JPS6040263A - Integrated circuit for driving double power source printing element - Google Patents

Abstract

PURPOSE:To check a heat generating element from operating under the non-control condition by operating a gate circuit under normal state by another low voltage being lowered from a high voltage during the lowering of a low voltage to prevent malfunctioning of an output transistor. CONSTITUTION:When the lowering of a low voltage from a terminal 2 is detected, a switch of a power source circuit 7 is changed over with a voltage detection circuit 9 for a low voltage power source and a low voltage is supplied to a gate circuit 3 from a voltage lowering circuit 8 for lowering the high voltage from a terminal 20. Consequently, the circuit 3 operates normally to generate a low level output without the supply of the power to a logic circuit 1 and an output transistor 5 is turned OFF through a level shifter and a buffer circuit 4 to prevent malfunctioning. Thus, a heat generating element 6 is checked from operating under the non-control state thereby eliminating breakdown of the element 6 due to overcurrent.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dual-source printing element driving integrated circuit, and more particularly, to
This invention relates to a new improvement for preventing output transistors from turning on their own when the low voltage supplied when driving a printing element such as a thermal head heating element with a two-wheel power source prevents an erroneous signal from being supplied to the thermal head. It is something.

In conventional thermal head drive circuits, when the low voltage supplied to the logic circuit for level shift and buffer control decreases,
Since the output transistor is connected to a high voltage 1M source and remains in the on state, the heating element connected to the output transistor will operate in an uncontrolled state, resulting in printing errors and destruction due to overcurrent. However, it turned out to be a serious flaw.

The present invention aims to provide extremely effective means for quickly eliminating the above-mentioned drawbacks, and in particular, it is an object of the present invention to provide extremely effective means for quickly eliminating the above-mentioned drawbacks. Connected to the output of the gate circuit 7'1. a level shift circuit, an output transistor connected to the output of the level shift circuit, a power supply switching circuit connected to the gate circuit, a step-down circuit connected to the power supply switching circuit, and the low voltage logic a low voltage input terminal for inputting the low voltage supplied to the circuit and the power supply switching circuit, and a degenerate voltage input terminal for inputting the high voltage supplied to the step-down circuit, and υ from the low voltage input terminal. The voltage of the supplied low voltage decreases and f? -, S combination, heavy pressure t for low voltage power supply
The ω output circuit detects this and outputs a signal, and this signal causes the power supply switching circuit to switch, supplying the gate circuit with the low voltage from the step-down circuit, and causing the output of the gate circuit to change. This configuration is such that the output transistor becomes L level and turns off the output transistor.

Hereinafter, preferred embodiments of the dual power supply type printing element driving integrated circuit according to the present invention will be described in detail with reference to the drawings.

In the drawings, the reference numeral 1 indicates a low voltage system (+57
), and each output of this logic circuit 1 is inputted to each input of a NAND gate circuit 6 to terminals 5a and 5b.

The output of this gate circuit 5 is connected to a level shift and bumper circuit 4, and the output of this level shift and bumper circuit 4 is connected to the gate of an output transistor 5 consisting of an N-type MO transistor. The source of this output transistor 5 is grounded, and its drain is connected to a heating element 6 constituting a thermal head (not shown), and the other end 6a of this heating cord 6 is connected to a power source for driving the heating element. ing.

The output terminal 7a of the power supply switching circuit 7 is connected to the gate circuit 5 as a gate power supply line 7d, and the step-down circuit connected to the high voltage input terminal 20 is connected to the first terminal 7b of the power supply switching circuit 7. 8 are connected.

Although not shown in the drawing, the power supply switching circuit 7 is composed of a known electronic switching circuit, and in order to control its operation, a low voltage power supply voltage detection circuit connected to the high voltage power supply input terminal 20 is used. A circuit 9 is connected to the low voltage power supply voltage detection circuit 9, and a low voltage is supplied from the low voltage input terminal 2.

Further, a low voltage is supplied from the low voltage input terminal 2 to the low voltage logic circuit 1 via the power line 10, and the other output of the logic circuit 1, that is, the other input terminal 6b of the gate circuit 5 is supplied with a low voltage. The resistor RL is grounded. Further, a high voltage is supplied to the level shift and bumper circuit 4 from a high voltage input terminal 20.

In the above configuration, when operating the dual power supply type printing element driving integrated circuit according to the present invention, a low voltage is supplied from the low voltage input terminal 2 and a high voltage υ is supplied from the high voltage power supply input terminal 20. , the voltage detection circuit 9 for low voltage power supply is activated and the output terminal 7 of the power supply switching circuit 7 is activated.
Since a is connected to the second terminal 7c, a low voltage (+5V
) is supplied to the gate circuit 5 and the logic circuit 1, and since each normal signal is output from the logic circuit 1, the gate circuit 6 is activated, and the output transistor 5 is turned on or off via the level shift and bumper circuit 4. It says off,
The heating cord 60 is turned on according to the signal output of the logic circuit 1,
Turning off is performed normally.

However, when the voltage of the low voltage supplied to the low voltage input terminal 2 drops, power is no longer supplied to the logic circuit 1 and the low voltage power supply voltage detection circuit 9 does not operate, so the power supply switching circuit The output terminal 7a of 7 is switched to be connected to the first terminal 7'b, and the low voltage 11i obtained by stepping down the high voltage by the step-down circuit 8 is connected to the gate TiL 6.
G, f+ are supplied to the logic circuit 5 via one line 7d,
Only logic circuit 5 can continue to operate.

In this case, the terminal voltage of the resistor RL connected to the other input terminal 5b of the logic circuit 5 is the low voltage 14'i,
Since the output of the logic circuit 5 goes to the B level in conjunction with the turning off of the transistor 2, the output transistor 5 turns off, so that the heating element 6 is not energized (V, J) and will not be destroyed. It is something that will disappear.

2. The power supply type printing drive integrated circuit according to the present invention has the above-described configuration and operation, so even if the low voltage supplied from the low voltage input terminal 2 decreases and the logic circuit is Even if it stops working, the gate circuit can still operate normally using the low voltage that is obtained by stepping down another high voltage, which prevents the output transistor from malfunctioning, thereby preventing printing errors and heating elements. destruction is something that can be prevented in a very specific way.

[Brief explanation of the drawing]

The drawing is a schematic diagram showing a 1.7H type thermal head driving integrated circuit according to the present invention. 1 is a logic circuit, 2 is a low voltage input terminal, 5 is a gate circuit, 58.5btd input terminal, 4 is a level shift and buffer circuit, 5 is an output transistor, 6 I;
:Heating element. 7 is a power supply switching circuit, 8 is a step-down circuit, 9 is a voltage detection circuit for a low voltage 1'A source, 10 is a power supply line, and 20 is a high-voltage, press-in connector. Applicant: Daini Seikosha Co., Ltd. Agent: Patent Attorney Mogami

Claims (1)

[Claims] A low voltage logic circuit, a gate circuit connected to the output of this logic circuit, a grounding resistor provided at one input terminal of this gate circuit, and a level shift connected to the output of the front gate circuit. and a buffer circuit, an output transistor connected to the output of the level shift and Vanonoa circuit, a power supply switching circuit connected to the gate circuit, the city switching circuit, the logic circuit, and a low voltage power supply. Low 11y supplied to 11L pressure detection circuit
a low current input terminal for inputting voltage, and a high voltage input terminal for inputting a high voltage having a voltage opposite to the low voltage MiJ supplied to the level shift and buffer circuit and the step-down circuit. , the voltage detection circuit for the low voltage power supply connected to the power supply switching circuit; Detected by the voltage detection circuit for low voltage power supply, the power supply switching circuit is turned off, and the low voltage from the step-down circuit is supplied to the gate circuit, and the output of the gate circuit becomes L level and the output transistor is configured to turn off.