JPH02204058A - Driving circuit of electronic device - Google Patents

Abstract

PURPOSE:To prevent the malfunction based on noise and potential difference between both low voltage lines by a method wherein high speed operation diodes are connected respectively between a low voltage line for functional device and a low voltage line of a logical operation circuit part and between a high voltage line of the logical operation circuit part and the low voltage line. CONSTITUTION:A diode 26 is connected between a GND line 17 and a Vss line. Further, a diode 28 is also connected between a Vcc line and the Vss line. When power is applied to a heating resister device 2 by driving it, a current flows through the GND line 17, and electric potential of the GND line 17 is raised thereby. Then, the GND line 17 is kept at the same potential as that of the Vss line via the diode 26, and a parasitic transistor is prevented from operating. Further, in the case where surge noise is applied to a power source Vcc line, the Vcc line is kept at constant electric potential with the diode 28. Therefore, a logic circuit part is prevented from malfunctioning and besides, malfunction such as latch up or the like can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a drive circuit for an electronic device such as a thermal head or an optical sensor, and particularly to a drive circuit for an electronic device that requires a large current to flow.

(Prior art) A drive circuit for a thermal head, etc. has a logic circuit section that selects and drives a plurality of arrayed functional elements such as heat-generating resistor elements, and a low voltage line for the functional elements that flows the current of one functional element. Contains. If noise is applied to lines to which high voltages are applied, such as the ttg line or signal line in the logic circuit section, the logic circuit will malfunction, so in order to prevent malfunctions due to noise, lines to which high voltages are applied and low voltage lines should be connected. It is common to connect a capacitor between the two to absorb noise.

(The problem to be solved by the invention) When the noise has a high peak, a capacitor alone cannot sufficiently absorb the noise. There is a possibility that 0MO8 in the logic circuit section may cause latch-up.

For example, in a thermal head, in addition to the low voltage line (Vss) of the logic circuit section, there is also a low voltage line (GND) for flowing the current of the heating resistor, and these two low voltage lines A potential difference occurs within the IC chip for the beating circuit, and this potential difference may turn on a parasitic transistor, causing a logic circuit to malfunction. This malfunction causes poor print quality, such as print data that is not printed even though it is data that should print a black dot.

The present invention provides a swing circuit that can prevent malfunctions caused by noise or leakage caused by potential differences between low voltage lines for functional elements and low voltage lines for logic circuits in electronic devices such as thermal heads and optical sensors. The purpose is to

(Means for Solving the Problems) In the present invention, a high-speed operation diode is connected between the low voltage line for functional elements and the low voltage line of the logic circuit section, and at least one of the lines to which the high voltage of the logic circuit section is applied is connected. A high-speed operation diode is also connected between one line and any of the low voltage lines.

The high-speed operation diode preferably has a switching speed of, for example, several nanoseconds or less, and particularly preferably has a response time to noise of about 10 picoseconds or less.

(Embodiment) The figure shows an embodiment in which the present invention is applied to a thermal head. This thermal head is a thermal head of a type in which one heating resistor element is divided into four groups and energization is controlled.

2 is a heating resistor element, a plurality of which are arranged in a row,
One end of each of the nine heating resistor elements 2 is connected to a common electrode 4, and the other end is connected to an individual electrode 6. Common electrode 4
is connected to the electric terminal IX terminal Vbd for energizing the heating resistor element 2 to generate heat, and one individual electric current i6 is connected to the quick-acting IC 8.

Four IC8s are arranged, and each IC8 controls the energization of a predetermined number of heating resistor elements I2, such as j-28 pieces or 256 pieces.

A print data signal is input to each IC 8 from the data input terminal DI, and the print data is transferred from the clock signal terminal 7 to
A shift register 10 is incremented by a clock signal from the GK, a latch 12 inputs and holds data in the shift register 1° by a load signal from a load signal/terminal/LD, and the data held in the latch 12 is transferred to one side. A predetermined number of AND gate circuits 14 input an input terminal and a printing signal (strobe signal SB) to the other input terminal, and each AND gate circuit energizes the heating resistor element 2 by the output No. 48 of li4. A predetermined number of switching transistors 16 are provided. One switching transistor 16 is provided for each heating resistor element 2, and the emitter of each switching transistor 16 is connected to a ground terminal GND via a ground line 17.

Do is a data output terminal. Vcc is a power supply terminal for operating IC8, and Vss is a ground terminal of IC8.

20 is a thermistor for measuring the temperature of the thermal head.

In this example, 1 heating resistor element 2 is grouped into units controlled by IC8, and 4 characters are printed for each group.
No.3 SBI~Sn4 have been assigned respectively,
The print signals SBI to SB4 are input from the print signal input terminal through each inverter 18 to the AND gate circuit [14] of the IC8.

To remove noise applied to Vhd.

A capacitor 22 is connected between the Vhd line (common electrode) 4 and the GNI''l line 16.
A capacitor 24 is connected between the Vcc line and the Vss line to remove noise applied to the m source.

In order to prevent the logic circuit from malfunctioning due to the rise in the potential of the GND line 17 due to the current flowing through the heating resistor element 2 and the generation of a potential difference with the Vss line, the GN
A diode 26 is connected between the D line 17 and the Vss line. In addition, in order to remove surge noise applied to the Vcc line, the Vcc line and Vss
A diode 28 is also connected between the line and the line. As these diodes 26 and 28, for example, PSKE series Zener diodes (GENERAL INSTRUMENT
(Company T) product) is used. This Zener diode has a noise response time of 1 picosecond or more. Diode 26 is G
The ND side is connected to the 7 node, the Vss side is connected to the cathode, and the diode 28 is connected to the Vss side as the anode,
It is connected so that the Vce side becomes the cathode.

In this embodiment, when the heating resistor element 2 is driven and energized, a current flows through the GND line 17 and the potential of the GND line ]-7 rises, and the diode 2
6, the GND line 17 is kept at the same potential as the Vss line, and parasitic transistors are prevented from operating.

Further, when surge noise is applied to the power supply Vec line, the Vcc line is kept at a constant potential by the diode 28.

In the embodiment, in the logic circuit section, the Vcc line and the Vcc line are connected to each other.
A Zener diode 28 is connected only between the ss line, but in addition to the Vcc line, there are also CK, LD, and SB
A diode may be connected between the GND line 17 and the Vss line with the Vss side serving as the anode, and a surge absorbing diode may be connected between the GND line 17 and the Vss line with the Vss side serving as the anode. A diode may be further connected to the line to which high voltage is applied in the logic circuit section, such as the Vcc line or CK line, and the GND line 1.
A surge absorbing diode may be connected between the terminal and the terminal 7 with the GND side serving as the anode.

Although the embodiment is an example in which the present invention is applied to a thermal head, the present invention can be similarly applied to other than thermal heads, for example, toe-claw sensors.

(Effect of the invention) In the present invention, a high-speed operation diode is connected to the lfJ between the low voltage line (GND) for the functional element and the low voltage line (Vss) of the logic circuit section, so that the functional element such as the 5 heat generating resistor Even if a current flows through the GND line due to operation and the potential changes, the V
It is possible to prevent the logic circuit section from malfunctioning by keeping it at the same potential as the ss line.

In addition, a high-speed operating diode is also connected between the line to which high voltage is applied and the low voltage line, so even if there is surge noise on the line to which high voltage is applied, the constant It is possible to maintain the voltage at a certain potential, thereby preventing malfunctions such as latch-up.

2... Heating resistor element, 8... Drive I
C, 10...Shift register, 12...
・Latch circuit, 14...AND gate circuit, 1
6...Switching transistor, 26.28
...High-speed operation Zener diode, GND...
...Low voltage terminal for heating resistor element, Vss...
...Low voltage terminal for IC.

Claims (1)

[Claims] (1) In a drive circuit including a logic circuit section that selects and drives a plurality of functional elements arranged in an array, and a low voltage line for functional elements that flows current of the functional elements, the low voltage line for functional elements and the logic circuit A high-speed operation diode is connected between the low voltage line of the logic circuit section, and a high-speed operation diode is also connected between at least one of the lines to which the high voltage of the logic circuit section is applied and any of the low voltage lines. A drive circuit characterized in that: