JP3713408B2 - Overcurrent control method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention uses a semiconductor relay system composed of a MOSFET (Metal Oxide Semiconductor-Field Effect Transistor) or the like as a semiconductor relay, particularly when changing a load such as a tail lamp or a stop lamp of a vehicle light. The present invention relates to an overcurrent control method that is effective in preventing erroneous short determination.
[0002]
[Prior art]
In recent years, in the case of relays used for electronic control of automobile engine control systems and safety control systems, instead of the conventional mechanical relays, high-speed switching, contactlessness, and reliability through self-protection functions, etc. Semiconductor relay systems using excellent MOSFETs with built-in thermal shutdown circuits and IPS (intelligent power switches) are frequently used.
[0003]
The power supply voltage from the in-vehicle battery is supplied to a lamp load or the like through a power supply line arranged in the vehicle body. If the power line insulation film on the power line wears out due to body vibration during use over time, excessive current continuously flows due to dead short, and so-called chattering short due to insulation failure causes excessive current to flow intermittently. Overcurrent flows through the power line. In the above-mentioned MOSFET with built-in thermal shutdown circuit, if an overcurrent exceeding the rated current flows through the semiconductor switch due to the occurrence of such a short circuit, and if the temperature rises above the specified temperature and the semiconductor switch generates heat, the semiconductor switch is protected. The switching function can be forcibly turned off.
[0004]
FIG. 2 is a circuit diagram showing an example of a conventional lighting control circuit using such a semiconductor relay system. A power supply voltage Vb from the in-vehicle battery is supplied to a lamp load such as a tail lamp 4 or a stop lamp 5 through a shunt resistor 2 that is a current detection resistor connected to the power supply line 1 and a MOSFET 3 with a built-in thermal shutdown circuit. In addition, a multi-communication microcomputer (microcomputer) 6 composed of a CPU or the like that operates based on a control program is provided. This microcomputer 6 is turned on / off from a plurality of switches SW for selectively turning on / off the various lamp loads. A signal s1 is sent. Further, a current detection circuit 8 including the shunt resistor 2 and the differential amplifier 7 is provided. In this current detection circuit 8, the current value Is flowing through the shunt resistor 2, that is, the load current flowing through the lamp load is calculated and calculated by the voltage drop due to the potential difference between both ends. Both ends of the shunt resistor 2 are connected to the non-inverting input terminal and the inverting input terminal of the differential amplifier 7, and a voltage value corresponding to the load current Is is output from the output terminal of the differential amplifier 7 as a detected current value. ing.
[0005]
The signal of the load current Is, which is the detected current value output from the current detection circuit 8 in this way, is sent to the A / D conversion port 9 of the microcomputer 6, where it is converted into a digital signal and captured by the microcomputer 6. The load current Is is monitored.
[0006]
The lighting control circuit also has a drive circuit 10 for turning on / off the MOSFET 3 with a built-in thermal shutdown circuit. The drive circuit 10 includes a charge pump circuit 11, a semiconductor switch circuit 12 including transistors Tr1, Tr2, and the like. When the MOSFET 3 with a built-in heat shut-off circuit is used on the high side of a lamp load such as the tail lamp 4 or the stop lamp 5, it is necessary to boost the power supply voltage Vb in order to increase the voltage applied to the gate G. The charge pump circuit 11 operates only when it receives a positive logic signal from the microcomputer 6 and generates a drive voltage necessary to increase the power supply voltage Vb to turn on the MOSFET 3 with a built-in thermal shutdown circuit. This drive voltage is supplied to the semiconductor switch circuit 12. When one transistor Tr1 of the semiconductor switch circuit 12 is turned on and the other transistor Tr2 is turned off, the drive voltage from the charge pump circuit 11 that boosts the power supply voltage Vb is applied to the gate G of the MOSFET 3 with a built-in thermal shutdown circuit. Apply and turn on. Therefore, when one transistor Tr1 is turned off and the other transistor Tr2 is turned on, the gate G is turned off.
[0007]
[Problems to be solved by the invention]
In general, a rush current is generated immediately after lighting of a load such as a lamp is started. Therefore, if any load lamp is broken, such as any one of the tail lamps 4 or any one of the stop lamps 5, replace the new one with the switch on. There are many exchanges.
[0008]
However, in the vehicle lighting control circuit using the above-described conventional semiconductor relay system, the microcomputer erroneously determines that the inrush current generated by the replacement of the new lamp by such replacement is short-circuited, and unintentionally with improper control. There is also the inconvenience of instructing to turn off. This lowers the reliability of short circuit detection, and such misjudgment is drawn out by the following control procedure.
[0009]
When the switch SW is selected and turned on to light the target lamp load, the switch-on signal s1 is sent to the microcomputer 6, and the microcomputer 6 receives it and sends a lamp lighting command signal s2 to the drive circuit 10. . In the drive circuit 10, the power supply voltage Vb is boosted by the charge pump circuit 11 to turn on / off the transistors Tr 1 and Tr 2 of the semiconductor switch circuit 12, and the boosted drive voltage signal s 3 is supplied to the gate G of the MOSFET 3 with built-in thermal shutdown circuit. Apply.
[0010]
When the operation of the MOSFET 3 with built-in heat shut-off circuit is turned on, a lighting output current flows through the target lamp load, and the current detection circuit 8 detects the current flowing through the load. That is, the load current Is flowing through the shunt resistor 2 is calculated by the differential amplifier 7. The differential amplifier 7 outputs a voltage signal s4 corresponding to the load current Is and sends it to the A / D conversion port 9 of the microcomputer 6. Here, the microcomputer 6 constantly monitors the load current Is flowing in the lamp load by digitally converting and taking in the voltage output from the differential amplifier 7.
[0011]
When the monitored load current Is is larger than the reference current stored in the control program in advance, the microcomputer 6 is caused by the inrush current that is temporarily generated at the start of lighting by lamp replacement. When the load current Is exceeding the detected value is detected for a certain period of time, it is determined that a short circuit has occurred. Since a command signal based on such a misjudgment is sent to the drive circuit 10 and the off-output from the drive circuit 10 turns off the MOSFET 3 with a built-in thermal shutdown circuit, the supply of the power supply voltage Vb to the target lamp load is cut off. is there.
[0012]
Accordingly, an object of the present invention is to erroneously determine that a short circuit is caused by an inrush current generated when replacing a lamp load such as a tail lamp of a vehicle light by using a semiconductor relay system including a MOSFET with a built-in heat shut-off circuit. An object of the present invention is to provide an overcurrent control method that is effective in preventing problems and can improve the reliability of short circuit detection.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the overcurrent control method according to claim 1 according to the present invention suppresses the possibility that an inrush current generated at the start of lighting of a lamp load as a vehicle lamp is erroneously determined as a short circuit. A control method,
Based on the load current flowing through the lamp load is sampled every predetermined time, when it detects the disconnection core state of the lamp load, and replaced the lamp load remains energized with respect to the lamp load, Immediately after changing the lamp load, the load current flowing in the lamp load is sampled and detected,
It is determined that the lamp load has been replaced by sampling detection of the load current, and this is used as a condition for the next control, and the detected current value is stored in a microcomputer in advance as a reference current. Calculate whether it is less than or greater than the value,
When it is detected that the load current is larger than the reference current and the load current value is greater than the reference current value, an inrush current is detected with respect to the first abnormality detection time t1 counted from the time when the abnormality due to the overcurrent is detected. A second abnormality detection time T is calculated by adding a presumed rush occurrence time t2, and an abnormality due to a short circuit is determined when the detection count exceeds the second abnormality detection time T. .
[0014]
From the above, it is a condition that the control is performed when the disconnected lamp load is replaced with a new lamp while being energized, and in that case, if the detection count is within the range of the second abnormality detection time T, the inrush current In such a case, it is not immediately judged as a short circuit. When the detection count exceeds the second abnormality detection time T, it also means that the rush generation time t2 due to the expected inrush current has been exceeded. Therefore, it cannot be an abnormality due to the inrush current. judge. As a result, the inrush current generated at the time of replacing the new lamp is not erroneously determined as a short circuit, and the inconvenience of turning off the output to the lamp load due to the erroneous determination can be solved.
[0015]
The overcurrent control method according to claim 2 is characterized in that it is possible to simultaneously determine whether the abnormality determination due to the short circuit is a dead short or a chattering short depending on the number of overcurrent detections within a predetermined time.
[0016]
From the above, even if it is judged as a short circuit, it is possible to determine whether it is a dead short circuit in which excessive current continuously flows or chattering short circuit in which excessive current flows intermittently. is there.
[0017]
According to a third aspect of the present invention, there is provided an overcurrent control method before the second abnormality detection time T is reached when a MOSFET with a built-in thermal shutdown circuit is used as a semiconductor relay on the high side of the lamp load. Further, the MOSFET with a built-in heat shut-off circuit operates a self-heat shut-off function to turn off the supply voltage to the lamp load.
[0018]
From the above, by using the MOSFET with built-in heat shut-off circuit as a semiconductor relay, if a short circuit occurs before the second abnormality detection time T is reached, it can be shut off immediately with its own overheat shut-off function.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, as an embodiment of an overcurrent control method using a semiconductor relay system according to the present invention, an application example to a short circuit misjudgment prevention control in a vehicle lighting control circuit will be described in detail with reference to FIG.
[0020]
In this vehicle lighting control circuit, the power supply voltage Vb from the vehicle-mounted battery is supplied from the power supply line 1 to the tail lamp 4 and the stop lamp 5 through the shunt resistor 2 of the current detection circuit 8 and the MOSFET 3 with a built-in semiconductor circuit thermal shutdown circuit. Supplied to the lamp load. Further, the microcomputer 6 is provided, the current detection circuit 8 is provided with a differential amplifier 7 together with the shunt resistor 2, and the drive circuit 10 is constituted by a charge pump circuit 11, a semiconductor switch circuit 12, and the like.
[0021]
The thermal shutdown circuit built-in type MOSFET 3 is, for example, a logic level (4 volts or more) driving type, and after the operation of the thermal shutdown circuit by a latch type thermal shutdown system, returns with a bias of zero (0) potential of the gate G. ing. The shunt resistor 2 used as a current detection resistor has a low resistance value of 20 mΩ, for example. In addition, the overheat cutoff mentioned here generates heat when an overcurrent exceeding the rated current flows, but when the heat generation temperature reaches, for example, 165 ° C., the MOSFET 3 with a built-in heat cutoff circuit has a function of cutting the current flowing to the lamp load. It means to have.
[0022]
Next, a control operation relating to prevention of erroneous short determination of the vehicle lighting control circuit, which is an embodiment of the overcurrent control method, will be described using the control flowchart of FIG.
[0023]
When the power supply voltage Vb from the in-vehicle battery is supplied through the power supply line 1, when the switch SW corresponding to any lamp load such as the tail lamp 4 or the stop lamp 5 is turned on as in step S1, A Hi (high) level switch-on signal s1 is output, and a microcomputer 6 that receives the switch-on signal s1 outputs a drive command signal s2 toward the drive circuit 10. Based on the drive command signal s2 from the microcomputer 6, the charge pump circuit 11 boosts the power supply voltage Vb to, for example, “Vb + 9V” to generate the drive voltage s3. This drive voltage s3 is supplied to, for example, the collector of the NPN transistor Tr1 of the semiconductor switch circuit 10 to turn it on, and similarly, the NPN transistor Tr2 is turned off to output the drive voltage s3 and to incorporate the heat cutoff circuit built-in MOSFET 3 Applied to the gate G.
[0024]
In step S1, the current of the lighting output flows through the target lamp load when the operation of the MOSFET 3 with built-in heat shut-off circuit is turned on, and the current flowing through this load is detected by the current detection circuit 8. That is, the load current Is flowing through the shunt resistor 2 is calculated by the differential amplifier 7. The differential amplifier 7 outputs a voltage signal s4 corresponding to the load current Is and sends it to the A / D conversion port 9 of the microcomputer 6. Here, the microcomputer 6 monitors the load current Is flowing in the lamp load by digitally converting and taking in the voltage output from the differential amplifier 7.
[0025]
In step S2, the microcomputer 6 compares the reference value of the current stored in the control program in advance with the value of the load current Is detected by the monitor. When the load current Is falls below the reference value and Is <(No), the detection count is cleared in step S3. When the load current Is exceeds the reference value and is Is> (Yes), sampling of the monitor current is started at a predetermined time such as 5 ms (seconds) in step S4, for example, about 200 times / second, and the detection count Up.
[0026]
In such a lamp load output-on state, lamp replacement is normally performed in a current non-energized state, but it is assumed that either the tail lamp 4 or the stop lamp 5 is replaced during the energization. Since the state immediately before the replacement of the new lamp to be replaced is a state in which one new lamp has been removed, it can be considered that the load current Is is reduced by one lamp. For convenience, this state is referred to as “disconnection state due to lamp piece breakage”, and it is necessary to determine whether or not the lamp piece is broken and disconnected when the output to the lamp load is on. That is, even if it is detected that the value of the load current Is exceeds the value of the reference current, it cannot be determined whether the load current Is is caused by the “rush current” immediately after the start of lamp lighting or by a short circuit.
[0027]
Therefore, it is necessary to include in the trigger of the control on the condition that the lighting output is on and the lamp piece is cut and disconnected. If the value of the detected load current Is becomes larger than the reference current value in spite of the lamp piece breakage state, it may be due to the inrush current immediately after the new lamp is mounted and turned on. .
[0028]
Based on the above, in this example, in step S5, the microcomputer 6 determines whether or not “the lamp piece is in a broken core state”. When it is determined that the lamp piece is broken and broken (Yes), the first abnormality detection time t1 is counted by using the determined time as a trigger, and a rush that is expected in advance as an inrush current at the first abnormality detection time t1 is generated. The time t2 is added to calculate a second abnormality detection time t1 + t2 = T (step S6). That is, when the second abnormality detection time T is set to, for example, 100 ms (seconds), since a rush current is expected for 100 ms from the start of lamp lighting, a condition that short detection is not performed during that time is included. .
[0029]
Accordingly, in step S7, it is determined whether or not the second abnormality detection time T is within the range. If it is within the range of the second abnormality detection time T (No), even if the load current Is exceeds the reference current, it is not regarded as a short circuit and a short detection determination is not performed. Control proceeds to the waiting time processing control in step S9. When the detection count exceeds the second abnormality detection time T (Yes), it is determined as an abnormality due to a short circuit (step S8). By such overcurrent control, even if the monitored load current Is is larger than the reference current within the generation time of the inrush current generated at the time of lamp replacement, it is not necessary to mistakenly determine that it is a short circuit.
[0030]
In such control, by using the MOSFET 3 with a built-in thermal shutdown circuit, the detection of the load current Is is monitored once every 5 ms (seconds), and if the reference current exceeds 6 times continuously, it is It is regarded as a dead short, and its own overheat cutoff function is immediately activated to control off even before the second abnormality detection time T. Further, when the load current Is exceeds the reference current 20 times or more continuously for one second, it can be regarded as a chattering short circuit, and the circuit can be cut off immediately when the counter reaches 20 times. Thus, the fail safe of this control can be achieved.
[0031]
【The invention's effect】
As described above, the overcurrent control method according to the first aspect of the present invention is based on the condition that the control is performed when the disconnected lamp load is replaced with a new one while being energized, and in that case If the detection count is within the range of the second abnormality detection time T, the inrush current may be affected, and in this case, it is not immediately determined that a short circuit has occurred. When the detection count exceeds the second abnormality detection time T, it also means that the rush generation time t2 due to the expected inrush current has been exceeded. Therefore, it cannot be an abnormality due to the inrush current. judge. From the above, the inrush current generated when replacing the new lamp is not erroneously determined as a short circuit, and the inconvenience of turning off the output to the lamp load due to the erroneous determination can be solved.
[0032]
Further, the overcurrent control method according to claim 2 can determine whether it is a dead short in which excessive current continuously flows or a chattering short in which excessive current flows intermittently even when it is determined as a short. There is an advantage that it is possible to appropriately cope with the subsequent control.
[0033]
Further, the overcurrent control method according to claim 3 uses its own built-in thermal shutdown circuit MOSFET as a semiconductor relay, so that if the short circuit occurs before the second abnormality detection time T is reached, the overheat cutoff function of itself is provided. Can be shut off immediately.
[Brief description of the drawings]
FIG. 1 is a control flowchart showing the operation of a vehicle lighting control circuit as an embodiment to which an overcurrent control method according to the present invention is applied.
FIG. 2 is a vehicle lighting control circuit diagram shown as an example of the present control method.
[Explanation of symbols]
1 Power line 2 Shunt resistor 3 Thermal shutdown circuit built-in MOSFET
4 tail lamp 5 stop lamp 6 microcomputer 7 differential amplifier 8 current detection circuit 9 A / D conversion port 10 drive circuit 11 charge pump circuit 12 semiconductor switch circuit

Claims (3)

An overcurrent control method that suppresses the possibility of erroneously determining that the inrush current generated at the start of lighting of a lamp load, which is a vehicle light, is a short circuit,
Based on the load current flowing through the lamp load is sampled every predetermined time, when it detects the disconnection core state of the lamp load, and replaced the lamp load remains energized with respect to the lamp load, Immediately after changing the lamp load, the load current flowing in the lamp load is sampled and detected,
It is determined that the lamp load has been replaced by sampling detection of the load current, and this is used as a condition for the next control, and the detected current value is stored in a microcomputer in advance as a reference current. Calculate whether it is less than or greater than the value,
When it is detected that the load current is larger than the reference current and the load current value is greater than the reference current value, an inrush current is detected with respect to the first abnormality detection time t1 counted from the time when the abnormality due to the overcurrent is detected. A second abnormality detection time T is calculated by adding a presumed rush occurrence time t2, and an abnormality due to a short circuit is determined when the detection count exceeds the second abnormality detection time T. Overcurrent control method.   2. The overcurrent control method according to claim 1, wherein the abnormality determination by the short circuit can simultaneously determine whether it is a dead short or a chattering short according to the number of overcurrent detections within a predetermined time.   When a MOSFET with a built-in thermal shutdown circuit is used as the semiconductor relay on the high side of the lamp load, the MOSFET with a built-in thermal shutdown circuit has a self-overheat cutoff function even before the second abnormality detection time T is reached. The overcurrent control method according to claim 2, wherein the overcurrent control method is operated to turn off a supply voltage to the lamp load.

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