JPS62251677A - Disconnection detecting circuit for operational amplifier feeder - Google Patents

Abstract

PURPOSE:To enable a normal operational amplifier to be used by making the absolute value of a voltage between one feeder and the output terminal of the operational amplifier lower than the minimum absolute value of a voltage developed when there is no disconnection when the other feeder of a DC power source between a signal processing circuit and the operational amplifier is broken. CONSTITUTION:This circuit has the operational amplifier 3 of a sensor part, the signal processing circuit 1 which inputs the output voltage of the amplifier 3, and the DC power source 2. Then a resistance Rl is connected between the output terminal O of the amplifier 3 and a power source input terminal Q. Further, when the power source line 4 of the power source 2 between the circuit 1 and amplifier 3 is broken at 4a, the absolute value of the voltage between the grounding line 5 and the output terminal O of the amplifier 3 is made lower than the minimum absolute value of the voltage generated when the line is not broken. Consequently, an operational amplifier having specific internal resistance need not be used selectively and only an external additional resistance Rl is changed according to the input resistance and source voltage of the control circuit, the specification of the operational amplifier circuit, etc., to obtain a prescribed disconnection detection voltage.

Description

[Detailed description of the invention] [Technical field to which the invention pertains]

For example, in a signal processing circuit of a pressure sensor for an automobile, the present invention connects an operational amplifier of a pressure sensor section and a signal processing circuit such as a microcomputer that inputs and processes the output voltage of this operational amplifier to generate this signal. The present invention relates to a circuit connected to a common DC power supply provided on a processing circuit side, for detecting a disconnection of a power supply line running from the signal processing circuit to the operational amplifier. Note that in the following figures, the same reference numerals indicate the same or corresponding parts.

[Prior art and its problems]

In this type of disconnection detection circuit, when the power supply line is disconnected, it may be necessary to detect this disconnection with a signal processing circuit and issue an alarm or change the subsequent control state. In this case, the output voltage value of the operational amplifier must be clearly different from the state in which there is no disconnection. FIG. 3 is a basic configuration diagram of such a conventional disconnection detection circuit, and FIG. 4 is a simplified equivalent circuit diagram of FIG. 3. In FIG. 3, l is a signal processing circuit (also called a control circuit) equipped with a microcomputer, etc., and in this example, it has a built-in DC power supply 2 of voltage Vp. 3 is an arithmetic amplifier of the pressure sensor section, 4.5 is a power line from the DC power source 2, and the feed line 5 is the vehicle body in the case of an automobile. In this case, it is assumed that the feeder line 4 is disconnected at a point 4a. For convenience of explanation, the feeder lines 4 and 5 will be referred to as a power supply line and a ground line, respectively. Now, the output resistance of the operational amplifier 3 when the power line 4 is disconnected is Ra.
, the resistance between the power supply terminal P and the signal input terminal R of the control circuit l is Rp, and the resistance between the ground terminal G and the signal input terminal R is Rg. If the circuit in the control circuit 1 shown in FIG. 3 is rewritten into an equivalent circuit in which a voltage source and a resistor are connected in series according to Thepnan's theorem, it becomes as shown in FIG. 4. Here, Rg+Rp. Therefore, when the power line 4 is disconnected, the operational amplifier 3
Voltage between output terminal O and ground terminal S (disconnection detection voltage) V
d is represented by (3) 2 below. Usually, this disconnection detection voltage Vd is the lower limit value Vmin of the output voltage that the operational amplifier 3 can output when the power supply line 4 is not disconnected.
is selected to be the smaller value. That is, Vd<V+++in ・−−−−−−−−=−−−−
−−−−−−−−−−−−−−−−−(4) Therefore, the formula (
From 3) and (4), the output resistance Ra in the operational amplifier 3 is
It must be limited to the range of equation (5) below. However, the amplifier output resistance RaO value takes different values depending on the circuit configuration of the operational amplifier output means (for example, the size of the transistor area). Therefore, in the conventional method, an operational amplifier 3 having an output resistance Ra value that satisfies equation (5) is selected and used. However, this method has the following drawbacks. - Usable operational amplifiers are limited. ■If the circuit specifications are changed, it may be necessary to select an arithmetic amplifier with a different output resistance Ra, which poses an obstacle in expanding the range of models such as pressure sensors.

[Purpose of the invention]

The present invention eliminates the above-mentioned drawbacks, allows the use of a normal operational amplifier, and allows the disconnection detection voltage to be lower than a predetermined value without changing the operational amplifier even when circuit specifications are changed. The purpose is to provide circuits.

[Key points of the invention]

The main points of the present invention are an operational amplifier (such as a sensor section), a signal processing circuit (such as a microcomputer) that inputs the output voltage of this operational amplifier, and a common connection between the operational amplifier and the signal processing circuit. A circuit comprising a DC power source, the circuit configured such that the DC power source is not included in a feeder line of the DC power source when viewed from the signal processing circuit to the operational amplifier side, A resistor is connected between the output terminal of the operational amplifier and the power supply terminal of the operational amplifier, and a predetermined feeding path of the DC power supply between the signal processing circuit and the operational amplifier is controlled. When one side (non-grounded side, etc.) is disconnected, the absolute value of the voltage between the other side of the feeder line and the output terminal of the operational amplifier is the minimum of the voltage that would occur if there was no disconnection. The point is that it is possible to change the disconnection detection voltage over a wide range by simply changing the value of the externally connected resistor, without using a predetermined internal resistance operational amplifier. It is in.

[Embodiments of the invention]

The present invention will be explained in detail below based on FIGS. 1 and 2. FIG. 1 is a basic configuration circuit diagram as an embodiment of the present invention, and corresponds to FIG. 3, and FIG. 2 is a simplified equivalent circuit diagram of FIG. 1, and corresponds to FIG. 4. be. In Fig. 1, 3 is the operational amplifier mentioned above, O is the output terminal of the operational amplifier 3, Q is the same (power input terminal), and S is the same (
This is a ground terminal. Add a new resistor R1 between terminal 0 and terminal Q.
is connected. The control circuit 1 supplies the power supply voltage Vp and processes the output voltage signal of the operational amplifier 3. Here, Rp is between the power supply voltage output terminal P and the voltage signal input terminal R.
Further, Rg is an internal resistance in the control circuit 1 between the voltage signal input terminal R and the ground terminal 0, respectively. Terminal O and terminal R are connected, and terminal S and terminal G are connected. Further, the power supply line 4 between the terminal Q and the terminal 2 is normally connected, but in this embodiment, it is assumed that it is disconnected at a point 4a. The internal equivalent circuit of the operational amplifier 3 in Fig. 1 is simplified using only a resistor, and the internal equivalent circuit of the control circuit l is connected in series with the voltage source ■r and the resistor Rr using Thepnan's theorem as in the case of Fig. 4. If you rewrite it in a connected form, it will look like Figure 2. However, the resistances Ra and Rb are the internal resistances of the operational term [11 unit 3 side, and the resistance Ra is the resistance between the terminals O and S.
It is a 3-hour resistance. Note that terminal 0. The internal resistance between Q is extremely large when the power supply line 4 is disconnected, so it will be omitted. In addition, Vr and R' are expressed by the above formulas (1) and (21), respectively. In this configuration, the combined resistance RX including the resistor R1 when looking in the direction of the operational amplifier 3 from the terminal O2S is calculated by the following formula. (
6). Ra + Rh + Rj2 Therefore, the output voltage between the output terminal 0 of the operational amplifier 3 and the ground terminal S when the power supply line 4 is disconnected (disconnection detection voltage)
Ve is expressed by the following formula. Rx+Rr As in the case of the prior art, this disconnection detection voltage Ve is normally selected to be smaller than the voltage lower limit value V+sin that the operational amplifier 3 can output when the power line 4 is not disconnected. That is, V e < V v a i n −−−−−−−−−−
−−−−−−−−−−−−=−−−−−−−−−−−=
(8) Therefore, from equations (7) and (8), the resistance Rx needs to be limited to the range of the following equation. Vr-V, so-called in Furthermore, according to equations (9) and (6), the resistance R1 must be limited to the range of the following equation. However, the lower limit value of the resistor R1 is determined by the limit value of the output sink current of the operational amplifier 3 when the power supply line is not disconnected. Therefore, by selecting the value of the resistor RIl that satisfies 200 and is within the limit of the output sink current of the operational amplifier 3, a desired disconnection detection voltage Ve can be obtained. Note that even when the resistor Re is connected between the operational amplifier output terminal O and the ground terminal S, the same result as in this embodiment, that is, when the resistor R1 is connected between the operational amplifier output terminal O and the power supply terminal Q, is obtained. Effects can be obtained. However, since the sink current of an operational amplifier is usually warmer than the source current, this embodiment makes it possible to lower the lower limit value of R1 and widen the range of disconnection detection voltage. Become.

【Effect of the invention】

As is clear from the above description, according to the present invention, an operational amplifier of a sensor section, a signal processing circuit such as a microprocessor that inputs the output voltage of this operational amplifier, the operational amplifier and signal processing A circuit including a DC power supply common to the circuit, the circuit being configured such that the DC power supply is not included in the WI circuit of the DC power supply when looking from the signal processing circuit to the operational amplifier side. In the circuit, a resistor R1 is connected between the output terminal of the operational amplifier and the power supply terminal of the operational amplifier, and the DC power source is connected between the signal processing circuit and the operational term 11 unit. When the non-grounded side of the feeder line is disconnected, the absolute value of the voltage between the ground side of the feeder line and the output terminal of the operational amplifier is the minimum absolute value of the voltage that would occur if there was no disconnection. It is not necessary to select and use an operational amplifier with a predetermined internal resistance, and the external additional resistance can be adjusted according to the input resistance of the control circuit, power supply voltage, specifications of the operational amplifier circuit, etc. By selecting the value of R1, it is possible to set the disconnection detection voltage to a predetermined value by changing only one resistor R1. In addition, since Ra>Rb usually holds in equation (6), by changing the value of the external additional resistance R1, the combined resistance R
The value of x can be changed widely, and from equation (7),
It becomes possible to change the value of the disconnection detection voltage Ve over a wide range. Therefore, disconnection detection voltage Ve due to changes in voltage signal specifications
can be easily changed. Therefore, the operational amplifier to be used is not limited, and even if the specifications of two circuits change, it is only necessary to change the resistor R1, which has the effect of eliminating the need to change the operational amplifier. .

[Brief explanation of drawings]

FIG. 1 is a basic configuration circuit diagram as an embodiment of the present invention, FIG. 2 is a simplified equivalent circuit diagram of FIG. 1, and FIG. 3 is a conventional configuration circuit diagram corresponding to FIG. 1. FIG. 4 is a simplified equivalent circuit diagram of FIG. 3 and corresponds to FIG. 2. 1: Signal processing circuit (control circuit), 2: DC power supply, 3: 11 operational elements, 4 two feeder lines (power line), 5: Load line (ground line), Ra, Rb, RCRp, Rg: resistance. Figure 1 Figure 2 Figure 4 Procedural Amendment (Voluntary) August 1986 228 (Other Names) 4. Agent Address No. 111-1 Tanabeshin, Kawasaki-ku, Kawasaki City , Contents of height correction 1, Formula % Formula % in lines 14 to 15 on page 8 of the specification

Claims (1)

[Scope of Claims] 1) A circuit comprising an operational amplifier, a signal processing circuit that inputs the output voltage of the operational amplifier, and a common DC power supply for the operational amplifier and the signal processing circuit. In a circuit configured such that the DC power source is not included in a feed line of the DC power source when viewed from the signal processing circuit to the operational amplifier side, the output terminal of the operational amplifier and , a resistor is connected between the power supply terminal of the operational amplifier, and when a predetermined one of the feeder lines of the DC power supply between the signal processing circuit and the operational amplifier is disconnected, the feeder line and the output terminal of the operational amplifier, the absolute value of the voltage being lower than the minimum absolute value of the voltage that would occur in the absence of the disconnection. Disconnection detection circuit for power supply circuit.