JP2002271183A - Overvoltage protective circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an overvoltage protective circuit which is formed at a low cost and capable of protecting a circuit as an object of protection against overvoltage, without having to modify the structure of the circuit itself. SOLUTION: A functional circuit 14 as an object of protection and a transistor Q11 are connected in series between a power supply wires 17 and 18. The transistors Q12 and Q11 of an overvoltage detecting circuit go into off and on state respectively at normal operation times. When an overvoltage occurs between the power supply wires 17 and 18, the transistor Q12 is turned on, and the transistor Q11 is turned off. At this point, the withstand voltage of the functional circuit 14 to a power supply voltage Vcc is increased by the withstand voltage of the transistor Q11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overvoltage protection circuit for protecting a protected circuit interposed between power supply lines from overvoltage generated between the power supply lines.

[0002]

For example, an electronic control unit (hereinafter, referred to as an ECU) mounted on a vehicle receives a supply of voltage from a vehicle-mounted battery via a battery line, and receives the supplied battery voltage. Some operate with the power supply voltage. This battery voltage is typically 12
It has a voltage value of about V. However, since various loads such as solenoid coils are connected to the battery line in addition to the ECU, an overvoltage called a load dump may occur in the battery line due to power cutoff to such a load. is there.

Therefore, the following two means are used to protect the ECU from this overvoltage. The first means is a means for connecting a discrete protection element, for example, a power zener diode between power supply terminals of the ECU, and causing the power zener diode to consume power accompanying overvoltage. According to this means, the ECU can be protected without changing the circuit configuration inside the ECU, but there is a problem that the cost increases and the device size increases.

[0004] The second means is to increase the withstand voltage of the circuit itself constituting the ECU. For example, in a circuit composed of bipolar transistors, paying attention to the fact that the breakdown voltage of the transistor is about twice as high for VCBO as for VCEO.
By designing the circuit based on the grounded base circuit, the withstand voltage of the circuit itself constituting the ECU can be improved. Here, VCEO depends on the manufacturing process,
For example, the voltage value is about 35V. However, when such restrictions on circuit design are imposed, the degree of freedom in circuit selection is reduced, making it difficult to design a desired circuit, and new problems such as circuit redundancy and an increase in design man-hours arise.

Therefore, instead of restricting the grounding method of the transistor circuit, a means for increasing the breakdown voltage by connecting the transistors in a vertical stack is also conceivable. FIG. 4 shows an example of a circuit configuration using a vertically stacked connection in a control IC constituting the ECU. In FIG. 4, the control IC 1 includes an overvoltage detection circuit 2, a constant current circuit 3, and a function circuit 4.
(Only a part is shown). These circuits are connected between power supply terminals 5 and 6 connected to the battery line.

[0006] The functional circuit 4 is a circuit that executes various functions of the ECU 1, and is a protected circuit to be protected from the above-mentioned overvoltage. In the input section, transistors Q1 and Q2 and transistors Q3 and Q4 are connected in cascade to increase the breakdown voltage, and a resistor R is connected between power supply terminals 5 and 6.
1. A circuit configuration in which the emitter-collector of the transistor Q2 and the emitter-collector of the transistor Q4 (and the base-emitter of the transistor Q5) are connected. According to this configuration, the transistor Q
2, the withstand voltage between the collector and the emitter of Q4 becomes VCEO, and the withstand voltage of the functional circuit 4 rises to approximately 2.VCEO.

However, when such a vertical connection is adopted, the minimum operating voltage of the functional circuit 4 becomes lower than the V of the transistor.
It will be higher by BE (about 0.7V). Further, in this means, it is necessary to vertically connect all the circuit parts having a low withstand voltage connected between the power supply terminals 5 and 6 in the functional circuit 4, which leads to an increase in the number of transistors and an increase in power consumption. Further, the collector-emitter voltage of the transistor Q2 is different between the case of the single-stage configuration including the transistors Q1 and Q2 (not shown) and the case of the two-stage configuration with the addition of the transistors Q3 and Q4 (FIG. 4). If the design of the number of stages is changed, there is an inconvenience that circuit characteristics change.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an overvoltage protection circuit that can be configured at low cost and that can protect a protected circuit from overvoltage without changing the configuration of the protected circuit itself. Is to do.

[0009]

According to the first aspect of the present invention, a protected circuit and a transistor are connected in series between power supply lines. This transistor is turned on when the voltage between the power supply lines is equal to or lower than a predetermined protection voltage value, and the voltage between the power supply lines is applied to the protected circuit almost as it is. On the other hand, the transistor is driven off when the voltage between the power supply lines exceeds a predetermined protection voltage value, and protects the protected circuit from an overvoltage generated between the power supply lines. According to this means, the withstand voltage against overvoltage is an added value of the withstand voltage of the protected circuit itself and the withstand voltage of the transistor, so that the withstand voltage can be improved without changing the configuration of the protected circuit itself, that is, overvoltage protection. Is achieved. In addition, an element that consumes power due to an overvoltage, such as an external power zener diode that has been conventionally used, is not required. In addition, since the transistor, the overvoltage detection circuit, and the driving circuit are easily integrated with the protected circuit as an IC, the overvoltage protection circuit is used. Can be reduced.

According to the second aspect, the collector and the emitter of the bipolar transistor are connected between the power supply line and the circuit to be protected, and the resistor is connected between the base and the emitter. According to this connection form, the withstand voltage of the bipolar transistor becomes VCER higher than VCEO, so that the protection performance against overvoltage is further enhanced.

According to the third aspect of the present invention, the drain and source of the FET are connected between the power supply line and the circuit to be protected, and the gate protection circuit is connected between the gate and source. According to this connection form, the withstand voltage is improved while protecting the gate of the FET, that is, overvoltage protection is achieved.

According to the fourth aspect of the present invention, the drive circuit operates as a constant current circuit while the voltage between the power supply lines is equal to or lower than the predetermined protection voltage value, and the transistor operates from the constant current circuit. It is turned on by receiving the current.
By configuring the transistor driving circuit as a constant current circuit in this manner, the driving of the transistor is less likely to be affected by voltage fluctuation between power supply lines.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment in which the present invention is applied to overvoltage protection of an electronic control unit (hereinafter referred to as an ECU) will be described with reference to FIG. An ECU (not shown as a whole) mounted on the vehicle is provided with one or a plurality of control ICs, and FIG. 1 shows an example of an electrical configuration of such a control IC. The control IC 11 shown in FIG. 1 includes an overvoltage detection circuit 12, a constant current circuit 13, an NPN transistor Q11, a resistor R11 connected between the base and the emitter of the transistor Q11, and a functional circuit 14 (only a part is shown). ) Is formed. Of these, the circuit portion excluding the functional circuit 14 is an overvoltage protection circuit. A positive terminal and a negative terminal of an unillustrated in-vehicle battery are connected to the positive and negative power terminals 15 and 16 of the control IC 11, respectively.
The control IC 11 operates using the battery voltage as the power supply voltage Vcc.

A power supply terminal 1 is provided inside the control IC 11.
Power supply lines 17 and 18 connected to the power supply lines 5 and 16 are formed, and the overvoltage detection circuit 12 and the constant current circuit 13 are connected between the power supply lines 17 and 18. The overvoltage detection circuit 12 includes a resistor R12 connected between the power supply lines 17 and 18, zener diodes ZD11 to ZD13 having the illustrated polarity, a diode D11 having the illustrated polarity,
It comprises a series circuit 19 comprising a resistor D13 and a resistor R13, and an NPN transistor Q12 having a base and an emitter connected between both terminals of the resistor R13.

The constant current circuit 13 (corresponding to a drive circuit) includes an NPN transistor Q13 connected to the power supply line 18,
A first current mirror circuit 20 composed of Q14, and PNP transistors Q15 and Q connected to the power supply line 17;
And a second current mirror circuit 21 comprising 16
The collectors of the transistors Q14 and Q15 are connected to each other. The resistor R14 is connected between the power supply line 17 and the collector (base) of the transistor Q13, and the resistor R11 and the collector and emitter of the transistor Q11 are connected between the collector of the transistor Q16 and the power supply line 18. ing. The common base line of the current mirror circuit 21 is connected to the power supply line 18 via the resistor R15 and the emitter-collector of the PNP transistor Q17. The base of the transistor Q17 is connected to the collectors of the transistors Q14 and Q15. It is connected. A resistor R16 is connected between the base and the emitter of the transistors Q15 and Q16.

The functional circuit 14 is a circuit that performs various functions of the control IC 11 and is a protected circuit that is protected from overvoltage generated between the power supply lines 17 and 18. This functional circuit 14 is connected between the power supply line 17 and the collector of the transistor Q11. In the present invention, the functional circuit 1
Although there is no restriction on the circuit configuration for No. 4, this embodiment has the following configuration.

That is, between the input terminal 22 and the power supply line 18, the emitter-collector of the PNP transistor Q18 and the collector-emitter of the NPN transistor Q19 are connected in series. Transistor Q1
8 base is connected to its collector and PNP
The transistor Q19 is connected to the base of the current mirror circuit 2
0 is connected to the common base line. Transistor Q2
0 is connected to the power supply line 17 via a resistor R17, and one of the two collectors is directly connected to the other one.
One is connected to the collector of the transistor Q11 via the collector and the emitter of the NPN transistor Q21. The transistor Q22 forms a current mirror circuit 23 together with the transistor Q21.

Next, the operation of the control IC 11 will be described. Battery voltage (power supply voltage V) supplied to the ECU
cc) usually has a voltage value of about 12V. But,
Since various loads such as solenoid coils are connected to the vehicle-mounted battery in addition to the ECU, an overvoltage called a load dump may be generated in the battery voltage due to the power cutoff to such a load. Therefore, in the overvoltage detection circuit 12, a protection voltage Va having a voltage value higher than the normal voltage value and lower than the withstand voltage of the functional circuit 14 is set, and the power supply voltage Vcc is set to an overvoltage equal to or higher than the protection voltage Va. Then, the transistor Q12 is turned on (corresponding to the output of the overvoltage signal), thereby performing overvoltage protection.

Here, Zener diodes ZD11-ZD
The zener voltage of D13 is Vz, the diodes D11, D1
Assuming that the forward voltage of 2 and VBE of the transistor Q12 in the ON state are VF and the resistances of the resistors R12 and R13 are R12 and R13, respectively, the protection voltage Va is expressed by the following equation (1). Is determined. Va = 3 · Vz + 3 · VF + VF · R12 / R13 (1)

During normal operation, that is, when the power supply voltage Vcc is lower than the protection voltage Va, the resistance R of the overvoltage detection circuit 12
13 becomes lower than VF and the transistor Q
12 turns off. In this case, the constant current circuit 13 performs a constant current operation, and sets the resistance value of the resistor R14 to R
If it is 14, the collector current Ic of the transistors Q16 and Q19 is as shown in the following equation (2). Ic = (Vcc-VBE) / R14 (2)

The collector current of the transistor Q16 flows through the resistor R11 and becomes the base current of the transistor Q11, so that the transistor Q11 is turned on. As a result, the voltage between the collector and the emitter of the transistor Q11 becomes sufficiently small, and a voltage substantially equal to the power supply voltage Vcc is applied to the functional circuit 14. Functional circuit 1
Reference numeral 4 denotes a circuit for detecting a voltage difference between a predetermined voltage Vb applied to the input terminal 22 and the power supply voltage Vcc and outputting a current corresponding to the voltage difference as a collector current of the transistor Q22. When the current shown by the equation (2) flows, the operation state is established.

On the other hand, at the time of overvoltage, that is, the power supply voltage Vcc
Is higher than the protection voltage Va, the voltage across the resistor R13 of the overvoltage detection circuit 12 becomes higher than VF, and the transistor Q12 is turned on. When the transistor Q12 is turned on, the base-emitter voltage of the transistor Q13 decreases to the saturation voltage of the transistor Q12, and the transistor Q13 is turned off. Along with this,
The constant current circuit 13 stops its constant current operation, and the transistors Q14 to Q17, and thus the transistors Q11 and Q18
To Q22 are all turned off.

In this state, the overvoltage applied between the power supply lines 17 and 18 is applied to the overvoltage detection circuit 12, the constant current circuit 13, and the series circuit of the function circuit 14 and the transistor Q11. In the constant current circuit 13, the breakdown voltages of the transistors Q14, Q15, Q16, and Q17 are VCES, VCER, VCER, and VCEO, respectively. Generally, the breakdown voltage of the transistor is VCES>VCER> V
Because of the CEO relationship, transistor Q17
Has the lowest breakdown voltage. However, this transistor Q1
7, a resistor R15 is connected in series, so that the current is limited by the resistor R15, thereby improving the withstand voltage.

The breakdown voltage of the functional circuit 14 is determined by VCEO of the transistor Q20 only in the circuit portion shown in FIG.
Of course, if there is a circuit portion having a lower withstand voltage in a circuit portion not shown, it is determined by the withstand voltage. In the conventional configuration in which the functional circuit 14 is directly connected between the power supply lines 17 and 18 (see FIG. 4), a transistor Q20 having a high withstand voltage enough to withstand the above-mentioned overvoltage, a vertically stacked connection, It has been necessary to add an external element, for example, a power zener diode, in order to prevent intrusion of overvoltage.

On the other hand, in this embodiment in which the functional circuit 14 and the transistor Q11 are connected in series, the power supply line 1
Since transistors Q20 and Q11 are connected in series between 7 and 18, the withstand voltage as a whole is a value obtained by adding VCEO of transistor Q20 and VCER of transistor Q11. In particular, since the resistor R11 is connected between the base and the emitter of the transistor Q11,
The withstand voltage of the transistor Q11 is VCER higher than VCEO.

As described above, according to the present embodiment, the power line 1
7 and 18, the functional circuit 14 and the transistor Q11 are connected in series, and the transistor Q11 is turned off in an overvoltage state.
4 is increased by the withstand voltage VCER of the transistor Q11, whereby overvoltage protection is achieved. Therefore, the function circuit 14
In order to protect the transistor from overvoltage, a functional circuit 1 such as adopting a transistor having a high withstand voltage as the transistor Q20 or connecting the transistor Q20 in a vertical connection is used.
There is no need to change the design of 4 itself to increase the breakdown voltage.
Therefore, it is possible to reduce the design cost required for the circuit change or the adjustment of the circuit characteristics, and to be free from the problems such as an increase in the minimum operating voltage and an increase in the power consumption due to the vertical connection.

Further, while external elements such as a power Zener diode are not required, the overvoltage detection circuit 12, the constant current circuit 13, the resistor R11 and the transistor Q11 are
Since the circuit configuration is suitable for C, manufacturing costs can be reduced.

Further, since the resistor R11 is connected between the base and the emitter of the transistor Q11, the breakdown voltage of the transistor Q11 increases to VCER. Further, during normal operation without intrusion of overvoltage, the transistor Q11 is in the saturation ON state, so that the collector loss of the transistor Q11 can be reduced as much as possible and the function circuit 14
Can be minimized.

(Second Embodiment) Next, the present invention is applied to an ECU.
A second embodiment applied to the overvoltage protection will be described with reference to FIG. FIG. 2 shows an electrical configuration of a control IC used in the ECU, and the same components as those in FIG. 1 are denoted by the same reference numerals. In the control IC 24 shown in FIG. 2, an overvoltage detection circuit 12, a resistor R18 corresponding to a drive circuit, a transistor Q11, a resistor R11, and a function circuit 25 (only a part is shown) are formed.

The common connection point between the resistor R11 and the base of the transistor Q11 is connected to the power supply line 17 via the resistor R18 and to the collector of the transistor Q12. In the functional circuit 25, the power supply line 17
And a collector of the transistor Q11.
9 and the collector and emitter of the NPN transistor Q23 are connected in series, and between the collector of the transistor Q18 and the collector of the transistor Q11,
The collector and the emitter of the NPN transistor Q24 are connected. These transistors Q23 and Q24
Form a current mirror circuit 26, and the current mirror circuit 26 and the resistor R19 form a constant current circuit 27.

The control IC 24 has the same configuration as the control IC 11 described in the first embodiment in that the functional circuit 25 and the transistor Q11 are connected in series. The configuration is different in that a constant current circuit 27 necessary for the operation is provided in the functional circuit 25.

According to the control IC 24, during normal operation, the transistor Q12 is turned off, a base current flows to the transistor Q11 via the resistor R18, and the transistor Q11 is turned on in saturation. On the other hand, at the time of overvoltage, the transistor Q12 is turned on, and the transistor Q11 is turned off with the base and the emitter almost short-circuited. Therefore, according to the present embodiment, the same effect as that of the first embodiment can be obtained.

The transistor Q1 at the time of overvoltage
The breakdown voltage of 1 is not VCER but VCES. As described above, since VCES is higher than VCER, the withstand voltage of the functional circuit 25 with respect to the power supply voltage Vcc is further increased. Further, since the constant current circuit 27 is formed in the functional circuit 25, the constant current circuit 27 is also protected from overvoltage. Therefore, the control IC 24
As a whole, sufficient overvoltage protection is achieved.

(Third Embodiment) Next, a third embodiment, which is a modification of the first embodiment, will be described with reference to FIG. 3, which shows the electrical configuration of a control IC. This figure 3
1 is different from the control IC 11 shown in FIG. 1 in that an N-channel MOS
The difference is that the FET Q25 is used, and that a Zener diode ZD14 (corresponding to a gate protection circuit) having the illustrated polarity is connected between its gate and source. According to this configuration, the same operation and effect as those of the first embodiment can be obtained.

Further, a MOSFET Q having a small on-resistance
25, the drain-source voltage in the ON state can be kept low. Therefore, even if the size of the functional circuit 14 is large to some extent, the entire functional circuit 14 and M
A circuit configuration in which the OSFET Q25 is connected in series can be provided.
As a result, the entire functional circuit 14 can be uniformly protected, and it is not necessary to investigate and selectively protect the functional circuit 14 having a low breakdown voltage.

(Other Embodiments) The present invention is not limited to the embodiments described above and shown in the drawings. For example, the present invention can be modified or expanded as follows.
Instead of the transistor Q11 and the MOSFET Q25, or together with the transistor Q11 and the MOSFET Q25, a transistor may be connected between the power supply line 17 and the functional circuits 14 and 25, and the transistor may be turned off when an overvoltage occurs.

The overvoltage detection circuit may have another circuit configuration as long as the circuit outputs an overvoltage signal while the power supply voltage Vcc between the power supply lines 17 and 18 exceeds the protection voltage Va. The drive circuit is not limited to the constant current circuit 13 and the resistor R18, and may be a circuit that drives the transistor Q11 and the MOSFET Q25 off while the transistor Q12 of the overvoltage detection circuit 12 is in an on state (that is, a period during which an overvoltage signal is output). Good.

In the first and third embodiments, a resistor is connected between the collector of the transistor Q14 and the base of the transistor Q17, and between the collector of the transistor Q16 and the base of the transistor Q11 (gate of the MOSFET Q25). The constant current circuit 1
3, the withstand voltage can be increased. In the third embodiment, the MO
An IGBT may be used instead of the SFET Q25. The above-described overvoltage protection circuit is not limited to application to an ECU mounted on a vehicle, but can be applied to a circuit in which an overvoltage may enter (generate).

[Brief description of the drawings]

FIG. 1 is an electrical configuration diagram of a control IC showing a first embodiment of the present invention;

FIG. 2 is a view corresponding to FIG. 1, showing a second embodiment of the present invention;

FIG. 3 is a view corresponding to FIG. 1, showing a third embodiment of the present invention;

FIG. 4 is a diagram corresponding to FIG. 1 showing a conventional technique.

[Explanation of symbols]

12 is an overvoltage detection circuit, 13 is a constant current circuit (drive circuit), 14 and 25 are functional circuits (protected circuits), 17, 1
8 is a power supply line, Q11 is a transistor, Q25 is a MOSF
ET (transistor), R11 is a resistor, R18 is a resistor (drive circuit), and ZD14 is a Zener diode (gate protection circuit).

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H03K 17/687 G05F 1/10 304G 5J055 19/003 3/26 // G05F 1/10 304 H03K 17/60 A 3/26 17/687 A F-term (reference) 5G004 AA04 AB02 BA08 DC04 DC10 EA01 FA01 5G053 AA09 BA04 CA01 DA01 EC03 FA05 5H410 BB02 CC02 EA10 EB01 FF03 LL02 5H420 BB12 CC02 EA11 EA18 EB01 A035A03 5A02 5A04 AX55 AX64 BX16 CX28 DX03 DX22 DX55 EX06 EX07 EY01 EY12 EY13 EY17 EY21 EZ03 EZ04 FX12 FX17 FX35 FX36 GX01

Claims (4)

[Claims] 1. An overvoltage protection circuit for protecting a protected circuit interposed between power supply lines from overvoltage generated between the power supply lines, comprising: a transistor connected between the power supply line and the protected circuit; An overvoltage detection circuit that outputs an overvoltage signal during a period when the voltage between the lines exceeds a predetermined protection voltage value; and an overvoltage detection circuit that turns on the transistor while the overvoltage signal is not output from the overvoltage detection circuit. A drive circuit that turns off the transistor during a period in which the overvoltage signal is being output. 2. The transistor is a bipolar transistor, wherein a collector and an emitter are connected between the power supply line and the protected circuit, and a resistor is connected between the base and the emitter. The overvoltage protection circuit according to claim 1, wherein: 3. The semiconductor device according to claim 1, wherein the transistor is an FET, a drain and a source are connected between the power supply line and the protected circuit, and a gate protection circuit is connected between the gate and the source. The overvoltage protection circuit according to claim 1, wherein 4. The constant current circuit which operates on condition that no overvoltage signal is output from the overvoltage detection circuit, wherein the transistor receives a current from the constant current circuit. 4. The overvoltage protection circuit according to claim 1, wherein the overvoltage protection circuit is turned on.