JPH01270733A - Overvoltage protecting circuit for load driver - Google Patents

Abstract

PURPOSE:To prevent thermal breakdown by switching the driving voltage of semiconductor switching means of output stage by second voltage control means for limiting a first power source voltage to a third limiting voltage lower than the second voltage to limit it when the first voltage exceeds the second voltage. CONSTITUTION:When a surge voltage of 110V is input to an output terminal 23, the potential of the terminal 23 rises like a line l3. A line 39 is clamped at this level at a time t2 when the level of the terminal 23 arrives at an operation voltage 27V of a second limiting voltage set by Zener diodes (Z) D5-8, and transistors(Tr) 37, 38 maintain conductive. Thus, a voltage is supplied to the base of the Tr 42 to conduct it. Accordingly, the line 39 is clamped at a third limiting voltage 20V of an operating voltage to be fundamentally restricted by ZD5, 11, 12, and the potential of the terminal 23 is reduced. Thus, the power consumption of the Trs 32, 33 is reduced to prevent thermal breakdown.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a circuit for protecting a device that drives a load such as various lamps mounted on a vehicle from overvoltage.

BACKGROUND OF THE INVENTION For example, in in-vehicle electronic equipment, driving integrated circuits are widely used which have functions such as lighting various alarm lamps based on outputs from various detection devices regarding exhaust gas temperature, door opening/closing status, and the like. Such an iA product circuit for driving includes an input stage including a comparison section that compares and determines whether the output signal is a signal at a normal level, and an input stage that includes a comparison section that compares and determines whether the output signal is a signal at a normal level. and an output stage for driving.

FIG. 14 is a block diagram showing a configuration related to a typical conventional driving integrated circuit (hereinafter referred to as a driving circuit) 1. Referring to FIG. 14, the first conventional example will be explained. explain. In the first conventional example, the output terminal 2 of the drive circuit 1 is connected to a load 4 via a resistor 3, and the load 4 is connected to a power line 7 connected to a power source 5 such as a battery via a switch 6. . Further, a power supply terminal (+B) 9 of the drive circuit 1 is connected to the power supply line 7 via a pull-down resistor 8.

The drive circuit 1 includes a comparator 10 to which drive power is supplied from a power supply terminal 9, and a Darlington-connected transistor 11.
12. A reference voltage is connected to one of the inverting input terminal and non-inverting input terminal of the comparator 10, and signals from the various sensors mentioned above are input to the other input terminal, and the input signal is at an appropriate level. Determine whether or not.

FIG. 15 is a block diagram showing the configuration of the second conventional example. This conventional example is similar to the first conventional example, and corresponding parts are given the same reference numerals. In this conventional example, a stabilizer 1 is provided to the power supply terminal 9 of the drive circuit 1 to stabilize the voltage (+B) from the power supply 5.
The output Vcc from 3 is supplied.

In other words, in-vehicle electronic devices are supplied with a +B system power supply as a power supply voltage (the voltage value varies depending on the type of vehicle;
2V) and the Vcc power supply (5V or 8V).
There is a grid power supply, and the above-mentioned figure 14 or 15 [! A configuration like this is used.

In such a configuration, a positive surge may occur in the +B system power supply, and in order to prevent the drive circuit 1 from being destroyed by this, overvoltage is It is necessary to have a protective function.

In other words, regarding the resistance of the control unit (ECU) to positive polarity surges in the above-mentioned 10B system power supply, JIS (Japanese Industrial Standards) states that it will not be destroyed even if a positive surge voltage of maximum 110cm and duration of 0.188 seconds is applied. Must not be” (
load dump test). On the other hand, the withstand voltage of automotive integrated circuits is ■. ,. =40-60V. Therefore, if the power supply terminal (assumed to be the Vcc terminal) of the integrated circuit is directly connected to the 10B power supply, the integrated circuit will be destroyed in the case of the above-mentioned surge voltage.

Furthermore, if the lamp load connected to the output terminal of an integrated circuit is directly pulled up to a 10V power source, the output transistor will be destroyed when the output is cut off. It is also assumed that the battery will be charged with a power source (approximately 24V) from a truck or the like when the voltage is "high", and the clamp voltage to be described later for protection is selected to be 26V or higher.

FIG. 16 is an electric circuit diagram showing the configuration of a third conventional example that meets such a request. In this conventional example, in the configuration shown in No. 14121, the output terminal of the comparator 10, that is, the base of the transistor 11, A clamp circuit 14 made of a Zener diode and having an operating voltage of about 27 V is provided between the power supply terminal 9 and the power supply terminal 9.

In such a configuration, when the power supply line 7 has an overvoltage exceeding a preset limit voltage in the clamp circuit 14, the potential of the power supply terminal 9 is maintained at the limit voltage by the clamp circuit 14. On the other hand, transistor 11
．． 12 becomes conductive, and the load 4 is grounded, thereby preventing the transistor 12 from being destroyed by a large voltage.

However, in such a configuration, in a vehicle or the like, the load 4 is placed at a distance from the drive circuit 1, and relatively long wiring is routed.

Therefore, if a surge voltage occurs in the power line 7,
It is not always the case that the power supply terminal 9 rises in voltage and the bell rises before the output terminal 2, but the potential of the output terminal 2 may rise first. In such a case, the transistors 11.12 are not turned on in time by the action of the clamp circuit 14, and the surge voltage causes the transistors 11.12 to become conductive.
There is a problem that 12 is broken down and destroyed.

FIG. 17 is a block diagram showing the configuration of a fourth conventional example that attempts to solve such problems.

In this conventional example, a resistor 15, a diode 16, and a transistor 17 are provided between the output terminal 2 and the power supply terminal 9 from the output terminal 2 side. Diode 16 is resistor 15
The transistor 17 is an NPN transistor while the remaining transistors 11 and 12 are NPN transistors.
PNP) - configured as a transistor.

With this configuration, an overvoltage occurs at the output terminal 2, and when no overvoltage occurs at the power supply terminal 9, the overvoltage at the output terminal 2 causes the power supply terminal (Vcc
The potential difference with the voltage (approximately 13 V) at the terminal) increases, transistor 17 becomes conductive, and the base potential of transistor 11 increases. As a result, the transistors 11 and 12 become conductive, and the output terminal 2 becomes low level. This level is clamped to Vcc voltage 13V by the clamp circuit 14. That is, by keeping the potential of the output terminal 2 at a relatively low level as described above, the transistor 11
．． 12 destruction is prevented.

However, in such a configuration of the prior art, when Vcc power is supplied to the power supply terminal 9, the potential of the transistor 17 becomes Vccc$ pressure, and the transistor 17 is always in a conductive state.
2 becomes conductive and current flows through the load 4, causing malfunctions such as lamps being constantly lit.

Therefore, the power supply terminal 9 is connected to the above-mentioned Vcc power supply or +
If any of the B-system power sources is to be used, it is necessary to configure the system as shown in FIG. 18.

Another conventional technique that attempts to solve such a problem is the configuration shown in FIG. 18. In this conventional example, clamp circuits 14 and 18 are separately provided to clamp the potentials at the power supply terminal 1 and the output terminal 2. As a result, even if an overvoltage is applied from either side of the power supply terminal 9 or the output terminal 2, it can be clamped to a predetermined constant level at each terminal 9, 2. Further, even when the Vcc voltage is applied to the power supply terminal 9, it is possible to avoid a situation in which the transistor 17 is always in a conductive state.

However, in such conventional technology, when an overvoltage occurs on the output terminal 2 side, the base potential of the transistor 17 is clamped to the voltage of four Zener diodes forming the clamp circuit 18, and therefore the potential of the output terminal 2 is also clamped to this voltage. It is stabilized at a voltage corresponding to (about 30V). As a result, the output terminal 2 cannot be switched to a low level, and the power consumption of the transistors 11 and 12 increases, resulting in thermal damage.

In other words, as shown in Figure 19, such a situation occurs as follows.
In an on-vehicle drive integrated circuit, the load 4 is normally used by being pulled up to a 10B power supply. Therefore, if a positive surge voltage of about 110V at the peak occurs in the 10B power supply,
Since a voltage (30V) clamped by the clamp circuit 18 is applied to the transistors 11 and 12, and a large current flows due to the peak voltage, the transistor 1
Since the power consumed in 1.12 becomes large, these transistors cause breakdown damage.

Problems to be Solved by the Invention In each of the conventional techniques described above, the output terminal 2 of the transistors 11 and 12 constituting the output stage of the drive circuit 1 is
When an overvoltage occurs in the circuit, there is a problem that it is not possible to prevent its destruction, and when trying to prevent thermal damage, both the Vcc system and the +B system are used as the @ source of the drive circuit 1. The problem was that it was not possible to do so.

The purpose of the present invention is to solve the above-mentioned technical problems and to
A load driving device that prevents thermal breakdown when an overvoltage occurs in a device, and that can use either a first power source voltage or a second power source voltage different from the first power source voltage as the power source for the load driving circuit. The purpose of this invention is to provide an overvoltage protection circuit.

Means for Solving the Problems The present invention provides an output stage including a semiconductor switching means interposed between a ground potential and the other end of a load whose one end is connected to a first power supply voltage; The second fi is different! voltage is input, and limits this to a predetermined first limit voltage, and controls the semiconductor switching means to be in a conductive state when the limit voltage is inputted.
voltage limiting means; a second pressure limiting means provided in parallel with the output stage and limiting the driving voltage of the semiconductor switching means to a second limiting voltage; an overvoltage protection circuit for a load driving device, characterized in that the overvoltage protection circuit for a load drive device includes switching limiting means for switching and limiting the driving voltage to a third limiting voltage lower than the second limiting voltage when the driving voltage exceeds the second limiting voltage. .

Furthermore, the present invention provides an output stage including a semiconductor switching means interposed between a ground potential and the other end of a load whose one end is connected to a first power supply voltage;
A first voltage limiting means receives a power supply voltage and limits it to a predetermined first limiting voltage, and controls the semiconductor switching means to be in a conductive state when the voltage is limited; and the semiconductor switching means is provided in parallel with the output stage. a second voltage limiting means for limiting the drive voltage of the output stage to a second limited voltage; An overvoltage protection circuit for a load driving device, characterized in that the overvoltage protection circuit for a load driving device includes a switching driving means for detecting the overvoltage and switching the semiconductor switching means to a conductive state when the overvoltage occurs. According to the present invention, when the first leakage voltage exceeds the second limiting voltage, the driving voltage of the semiconductor switching means in the output stage is controlled by the second voltage control means that limits the first power supply voltage. A switching limiting means switches and limits the voltage to a third limiting voltage that is lower than the second limiting voltage. If this third limited voltage is applied to such an extent that the semiconductor switching means is not destroyed, thermal destruction of the semiconductor switching means in such a case can be prevented. Further, the second leakage voltage input to the first voltage limiting means is limited to a predetermined first limiting voltage. When the second power supply voltage rises and exceeds the first limiting voltage, the first voltage limiting means controls the semiconductor switching means to be conductive. Thereby, the load driving device is protected even if the first power supply voltage and the second power supply voltage each become an overvoltage.

Furthermore, in the present invention, when an overvoltage exceeding the second control voltage occurs in either the first power supply voltage or the second power supply voltage or the output stage, the switching drive means detects this overvoltage and turns the semiconductor switching means into conduction. The state may be changed. This also protects the load drive device from overvoltage.

Embodiment FIG. 1 is a block diagram showing the basic configuration of an embodiment of the present invention, and FIG. 2 is an electric circuit diagram showing the example of the configuration shown in FIG. The configuration of this embodiment will be described with reference to FIGS. 1 and 2. For example, the load 21 such as various warning lights placed on the instrument panel of a vehicle is
It is connected via a resistor 24 to an output terminal 23 of a drive circuit 22, which is a load drive device realized by an f1 circuit element or the like. Such a load 21 is connected to the +B system power supply line 25 as described in the section of the prior art. Power supply line 25 is connected to power supply terminal 27 of drive circuit 22 via resistor 26 .

The drive circuit 22 is provided with input terminals 28 and 29. Signals from various sensors, etc. are input to one of the input terminals 28 and 29, a reference voltage is given to the capacity input terminal, and a comparator 30 to determine whether the signal level is a normal level or not. This comparator 30 is supplied with a power supply Vcc from the power supply terminal 27.

The output of the comparator 30 is input to the base of a transistor 32 constituting an output stage 31, the collector of the transistor 32 is connected to the output terminal 23, and the emitter is connected to the transistor 32.
Connected to the base of 3.

The collector of transistor 33 is connected to the collector of transistor 32, and the emitter is grounded.

Between the power supply terminal 27 and the output stage of the comparator 30, a first voltage limiting means 34 having a configuration as described later is connected, and a second voltage limiting means 34 is connected between the output terminal 23 and the base of the transistor 32. A limiting means 35 is connected.

As shown in FIG. 2, the first voltage limiting means 34 includes, for example, Zener diodes Di, D with an operating voltage of 6.7V.
2. D3. This is a configuration in which D4 are connected to each other. The second voltage limiting means 35 is connected to the output terminal 23 via a resistor 36, and includes transistors 37 and 38 whose respective emitters are connected to the resistor 36. Each transistor 37.
38 are connected in common by a line 39, the collector of the transistor 37 is connected via a resistor 40, and the collector of the transistor 38 is connected directly to a line 41 connecting the output stage of the comparator 30 and the base of the transistor 32. be done.

Between lines 39 and 40 there is, for example, a Zener diode D5. with an operating voltage of 6°7. D6. D7. D8 are connected in series with the line 40 side serving as an anode. Also, Zener diode D5. For example, between D6, Zener diodes D11 and D12 with an operating voltage of 5.4μ are connected in series with the Zener diode D5 side as the cathode, and the anode of the Zener diode D12 is connected to the collector of the transistor 42, and its emitter is connected to the line. 41.

Further, the base is connected to the collector of the transistor 37. The Zener diodes Dll, D12 and the transistor 42 constitute a first voltage limiting means.

3 to 8 are diagrams and graphs schematically showing the operation of the drive circuit 22 of this embodiment. This embodiment will be described with reference to these drawings.

■Normal state Voltage Vcc is applied to the power supply terminal 27, and the power supply line 25
If the power supply is normally connected to the terminal 10B, the first and second voltage limiting means 34 , 35 do not operate, and the operation of the output stage 31 is determined by the output of the comparator 30 . That is, when the output of the comparator 30 is at a high level or a low level, the transistors 32 and 33 are in a conducting/cutting state, respectively, and the load 21 is turned on/off, for example.

(2) Overvoltage of the power supply terminal 27 A case in which a surge voltage reaching a maximum of 110 V is about to flow into the power supply terminal 27 will be described. In FIG. 5, the horizontal axis is the surge voltage, and the vertical axis is the potential of the power supply terminal 27.

Due to the inflow of the surge voltage, the potential of the power supply terminal 27 increases as shown by the line 11 in FIG. 4, and the first voltage I
Zener diodes D1 to D4 constituting the II limiting means 34
When the first voltage limiting means 3 reaches the first limiting voltage set by , i.e. the operating voltage determined by the series-connected Zener diodes D1 to D4, for example approximately 27V, the first voltage limiting means 3
4 operates, and the power supply terminal 27 is maintained at the first limited voltage.

At this time, charge is injected into the transistor 32 by the current passing through the first voltage limiting means 34, and
2 Therefore, transistor 33 becomes conductive, and the line ! indicating the level of output terminal 23 in FIG. 2, the output terminal 23 is switched to low level.

(2) During overvoltage of the output terminal 23 A case in which a surge voltage of, for example, a maximum of 11 oV flows into the output terminal 23 will be described. Assume that the source terminal 27 is connected to a 10B power source. When the potential of the output terminal 23 increases as shown by line 11 in FIG.
When is not operating, line 41 is low and transistor 42 is cut off. Therefore, the level of the output terminal 23 is the line ! of FIG. As shown at 9, the second
At time t2 when the operating voltage, which is the limiting voltage, reaches the target of 27V, for example, the line 39 is clamped to this voltage, and the transistors 37 and 38 remain conductive.

As a result, a voltage is supplied to the base of the transistor 42, and the transistor 42 becomes conductive. Therefore line 39
is the Zener diode D5. Dll.

The third voltage is the operating voltage basically defined by D12.
Limit voltage For example, approximately 20V 6.7V+5.4Vx2+0.7VX3=20.7V
...(1) 6.7V: l- Operating voltage of transistor D5 5.4V: Operating voltage of Zener diode Dll, 12 0.7V: Clamped to the base-emitter voltage of transistor 42, 6, the potential of the output terminal 23 decreases as shown in FIG. As a result, the transistor 32
．． The power consumption of transistors 32 and 33 can be reduced, and thermal damage to transistors 32 and 33 can be prevented.

When the potential of the output terminal 23 decreases from the third limit voltage (18V), even if the surge voltage that is about to flow into the output terminal 23 gradually decreases, the output terminal 23 will be lower than the third limit voltage (18V).
It is clamped at a limited voltage (approximately 18 cm), and therefore, when the surge voltage drops, the transistor 42 becomes 3
! ! The transistors 37 and 38 become disconnected. As a result, the potential of the output terminal 23 decreases in accordance with the surge voltage that decreases below the third limit voltage.

■Overvoltage power supply terminal 27 between power supply terminal 27 and output terminal 23
A case will be described in which a maximum surge voltage of 110V is applied to both the output terminal 23 and the output terminal 23. As the surge voltage gradually increases as shown in FIG. 8, the potentials of the power supply terminal 27 and the output terminal 23 also increase correspondingly. When the surge voltage exceeds the second limiting voltage (approximately 27 cm), the first voltage limiting means 34 operates at the power supply terminal 27, and the output terminal performs the operation as described in item 0 above. In step 23, the operation described in section 0 above is performed. Here, in the above term 0, the output terminal 23 is a Zener diode D5. However, in this operation example, the output stage 31 is electrically connected to the ground potential, so the ground potential (
OV).

In this way, in this embodiment, even if an overvoltage occurs in at least one of the power supply terminal 27 and the output terminal 23, an excessive current flows into the drive circuit 22 and the drive circuit 22 is destroyed, especially in the case where the output terminal 23 It is possible to prevent thermal destruction of the transistors 32 and 33 in the output stage 31 due to excessive voltage.

Furthermore, according to this embodiment, even if the power supply terminal 27 is used in such a manner that the Vcc voltage is supplied, the situation where the output terminal 23 is always at a low level as described in the section of the prior art can be avoided. This greatly improves usability.

No. 9121 is an electric circuit diagram showing a detailed configuration of another embodiment of the present invention. Embodiment 6 This embodiment will be described with reference to FIG. 9. This embodiment is similar to the previously described embodiment, and corresponding parts are given the same reference numerals.

In the configuration of this embodiment, in addition to the configuration of the above embodiment, a delay circuit 44 to which power is supplied from the power supply terminal 27 is provided in parallel with the first voltage limiting means 34. Delay circuit 44
is equipped with a constant current source 45 supplied with power by the power supply terminal 27, and a capacitor 47 is connected between this constant current source 45 and a ground line 46. A connection point 48 between the constant current source 45 and the capacitor 47 is connected to the collectors of the four transistors and to the inverting input terminal of the comparator 50. A constant voltage is supplied from a power supply 51 to a non-inverting input terminal of the comparator 50 . On the other hand, the emitter of the transistor 49 is connected to the ground line 46, and the base is connected to the collector of the transistor 37 (multi-collector type).

The output of the comparator 50 is connected to the base of a transistor 53 forming a drive circuit 52. The emitters of the transistors 1 to 53 are connected to the ground line 46, and the collectors are connected to the base of the transistor 54 which also constitutes the drive circuit 52. The collector of the transistor 54 is also connected to the base of the transistor 55 constituting the drive port i\fi 52, and the emitter of the transistor 54 and the collector of the transistor 55 are connected to the output terminal 23. The emitter of the transistor 55 is connected to the base of the transistor 33 constituting the output stage.

On the other hand, the second voltage limiting means 35 includes the transistor 37.
．． The bases of 39 are connected in common, and transistors 56 and 57 of the same conductivity type as these are provided. The emitters of the transistors 56 and 57 are connected in common and are connected to a drive output terminal 59 of the drive circuit 22 via a resistor 58. The drive output terminal 59 is connected to the power supply line 25 via a resistor 60. The collector of transistor 57 is connected to the base of transistor 32, and the collector of transistor 56 is connected to the base of transistor 42, with the remaining collectors of transistor 37 other than the one directed to transistor 49.

Here, an output stage 31 is configured including transistors 32 and 33.

10 to 12 are graphs illustrating the configuration shown in FIG. 9. The operation of this embodiment will be described with reference to these drawings.

(2) At the time of overvoltage of the power supply terminal 27 As shown in section 10, the surge voltage gradually rises, and therefore the voltage Vce of the power supply terminal 27 also rises, and the first limit voltage (for example, 27
■) Until you reach the 10th U line! 5, it increases in response to an increase in surge voltage. At time t5 in FIG. 10 when the potential of the power supply terminal 27 reaches the first limiting voltage, the first voltage limiting means 34 operates and injects charge into the base of the transistor 55.
Switch 3 to make it conductive. Especially the level of output terminal 23 is the 10th U3 line! 5, it is forcibly switched to low level.

Further, the level of the power supply terminal 27 is clamped to the first limited voltage by the first voltage limiting means 34.

(2) Overvoltage at the drive output terminal 59 As shown in FIG. 11, when the surge voltage flowing into the five drive output terminals increases, the output voltage VDR at the drive output terminal 59 also increases accordingly.

When the voltage VDR reaches a second limiting voltage (for example 27) set by the second voltage limiting means 35, the transistor 56.5
7 becomes conductive, and transistor 42 becomes conductive. As a result, the second voltage limiting means is the diode D6. Third limit voltage by D7 (for example, about 20 ■ = operating voltage, for example, 6.7 ■)
It is clamped to three Zener diodes. When the operating voltage decreases from the state exceeding 27V, when the third limit voltage is reached, the transistor 42
is cut off, but at this time the level of the drive output terminal 59 is lower than the second limit voltage, so a level according to the surge voltage is output. This is shown at line 17 in FIG.

On the other hand, at time t6 when the surge voltage reaches 27V, the transistors 56, 57 and 32 become conductive, and the transistor 33 becomes conductive. As a result, the level of the output terminal 23 is switched to low level as shown by line 17 in FIG. Further, when the surge voltage decreases, at time t7 when the surge voltage reaches 20V, the transistors 37 and 3
9: The transistors 56 and 57 are cut off, and therefore the transistors 32 and 33 are also cut off, and the level of the output terminal 23 becomes a high level (for example, 14).

■When the surge voltage rises at the output terminal 23 When the surge voltage rises at the output terminal 23 Similarly to the above-mentioned case, when the surge voltage reaches 27V, the second voltage limiting means 35 operates, and the transistor 4
2 becomes conductive and clamps the level of the output terminal 23 to the third @ voltage.

On the other hand, due to the conduction of the transistor 37, the transistor 49
Charge is also injected into the base of transistor 49, making transistor 49 conductive. As a result, the charge in the capacitor 47 that had been charged by the constant current source 45 is rapidly discharged, and the output of the comparator 50 is switched from a low level to a high level.

As a result, the output of the comparator 50 is inverted from low level to high level, and the transistor 53 becomes conductive.
4 is also conductive. This causes transistor 55.33 to also become conductive, so that output terminal 23 is switched to a low level as shown in line No. 8 of FIG.

When the output terminal 23 becomes low level, the transistors 37, 39, 56, and 57 are cut off as in each case described above, and therefore the four transistors are also cut off, and the capacitor 47 is charged with a constant current from the constant current source 45. Supplied. As a result, after the time t shown in the second equation, the output of the comparator 50 is inverted from high level to low level, and the transistor 53 is also cut off. As a result, the transistor 54 is also cut off, and the level of the output terminal 23 becomes the clamp level determined by the diodes D5 to D7.

Assuming that the surge voltage gradually increases, the level of the output terminal 23 becomes 27V or more, and the above-described operation is performed again to switch the level of the output terminal 23 to the low level. That is, when the surge voltage rises above 27V, the level of the output terminal 23 repeatedly changes between the above-mentioned 20V and the ground potential.

On the other hand, assume that the surge voltage decreases from a state exceeding 27V. In this case, transistors 53, 54,
55.33 is cut off, and when the potential becomes 20 V or less with the output terminal 23 cut off from the ground potential, the transistor 42 is cut off, and the transistors 37.38, 56.
57 remains blocked. Therefore, the delay circuit 44
does not operate, and the level of the output terminal 23 decreases in response to the surge potential.

According to each of the embodiments described above, the output terminal 23,
Even if an overvoltage is applied to either the power supply terminal 27 or the drive output terminal 59, it can be clamped to a voltage that does not destroy the drive circuit 22, or forced to the ground potential. This prevents damage to the drive circuit 22 due to overvoltage or heat due to fire extinguishing power. Further, as this i source, either a Vcc type or a +B type can be used.

FIG. 13 is an electric circuit diagram showing still another configuration example of the present invention. This configuration example is similar to the configuration example shown in FIG. 9, and corresponding parts are given the same reference numerals.

In this configuration example, the first voltage limiting means 34 is composed of a constant current source 61 and diodes 62, 63, and 64. Further, in the delay circuit 44, the comparator 50 is connected to a transistor 65 whose collector is connected to the base of the transistor 49, whose collector is connected to the power supply terminal 27, and whose collector is connected to the base of the transistor 65, whose base is connected to the transistor 65. A transistor 66 connected to the emitter of 65 is used.

A resistor 67 is interposed between the emitter and base of transistor 56, and this resistor is connected to ground line 46 via diode 68 and resistor 69. Also diode 6
The cathode of 8 is connected to the base of transistor 70,
The collector of the transistor 70 is connected to the cathode of the diode 64 constituting the first voltage limiting means, and the emitter is connected to the ground line 46. With such a configuration, the above-described operations and effects can be similarly achieved.

Effects of the Invention As described above, according to the present invention, the first power supply voltage is controlled by the second voltage.
When the voltage exceeds the voltage, the driving voltage of the semiconductor switching means of the output stage is switched by the second voltage control means for limiting the first power supply voltage to a third limiting voltage lower than the second limiting voltage, and the limiting means switches the drive voltage of the semiconductor switching means in the output stage. Restrict. If this third limit voltage is selected to such an extent that the semiconductor switching means will not be destroyed, thermal destruction of the semiconductor switching means in such a case can be prevented. Further, in the load driving device, even if the first power supply voltage and the second power supply voltage each become an overvoltage, the load driving device is protected.

Furthermore, in the present invention, when an overvoltage exceeding the second control voltage occurs in either the first power supply voltage or the second power supply voltage or the output stage, the switching drive means detects this overvoltage and turns the semiconductor switching means into conduction. This also protects the load drive device from overvoltages.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 2 is an electric circuit diagram showing the configuration example of FIG. 1, and FIGS.
7 are block diagrams showing detailed operating states of this embodiment, FIGS. 4, 6, and 8 are graphs explaining the operation of this embodiment, and FIG. 9 is a block diagram showing the operation state of this embodiment in detail. An electric circuit diagram explaining the embodiment, FIGS. 10 to 12 are graphs explaining the operation of this embodiment, FIG. 13 is an electric circuit diagram showing the configuration of still another embodiment of the present invention, and FIG. 14 , Figure 15 shows a typical first
FIG. 16 is an electric circuit diagram illustrating the configuration of a typical third prior art; FIG.
FIG. 18 is an electric circuit diagram showing the configuration of the fourth conventional example, FIG. 18 is an electric circuit diagram showing the configuration of the fifth conventional example, and FIG. 19 is an electric circuit diagram for explaining the problem. 21... Load, 22... Drive circuit, 23... Output terminal, 25... Power supply line, 27... Power supply terminal, 3
1... Output stage, 34... First voltage limiting means, 35.
...Second voltage limiting means, 44...Delay circuit, 52...
・Drive circuit, 59...drive output terminal nv sir';

Claims (2)

[Claims] (1) An output stage including a semiconductor switching means interposed between the ground potential and the other end of a load whose one end is connected to a first power supply voltage; and a second power supply voltage different from the first power supply voltage is inputted. , which limits the voltage to a predetermined first limit voltage, and controls the semiconductor switching means to be conductive when the voltage is limited.
Voltage limiting means; Second voltage limiting means provided in parallel with the output stage and limiting the driving voltage of the semiconductor switching means to a second limiting voltage; 1. An overvoltage protection circuit for a load driving device, comprising: switching limiting means for switching and limiting the driving voltage to a third limiting voltage lower than the second limiting voltage when the driving voltage exceeds the second limiting voltage. (2) an output stage including a semiconductor switching means interposed between the ground potential and the other end of the load whose one end is connected to the first power supply voltage; and a second power supply voltage different from the first power supply voltage is inputted. , which limits the voltage to a predetermined first limit voltage, and controls the semiconductor switching means to be conductive when the voltage is limited.
Voltage limiting means; A second voltage limiting means provided in parallel with the output stage and limiting the drive voltage of the semiconductor switching means to a second limited voltage; A second voltage limiting means provided in the output stage and configured to control the first power supply voltage or the second power supply voltage. or switching drive means for detecting an overvoltage exceeding the second limit voltage and switching the semiconductor switching means to a conductive state when an overvoltage exceeding the second limit voltage occurs in at least one of the output stages. protection circuit.