JP2010057289A - Surge protection circuit, electronic control circuit, and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surge protection circuit that prevents a surge current from an input terminal from flowing into a load circuit, and to provide an electronic control circuit and an electronic apparatus. <P>SOLUTION: A surge protection circuit 1 consists of an air gap 11, and wiring patterns 12 and 13, wherein the air gap 11 consists of two patterns 111 and 112 facing each other through a gap 113. The wiring pattern 12 to which the pattern 111 is connected is connected with a wiring pattern 31 which is connected with an external terminal 21, and the wiring pattern 13 to which the pattern 112 is connected is connected with a wiring pattern 33 which is connected with a low impedance line 25, and these four wiring patterns are formed on the same straight line on a substrate. A wiring pattern 32 to which resistor elements 22 and 23 are connected is connected to the wiring patterns 31 and 12 at an angle of 90 degree. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a surge protection circuit, an electronic control circuit, and an electronic device that protect a load circuit from a surge current.

  FIG. 1 is a diagram showing a connection configuration of a surge protection circuit 9 according to a conventional technique. The external terminal 21 provided on the substrate is a terminal for inputting an electric signal to a load circuit mounted on the substrate, for example, a microcomputer (hereinafter referred to as “microcomputer”) 24. The external terminal 21 is connected to the microcomputer 24 via the resistance element 23 by the wiring patterns 31, 32, and 37 and to the resistance element 22 by the wiring patterns 31, 32, and 38. The resistance element 23 is a chip resistor for protecting the microcomputer 24 from a surge current. The resistance element 22 is a chip resistor for protecting the load circuit from a surge current. One end of the resistance element 22 is connected to a low impedance line 26 having a low impedance, for example, a DC power supply voltage or a ground pattern, and the other end is a wiring pattern 38. Thus, the connection point 45 between the wiring pattern 32 and the wiring pattern 37 is connected.

  A substrate on which a load circuit such as the microcomputer 24 is mounted may be handled manually, and static electricity charged on the human body may flow as a surge current from the external terminal 21 and the load circuit may be destroyed. The resistance element 22 and the resistance element 23 are chip resistors for protecting the load circuit from a surge current, but a surge protection circuit 9 is provided to reduce the size of the resistance element 22 and the resistance element 23.

  The surge protection circuit 9 is a circuit for protecting the microcomputer 24 from a surge current, and includes an air gap 91. The air gap 91 is constituted by a lightning rod pattern, for example. The lightning rod pattern is composed of two conductors facing each other through an insulator, for example, air, for example, a pattern portion. One pattern portion is connected to a connection point 44 between the wiring pattern 31 and the wiring pattern 32 by the wiring pattern 92. The other pattern portions are connected to a low impedance line 27 having a low impedance by the wiring pattern 93, for example, a pattern such as a DC power supply voltage or a ground.

  The length L1 of the wiring pattern 92 from the connection point 44 to the pattern portion of the air gap 91 is shorter than the total length L2 of the wiring pattern 32 and the wiring pattern 38 from the connection point 44 to the resistance element 22. The wiring pattern 92 extends in a direction of 90 degrees with respect to the wiring pattern 31 at the connection point 44, and the wiring pattern 32 extends in a direction of 90 degrees with respect to the wiring pattern 31 at the connection point 44 and the wiring pattern 92. Extends in the opposite direction.

  The surge protection circuit of the printed circuit board pattern arrangement method described in Patent Document 1 is an example of the surge protection circuit 9.

  In the lightning protection system described in Patent Document 2, a protection circuit is connected in parallel to a transmission line that transmits signals between a plurality of devices. In the protection circuit, two discharge gap type arresters (protectors) and a series connection portion are connected in parallel to each other. Since the time until the arrester reacts is slow, a series connection is provided to escape the surge current to ground during that time. The series connection portion is configured by connecting a resistance element and a bidirectional Zener diode in series.

JP-A-5-41568 JP 2003-70156 A

  However, in the surge protection circuit 9 shown in FIG. 1, when a surge current flows into the external terminal 21, the surge current that flows into the air gap 91 flows as the surge current S1 and flows into the resistance element 22 as the surge current S2. Therefore, the resistance element 22 or the resistance element 23 may be destroyed. This is because the air gap 91 is provided in the direction of 90 degrees with respect to the wiring pattern 31. Even if the distance L1 is shorter than the distance L2, the surge current flows also to the resistance element 22. There is a problem. The lightning protection system described in Patent Document 2 needs to use a resistance element and a bidirectional Zener diode.

  An object of the present invention is to provide a surge protection circuit, an electronic control circuit, and an electronic device that can prevent a surge current from an input terminal from flowing into a load circuit.

The present invention (1) is formed on a substrate provided with a load circuit and an external terminal for inputting an electric signal to the load circuit, and a surge protection unit for flowing a surge current;
A linear first wiring pattern formed on the substrate and connecting the external terminal and one end of the surge protection unit;
A linear second wiring pattern formed on the substrate on the same straight line as the first wiring pattern and connecting the other end of the surge protection unit and a low impedance part having a small impedance;
A third wiring pattern that branches off from the middle of the first wiring pattern and transmits an electric signal from the external terminal to the load circuit via a resistance element provided in a preceding stage of the load circuit. This is a surge protection circuit.

  The present invention (4) is an electronic control circuit comprising the surge protection circuit.

  The present invention (5) is an electronic apparatus comprising the electronic control circuit.

  According to the present invention (1), a surge current is caused to flow by the surge protector formed on the substrate on which the load circuit and the external terminal for inputting an electric signal to the load circuit are provided. The external terminal and one end of the surge protection unit are connected by a linear first wiring pattern formed on the substrate, and a linear shape formed on the substrate on the same straight line as the first wiring pattern. The second wiring pattern connects the other end of the surge protector and the low impedance part having a small impedance. Then, an electrical signal from the external terminal is transmitted to the load circuit via a resistance element provided in a preceding stage of the load circuit by a third wiring pattern that branches from the middle of the first wiring pattern.

  Therefore, since the surge protector is connected to the wiring pattern that connects the input terminal and the low impedance part in a straight line, a surge current having a straight traveling characteristic flows from the input terminal to the resistance element for protecting the load circuit and the load circuit. Can be prevented.

  According to the invention (4), since the electronic control circuit includes the surge protection circuit, the electronic control circuit can be protected from a surge current.

  According to the present invention (5), since the electronic device includes the electronic control circuit, the electronic control circuit can be prevented from being destroyed by a surge current, and the electronic device is resistant to surge. can do.

  FIG. 2 is a diagram showing a connection configuration of the surge protection circuit 1 according to the embodiment of the present invention. The surge protection circuit 1 is a circuit for protecting a load circuit such as a microcomputer (hereinafter referred to as “microcomputer”) 24 and a load circuit protection resistor for protecting the load circuit from surge current from the surge current. And is constituted by the air gap 11 and the wiring patterns 12 and 13. The air gap 11 which is a surge protector is constituted by, for example, a lightning rod pattern, specifically, two conductors facing each other via an insulator, for example, a gap 113 made of air, for example, the pattern portions 111 and 112. One pattern portion 111 is connected to the wiring pattern 12, and the other pattern portion 112 is connected to the wiring pattern 13. The width of the gap 113 is, for example, 0.1 mm.

  The wiring pattern 12 is connected to a wiring pattern 31 connected to an external terminal 21 for inputting an electric signal to the microcomputer 24 at a connection point 41. The wiring pattern 31 and the wiring pattern 12 are formed on the substrate on the same straight line. The wiring pattern 13 is connected to a wiring pattern 33 connected to a low impedance line 25 having a low impedance, for example, a 12 V (volt) DC power supply voltage such as a battery, or a pattern such as a ground, at a connection point 42. The wiring pattern 33 and the wiring pattern 13 are formed on the substrate on the same straight line as the wiring pattern 31 and the wiring pattern 12. The low impedance line 25 is a low impedance part.

  The resistance element 22 is a chip resistor for protecting the microcomputer 24 from a surge current, and a wiring pattern 35 connected to one end is connected to the wiring pattern 32 at a connection point 43. The wiring pattern 32 is connected to the connection point 41 at an angle of 90 degrees with respect to the wiring pattern 31 and the wiring pattern 12. The other end of the resistance element 22 is connected to the wiring pattern 13 and the wiring pattern 33 at a connection point 42 by a wiring pattern 34. The microcomputer 24 is connected to the connection point 43 by a wiring pattern 36 through a resistance element 23 that is a chip resistance for protecting the microcomputer 24 from a surge current. The wiring pattern 33 and the wiring pattern 13 constitute a first wiring pattern, the wiring pattern 31 and the wiring pattern 12 constitute a second wiring pattern, and the wiring pattern 32 constitutes a third wiring pattern. is doing.

  When a surge current flows from the external terminal 21, the surge current has a straightness, so that most of the surge current flowing from the external terminal 21 passes through the air gap 11 and flows to the low impedance line 25 as the surge current S 3. Although current has a property of flowing in a direction with less inductance, the corner portion where the wiring pattern is bent has high inductance, so the current tends to travel in a direction with less inductance, that is, straight. Since the wiring pattern 32 is connected to the wiring pattern 31 and the wiring pattern 12 at an angle of 90 degrees, the surge current S4 flowing into the wiring pattern 32 has a very small current value, that is, almost “0”. Thus, even if the resistance elements 22 and 23, which are chip resistors, are miniaturized chip resistances, the resistance elements 22 and 23 are not destroyed, and the microcomputer 24 is not destroyed. .

  Surge has a voltage of 5 KV or more, such as those caused by static electricity accumulated in the human body, those generated from the spark plug when turning the ignition key of the vehicle, or those generated when the motor is driven, The surge protection circuit according to the present invention can protect the chip resistor for surge protection and the load circuit from surge current caused by these surges.

  Thus, a surge current is caused to flow by the air gap 11 formed on the substrate on which the microcomputer 24 and the external terminal 21 for inputting an electric signal to the microcomputer 24 are provided. The external terminal 21 and one end of the air gap 11 are connected by the linear wiring pattern 33 and the wiring pattern 13 formed on the substrate, and are formed on the substrate on the same straight line as the wiring pattern 33 and the wiring pattern 13. The other end of the air gap 11 and the low impedance line 25 having a small impedance are connected by the linear wiring pattern 31 and the wiring pattern 12. Then, the electrical signal from the external terminal 21 is transmitted to the microcomputer 24 via the resistance element 23 provided in the previous stage of the microcomputer 24 by the wiring pattern 32 branched from the middle of the wiring pattern 33 and the wiring pattern 13.

  Therefore, since the surge protection unit is connected to the wiring pattern that linearly connects the input terminal and the low impedance unit, it is possible to prevent a surge current having straight travel from flowing from the input terminal to the load circuit such as the microcomputer 24. it can.

  Further, since the gap 113 is composed of two pattern portions 111 and 112 facing each other with the gap 113 interposed therebetween, it can be formed on the substrate as a part of the wiring pattern, and can be realized with a simple circuit configuration. it can.

  Furthermore, while the wiring pattern 32 branches at an angle of 90 degrees with respect to the wiring pattern 33 and the wiring pattern 13, the wiring pattern 33, the wiring pattern 13, and the wiring pattern 31 that connect the air gap 11 Since the wiring pattern 12 is on the same straight line, the surge current is more likely to flow toward the air gap 11 than the microcomputer 24, and the air gap 11 causes the resistance element 23 and the microcomputer 24 in the previous stage of the microcomputer 24 to be separated from the surge current. Can be protected.

  The surge protection circuit 1 can be applied to a vehicle-mounted electronic control circuit, and can also be applied to a vehicle-mounted electronic device such as a navigation device, an audio device, or a video device.

  Thus, since the electronic control circuit includes the surge protection circuit 1, the electronic control circuit can be protected from the surge current.

  Furthermore, since the electronic device includes the electronic control circuit, the electronic control circuit can be prevented from being destroyed by a surge current, and the electronic device can be made strong against a surge.

It is a figure which shows the connection structure of the surge protection circuit 9 by a prior art. It is a figure which shows the connection structure of the surge protection circuit 1 which is one Embodiment of this invention.

Explanation of symbols

1,9 Surge protection circuit 11,91 Air gap 12,13,31-38,92,93 Wiring pattern 22,23 Resistance element 24 Microcomputer 25-27 Low impedance line 111,112 Pattern part 113 Gap

Claims (5)

Formed on a substrate provided with a load circuit and an external terminal for inputting an electric signal to the load circuit, and a surge protection unit for flowing a surge current;
A linear first wiring pattern formed on the substrate and connecting the external terminal and one end of the surge protection unit;
A linear second wiring pattern formed on the substrate on the same straight line as the first wiring pattern and connecting the other end of the surge protection unit and a low impedance part having a small impedance;
A third wiring pattern that branches off from the middle of the first wiring pattern and transmits an electric signal from the external terminal to the load circuit via a resistance element provided in a preceding stage of the load circuit. Surge protection circuit.   The surge protection circuit according to claim 1, wherein the surge protection unit includes two conductors facing each other through an insulator.   The surge protection circuit according to claim 1 or 2, wherein the third wiring pattern is branched at an angle of 90 degrees with respect to the first wiring pattern.   An electronic control circuit comprising the surge protection circuit according to claim 1.   An electronic apparatus comprising the electronic control circuit according to claim 4.

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