JPH0670442U - Protection circuit - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] To provide a protection circuit that reduces the number of parts of the protection circuit associated with an operational amplifier, shortens the mounting time on the board, and realizes high-density mounting. [Configuration] Two diodes are connected in parallel to the + input terminal and the − input terminal of the operational amplifier, and two diodes are connected in series from one of the + input terminal and the − input terminal of the operational amplifier to GND. To form a protection circuit, and the protection circuit is integrated into one single in-line package.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a protection circuit and a protection circuit device for preventing an operational amplifier from being destroyed by an excessive input voltage.

[0002]

[Prior art]

 If the operational amplifier has an excessive input voltage that exceeds the maximum common mode voltage or the maximum differential voltage, it may be destroyed. Conventionally, four diodes D5 shown in Fig. 4 were used to protect the excessive input voltage of the common mode voltage. When a protection circuit is used and a protection circuit using two diodes D6 shown in Fig. 5 is used for protection against excessive input voltage of differential voltage, and protection is performed simultaneously from excessive input voltage of common mode voltage and differential voltage. As shown in FIG. 6 which is a combination of FIGS. 4 and 5, a total of 6 diodes are used.

In the case of the above-mentioned conventional protection circuit, six diodes are required to protect one operational amplifier, and in the case of a large-scale analog circuit, the number of parts becomes enormous, resulting in an increase in mounting time on the board and mounting. There was a problem of large area. (2)

FIG. 4 is a conventional common-mode excessive input voltage protection circuit, FIG. 5 is a conventional differential-voltage excessive input voltage protection circuit, and FIG. 6 is a protection that can simultaneously protect common-mode and differential voltage excessive input voltages. A circuit, 1 is a linear IC, 2 is an operational amplifier, 3 is a + input terminal, and 4 is a-input terminal.

[0005]

[Problems to be solved by the device]

 The problem to be solved is to provide a protection circuit that reduces the number of components of the protection circuit, shortens the mounting time on the board, and realizes high-density mounting.

[0006]

[Means for Solving the Problems]

 A protection characterized by connecting two diodes in parallel to the + and-input terminals of the operational amplifier, and connecting two diodes in series from one of the + and-input terminals of the operational amplifier to GND. A circuit was formed and the protection circuit was integrated in one single in-line package.

[0007]

[Action]

 According to the present invention, when an excessive input voltage of differential voltage is applied to the + input terminal of the operational amplifier, a current flows through the first diode, and when an excessive input voltage of differential voltage is applied to the − input terminal, the second input voltage is applied. Current flows through the diode and protects the operational amplifier. Further, when an excessive input voltage of the common mode voltage is applied to the + input terminal of the operational amplifier, the current flows through the first diode and then through the third and fourth diodes to the GND. When an excessive input voltage of the common-mode voltage is applied to the-input terminal of the operational amplifier, a current flows through the third and fourth diodes to GND and protects the operational amplifier. (3)

[0008]

【Example】

 FIG. 1 shows one embodiment of the present invention. The main part of the present invention is to connect a first diode D1 between the + input terminal 3 and the − input terminal 4 of an operational amplifier of the linear IC 1 or the voltage comparator 2. , A second diode D2 is connected in parallel to the first diode D1 so that polarities are opposite to each other, and a third diode is connected in series from the first diode D1 and the second diode D2 to GND. A protection characterized in that the anode of D3 is connected, the cathode of the third diode D3 and the cathode of the fourth diode D4 are connected in series, and the anode of the fourth diode D4 is connected to ground. A circuit was formed and the protection circuit was integrated in one single in-line package as shown in FIG.

The first diode D1 and the second diode D2 are for protecting an excessive input voltage of a differential voltage, and as shown in FIG. 3, the potential difference VdM between the + input terminal and the − input terminal is the first diode. When the forward voltage of D1 and the second diode D2 is larger than the forward voltage, a current flows through the first diode D1 or the second diode D2 to protect the linear IC1. At this time, if the forward delay time of the first diode D1 and the second diode D2 is delayed, the instantaneous excessive differential input voltage does not flow to the first diode D1 and the second diode D2, and the linear IC1 cannot be protected. . Therefore, in this embodiment, a Schottky barrier diode having a fast forward delay time is used.

The third diode D3 and the fourth diode D4 are for protecting the common mode input voltage, and as shown in FIG. 3, the potential difference VCM between the + input terminal 3 and the ground and between the − input terminal 4 and the ground is VCM. , When the Zener voltage of the third diode D3 and the forward voltage of the fourth diode D4 are larger than the sum, a current flows through the third diode D3 and the fourth diode D4 to protect the operational amplifier. In this embodiment, a Zener diode having a Zener voltage lower than the power supply voltage of the operational amplifier by about 2 V is used. (4)

FIG. 2 shows an embodiment of the protection circuit device according to the present invention in which the protection circuit is integrated in one single in-line package 5. The first diode D1 and the second diode D2 are connected to each other. The external terminals 6 and 7 of the single in-line package 5 have the same width as the + input terminal 3 and the − input terminal 4 of the operational amplifier, for example, 2.54 mm, and the external terminal 8 connected to the ground is the wiring of the linear IC. A width that does not cause an obstacle, for example, 5.08 mm.

It should be noted that the first diode D1 and the second diode D2 can use diodes other than Schottky barrier diodes depending on the characteristics of the operational amplifier and its application, and since only the diode forward characteristics are used, one varistor is used. Can be replaced with Also, as the third diode D3 and the fourth diode D4, diodes other than the Zener diode can be used depending on the characteristics of the operational amplifier and its application, and can be replaced with one three-layer diode.

[0013]

[Effect of device]

 The present invention reduces the number of components of the operational amplifier protection circuit, and by integrating them into a single in-line package, we were able to reduce the mounting time on the board and achieve high-density mounting. In addition, because the wiring of the protection circuit is short, high speed and low noise were achieved. As mentioned above, the industrial applicability is great. (5)

[Brief description of drawings]

FIG. 1 shows an embodiment of a protection circuit according to the present invention.

FIG. 2 shows an embodiment of a protection circuit device according to the present invention

FIG. 3 is an explanatory diagram of an excessive input voltage.

FIG. 4 A conventional excessive input voltage protection circuit for common mode voltage

FIG. 5: Conventional excessive input voltage protection circuit for differential voltage

FIG. 6 is a conventional protection circuit capable of simultaneously protecting an excessive common-mode voltage and an excessive input voltage of a differential voltage.

[Explanation of symbols]

 1 linear IC 2 operational amplifier 3 + input terminal 4-input terminal 5 single inline package 6 + external terminal connected to input terminal 7-external terminal connected to input terminal 8 external terminal connected to GND

Claims (2)

[Scope of utility model registration request] 1. A first diode is connected between a + input terminal and a − input terminal of an operational amplifier, and a second diode is connected in parallel to the first diode so as to have opposite polarities. The anode of the third diode is connected in series from the first and second diodes to the GND, the cathode of the third diode and the cathode of the fourth diode are connected in series, and the anode of the fourth diode is connected. A protection circuit characterized by being connected to ground. 2. The protection circuit device according to claim 1, wherein the protection circuit is integrated in one single in-line package.