JPH0354632B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a device for driving a heating element on a thermal head in a thermal recording device.

Configuration of a conventional example and its problems FIG. 1 is a schematic circuit diagram of a conventional heating element driving device. In this figure, heating elements 1-1 to 1-N are arranged in a line on the thermal head. One end of these heating elements 1-1 to 1-N is directly connected to one terminal 3 of the recording power source 2, and the other end is connected to the other terminal of the recording power source 2 via switch circuits 4-1 to 4-N, respectively. is connected to terminal 5 of. Each control input of the switch circuits 4-1 to 4-N is
It is connected to the outputs of corresponding ones of AND gates 6-1 to 6-N. AND gate 6-1 to 6-
One input of N is connected to the terminal 7, and the other input is connected to the corresponding output of the N-bit parallel output shift register 8. The data input of shift register 8 is connected to terminal 9, and the clock input is connected to terminal 10.

Next, the operation will be explained. Image information is transferred from the outside to terminal 9, and an image information sampling clock is applied to terminal 10. The shift register 8 sequentially takes in and stores image information at clock timing. When N bits of image information to be stored in one recording operation are stored in the shift register 8, a recording pulse with a constant pulse width is inputted to the terminal 7 from the outside. During the period when this recording pulse is at the '1' level,
Among the AND gates 6-1 to 6-N, the corresponding output of the shift register 8 is at the '1' level, that is, the AND gate corresponding to the black pixel outputs the '1' level. The switch circuits 4-1 to 4-N become conductive when a '1' level is applied to the control input. Therefore, among the heating elements 1-1 to 1-N, the heating element corresponding to the black pixel is energized for a time corresponding to the pulse width of the recording pulse.

Now, at present, the resistance value of the heating element is about 1 kilohm at most, and the allowable power of the heating element is about 1 watt at most, so the voltage of the recording power source 2 has to be made quite low. Further, depending on the image information to be recorded, the number of heating elements to be energized varies, but this directly results in a variation in the load current of the recording power source. For this reason, there has conventionally been a problem that the recording power source has become complicated and large. In other words, if the resistance value of the heating element is large enough and the voltage value of the recording power supply voltage can be set sufficiently high, and if the fluctuation of the load current is small, then the
It is possible to use a simple recording power supply that directly rectifies and smoothes 100V without stepping down the voltage, but in the past, commercial AC was stepped down using a transformer, then rectified and smoothed, and then a voltage stabilization circuit was used. Therefore, it was necessary to use a large and complex recording power supply with a voltage stabilization structure.

Purpose of the invention The present invention solves the above-mentioned conventional problems.
It is an object of the present invention to provide a heating element driving device that can simplify and downsize a recording power source compared to the conventional one.

Structure of the Invention The present invention does not connect individual heating elements to a recording power source in parallel, but connects a plurality of heating elements in series via a first switch circuit, and connects the heating elements and the first switch circuit. A series circuit consisting of a resistor having a resistance value equivalent to that of the heating element and a second switch circuit is connected in parallel to each series circuit consisting of the circuit, so that the load resistance value of the recording power source is increased and kept constant. This aims to achieve the above objectives.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a schematic circuit diagram of a heating element driving device according to an embodiment of the present invention. In this figure, 11 ₁
~11 _N are heating elements arranged in a row on the thermal head. These heating elements are successively connected in series via first switch circuits 12 ₁ to 12 _N , and are connected to terminals 14 and 15 of the recording power source 13.
16 ₁ to 16 _N are resistors having a resistance value equivalent to that of the heating elements 11 ₁ to 11 _N , and 17 ₁ to 17 _N are second switch circuits. A series circuit consisting of a resistor 16 ₁ and a second switch circuit 17 _{1 is connected in parallel to a series circuit consisting of a heating element 11 1 and} a first switch circuit 12 ₁ . Similarly, a series circuit consisting of a resistor and a second switch circuit is connected in parallel to each series circuit consisting of another heating element and a first switch circuit.

18 ₁ to 18 _N are first switch circuits 12 ₁ to 1
_2N , and the outputs of these AND gates are connected to the control inputs of the corresponding first switch circuits ₁₂₁ to _12N . 19 ₁ to 19 _N is the second switch circuit 17
₁ to 17 _N , and the outputs of these AND gates are connected to the control inputs of the corresponding second switch circuits 17 ₁ to 17 _N , respectively. AND gate 18 ₁ ~ 18 _N
One input is connected to the terminal 20, and the other input is connected to the outputs Q ₁ to Q _N of the shift register 21, respectively. 22 ₁ to 22 _N are inverters, and each input is connected to a corresponding one of the outputs Q ₁ to Q _N of the shift register 21.
One input of AND gates 19 ₁ to 19 _N is terminal 2
0, and the other input is connected to inverter 22 ₁ ~
22 _N is connected to the output of its corresponding one.
The data input of shift register 21 is connected to terminal 23, and the clock input is connected to terminal 24.

Next, the operation will be explained. During a period in which no recording pulse is applied to the terminal 20, the outputs of the AND gates 18 ₁ to 18 _N and the AND gates 19 ₁ to 19 _N are all at "0" level, and the outputs of the first switch circuits 12 1 to 12 N and the first switch circuits 12 ₁ to 12 _N and the 2 switch circuit 17
₁ to 17 _N are all in the off state, so no current flows from the recording power source 13. This is the non-recording operating state.

The recording operation is as follows. First, image information to be recorded is sequentially transferred to the terminal 23, and an image information sampling clock is supplied to the terminal 24.
This image information is taken into the shift register 21 and stored at the timing of the sampling clock. When the image information to be recorded in one recording operation is accumulated in the shift register 21, a recording pulse (“1” level signal) with a constant pulse width is sent to the terminal 2.
It is input to 0. Here, the image information heating element 11 ₁
Assume that the pixel corresponding to is a black pixel. In this case, the output _Q1 of the shift register 21 is at the "1" level, so the output of the AND gate ₁₈₁ is "1".
level, and the output of the AND gate ₁₉₁ becomes "0" level. Therefore, the first switch circuit 12 ₁ is turned on and the second switch circuit 17 ₁ is turned off, so that current flows through the heating element 11 ₁ . Also heating element 1
If the pixel corresponding to 1 ₂ is a white pixel, the output Q ₂ of the shift register 21 will be at the “0” level.
The output of AND gate 18 ₂ is “0” level, AND
The output of gate ₁₉₂ becomes “1” level, and the first
The second switch circuit 12 ₂ is turned off, and the second switch circuit 17 ₂ is turned on. Therefore, the current flows through the resistor 16 ₂
It flows to the heating element 112 and does not flow to the heating element ₁₁₂ . In this way, among the heating elements 11 ₁ to 11 _N , only those corresponding to black pixels are selectively energized for a time corresponding to the pulse width of the recording pulse.

As is clear from the above explanation, the heating element 11 ₁
~11 _N and the resistance value of the resistor 16 ₁ ~16 _N is R,
If the resistance of the switch circuits 12 ₁ to 12 _N , 17 ₁ to 17 _N and wiring is ignored, the load resistance value of the recording power supply 13 during recording operation, that is, the resistance value measured from the terminals 14 and 15 is R×N. Moreover, the resistance value is constant regardless of the image information. Therefore, if the number N of heating elements connected in series is appropriately determined, an extremely simple power source that does not include a step-down transformer or a voltage stabilization circuit can be used as a recording power source.

In the above embodiment, all the heating elements 11 ₁ to 11 _N on the thermal head were connected in series, but the heating elements on the thermal head were divided into several groups, and the heating elements were connected to each group. They may also be connected in series. Also, the heating element 11
In addition to ₁ to 11 _N , low antibodies 16 ₁ to 16 _N , switch circuits 12 ₁ to 12 _N , 1 ₁ to 16 _N , and even
AND gates ₁₈₁ to _18N , ₁₉₁ to _19N , inverters ₂₂₁ to _22N , and shift register 21
It is also possible to provide it integrally on the thermal head, etc. Furthermore, the switch circuits 12 ₁ -
The means for controlling 12 _N , 17 ₁ to 17 _N is not limited to the configuration of the above embodiment, and may be modified as appropriate.

Effects of the Invention As described above, the present invention connects the heating elements in series via the first switch circuit, and connects the heating elements and the first switch circuit to each other in series.
A series circuit consisting of a resistor and a second switch circuit is connected in parallel to each series circuit consisting of a switch circuit, and the heating element is selectively energized by controlling conduction between the first and second switch circuits. Therefore, it is possible to use an extremely simple and compact power source that directly rectifies and smoothes commercial alternating current as a recording power source.

[Brief explanation of drawings]

Figure 1 is a schematic circuit diagram of a conventional heating element drive device.
FIG. 2 is a schematic circuit diagram of a heating element driving device according to an embodiment of the present invention. 11 ₁ to 11 _N ... heating element, 12 ₁ to 12 _N ... first switch circuit, 13 ... recording power supply, 16 ₁
~ _16N ...Resistor, _{171~ 17N} ...Second switch circuit, ₁₈₁ ~ _18N , _{191~ 19N} ...
AND gate, 21...shift register, 22 ₁ ~
22 _N ...Inverter.

Claims (1)

[Claims] 1 The heating elements on the thermal head are successively connected in series via a first switch circuit, and a series circuit of a resistor having the same resistance value as the heating element and a second switch circuit is connected between the heating element and the first switch circuit. The first switch circuit or the second switch circuit is connected in parallel to each series circuit consisting of a switch circuit.
A heating element driving device characterized by comprising means for making either one of the switch circuits conductive.