JP3567107B2 - Circuit breaker in case of overcurrent - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor relay system using a semiconductor relay, and particularly, when an overcurrent flows due to a short circuit or the like on a load side, a microcomputer reliably detects an overcurrent and shuts off current supply to a load. The present invention relates to a circuit interruption method at the time of current and a circuit interruption device at the time of overcurrent.
[0002]
[Prior art]
In general, in a vehicle, power from a vehicle-mounted battery is supplied to loads disposed in various parts of the vehicle via a power MOSFET and a power line covered with an insulating film. This power line is routed along the vehicle body in an engine room or the like that is constantly vibrating. If the power line is located close to the corner of the vehicle body, for example, The contact of the power supply line will be repeated for a long time and the coating of the power supply line will be gradually cut off by the corners of the vehicle body, and the inner conductor will be exposed, albeit minutely. As a result, a dead short circuit or a rare short circuit occurs in the power supply line, and an overcurrent flows.
In recent years, power MOSFETs and IPSs (Intelligent Power Switches) have been used as semiconductor relays for automobiles. In such semiconductor relays and IPSs, various current limiter systems have conventionally been adopted as shown in FIG. 6 in order to prevent heat generation of the device. For example, when considering only an inrush current in which a large current flows through the lamp load when the lamp switch is turned on, a PWM method in which the power MOSFET is completely turned off with an overcurrent set value is optimal, but as shown in FIG. When an overcurrent flows for some reason (for example, ground fault) during energization (during supply of a steady current), the current flowing to the lamp load is reduced to zero. For this reason, sampling the current value at a predetermined interval using a microcomputer and reading the current monitor value and judging in a software manner whether or not an overcurrent state occurs is because the sampling value is ramped as in the timing of t2 in FIG. It could not hit when the current flowing through the load was zero.
[0003]
In addition, when there is a biting short circuit in which a current that does not reach the soft overcurrent determination value is continuously flowing to the lamp load, in the case of FIG. Thermal stress was applied (for normal FET). In addition, in the case of the biting short circuit shown in FIG. 7B, thermal stress is applied to the device for a long time even when software judgment cannot be made, and the life of the MOSFET with a built-in thermal cutoff circuit can be further increased. It has become difficult.
[0004]
[Problems to be solved by the invention]
Such a conventional overheat shutoff function and overcurrent protection function with a built-in IPS are merely functions for self-protection, and no consideration is given to protection of a wiring harness or a circuit routed in an automobile. For this reason, in the conventional semiconductor relay and IPS, overheating can be cut off in order to prevent heat generation of the device, but there is a problem that the circuit cannot be cut off without difficulty at the time of overcurrent.
[0005]
An object of the present invention is to perform sufficient overcurrent judgment with respect to an overcurrent due to a short circuit on the load side. An object of the present invention is to make it possible to perform an overheat cutoff function by the MOSFET itself and make an overcurrent judgment.
[0006]
[Means for Solving the Problems]
To achieve the above object, a circuit breaker for overcurrent according to claim 1 is a semiconductor relay system for supplying power to a load by controlling on / off of a microcomputer using a semiconductor relay. Setting means for setting a maximum current value flowing through the load by connecting a current detection resistor to the drain side of the loader; and a current value lower than the current value set by the first setting means. Second setting means for setting a current value higher than the supplied rated current, load current detecting means for detecting current from the voltage across the current detecting resistor, and voltage across the current detecting resistor are compared. A comparator is provided. When a load current detected by the load current detecting means exceeds a current value set by the first setting means based on an output from the comparator, the comparator is provided. A gate logic circuit for controlling a gate voltage of the semiconductor relay with a predetermined current value width not smaller than a current value set by the second setting means based on the set value; and a first setting means based on an output from the comparator. Hysteresis means for increasing the gate voltage of the semiconductor relay output from the gate logic circuit when the set current value falls to a preset current value and providing hysteresis with a predetermined current value width to the current supplied to the load; An overcurrent determination unit configured to determine that the load current is an overcurrent when the load current detected by the load current detection unit is counted a predetermined number of times as a current value higher than the current value set by the second setting unit. It was done.
With this configuration, according to the first aspect of the present invention, it is possible to perform a sufficient overcurrent determination with respect to an overcurrent due to a short circuit on the load side, and to control when using a MOSFET with a built-in thermal cutoff circuit. Even if the power loss at the time is large, it is possible to determine the overcurrent by exerting the overheat shutoff function by the MOSFET with a built-in heat shutoff circuit itself.
[0009]
To achieve the above object, the circuit breaker during overcurrent according to claim 2, the semiconductor relay, Some configured in thermal shutdown circuit built-in MOSFET.
With this configuration, according to the second aspect of the present invention, it is possible to perform a sufficient overcurrent determination with respect to an overcurrent due to a short circuit on the load side, and to perform a thermal cutoff circuit even if a large power loss occurs during control. The overheat interruption function by the built-in MOSFET itself can be exhibited to determine an overcurrent.
[0010]
In order to achieve the above object, a circuit breaker at the time of an overcurrent according to claim 3 sets the second set value set by the second setting means to a current value several times the rated load current. It is set.
With this configuration, according to the third aspect of the invention, when an overcurrent due to a short circuit flows to the load side, the overcurrent can be reliably detected.
[0011]
In order to achieve the above object, a circuit breaker at the time of an overcurrent according to claim 4 sets the second set value by software using a microcomputer.
With this configuration, according to the invention described in claim 4 , when an overcurrent due to a short circuit flows to the load side, the overcurrent can be reliably detected by the software of the microcomputer.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
FIG. 1 shows an embodiment of a circuit breaking method at the time of overcurrent and a circuit breaking device at the time of overcurrent according to the present invention.
[0013]
In the figure, a power supply voltage VB from a vehicle-mounted battery 1 includes a current detection resistor (shunt resistor) Rs for detecting a current supplied to a load, and a drain D-source S of a MOSFET 2 with a built-in heat cutoff circuit as a semiconductor switch element. It is supplied to a load 3 such as a stop lamp or a headlight through the interval.
The MOSFET 2 with a built-in thermal cutoff circuit is, for example, a power MOSFET driven at a logic level (4 V or more) and has a built-in thermal cutoff circuit, which enables protection of a power MOSFET in an overheated state. After the operation of the overheat cutoff circuit, the circuit returns with a gate voltage of 0 bias.
[0014]
The drive circuit 4 includes an NPN-type switching (SW) transistor Tr1 having a collector connected to a charge pump output voltage VP obtained by boosting the power supply voltage VB by the charge pump circuit 5, and an NPN transistor having a collector connected to the emitter of the SW transistor Tr1. And a contact point between the emitter of the SW transistor Tr1 and the collector of the SW transistor Tr2 is connected to the gate G of the MOSFET 2 with a built-in thermal cutoff circuit.
[0015]
Then, the drive circuit 4 applies the charge pump output voltage VP to the gate G of the MOSFET 2 with a built-in heat cutoff circuit by turning on the SW transistor Tr1 and turning off the SW transistor Tr2, thereby turning on the MOSFET 2 with a built-in heat cutoff circuit. Turn on.
Further, by turning off the SW transistor Tr1 and turning on the SW transistor Tr2, the application of the charge pump output voltage VP to the gate G of the MOSFET 2 with built-in thermal shutdown circuit is stopped, and the MOSFET 2 with built-in thermal shutdown circuit is turned off.
[0016]
A shunt resistor Rs provided between the vehicle-mounted battery 1 and the MOSFET 2 with a built-in thermal shutdown circuit is a low resistance for converting a current IL flowing through a power supply line between the vehicle-mounted battery 1 and the load 3 into a voltage. By detecting the voltage between both ends, the current IL flowing through the power supply line is detected. Both ends of the shunt resistor Rs are connected to a (+) input terminal and a (-) input terminal of the amplifier 6, and the amplifier 6 functions as a current detecting means and outputs a voltage corresponding to a voltage between both ends of the shunt resistor Rs. The current IL is detected by output. The shunt resistor Rs uses a resistance of, for example, several tens of mΩ, and determines a hard overcurrent determination value (first setting value), for example, several tens of amperes.
[0017]
The output of the amplifier 6 is digitally converted by an A / D converter 7 and then supplied to a microcomputer (microcomputer) 8. One end of the microcomputer 8 is connected to the ground via a resistor R1, and the other end of the switch SW is connected to the power supply voltage VB. A level ON operation signal S1 is supplied.
The microcomputer 8 has a built-in A / D converter 7 and operates in accordance with a preset control program. A CPU 10 stores a control program for the CPU 9 in advance. When an H-level ON operation signal S1 is input to the microcomputer 8 by turning on the switch SW, a drive instruction signal S2 is sent to the gate logic circuit 14. Is output.
[0018]
On the other hand, a comparator 12 is connected to both ends of the shunt resistor Rs, and a gate logic circuit 14 is connected to an output terminal of the comparator 12. The gate logic circuit 14 is connected to the drive circuit 4. A hysteresis circuit 13 is connected to a (+) input terminal of the comparator 12.
The comparator 12 outputs a predetermined voltage to the gate logic circuit 14 with a hysteresis of a predetermined voltage value provided by the hysteresis circuit 13 in accordance with the voltage across the shunt resistor Rs. The comparator 12 outputs to the gate logic circuit 14 to turn off the gate voltage applied from the drive circuit 4 to the gate G of the MOSFET 2 with a built-in thermal cutoff circuit. As a result, the current flowing through the shunt resistor Rs decreases. The hysteresis circuit 13 applies a gate voltage from the drive circuit 4 to the gate G of the MOSFET 2 with a built-in heat cutoff circuit again to the gate logic circuit 14 with a predetermined amount of hysteresis from the current initially flowing through the shunt resistor Rs. The comparator 12 outputs an ON signal. This current control continues until the drive instruction signal S2 output from the microcomputer 8 to the gate logic circuit 14 is turned off. As described above, the hysteresis circuit 13 substantially determines the ON / OFF threshold value of the comparator 12.
[0019]
The operation of the circuit breaker at the time of overcurrent configured as described above will be described.
First, when the power is turned on, as shown in FIG. 2, when a voltage Vin is applied from the microcomputer 8 to the gate logic circuit 14, this voltage passes through the drive circuit 4 via the gate logic circuit 14 and is thermally shut off. This is applied to the gate G of the MOSFET 2 with a built-in circuit. Then, the voltage VGS between the gate G and the source S of the MOSFET 2 with a built-in thermal shutdown circuit gradually increases as shown in FIG. In the figure, a is a period from when Vin is turned on until the MOSFET 2 with a built-in thermal shutdown circuit reaches VGS (th) to the second set voltage, and b is a period during which the active region shifts from the active region to the saturation region. The built-in MOSFET 2 is completely turned on. Also, c in the figure is a period during which the current ID (IL in FIG. 1) flowing from the VGS (th) to the load starts flowing, and d1 turns Vin off when the current ID passes through the off threshold of the comparator 12. During the period d2, when the voltage VGS between the gate G and the source S of the MOSFET 2 with a built-in thermal cutoff circuit decreases to the voltage VGS between the gate G and the source S for maintaining the peak current, the current ID flowing to the load decreases. It is a turning period. Further, in the figure e, during the period in which Vin is turned on after the current ID flowing to the load passes the on threshold, f is turned off after passing the off threshold, and the voltage VGS between the gate G and source S decreases. Indicates a period in which the current ID flowing to the load drops when the voltage drops to the gate G-source S voltage VGS (on) for maintaining the peak current.
[0020]
Further, the microcomputer 8 constantly samples the output of the amplifier 6 digitally converted by the A / D converter 7 every predetermined time, and the current IL flowing through the sampled load is equal to a second set value (predetermined current value). And if the current IL flowing through the load exceeds the second set value and counts the set number of times (for example, several times) continuously, an overcurrent is detected. Upon detecting this overcurrent, the microcomputer 8 stops outputting the drive instruction signal S2 to the gate logic circuit 14.
When the drive instruction signal S2 from the microcomputer 8 to the gate logic circuit 14 is turned off, the application of the charge pump output voltage VP to the gate G of the MOSFET 2 with a built-in heat cutoff circuit is stopped.
[0021]
FIG. 3 shows a constant current control waveform at the time of an actual ground fault.
FIG. 4 shows the overheat interruption time of the MOSFET 2 with a built-in heat interruption circuit in the constant current control.
In the figure, △ indicates a MOSFET with a built-in thermal cutoff circuit at a cutoff temperature of 200 ° C., and □ indicates an overheat cutoff time in a constant current control of a MOSFET with a cutoff temperature of 165 ° C. In FIG. 4, it can be seen that overheating is interrupted at 30 to 70 msec at normal temperature. This characteristic diagram was obtained by intentionally generating heat from a MOSFET with a built-in thermal shutdown circuit at a cutoff temperature of 200 ° C. and a MOSFET with a built-in thermal shutdown circuit at a cutoff temperature of 165 ° C., and cutting the current to the load side. It can be seen that cutting the current to the load side contributes to suppressing the temperature rise of the wire harness.
[0022]
FIG. 5 shows a state of constant current control when a MOSFET with a built-in thermal cutoff circuit is actually used, together with a current monitor.
In FIG. 5, the hardware overcurrent determination value is several tens of A, and in the case of a ground fault, the current is limited at a period of about several tens of μsec. Further, the soft overcurrent determination value is set to twice the rated load (21 W × two lamps) current, and the hysteresis of the comparator 12 is set. When the soft overcurrent determination value is set to twice the rated load current, if the hysteresis of the comparator 12 is set, the current drop becomes the lower limit value. Therefore, the microcomputer 8 monitors the current (current value sampling). (Comparing with the overcurrent determination value set by the microcomputer 8), the overcurrent state can be read. In this case, data sampling by the microcomputer 8 is regarded as an overcurrent state by reading several times for several msec, for example.
[0023]
In the case of chattering short, when the load changes from off to on in the short state, current detection is performed after a predetermined time has elapsed after the load is turned on. If an overcurrent is detected several tens of times a second during this current detection, it is determined as an overcurrent, and the microcomputer 8 stops outputting the drive instruction signal S2 to the gate logic circuit 14.
[0024]
If the microcomputer 8 cannot detect the overcurrent state in any situation, the overheat cutoff is performed by the function of the overheat cutoff function of the MOSFET 2 with a built-in heat cutoff circuit itself. In addition, the temperature rise of the load side harness can be suppressed.
As described above, in the present embodiment, the current value is determined by the microcomputer by performing the constant current control (the first set value) on the supply current to the load side with respect to the overcurrent due to the short circuit on the load side. Allows sufficient overcurrent judgment (comparison of the second set value and the detected current value) without dropping below the value (second set value). If the power loss during control is large, a built-in heat cutoff circuit The FET itself is turned off by the overheat cutoff function of the MOSFET, so that no current flows to the load side.
[0025]
【The invention's effect】
The present invention is configured as described above, and has the following effects.
[0026]
According to the invention of claim 1, it is possible to perform sufficient overcurrent determination with respect to an overcurrent due to a short in the load side, power loss at the time of control in the case of using a thermal shutdown circuit-integrated MOSFET is rather large Also, the overcurrent cutoff function can be performed by the MOSFET itself with the built-in heat cutoff circuit to determine the overcurrent.
[0029]
According to the second aspect of the present invention, it is possible to make a sufficient overcurrent determination with respect to an overcurrent due to a short circuit on the load side, and to perform overheat interruption by the MOSFET with a built-in thermal shutdown circuit itself even if the power loss during control is large. The function can be exercised to determine overcurrent.
[0030]
According to the third aspect of the invention, when an overcurrent due to a short circuit flows to the load side, the overcurrent can be reliably detected.
[0031]
According to the fourth aspect of the present invention, when an overcurrent due to a short circuit flows to the load side, the overcurrent can be reliably detected by software of the microcomputer.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an embodiment of a circuit breaking method at the time of overcurrent and a circuit breaking device at the time of overcurrent according to the present invention.
FIG. 2 is a time chart for explaining the operation of the MOSFET with a built-in thermal cutoff circuit shown in FIG. 1;
FIG. 3 is a diagram showing a constant current control waveform at the time of an actual ground fault.
FIG. 4 is a diagram showing an overheat cutoff time of a MOSFET with a built-in heat cutoff circuit in constant current control.
FIG. 5 is a diagram showing a state of a current monitor for constant current control when using a MOSFET with a built-in thermal cutoff circuit.
FIG. 6 is a diagram showing characteristics of a conventional current limiter method.
FIG. 7 is an overheat cutoff characteristic diagram for explaining overcurrent control by a conventional PWM method.
[Explanation of symbols]
1 …………………………………………………………………………………… MOSFET with built-in thermal cutoff circuit
3 Load 4 Drive circuit 5 Charge pump circuit 6 Charge pump circuit 6 ...... Amplifier 7 ...... A / D converter 8 ...... Microcomputer 9 ...... CPU
10… ROM… ROM
11 ………………… RAM
12 Comparator 13 Hysteresis circuit 14 Gate logic circuit

Claims (4)

In a semiconductor relay system that supplies power to a load by controlling on / off with a microcomputer using a semiconductor relay,
First setting means for connecting a current detection resistor to a drain side of the semiconductor relay to set a maximum current value flowing to a load;
A second setting unit that sets a current value lower than the current value set by the first setting unit and higher than a rated current supplied to the load in a steady state;
Load current detecting means for detecting a current from a voltage between both ends of the current detecting resistor;
A comparator for comparing voltages at both ends of the current detection resistor, wherein a load current detected by the load current detection means exceeds a current value set by the first setting means based on an output from the comparator; A gate logic circuit for controlling a gate voltage of the semiconductor relay with a predetermined current value width not less than a current value set by the second setting means based on the set value ;
And boosting the gate voltage of the semiconductor relay output from the gate logic circuit when the current value set by the first setting means drops to a preset current value based on the output from the comparator. Hysteresis means for providing hysteresis to the current supplied to the load with the predetermined current value width ;
An overcurrent determining means for determining that the load current detected by the load current detecting means is an overcurrent when counting a preset number of times as a current value higher than the current value set by the second setting means; ,
Circuit breaker at the time of overcurrent. The circuit breaker at the time of an overcurrent according to claim 1, wherein the semiconductor relay is a MOSFET with a built-in thermal cutoff circuit. 3. The overcurrent circuit breaker according to claim 1, wherein the second set value set by the second setting unit is a current value several times the rated load current. 4. 4. The circuit breaker according to claim 1, wherein the second set value is set by the microcomputer.

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