JP4110701B2 - Overvoltage protection circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an overvoltage protection circuit for protecting a load connected between the high-voltage level DC power supply line and the low-potential DC power supply line, the overvoltage occurring between both the DC power supply line.
[0002]
[Problems to be solved by the invention]
When a voltage is supplied from an external power supply to a load, for example, an IC circuit, via a high potential DC power supply line and a low potential DC power supply line, an excessive voltage caused by power supply voltage fluctuations or the DC power supply line is induced. In order to protect the circuit from excessive surge voltage, an overvoltage protection circuit may be provided.
[0003]
FIG. 2 shows an example of an overvoltage protection circuit conventionally employed. A power supply voltage VB is supplied to a power supply terminal of the IC 1 including a circuit to be protected from an overvoltage (hereinafter referred to as a protected circuit) through a high potential DC power supply line 2 and a low potential DC power supply line 3. A power Zener diode 4 having the illustrated polarity is connected between the power supply terminals.
[0004]
The Zener voltage of the power Zener diode 4 is set equal to the protection set voltage value for the circuit to be protected. When a voltage (overvoltage) exceeding the protection set voltage value is applied between the power supply terminals of the IC 1, the power Zener voltage is set. The diode 4 performs a constant voltage operation to limit the voltage between the power terminals of the IC 1 to the protection set voltage value.
[0005]
However, since a large current flows through the power Zener diode 4 performing the constant voltage operation, it is difficult to build the power Zener diode 4 in the IC 1 for reasons such as an increase in chip area and heat generation of the chip. Therefore, the power Zener diode 4 must be externally attached to the IC 1, and the component cost and mounting cost are high. Further, since the power Zener diode 4 has a large part size, it is an obstacle to downsizing the entire circuit.
[0006]
Therefore, in particular, when there is a strong demand for cost reduction and miniaturization, an overvoltage protection circuit suitable for the IC as shown in FIG. 3 is employed in place of the overvoltage protection circuit. In FIG. 3, an overvoltage protection circuit 5 includes an overvoltage detection circuit 6 connected between power supply terminals to detect an overvoltage, a MOS transistor 8 connected between the protected circuit 7 and the ground, and an overvoltage detection circuit 6. The control circuit 9 is configured to turn off the MOS transistor 8 while the overvoltage is detected. The overvoltage protection circuit 5 is built in the IC 10 together with the protected circuit 7. According to this overvoltage protection circuit 5, since the MOS transistor 8 is turned off while an overvoltage is applied between the power supply terminals, the protected circuit 7 is protected from the overvoltage.
[0007]
In this case, since the maximum value of the overvoltage that can be protected by the overvoltage protection circuit 5 is determined by the breakdown voltage of the MOS transistor 8, the breakdown voltage characteristics of the IC 10 can be improved by increasing the breakdown voltage of the MOS transistor 8. However, in order to increase the breakdown voltage of the MOS transistor 8, it is necessary to change the design of the IC 10 (for example, change of the element structure and manufacturing process), which requires a great deal of labor and cost.
[0008]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an overvoltage that can easily be integrated into an IC and can protect a load against a higher voltage than before without requiring a design change for increasing the element breakdown voltage. It is to provide a protection circuit.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the means described in claim 1 can be employed. According to this means, when the voltage between the high potential DC power supply line and the low potential DC power supply line (hereinafter referred to as the power supply voltage) is less than a predetermined voltage, the high potential DC power supply line is connected between the load and the load. Since the connected P-channel or PNP-type first transistor and the N-channel or NPN-type second transistor connected between the low-potential DC power supply line and the load are both turned on, these DC power supply lines A power supply voltage is supplied to the load.
[0010]
On the other hand, when the power supply voltage becomes equal to or higher than a predetermined voltage (overvoltage), the overvoltage detection circuit detects an overvoltage state. During detection of this overvoltage state, the first and second control circuits turn off the first and second transistors, respectively, so that the load is electrically disconnected from the high potential DC power supply line and the low potential DC power supply line, Protected from overvoltage.
[0011]
During this protection operation, the first and second transistors share the power supply voltage, so that the maximum power supply voltage (maximum protection voltage) that can protect the load is that of the first and second transistors. It becomes higher than the breakdown voltage of each element. Therefore, even if the conventional manufacturing process is used as it is for the IC, the load can be protected against an overvoltage exceeding the breakdown voltage of the element alone.
[0012]
Moreover, this overvoltage protection circuit, unlike an overvoltage protection circuit using a power zener diode, does not have a circuit that consumes the overvoltage energy in an overvoltage state, so that the chip area when integrated into an IC can be reduced. There is almost no fever. For these reasons, the circuit is particularly suitable for IC integration.
[0013]
Further, the present means is different from the configuration in which the first and second transistors are simply connected in series, and is connected between the high potential DC power supply line and the load and between the low potential DC power supply line and the load, Since the control terminals of the first and second transistors are controlled using each DC power supply line as a reference potential, the configuration of the first and second control circuits for controlling on / off of the first and second transistors is simplified.
[0014]
The overvoltage detection circuit has a configuration in which a first detection resistor, a Zener diode having a Zener voltage equal to the predetermined voltage, and a second detection resistor are connected in series between a high potential DC power supply line and a low potential DC power supply line. It has. When the power supply voltage becomes equal to or higher than a predetermined voltage (zener voltage), a current flows through the Zener diode, and a voltage drop occurs in the first and second detection resistors. The first and second control circuits turn off the first and second transistors based on these voltage drops, respectively. Further, when the power supply voltage is less than the predetermined voltage, no current flows through the overvoltage detection circuit, so that it is possible to reduce the power consumption when an IC is formed correspondingly.
[0015]
A first auxiliary resistor and a second auxiliary resistor are connected in parallel to the first and second transistors, respectively. When the first and second transistors are off, the ratio of the first and second transistors sharing the power supply voltage is determined by the first auxiliary resistor and the second auxiliary resistor. Therefore, by setting the values of the first and second auxiliary resistors according to the element breakdown voltage of the first and second transistors, the maximum protection voltage is set to the sum of the element breakdown voltages of the first and second transistors. Can be increased to.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIG.
FIG. 1 shows an electrical configuration of an overvoltage protection circuit built in a control IC of an in-vehicle electronic device. In FIG. 1, an IC 21 includes an overvoltage protection circuit 22 and a device control circuit 23 (corresponding to a load) that is a control circuit for an in-vehicle electronic device on an SOI (Silicon On Insulator) substrate. The power supply voltage VB is supplied from the in-vehicle battery to the power supply terminal of the IC 21. The device control circuit 23 is, for example, a 5V DC power supply control circuit.
[0017]
The overvoltage protection circuit 22 is supplied with the power supply voltage VB via a power supply line 24 (corresponding to a high potential direct current power supply line) and a ground line 25 (corresponding to a low potential direct current power supply line). Between the power supply line 24 and the ground line 25, between the source and drain of a P-channel type MOS transistor 26 (corresponding to a first transistor), a device control circuit 23, and an N-channel type MOS transistor 27 (second channel). The drain and the source of the transistor are connected in series. Here, the MOS transistors 26 and 27 have an element structure with a high breakdown voltage (for example, 60 V).
[0018]
Resistors 28 and 29 (corresponding to first and second auxiliary resistors) are connected between the drains and sources of the MOS transistors 26 and 27, respectively. These resistors 28 and 29 are used to determine the sharing ratio of the power supply voltage VB applied to the MOS transistors 26 and 27 when the MOS transistors 26 and 27 are in the OFF state. The ratio of the resistance 29 is set to be equal to the ratio of the breakdown voltage of the MOS transistor 26 and the breakdown voltage of the MOS transistor 27. In the present embodiment in which the MOS transistors 26 and 27 have a breakdown voltage of 60V, the resistance values of the resistors 27 and 28 are set to the same value. The resistance values of the resistors 28 and 29 are set to be sufficiently larger than the impedance of the device control circuit 23.
[0019]
Between the power line 24 and the ground line 25, there is an overvoltage detection circuit 33 comprising a series circuit of a resistor 30 (corresponding to a first detection resistor), a Zener diode 31, and a resistor 32 (corresponding to a second detection resistor). It is connected. Here, the Zener diode 31 is configured in such a manner that a plurality of Zener diodes 31a,..., 31b having the resistor 30 side as a cathode are connected in series, and the resistance values of the resistors 30 and 32 are set to the same value. .
[0020]
The Zener voltage VZ1 (corresponding to the predetermined voltage in the present invention) of the Zener diode 31 is the maximum value of the power supply voltage VB that can be applied to the device control circuit 23 or a voltage slightly lower than that, and the MOS transistor 26 , 27 is set to a voltage (for example, 30 V) lower than the breakdown voltage.
[0021]
Between the cathode of the Zener diode 31a and the gate of the MOS transistor 26, a gate control circuit 34 (corresponding to a first control circuit) operating with the power supply line 24 as a reference potential is connected. That is, the cathode of the Zener diode 31a is connected to the base of the PNP transistor 36 via the resistor 35, and the emitter and collector of the transistor 36 are connected to the power supply line 24 and the gate of the MOS transistor 26, respectively. The gate of the MOS transistor 26 is connected to the power supply line 24 through the anode and cathode of the zener diode 37 for gate protection, and is connected to the ground line 25 through the resistor 38. Here, the Zener voltage VZ2 of the Zener diode 37 is set to a gate-source voltage (for example, 8 V) necessary for the MOS transistor 26 to be sufficiently turned on.
[0022]
Similarly, a gate control circuit 39 (corresponding to a second control circuit) operating with the ground line 25 as a reference potential is connected between the anode of the Zener diode 31b and the gate of the MOS transistor 27. In other words, the anode of the Zener diode 31b is connected to the base of the NPN transistor 41 through the resistor 40, and the emitter and collector of the transistor 41 are connected to the ground line 25 and the gate of the MOS transistor 27, respectively. The gate of the MOS transistor 27 is connected to the ground line 25 through the cathode and anode of the Zener diode 42 for protecting the gate, and is connected to the power supply line 24 through the resistor 43. Here, the Zener voltage VZ3 of the Zener diode 42 is set to a gate-source voltage (for example, 8 V) necessary for the MOS transistor 27 to be sufficiently turned on.
[0023]
Next, the operation of this embodiment will be described.
First, when the power supply voltage VB is less than the Zener voltage VZ1 of the Zener diode 31, no current flows through the Zener diode 31, and no voltage drop occurs in the resistors 30 and 32. For this reason, the base current does not flow through the transistors 36 and 41, and the transistors 36 and 41 are off. When the power supply voltage VB is higher than the Zener voltages VZ2 and VZ3 of the Zener diodes 37 and 42, Zener voltages VZ2 and VZ3 are applied between the gates and sources of the MOS transistors 26 and 27, respectively. Is fully on (ie in the saturation region).
[0024]
In this state, a voltage substantially equal to the power supply voltage VB is applied to the device control circuit 23 from the power supply line 24 and the ground line 25 via the MOS transistors 26 and 27, respectively.
[0025]
On the other hand, when the power supply voltage VB between the power supply line 24 and the ground line 25 becomes a voltage higher than the zener voltage VZ1 (that is, an overvoltage) due to voltage fluctuation of the in-vehicle battery or induction of surge voltage, the resistors 30 and 32 are connected. Thus, a current flows through the Zener diode 31, and the Zener diode 31 performs a constant voltage operation. Since the resistance values of the resistors 30 and 32 are equal, the difference voltage between the power supply voltage VB and the zener voltage VZ1 is equally applied to the resistors 30 and 32, and the base current flows through the transistors 36 and 41 due to the voltage, so that the transistors 36, 41 are turned on almost simultaneously. When the voltage across the resistors 30 and 32 rises due to overvoltage, the resistors 35 and 40 bear the increased voltage so that the transistors 36 and 41 are protected.
[0026]
When the transistors 36 and 41 are sufficiently turned on, the collector currents flow through the resistors 38 and 43, respectively. At this time, the collector-emitter voltage of the transistors 36 and 41 (that is, the gate-source voltage of the MOS transistors 26 and 27) becomes the saturation voltage (for example, about 0.2 V), and the MOS transistors 26 and 27 are turned off almost simultaneously. Transition.
[0027]
As described above, since the resistance values of the resistors 28 and 29 are set to a value sufficiently larger than the impedance of the device control circuit 23, almost no voltage is applied to the device control circuit 23 when the MOS transistors 26 and 27 are off. The device control circuit 23 is substantially disconnected from the power supply line 24 and the ground line 25 without being applied.
[0028]
Since the resistance values of the resistors 28 and 29 are set to the same value on the basis of the equal breakdown voltage of the MOS transistors 26 and 27, the MOS transistors 26 and 27 are set to the power supply voltage when the MOS transistors 26 and 27 are off. Share VB equally. As a result, as long as the power supply voltage VB is an overvoltage that is twice or less (120V or less) of the withstand voltage (60V) of the MOS transistors 26 and 27, the MOS transistors 26 and 27 can maintain the off state. It can be prevented from being applied.
[0029]
As described above, the overvoltage protection circuit 22 has a circuit configuration in which the MOS transistor 26 and the MOS transistor 27 are connected between the power supply line 24 and the device control circuit 23 and between the device control circuit 23 and the ground line 25, respectively. It has. When the power supply voltage VB is lower than the Zener voltage VZ1, the MOS transistors 26 and 27 are turned on to supply the power supply voltage VB to the device control circuit 23, and the power supply voltage VB becomes an overvoltage higher than the Zener voltage VZ1. In some cases, MOS transistors 26 and 27 are turned off, and device control circuit 23 is substantially disconnected from power supply line 24 and ground line 25. Thereby, the device control circuit 23 is protected from an overvoltage of the power supply voltage VB.
[0030]
Unlike the conventional overvoltage protection circuit shown in FIG. 2, this overvoltage protection circuit 22 does not include a circuit that consumes overvoltage energy, so that the chip area can be reduced when an IC is formed, and an overvoltage is generated. There is almost no heat generation due to. That is, the overvoltage protection circuit 22 has a circuit configuration suitable for IC integration. Since an external component for overvoltage protection can be eliminated by using an IC, the entire circuit can be reduced in size and cost.
[0031]
According to the overvoltage protection circuit 22, the device control circuit 23 can be protected against an overvoltage exceeding the element withstand voltage (60 V) even when the IC 21 is manufactured by using a manufacturing process that has been used conventionally. It becomes like this. As a result, a design change (an element structure change or a manufacturing process change) for increasing the element withstand voltage is not required, and the cost required for forming the overvoltage protection circuit 22 in the IC 21 can be kept low.
[0032]
In this embodiment, the withstand voltages of the MOS transistors 26 and 27 and the resistance values of the resistors 28 and 29 are set to be equal to each other, and the MOS transistors 26 and 27 equalize the power supply voltage VB when the MOS transistors 26 and 27 are off. to share the load. Therefore, the overvoltage protection circuit 22 can protect the device control circuit 23 to an overvoltage that is twice the breakdown voltage of the MOS transistors 26 and 27.
[0033]
Further, the MOS transistor 26 connected to the power supply line 24 side employs a P-channel type, and the MOS transistor 27 connected to the ground line 25 side employs an N-channel type. The gate voltage of the MOS transistors 26 and 27 can be controlled using the ground line 25 as a reference potential. For example, the circuit configuration of the gate control circuits 34 and 39 is different from that in the case where two N-channel MOS transistors are connected in series. It will be easy.
[0034]
Further, when the power supply voltage VB is less than the Zener voltage VZ1, no current flows through the overvoltage detection circuit 33, so that it is possible to reduce power consumption when an IC is formed correspondingly.
[0035]
The present invention is not limited to the embodiment described above and shown in the drawings. For example, the present invention can be modified or expanded as follows.
The overvoltage detection circuit includes, for example, a voltage dividing circuit that divides the power supply voltage VB, and a comparison circuit (such as a comparator) that compares the voltage divided by the voltage dividing circuit with a predetermined voltage so as to detect the overvoltage. It may be configured.
The first and second transistors are not limited to MOS transistors, and may be, for example, bipolar transistors or IGBTs.
[0036]
The breakdown voltages of the MOS transistors 26 and 27 may not be equal to each other. When the ratio between the resistance value of the resistor 28 and the resistance value of the resistor 29 is set to be equal to the ratio between the breakdown voltage of the MOS transistor 26 and the breakdown voltage of the MOS transistor 27, the breakdown voltages of the MOS transistors 26 and 27 are added. The device control circuit 23 can be protected against overvoltage up to the voltage value.
[0037]
Resistors 28 and 29 connected between the drains and sources of the MOS transistors 26 and 27 are provided so that the MOS transistors 26 and 27 share the power supply voltage VB sufficiently evenly when the MOS transistors 26 and 27 are off. Is .
[Brief description of the drawings]
FIG. 1 is an electrical configuration diagram of an overvoltage protection circuit showing an embodiment of the present invention. FIG. 2 is a diagram corresponding to FIG. 1 showing a prior art. FIG. 3 is a schematic electrical configuration diagram of the overvoltage protection circuit. Explanation】
22 is an overvoltage protection circuit, 23 is a device control circuit (load), 24 is a power supply line (high potential DC power supply line), 25 is a ground line (low potential DC power supply line), 26 is a MOS transistor (first transistor), 27 is a MOS transistor (second transistor), 28 is a resistor (first auxiliary resistor), 29 is a resistor (second auxiliary resistor), 30 is a resistor (first detection resistor), 31, 31a,. 31b is a Zener diode, 32 is a resistor (second detection resistor), 33 is an overvoltage detection circuit, 34 is a gate control circuit (first control circuit), and 39 is a gate control circuit (second control circuit).

Claims (1)

In an overvoltage protection circuit for protecting a load connected between a high potential DC power supply line and a low potential DC power supply line from an overvoltage generated between the high potential DC power supply line and the low potential DC power supply line,
A P channel type or PNP type having a control terminal and connected between the high potential DC power supply line and the load, and is turned on and off by controlling the control terminal with the high potential DC power supply line as a reference potential . A first transistor;
An N channel type or NPN type having a control terminal and connected between the low potential DC power supply line and the load, and which is turned on and off by controlling the control terminal using the low potential DC power supply line as a reference potential . A second transistor;
An overvoltage detection circuit for detecting an overvoltage state in which a voltage between the high potential DC power supply line and the low potential DC power supply line is equal to or higher than a predetermined voltage;
A first control circuit that controls to turn off the first transistor while the overvoltage detection circuit detects the overvoltage state;
A second control circuit that controls to turn off the second transistor while the overvoltage detection circuit detects the overvoltage state ;
In the overvoltage detection circuit, a first detection resistor, a Zener diode having a Zener voltage equal to the predetermined voltage, and a second detection resistor are connected in series between the high potential DC power supply line and the low potential DC power supply line. Provided with
The first control circuit turns off the first transistor based on a voltage across the first detection resistor,
The second control circuit turns off the second transistor based on a voltage across the second detection resistor;
A first auxiliary resistor and a second resistor for determining respective voltage sharing ratios when the first and second transistors are in an off operation in parallel with the first and second transistors, respectively. An overvoltage protection circuit characterized by connecting an auxiliary resistor .

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