JPS60245310A - Driving circuit - Google Patents

Abstract

PURPOSE:To select whether a voltage corresponding to a set reference voltage is outputted by a switching circuit which is turned on and off by a control signal, or a high impedance state is set, by providing an operational amplifier for outputting said voltage. CONSTITUTION:When a control signal of a terminal 78 is L, each transistor of a switching circuit 6 is off and an outputting circuit 4 is controlled to a voltage output state, and reference voltages Vdh, Vdi are inputted selectively to an operational amplifier 2 and the same voltage is outputted from a terminal 46 of the outputting circuit 4. On the contrary, when the control signal H, each transistor of the switching circuit 6 becomes on, transistors 14, 18 of the outputting circuit 4 become off, and the output terminal 46 is released from generation of the voltage and becomes a high impedance output state. An optional voltage output state and a high impedance output state can be switched by the control signal, and this circuit is effective as a bus line driving circuit in case of an inspection, etc. of a control device.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a drive circuit, and in particular, has three output states: a low level output, a high level output, and a high impedance output when the output is released. (tr
i-5tate).

[Conventional technology]

In testing and measuring the control functions and output status of various control devices such as microcomputers,
A drive circuit is sometimes used to drive the pass line, but this drive circuit is required to have the ability to set a desired signal level and to put the signal line in an open state.

Conventionally, it has been impossible to achieve such signal level settings and high impedance output states with a single circuit.

[Problem that the invention seeks to solve]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to be able to arbitrarily set the output voltage level, and also to release the output and switch to a high impedance state using a single circuit.

[Means for solving problems]

The present invention includes an operational amplifier that outputs a set arbitrary reference voltage, a switching circuit that switches in response to a control input, and an operational amplifier that is installed on the output side of the operational amplifier and outputs the output voltage set by the operational amplifier. and an output circuit that releases voltage output in response to the switching output of the switching circuit and makes the output point high impedance.

[For production]

By switching the switching circuit, the output circuit generates an arbitrary voltage set by the operational amplifier, or releases the voltage generation and makes the output point high impedance.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.

FIG. 1 shows an embodiment of the drive circuit of the present invention.

In FIG. 1, this drive circuit includes an operational amplifier 2
An output circuit 4 is installed on the output side of the output circuit 4, and a switching circuit 6 for controlling the output state of the output circuit 4 is installed.

The non-inverting input terminal (+) of the operational amplifier 2 has a reference voltage Vdh set to the voltage setting terminal 8A, and a voltage setting terminal 8B.
The reference voltage Vdl set to switch IOA, IOB
It has been added via.

In this case, the magnitude relationship between the reference voltages Vdh and Vdl is V
The switch IOA is set such that dh>Vdl.

10B is selectively opened and closed by the opening/closing control operation of the switching control circuit 12 based on a control input applied to the control input terminal 11. In this embodiment, two types of reference voltages are set, but it is also possible to set three or more levels of reference voltages with different levels.

The output circuit 4 also includes transistors 14, 16, 18, .
20, diode 22.24.26.28 and resistor 3
A positive voltage +Vc is applied to the terminal 42, a negative voltage -Vc is applied to the terminal 44, and a desired output state is formed at the output terminal 46.

The switching circuit 6 has a buffer circuit 48 installed in its human power section, and transistors 50 and 52.
．． 54.56, diode 58 and resistor 60.62.
A driving voltage Vll is applied between the terminal 76 and the ground point (GND), and a switching control voltage Vll is applied to the control input terminal 78.
s is added.

The operation will be explained based on the above configuration.

When the switching control voltage applied to the control input terminal 78 is at a low level, the transistors 50, 52, 54, 56 of the switching circuit 6 remain non-conductive and the output circuit 4 is controlled to the voltage output state.

In this case, the switches IOA and IOB are selectively opened and closed by the opening and closing control of the switching control circuit 12 based on the control input applied to the control input terminal 11, and the input terminal 8A
, 8B are selectively applied to the non-inverting input terminal (+) of the operational amplifier 2.

This applied voltage is generated at the output of the operational amplifier 2, and a similar voltage can be taken out from the output terminal 46.

That is, from transistor 14.18 to resistor 38.40
Since the voltage at the output terminal 46 connected via
+-) is equal to the set potential.

Therefore, by arbitrarily selecting and setting the reference voltage to be set at the terminals 8A and 8B, that value is transferred to the output terminal 46.
It can be taken out from.

Further, when the switching control voltage applied to the control input terminal 78 is at a high level, the output of the buffer circuit 48 becomes a high potential accordingly, and the transistor 50 becomes conductive. Therefore, the base of transistor 52 becomes low potential through transistor 50, and transistor 52 also becomes conductive, so that each transistor 54, 56 becomes conductive.

As a result, the potential on the anode side of the diode 22.26, that is, the potential at the point a, becomes approximately negative potential -Vc via the transistor 56, and the potential on the cathode side of the diode 24.28, that is, the potential at the point b, becomes approximately negative potential -Vc through the transistor 56. The potential is changed to approximately positive potential +Vc through the voltage.

Therefore, the transistor I4.18 enters the cut-off state, and the output terminal 46 is released from voltage generation and is switched to a high impedance output state.

In this case, the diodes 22 and 24 are for voltage resistance and prevent malfunction of the transistors 14 and 18 in this state.

As explained above, according to such a configuration, the output state can be selectively changed from low voltage output to high voltage output and high impedance according to the switching operation of the switching circuit 6 and the setting of the reference voltage for the operational amplifier 2. Therefore, a tri-state output state can be achieved.

Further, in the drive circuit of this embodiment, it is possible to lower the driving voltage, for example, it is possible to drive at 5V.

FIG. 2 shows an example of application of the drive circuit of the present invention, in which the same parts as in the previous embodiment are given the same reference numerals. This application example shows an inspection circuit for inspecting a drive circuit of a liquid crystal display and its control circuit.

That is, the control circuit 80 is composed of a microcomputer or the like, and there is a bidirectional line between the pass lines 84a and 84b that connects the control circuit 8o and the drive circuit 82 that generates a drive output according to the control output of the control circuit 80. Sexual drive equipment M
86 has been installed.

The drive device 86 includes a drive circuit 86a of the present invention,
86b. That is, the drive circuit 86
a has an output terminal 46 and a pass line 8 on the pass line 84a side.
4, the control input terminal 11 is connected to the b side, and the drive circuit 86b is connected so that the output terminal 46 is connected to the pass line 84a side, and the control input terminal 11 is connected to the pass line 84b side. Both drive circuits 86a, 86b are connected to pass lines 84a, 84b via common terminals 87a, 87b.

In this way, if the drive device 862 is installed in the pass line 84, a predetermined control input and a second
Input terminal 8A not shown in the figure.

Set the signal level to a desired potential by setting reference potentials Vdh and Vdl to terminals 87a and 87B.
control input terminal 78 of drive circuit 86a, 86b from b
By applying the switching control voltage Vs to , the output can be canceled and the output state can be set to a high impedance state, so that predetermined inspections and characteristic measurements can be performed on the drive circuit 82 and the like.

These mode settings also apply to a single drive W86
Since the inspection can be carried out with a

Although the driving of a pass line has been described as an application example, the present invention can be used in various devices that require a tri-state output state.

〔Effect of the invention〕

As explained above, according to the present invention, the following effects can be obtained.

+11 An arbitrary output voltage can be generated by setting the reference voltage, and a high impedance output state can be obtained by canceling the output voltage.

(2) Alternatively, these output states can be realized by a single circuit, and each output state can be arbitrarily set by a switching operation.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the drive circuit of the present invention, and FIG. 2 is a block diagram showing an example of its application. 2... operational amplifier, 4... output circuit, 6... switching circuit.

Claims (1)

[Claims] an operational amplifier that outputs an arbitrary voltage according to an arbitrary set reference voltage; a switching circuit that switches in response to a control input; and a switching circuit that is installed on the output side of the operational amplifier and outputs the output voltage set by the operational amplifier. and an output circuit that releases the voltage output in response to the switching output of the switching circuit and places the output point in a high impedance state.