JP2006217768A - Surge protection circuit and car on which this circuit is mounted - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surge protection circuit that is structured so as not to cause an excessive voltage to be impressed to an electronic circuit even when a Zener diode with low-voltage resistance is used, and that protects a load circuit by absorbing a generated surge. <P>SOLUTION: This surge protection circuit comprises a diac 3 connected between a DC power source 1 and a load 2 and connected in parallel to the load 2, and a Zener diode 4 connected between the DC power source 1 and the load 2 and connected in parallel to the load 2. The Zener diode 4 is connected in the reverse voltage direction to the DC power source 1 and connected in series to the diac 3. No excessive voltage is impressed to the electronic circuit even when the Zener diode 4 with low-voltage resistance is used so that surge absorbing energy at the time of surge absorption can be reduced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a surge protection circuit used in an electronic device mounted on a vehicle, for example, and an automobile equipped with the same, which prevents a transient excessive voltage from being applied to a load by absorbing the surge voltage. is there.

2. Description of the Related Art Conventionally, for example, a surge protection circuit of an electronic device mounted on a car is connected between an in-vehicle power source and a load, and a Zener diode connected in parallel with the load is used as a surge absorbing element. When the surge voltage is applied to a circuit in the electronic device, the surge voltage is absorbed by the surge protection circuit. The peak energy at the time of surge absorption (calculated assuming that the peak voltage is 100V and the in-circuit series resistance is 1Ω) is ((100V−40V) / 1Ω) × 40V (= 2400W). Such a surge voltage may act on electronic equipment.
When this surge voltage is applied, semiconductor integrated circuit devices such as ICs and LSIs in electronic devices are destroyed. Therefore, as described above, a surge protection circuit with a Zener diode is placed at the input of electronic devices. In general, the voltage is clamped, and the voltage is suppressed to 40 V, for example, to protect the entire circuit. For this reason, there were the following problems in this case.

Originally, the element voltage of the Zener diode may be a battery voltage of 12 V or more, but in the case of a car, two batteries may be used in series in a cold region. For this reason, a Zener diode having a breakdown voltage of 24V or more is generally used.
For this reason, the clamp voltage waveform during surge absorption increases between 24 V and 40 V (24 V + current value during surge absorption and element temperature rise at that time). For this reason, there is a problem that the withstand voltage of the semiconductor integrated circuit device used for the electronic device cannot be designed to be lower than this voltage, resulting in a disadvantage in IC design.
The presence of a surge absorbing element (surge protection circuit) when a surge occurs can reduce the surge voltage below a certain voltage. However, the higher this limitable voltage, the higher the breakdown voltage of the semiconductor integrated circuit device for surge protection ( The element breakdown voltage must be designed high. Increasing the element withstand voltage raises the demerit that the element price increases, the operating resistance inside the element increases, and heat generation increases. For this reason, it is preferable that the suppression voltage (withstand voltage) is low.

For example, a Zener diode with a withstand voltage of 40 V may be used as long as it satisfies the cold district specification power supply. For example, a Zener diode with a withstand voltage of 40 V may be used. In order to prevent an excessive voltage from being applied to a semiconductor integrated circuit device (LSI, IC, etc.), a Zener diode having a low withstand voltage is preferred.
In the prior art described in Patent Document 1, when a leakage current flows through the ground line and the voltage of the capacitor exceeds the trigger voltage, the diac conducts, the thyristor is turned on, and the display unit performs deterioration display. When the lightning impulse passes, the non-linear resistance element discharges and the Zener diode operates. When the switching surge current passes, the non-linear resistance element does not discharge, but the Zener diode operates because a voltage higher than the settling voltage is applied to both ends of the Zener diode. Diac and Zener diodes are used to drive the gates of thyristors.
JP-A-6-5350 (FIG. 1)

  The present invention provides a surge protection circuit that is configured so that an excessive voltage is not applied to an electronic circuit even when a Zener diode having a low breakdown voltage is used, and that absorbs a generated surge and protects the circuit.

  One aspect of the surge protection circuit of the present invention is a diac connected in parallel with a power source and an electronic circuit, connected between the power source and the electronic circuit device, the diac connected in series, and the power source A withstand voltage of the diac is set to be equal to or higher than the output voltage of the power supply, and the withstand voltage of the zener diode is set to be equal to or higher than the output voltage of the power supply. And it is characterized by being set equal to or lower than the withstand voltage of the diac.

  According to the above configuration, even if a Zener diode having a low breakdown voltage is used, an excessive voltage is not applied to the electronic circuit, and the surge absorption energy at the time of surge absorption can be reduced.

  Hereinafter, embodiments of the invention will be described with reference to examples.

First, Embodiment 1 will be described with reference to FIGS.
FIG. 1 is a characteristic diagram for explaining current-voltage characteristics of a diac and a Zener diode, FIG. 2 is a characteristic chart showing a current-voltage characteristic of a circuit in which a diac and a Zener diode are connected in series, and FIG. Fig. 4 is a schematic plan view of an on-vehicle electronic device to which a surge protection circuit according to this embodiment is connected, and Fig. 4 is a surge voltage waveform and a clamping voltage waveform when the surge protection circuit of Fig. 3 is used. FIG. 5 is a circuit diagram for explaining the connection method of the surge protection circuit of this embodiment, and FIG. 6 is a schematic sectional view showing the structure of the diac used in this embodiment and a diagram showing symbols of the diac. is there.

FIG. 3 is a schematic diagram in which a surge protection circuit is attached to an in-vehicle electronic device. A load circuit 2 is formed on a wiring board 5 on which electronic equipment is mounted. The load circuit 2 is electrically connected to a battery (vehicle power source) 1 outside the electronic device. The surge protection circuit 10 is formed on the wiring board 5 and connected in parallel with the load circuit 2. The diac 3 constituting the surge protection circuit 10 is connected between the battery 1 and the load circuit 2 and connected in parallel with the load circuit 2. Similarly, the Zener diode 4 constituting the surge protection circuit 10 is connected between the battery 1 and the load circuit 2, and is connected in parallel with the load circuit 2. The zener diode 4 is connected to the battery 1 in the reverse voltage direction. The diac 3 and the Zener diode 4 are connected in series.
Here, the diac (DIAC: Diode AC) 3 is a kind of thyristor and is a two-terminal AC control element. The diac 3 is composed of three semiconductor layers of NPN or PNP (NPN structure in this embodiment) sandwiched between a pair of electrodes (see FIG. 6), and exhibits negative resistance in contrast to both directions. It is represented by the symbol shown in FIG.

  Next, the operation of the surge protection circuit will be described with reference to FIG. 1, FIG. 2, FIG. 4 and FIG. The breakdown voltage of the diac 3 and the Zener diode 4 is set to be equal to or higher than the output voltage of each battery 1. The breakdown voltage of the Zener diode 4 is set equal to or lower than the breakdown voltage of the diac 3. In this embodiment, the withstand voltage of the Zener diode 4 is set to 12 V, which is equal to the output voltage (12 V to 15 V) for one battery 1. In this embodiment, 12V is the output voltage of one battery. The withstand voltage of the diac 3 is also 12V. It is assumed that, for example, a microcomputer having a withstand voltage of 40V is incorporated in the load circuit 2 of the electronic device in which the surge protection circuit 10 is mounted. The surge protection circuit 10 protects the microcomputer incorporated in the load circuit 2. Further, as shown in FIG. 5, the circuit configuration may be made in the order of “positive terminal of battery 1−diac 3−zener diode 4−” (FIG. 5A). The circuit configuration may be made in the order of “terminal-zener diode 4-diac 3-” (FIG. 5B), and there is no difference in the operational effect of the surge protection circuit 10.

  Normally, the load circuit 2 connected to the battery (vehicle power source) 1 functions without being affected by the surge protection circuit 10 shown in FIG. For example, a surge voltage having a peak voltage of 100 V having a waveform shown in FIG. 4A is applied to the load circuit 2. Before the surge voltage is applied, neither the diac 3 nor the zener diode 4 of the surge protection circuit 10 operates. When the power supply voltage rises, first the diac 3 breaks down. However, no current flows because the lower Zener diode 4 is blocked. That is, the surge protection circuit 10 is not operating. Further, the power supply voltage also breaks down the Zener diode 4 and the current flows through the surge protection circuit 10 for the first time.

  As shown in FIG. 2, by arranging a diac (withstand voltage of 12V or higher) and a 12V Zener diode in series with the surge protection circuit, the surge protection circuit can obtain a breakdown voltage of 24V. As a result, FIG. A waveform of the clamping voltage as shown in (b) is obtained. The voltage at the time of clamping is 24V. The peak energy at the time of surge absorption at this time is ((100V-24V) / 1Ω) × 24V = 1824W, and the above-described conventional surge protection circuit using only a Zener diode consumes 2400W of energy. The absorbed energy in this example is reduced by about 24%. Although the clamp voltage has risen to 40 V even if a Zener diode having a withstand voltage of 24 V is used in the past, it remains almost 24 V in this embodiment and is reduced by 40%.

As described above, conventionally, two in-vehicle batteries in a cold region may be used in series. For this reason, a Zener diode having a breakdown voltage of 24V or more is generally used. For this reason, the clamp voltage waveform during surge absorption increases between 24 V and 40 V (24 V + current value during surge absorption and element temperature rise at that time). However, there is a problem that the withstand voltage of a semiconductor integrated circuit device used for an electronic device cannot be designed to be lower than this voltage (which is a disadvantage in IC design). By using a surge protection circuit in which a Zener diode and a diac having a withstand voltage of 12V are connected in series, the clamp voltage can be suppressed to 24V.
The withstand voltage of the 12V Zener diode of this embodiment increases as in the case of the conventional withstand voltage 24V Zener diode alone, but the possibility of an increase from the 24V point is small because the withstand voltage of the Diac is lowered. Passing this point is instantaneous and the rise in breakdown voltage is small.
As described above, in this embodiment, even if a Zener diode having a low breakdown voltage is used, an excessive voltage is not applied to the electronic circuit constituting the load, and the surge absorption energy at the time of surge absorption can be reduced.

Next, Embodiment 2 will be described with reference to FIGS.
7 is a characteristic diagram showing the current-voltage characteristics of the diac and a characteristic chart showing the current-voltage characteristics of the Zener diode, and FIG. 8 is a characteristic showing the current-voltage characteristics of a circuit in which the diac and the Zener diode are connected in series. FIG. In the first embodiment, both the diac and the zener diode have a withstand voltage of 12V and are equal to one battery (12 to 15V). However, in this embodiment, both have a withstand voltage equal to or more than one battery. It is characterized in that the breakdown voltage is higher than that of the Zener diode.
In the present invention, the withstand voltages of the diac and the Zener diode are required to be equal to or more than that of one battery which is an in-vehicle power source. The peak withstand voltage when absorbing the surge of the surge protection circuit in which the diac and the Zener diode are connected in series needs to be equal to or lower than the withstand voltage of the semiconductor integrated circuit device incorporated in the load circuit. For example, in this embodiment, a microcomputer is described as a semiconductor integrated circuit device. However, since the withstand voltage of the microcomputer is 40V at present, the withstand voltage of the surge protection circuit is set to 40V or less.

The zener diode should be as close to 15V as possible without exceeding the output voltage for one battery (in this embodiment, 15V). Therefore, in this embodiment, the Zener diode has a breakdown voltage of 15V. The withstand voltage of the diac needs to be 15V or more obtained by subtracting the withstand voltage 15V of the Zener diode from two batteries (15V × 2 = 30V). Further, the withstand voltage of the diac needs to be suppressed below the withstand voltage of a semiconductor integrated circuit device such as an IC incorporated in a load circuit to be protected. In this embodiment, such a semiconductor integrated circuit device is a microcomputer having a withstand voltage of 40V. Therefore, it is appropriate that the withstand voltage of the diac is 40V-15V = 25V or less. Therefore, in this embodiment, the withstand voltage of the diac is 25V.
Such a diac and a Zener diode are connected in series to form a surge protection circuit, which is connected in parallel to a load circuit connected to a battery (vehicle power source) as shown in FIG. 3, for example.

Normally, the load circuit connected to the battery functions without being affected by the surge protection circuit. For example, a surge voltage having a peak voltage of 100 V having a waveform shown in FIG. 4A is applied to the load circuit. Before the surge voltage is applied, neither the diac nor the zener diode of the surge protection circuit operates. When the power supply voltage rises, the diac breaks down first. However, no current flows because the lower Zener diode is blocked. That is, the surge protection circuit is not operating. Furthermore, the power supply voltage rises, the Zener diode breaks down, and current flows through the surge protection circuit for the first time.
As shown in FIG. 8, the surge protection circuit can obtain a withstand voltage of 40V by arranging a diac (withstand voltage 25) and a 15V Zener diode in series with the surge protection circuit.
The breakdown voltage of the 15V Zener diode of this embodiment increases as in the case of the conventional surge protection circuit using only a Zener diode. However, since the breakdown voltage of the diac is decreased, there is little possibility of increase from the 40V point. Passing this point is instantaneous and the rise in breakdown voltage is small.

As described above, in this embodiment, even if a Zener diode having a low withstand voltage is used, an excessive voltage is not applied to the electronic circuit that constitutes the load, and the withstand voltage of the semiconductor integrated circuit device that constitutes the load circuit is to be protected. A possible surge protection circuit can be obtained.
The in-vehicle power supply and the semiconductor integrated circuit device are mounted on an automobile or a two-wheeled vehicle, and the semiconductor integrated circuit device is, for example, a microcomputer that controls an on-vehicle electronic device. This microcomputer is the surge protection described in the embodiment. Surge protection is provided by the circuit.

The characteristic view explaining the current-voltage characteristic of the diac and Zener diode of Example 1 which is one Example of this invention. The characteristic view which shows the current-voltage characteristic of the circuit which connected the diac and Zener diode which concern on Example 1 which is one Example of this invention in series. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic plan view of a vehicle-mounted electronic device to which a surge protection circuit according to a first embodiment which is an embodiment of the present invention is connected and a vehicle power supply is connected. The characteristic view which shows the surge voltage waveform at the time of using the surge protection circuit of FIG. 3, and the voltage waveform at the time of a clamp. The circuit diagram explaining the connection method of the surge protection circuit which concerns on Example 1 which is one Example of this invention. BRIEF DESCRIPTION OF THE DRAWINGS The schematic sectional drawing which shows the structure of the diac used in Example 1 which is one Example of this invention, and the figure which shows the symbol of a diac. The characteristic view which shows the current-voltage characteristic of the diac demonstrated in Example 2 which is one Example of this invention, and the characteristic figure which shows the current-voltage characteristic of a Zener diode. The characteristic view which shows the current-voltage characteristic of the circuit which connected the diac and the Zener diode in series.

Explanation of symbols

1 ... In-vehicle power supply (battery)
2 ... Load circuit 3 ... Diac 4 ... Zener diode 5 ... Wiring board 10 ... Surge protection circuit

Claims (4)

A diac connected in parallel with the power supply and the electronic circuit;
A zener diode connected between the power source and the electronic circuit, connected in series with the diac, and connected in a reverse voltage direction with respect to the power source;
The withstand voltage of the diac is set to be equal to or higher than the output voltage of the power source, the withstand voltage of the zener diode is set to be equal to or higher than the output voltage of the power source, and is set to be equal to or lower than the withstand voltage of the diac. Features a surge protection circuit. The surge protection circuit according to claim 1, wherein the electronic circuit is a semiconductor integrated circuit device. The surge protection circuit according to claim 2, wherein the semiconductor integrated circuit device is a microcomputer. An in-vehicle power supply and a semiconductor integrated circuit device are provided, and the semiconductor integrated circuit device is a microcomputer that controls an on-vehicle electronic device, and the microcomputer is surge protected by the surge protection circuit according to claim 1. A car equipped with a surge protection circuit characterized by

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