JPH04223712A - Driver circuit for logic circuit device - Google Patents

Abstract

PURPOSE:To decide and guarantee an output in spite of an input when a power voltage becomes less than a setting voltage value in the driver circuit of a logic circuit device. CONSTITUTION:A power voltage supervisory circuit 1 supervises the voltage of power supplied to the device. When the potential of the power voltage becomes less than a set point, the potential of the base voltage of a transistor 6 is speedily set to be low and the transistor 6 is turned off. Then, an output terminal 10 is set to be high resistance in spite of the state of an input terminal 7 and accordingly, noise owing to the malfunction of an internal part in the logic circuit is prevented from being outputted to an external circuit when the power voltage rises or drops.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a logic circuit device using semiconductor technology, and in particular, by having a power supply voltage monitoring circuit inside the circuit, when the power supply voltage falls below a certain voltage, it can be used regardless of the input signal. The present invention relates to a driver circuit for a logic circuit device that determines the output to be high resistance.

0002

[Prior Art] Conventionally, the driver circuit of this type of logic circuit device does not guarantee operation during the falling and rising stages of the power supply, and may fail due to noise input from the input terminal or internal operation of the circuit. It was outputting a definite logical signal.

0003

[Problems to be Solved by the Invention] When the driver circuit of the conventional logic circuit device described above is used as a driver circuit for an interface between devices each having an individual power supply, the problem is that when the power supply rises and falls, Since the operation is not guaranteed, they either output noise or have control means to prevent noise from being output to the outside.

An object of the present invention is to provide a driver circuit for a logic circuit device that determines the output regardless of the input signal when the power supply voltage falls below a certain voltage.

[0005]

[Means for Solving the Problems] In order to achieve the above object, a driver circuit for a logic circuit device according to the present invention includes a power supply voltage monitoring circuit inside the circuit for monitoring the power supply terminal voltage supplied to the device. It is.

Further, the power supply voltage monitoring circuit has a transistor on the output side, and when the power supply voltage becomes a potential lower than a set value, the base voltage of the transistor is immediately set to a low potential to turn off the transistor and output. This makes the terminals have high resistance.

[0007] Furthermore, the transistor has a pull-up resistor on the output side, and the resistance value of the pull-up resistor is sufficiently smaller than the current value drawn when the transistor is on, and the current value drawn when the transistor is off. This is set to a value that supplies sufficiently larger power.

[0008]

[Operation] The power supply voltage monitoring circuit 1 monitors the voltage of the power supply supplied to the device, and when the power supply voltage falls below the set value, the output terminal 10 is set to a high resistance, and the output is determined regardless of the input. , Guarantee.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention. In the figure, a power supply voltage monitoring circuit 1 receives power from a power supply terminal 2, compares the voltage with a ground terminal 3, and outputs a high potential to a power supply voltage monitoring circuit output terminal 4 if the potential is higher than a set value. It is something to do. The resistor 5 is used to apply a voltage sufficient to turn on the transistor 6 using the high potential supplied from the output terminal 4 of the power supply voltage monitoring circuit. At this time, when a high potential is input to the input terminal 7, the current flowing through the diode 8 is either small or
Or because it is so small, the transistor 6 is turned on. Since the emitter terminal 9 of the transistor 6 is connected to the ground, an external current is drawn from the output terminal 10 on the collector side of the transistor 6 and a low potential is output. The pull-up resistor 11 is a resistor of an external circuit, and receives power from another power source different from the driver circuit of the logic circuit device of the present invention. The resistance value of the pull-up resistor 11 is an appropriate resistance value that supplies power that is sufficiently smaller than the current value drawn when the transistor 6 is on, and sufficiently larger than the current value drawn when the transistor 6 is off. . When a low potential is input to the input terminal 7 in this state, a current flows from the diode 8 to the input terminal 7 and the transistor 6 is turned off. Therefore, the output terminal 10 has a high potential. Therefore, when sufficient voltage is supplied, the inverted output of the input terminal 7 of the present logic circuit device appears at the output terminal 10. Next, the operation when the voltage at the power supply terminal 2 of the logic circuit device starts to decrease will be explained. The power supply voltage monitoring circuit 1 immediately switches the power supply voltage monitoring circuit output terminal 4 to a low potential when the potential of the power supply terminal 2 becomes lower than a set value. At this time, the transistor 6 is turned off regardless of the input to the input terminal 7, and the output terminal 10 is connected to the pull-up resistor 1.
1 gives a high potential. Next, the operation when the voltage at the power supply terminal 2 of the logic circuit device starts to rise will be explained. The power supply voltage monitoring circuit 1 keeps the power supply voltage monitoring circuit output terminal 4 at a low potential and the transistor 6 turned off until the potential of the power supply terminal 2 exceeds a set value. Immediately when the potential of the power supply terminal 2 exceeds a set value, the power supply voltage monitoring circuit output terminal 4 is set to a high potential so that the output is controlled by the input terminal 7.

0010

As explained above, the present invention has a power supply voltage monitoring circuit inside the logic circuit and determines the output regardless of the input when the power supply voltage falls below the set voltage. Also, there is an effect that the noise of the logic circuit at the time of disconnection is not outputted to the external circuit.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention.

[Explanation of symbols]

1 Power supply voltage monitoring circuit 2 Power terminal 3 Ground terminal 4 Power supply voltage monitoring circuit output terminal 5 Resistance 6 Transistor 7 Input terminal 8 Diode 9 Emitter terminal 10 Output terminal 11 Pull-up resistor

Claims (3)

[Claims] 1. A driver circuit for a logic circuit device, comprising a power supply voltage monitoring circuit inside the circuit for monitoring a power supply terminal voltage supplied to the device. 2. The power supply voltage monitoring circuit has a transistor on the output side, and when the power supply voltage becomes a potential lower than a set value, the base voltage of the transistor is immediately set to a low potential to turn off the transistor and output 2. The driver circuit for a logic circuit device according to claim 1, wherein the terminal has a high resistance. 3. A pull-up resistor is provided on the output side of the transistor, and the resistance value of the pull-up resistor is sufficiently smaller than the current value drawn when the transistor is on, and the current value drawn when the transistor is off. 3. The driver circuit for a logic circuit device according to claim 1, wherein the driver circuit is set to a value that supplies sufficiently larger power.