to a power supply VDD for the driving IC, while the heating resistor R is connected to a power supply VH for the heating resistor (hereinafter referred to as "heater"), and the driving IC
C power supply VDD and heater power supply VH are switched on.
Then, the drive voltage pulse-adjusted by the logic circuit section Lo in accordance with an external input signal acts on the switching transistor St to turn it on, FFt, and appropriately open and close the current flowing through the heating resistor R. As a result, the heating resistor R1 generates Joule heat, and printing is performed as appropriate. Incidentally, in reality, one IC (I) includes a large number (for example, 32) of switching transistors St,
The same number of heating resistors R□ are respectively connected to the transistor St, and the heating resistor R1 is connected to the transistor St by the control of the logic circuit section LO.
The figure shows this in a simplified manner.

(Problems to be Solved by the Invention) By the way, in the thermal print head with the above configuration, the driving IC (I) does not turn on the power supply VDD.
, when turning off, it passes through an unstable region, that is, a region in which the switching transistor St cannot be controlled. At this time, the heater power supply VH is set to the normal working voltage (24V or 12V
), the IC(I) will malfunction and the IC(I)
The heating resistor R□ is energized regardless of the output signal from the
Enough energy may be applied to burn out the heating resistor R□. FIG. 4 shows an example of this, and shows the order of the power supplies VDD and VH when the power supplies VDD and VH are turned on and off at the same time.

Point a in the figure is the switch ON point, and the power supply VDD
From point a, the voltage passes through the unstable region A (approximately 2 to 3 V) and reaches steady state B (approximately 5 V) in which normal performance is achieved. On the other hand, the power supply VH becomes steady at a higher voltage level (12v to 24v) later than the power supply VDD while drawing the same trajectory as the power supply VDD from point a at the same time as the switch is turned on. Also, the dot is the switch OFF point, and the power supply VDD is the switch OFF point.
When F is applied, the voltage reaches the zero level from point b through the unstable region C, contrary to the above, and the power supply VH reaches the voltage zero level later than this. In this way, the driving power supply VDD is turned ON.

When the power supply VH for the heater is in the unstable region when it is OFF, it already or still has energy E, E2 (shaded area in the figure), so if the drive IC (1) malfunctions for some reason, This energy E1゜E2 is the heating resistor R
Added to 1. The energy E when the power is turned on is normally about 0.02v x 1sec (J), and at this level there is little concern that the heating resistor R will burn out, but when the power is turned on,
Energy E2 during FF is normally 1.62 x 2sec
(J), which can sufficiently burn out the heating resistor R□. In order to avoid such burnout troubles, it is necessary to eliminate the above-mentioned energies E□ and E2 as much as possible, and to do so, as shown in Figure 5, while the drive power supply VDD is sufficiently stable, Turn on/off heater power supply VH
It is effective to arrange the power supply order so that the However,
In order to establish such a power supply order, it is necessary to provide a time difference between the power supplies VDD and VH, and therefore it is necessary to provide an extra control circuit on the printer main body side, which is not desirable in terms of cost. Furthermore, during head inspection, printer assembly, or printer inspection during the printer manufacturing process, heads are often replaced while the power is on, and in such cases, the power supply VDD is at a high level when the above-mentioned failure occurs. Since the stable state C is reached, the heat generating resistor R may burn out, which inevitably becomes a major bottleneck in the printer manufacturing process.

(Object of the invention) The present invention has been made to solve the above problems,
Regardless of the ON/OFF order of the IC driving power source and the heater power source, the heating resistor is always kept from thermal destruction.

(Means for Solving the Problems) The structure of the present invention for achieving the above object will be explained based on the attached embodiment drawings. Figure 1 is a basic circuit diagram of the thermal print head of the present invention, and Figure 2 is a power supply O in the same embodiment.
It is a figure showing the order of N and OFF. It should be noted that the same reference numerals in FIG. 1 as those in the preceding examples (FIGS. 3, 4, and 5) are used without modification. That is, the gist of the present invention is as follows:
In a thermal print head equipped with a heating resistor R□ and a driving IC (I) that generates an output for selectively driving the heating resistor R□ to generate heat, the driving IC (1)
), a Zener voltage VZd branched in parallel to the heat generating resistor R1 from a power supply VH for one heat generating resistor via a Zener diode Zd is used as a power supply VDD for the heat generating resistor R1. .

In the figure, the driving IC (I) includes a logic circuit portion LO and a switching transistor St, the Zener voltage VZd is input to the logic circuit portion Lo, and the heating resistor R1 is connected to the switching transistor St. has been done. In this case as well, a plurality of the transistors St are connected to one logic circuit portion LO, and the transistor S
As described above, the same number of heating resistors R are connected to each of t.

(Function) In the thermal print head with the above configuration, the input voltage (for example, 12V or 24V...voltage necessary to cause the heating resistor R2 to generate Joule heat) from the heater power supply VH when the switch is turned on is applied to the heating resistor R. and a Zener diode Zd, and the Zener diode Zd provides a constant voltage, that is, the voltage (for example, 5 V) necessary to drive the driving IC (1), VZd is the power supply VDD of the driving IC.
The signal is extracted as follows and input to the logic circuit section Lo. When the voltage of the power supply VDD input to the logic circuit portion LO reaches the above-mentioned constant voltage, the driving IC (1) is in a state where it can perform its normal functions. On the other hand, after the switch is turned on, the above-mentioned high level voltage is applied to the heat generating resistor R1, and the heat generating resistor R1 is brought into a state where it can be energized by the output signal of the driving IC (I).

The operational states of power ON and OFF will be described in further detail with reference to the power supply order shown in FIG. In the figure, a point α is the point where the power supply V11 is switched ONL, and from this point α, the voltage of the power supply VH1VDD simultaneously rises, and the power supply VDD passes through the unstable region A and reaches the controllable stable region B. This stable region B is maintained at the Zener voltage zD by the Zener diode Zd as described above. On the other hand, the voltage of the heater power supply VH increases thereafter and is maintained at the input high voltage level. When the power supply VH is switched off at point β, the voltage of the heater power supply VH simultaneously decreases and reaches the zero level. However, the voltage of the power supply VDD is such that the input voltage to the Zener diode Zd is
It does not fall until it reaches the control voltage of d (5V in the example in the figure), and when it reaches this control voltage (indicated by point γ in the figure), it traces the same trajectory as the voltage of the power supply VH above and falls through unstable region C. , will eventually reach the zero level. Therefore, when the power source VDD passes through this unstable region C, the energy E4 possessed by the heater power source VH has already become small, so even if the drive IC (1) malfunctions in the unstable region C, one heating resistor This means that enough energy is not added to the body radius to cause it to burn out. Even in the unstable region A when the switch is ○N,
Since the power supplies VH and VDD rise at the same time, the energy E possessed by the heater power supply VH corresponding to the unstable region A
, is small, and as above, the heating resistor R□ does not burn out.

(Example) Next, an example will be described.

In Fig. 1, from the power supply VH to the Zener diode Zd
A protective resistor RDD is interposed in the middle of the input line to the
The protective resistor RDD prevents instantaneous excessive current from flowing to the Zener diode Zd when the power supply VH is switched on. Furthermore, the other terminal of the Zener diode Zd is grounded, and the surplus voltage controlled by the diode Zd is consumed here, but this surplus voltage cannot be used as a supply voltage to other circuits. It is possible.

It goes without saying that the present invention is not limited to the above-mentioned embodiments, and that other changes can be made without departing from the scope of the present invention.

(Effects of the Invention) As described above, the thermal print head of the present invention uses the Zener voltage branched from the power source for the heat generating resistor via the Zener diode as the power source for the driving IC, so that there is no external power from the head. The only power supply terminal that can be drawn out to the main unit is the power supply for the heating resistor, which simplifies the electrical connection to the main body.Also, since there is only one power supply, there is no need for the conventional power supply order, and the power supply of the drive IC is in an unstable range. Even if the IC malfunctions, a large amount of energy will not be added to the heating resistor.
Trouble such as burnout of the heating resistor when F is avoided. Moreover, since such an effect is achieved by equipping the head with a Zener diode, there is no need for any circuit for controlling the power supply order on the printer main body side, which is advantageous in terms of cost. Furthermore, even if the head is removed from the printer body while the power is on, the above-mentioned troubles due to the power supply order will not occur, making processes such as head inspection, printer assembly, and printer inspection easier, resulting in great manufacturing benefits. .

As described above, the present invention has many advantages.
Its value is extremely great.

[Brief explanation of the drawing]

Figure 1 is a basic circuit diagram of the thermal print head of the present invention.
FIG. 2 shows the power turned on in the same embodiment. Figure 3 is a basic circuit diagram of a conventional thermal print head, Figure 4 is a diagram similar to Figure 2 of the same head, and Figure 5 is a similar diagram of an improved type. (Explanation of symbols) (1)...Drive IC, VDD...Power supply for drive IC, VH...Power supply for heating resistor, R construction...
Heat generating resistor, Zd... Zener diode, V
ZD...Zener voltage. 1 or more 1 Figure 2

Claims (1)

[Claims] 1. In a thermal print head equipped with a heating resistor and a driving IC that emits an output for selectively driving the heating resistor to generate heat, as a power source for the driving IC,
A thermal print head characterized in that a Zener voltage branched in parallel from a power supply for the heating resistor to the heating resistor via a Zener diode is used.