JP2000245055A - Control system of power source mounted on vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control system of a power source mounted on a vehicle, is effective in overcurrent protection and power saving. SOLUTION: An output node 20 is connected with a power supply line 11 from a power source 10 to a load electrical equipment. A first power supply control unit 1 limits a current flowing downstream from the output node to the electrical equipment. A second power supply control unit 1 is connected with the upstream between a power source and the output node. An overcurrent or the like generated downstream is limited and controlled by the first power control system. An overcurrent or the like generated upstream is limited by the second power supply control unit. Abnormal information due to an overcurrent or an excessively small current which are detected by the first power supply control unit is sent to also the second power supply control unit, which changes a current threshold every time on the basis of the abnormal information, and executes power cutting, squeezing, etc., at a level lower than the rating current of the power source. By the power supply control on the upstream side, power saving is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to power supply control of a vehicle-mounted power supply which is effective in protecting an overcurrent and a device by disconnection or short-circuit of a power supply cable forming a power supply line, particularly in an automobile, and saving power supply. About the system.

[0002]

2. Description of the Related Art Conventionally, as an apparatus related to power supply management of a vehicle-mounted power supply, for example, there is a vehicle abnormal current detecting apparatus described in Japanese Patent Application Laid-Open No. 7-43256. In this case, the power from the power supply battery 40 of the vehicle-mounted transformer is
1 supplies a plurality of electrical components 42a and 42b. On the upstream side of the power cable 41, a flowing current is detected by a current probe 44. Switch node 4
Reference numeral 5 has switches 45a and 45b of the number corresponding to the electrical components 42a and 42b, and outputs ON / OFF signals of these switches and sends them to the multiplex transmission line 46. Switch on/
The off signal is put on the multiplex transmission line 46 and output node 47
Sent to The output node 47 turns on a target one of the electrical components 42a and 42b based on the received switch on / off signal.

On the other hand, a decision circuit 48 detects the operating state of one of the electrical components 42a and 42b that has been activated by a switch signal on the multiplex transmission line 46 output from the switch node 45, and determines the current flowing therethrough as an actually measured value. Store in memory. Further, the determination circuit 48 predicts and calculates a current value to be passed through the power cable 41 based on the received detection signal, and compares the actual measurement value with the predicted value to determine whether there is an abnormality. Then, the current prediction value is learned and corrected.

That is, if it is determined from the comparison between the measured value and the predicted value of the current that excessive current has flowed through the power cable 41, the power is turned off by the relay 43 and the power cable 41 is turned off.
To cut off the power supply. As a criterion for determining whether or not an overcurrent occurs, the current value is determined by the operating state of the electrical components 42a and 42b as loads, that is, the number of switches 45a and 45b. For example, the switch 4 corresponding to the electrical component 42a
5 amps (A) when 5a is on,
Switch 45b of another 5 amp electrical component 42b
Is turned on, it is added and stored in a memory such as 10 amps in advance. It monitors whether or not the stored current value matches the current value of the power supply battery power source 40 on the upstream side, and whether or not the current value is consistent. If no matching is obtained, it is determined to be in an overcurrent state and turned off.

[0005]

However, in the conventional example of JP-A-7-43256, the output node 47 on the downstream side does not have a current detecting function, so that any one of the electrical components 42a and 42b is used. However, it is impossible to determine whether or not the overcurrent is caused by the short-circuit state of the electrical components on the downstream side unless a large current flows on the upstream side even though the current is actually short-circuited.

Accordingly, an object of the present invention is to make it possible to detect an abnormal location such as an excessive current caused by a short circuit or an undercurrent caused by an open circuit over the entire power supply cable forming a power supply line, and to detect an excessive current caused by a short circuit or the like on the downstream side. When an abnormality occurs, an electric power supply control system for a vehicle-mounted power supply that is effective for overcurrent prevention and power saving is provided by controlling power supply to be cut or throttled on the upstream side.

[0007]

According to a first aspect of the present invention, there is provided a power supply control system for a vehicle-mounted power supply, comprising: an output node connected to a power supply line from a power supply to a plurality of loads; Number of output nodes,
A plurality of semiconductor switch devices including a semiconductor switch device for limiting a current flowing from the output node to each load on the downstream side and outputting an abnormal signal due to an excessive current or an excessive current of the current flowing on the downstream side and placing the signal on a multiplex transmission line. A first power supply control device, which is basically the same circuit as the first power supply restriction device, is connected to the power supply line on the upstream side up to the output node, and has an output from the first power supply restriction device. One second power supply control device for cutting power flowing upstream of the power supply line based on each piece of information including the abnormal signal from the multiplex transmission line, and turning on / off the load. A corresponding number of switches are provided, and an on / off signal of each switch is output and put on the multiplex transmission line, and the first power supply control device is Calculating and storing a current threshold value of the second power supply control device each time the switch node receives an on / off signal of the switch by the multiplex transmission line. By changing each time to match the current value of the abnormal signal sent from the first power supply control device, the second power supply control device is turned off when the changed current threshold value is exceeded. A determination circuit for interrupting power supply from the power supply at a level lower than a rated current.

With the above configuration, the occurrence of an excessive current abnormality due to a short circuit or the like and the occurrence of an undercurrent abnormality due to an open circuit are detected and determined over the entire power supply line from the power supply to a plurality of loads. To save power supply. That is, the excessive current generated on the downstream side is limited and controlled by the first power supply control device built in the output node. Excessive current generated on the upstream side is limited by the second power supply control device. At this time, abnormality information due to an excessive current or an undercurrent detected by the first power supply control device on the downstream side is provided to the second power supply control device on the upstream side. By changing the current threshold value each time, the power is cut or reduced at a level lower than the rated current of the power supply. Such upstream power supply control makes it possible to save power without causing unnecessary current to flow.

According to a second aspect of the present invention, in the power supply control system for a vehicle-mounted power supply, the output node supplies an on / off signal of a switch received from the switch node via the multiplex transmission line to the first power supply. Via the controller to the corresponding one of the loads,
An electronic control comprising a microcomputer that sends a control signal to the multiplex transmission line to indicate the abnormal current value based on an abnormal detection signal due to an excessive current or an excessive current sent from the power supply control device and sends the control signal to the determination circuit. It is characterized by having a device.

In this case, the microcomputer detects the abnormality of the overcurrent or undercurrent detected by the second power supply control device on the downstream side, and electronically controls the current limitation to the load by the electric component such as the headlight of the vehicle. This leads to equipment protection.

According to a third aspect of the present invention, in the power supply control system for a vehicle-mounted power supply, the first and second power supply control devices are connected to a power supply line from the power supply to the load to limit power supply. And a reference voltage for detecting an excessive current flowing through the power supply line, which is connected in parallel with the main semiconductor switch element, and an abnormality detection signal due to the excessive current. And a first reference circuit for outputting a reference voltage for detecting an undercurrent flowing through the power supply line, the first reference circuit being connected in parallel with the main semiconductor switch element, and outputting the undercurrent. A second reference circuit that outputs an abnormality detection signal according to the above and sends the signal to the electronic control unit. It is an feature.

That is, since the device is basically formed by a device using a semiconductor switch element or the like, the cost is almost the same as that of a conventional switch device including a mechanical relay or a fuse. In addition, overcurrent protection, miniaturization, and high speed are achieved. This is effective for switching (duty control).

According to a fourth aspect of the present invention, there is provided the power supply control system for a vehicle-mounted power supply, wherein an arbitrary number of resistance values of a plurality of transistors connected in series that are turned on by the on / off signal from the determination circuit are combined. Thereby, the current threshold value of the second power supply control device can be changed.

In this case, the reference control of the current threshold value, that is, the current limit value in the second power supply control device on the upstream side can be performed by a plurality of transistors connected in series.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a power supply control system for a vehicle-mounted power supply according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a circuit configuration of a power supply control system according to the present embodiment. An output voltage VB from a power supply battery 10 mounted on a vehicle such as an automobile is output from a power supply line 11 through a power supply line 11, for example. This shows a case where the electric power is supplied to a plurality of types of electric components 12, 13, 14,... Such as a headlamp. The power supply 10 on the upstream side in the power supply side
And each of the electrical components 12, 13, 14 on the downstream side to be supplied with power.
The output node 20 is connected between.

The output node 20 contains the following devices. For example, three electrical components 12, 13, 14
The first power supply control devices 1 based on the semiconductor switch devices shown in FIG. The microcomputer 15 has an electronic control unit 15 including a CPU, a ROM, a RAM, and an I / O port. The microcomputer 15 includes three first power supply control units 1 for operating the electrical components 12, 13, and 14. Abnormal signals v1 and v2 due to overcurrent or undercurrent (open) according to the state are sent.

On the other hand, the switch node 30
Switches SW1, which turn on / off the switches 2, 13, 14
SW2 and SW3.
The off signal v3 is put on the multiplex transmission line 16 and further sent to the microcomputer 15 built in the output node 20.

A decision circuit 17 is connected to the multiplex transmission line 16. The control signal v4 output from the microcomputer 15 is sent to the determination circuit 17 via the multiplex transmission line 16.

A second power supply control device 1 is connected between the power supply line 11 and the output node 20 on the upstream side of the power supply line 11.
Sends a judgment signal v5. The second power supply control device 1 has the same circuit configuration based on a semiconductor switch device as the three first power supply control devices 1 in the output node 20 described below with reference to FIG. .

In this embodiment, the second power supply control device 1 is provided with a number of transistors Tr1, Tr2, Tr3 corresponding to the electrical components 12, 13, 14 connected in series. In this case, the on / off signal v5 from the determination circuit 17
Thus, the current threshold value, that is, the reference of the second power supply control device can be changed each time by the abnormality information by combining an arbitrary number of the resistance values of the transistors Tr1, Tr2, and Tr3 that are turned on.

Here, in FIG. 2, the first power supply controller 1 on the downstream side and the second power supply controller 1 on the upstream side
The circuit configuration and operation of the first
One of the power supply control devices 1 will be described.

The first power supply control device 1 is a device in which a semiconductor switch device or the like is integrated into one chip, and controls a current that supplies an output voltage VB of the battery power supply 10 to each load L of the electrical components 12, 13, and 14. As will be apparent from the following description, the device has a function particularly excellent in overcurrent protection.

That is, the main FET of the field effect transistor is connected to the power supply line 11 from the battery power source 10.
(Field Effect Transistor) QA is connected.
This main FET QA is an NMOS FE having a DMOS structure.
T. In this example, this F is used as the main FET QA.
A thermal FET having a heating cutoff function that is forcibly turned off when the temperature of the ETQA rises above a specified value is used. The main FET QA is a PMOS having a DMOS structure.
MOSFETs or other power MOSFETs can also be used.

Further, a first reference circuit for generating a reference voltage for detecting an excessive current flowing in the power supply line 11 in parallel with the main FET QA, and a reference voltage for detecting an undercurrent flowing in the power supply line 11 are generated. A second reference circuit is provided. The first reference circuit includes a first reference FET QB and a resistor Rr1.
And the second reference circuit is a second reference F
It consists of ETQC and resistor Rr2. Both FETs QB,
Each drain of the QC is connected to the drain D of the main FET QA, and the first and second reference FETs QB, QB
Each gate of C is connected to the gate of main FET QA,
Sources SB and SC of both FETs QB and QC are resistors Rr.
1 and Rr2.

Here, specifically, in the case of the present embodiment, the first reference circuit detects an excessive current I1 flowing through the load or the power supply line 11, and the second reference circuit detects the electrical components 12, 13, and 14 of the load. 14 is a current I2 slightly larger than the steady current I0 flowing when
Can be detected. Therefore, the magnitude ratio of each current is as follows: I0 <I2 <I1 (1)

Each of the FETs QA, QB, and QC is composed of a plurality of transistors, and the ratio of the number of transistors is QA.
> QB, QA> QC. For example, FET QA and Q
B, and the ratio of the number of transistors of each of the FETs QA and QC is 1
000: 1. The resistances Rr1 and Rr2 are set to values that cause the FET QB to generate the same drain-source voltage Vds as the FET QA when a load current of 5 amps (A) flows through the FET QA, for example. Therefore, when a drain current of 5 A flows through the FET QA, a drain current of 5 mA flows through the FETs QB and QC, and the drain-source voltages of the FETs QA, QB and QC match, and the FETs QA, QB and Q
The gate-source voltages of C also match.

The source SA of the FET QA is connected to a resistor R5.
To the + terminal of the comparator CMP1 through the FET QB
Of the comparator CMP1 via the resistor R6
Are connected to the negative terminals of the respective switches. The comparator CMP1 is for determining whether or not the current flowing through the power supply line 11 is an overcurrent, and includes a voltage between the drain and the source of the FET QA (a potential on the source SA side) and an FET QB.
, And outputs a Hi-level signal while the difference is equal to or less than the overcurrent determination value (while the SA potential is equal to or higher than the source SB potential). When the difference is larger than the overcurrent determination value (when the potential of SA becomes smaller than the potential of SB), the signal is inverted and a Lo level signal is output.

The output signal of the comparator CMP1 is FE
It is input to the drive circuit 2 that turns on and off the TQA. When the number of switches SW1, SW2, SW3 corresponding to the electrical components 12, 13, 14 is turned on,
Output voltage VB from battery power supply 10 via resistor R4
And a voltage VP (for example, VP = VB + 5V) boosted by the charge pump circuit 3 is applied. When the switch SW1 is turned on and a Hi-level signal is input from the comparator CMP1, the drive circuit 2 turns on the source-side transistor 2a and turns off the sink-side transistor 2b. The signal is output to the gate of the FET QA via R8 and R7, thereby turning on the FET QA. While the Hi level signal is being input, the drive circuit 2 keeps outputting the drive signal of the voltage VP. And
When the comparator CMP1 is inverted and the L signal is input, the drive circuit 2 turns off the source-side transistor 2a,
The sink-side transistor 2b is turned on to turn off the FET QA.

The source SA of the FET QA is connected to the (+) terminal of the comparator CMP2.
B is connected to the (-) terminal of the comparator CMP2. The comparator CMP2 is for determining whether or not the current flowing through the power supply line 11 is an undercurrent. The voltage between the drain and source of the FET QA (potential of the source SA) and the voltage between the drain and source of the FET QB ( And the potential of the source SA becomes lower than the potential of the source SB by a predetermined value or more.
It outputs an undercurrent determination signal, for example, a Hi level signal.

A comparator CMP1 is connected between the source SA of the FET QA and the output terminal of the drive circuit 2, that is, the collector terminal of the sink-side transistor 2b.
The resistors R5 and R9 and the diode D3 are connected in series in order to provide hysteresis in the operation of inverting the output state of the level signal to the state of outputting the Hi level signal. As a result, after the FET QA is turned off, a current flows from the source SA side to the ground through the resistors R5 and R9, the diode D3 and the sink side transistor 2b, and the potential of the source SA is reduced to the resistance R5.
Drops by the voltage drop at. This is hysteresis.

Further, the comparator CMP1 is connected to a return circuit for returning the FET QA to ON after the FET QA is turned OFF from ON due to an excessive current generation abnormality due to a short circuit or the like. This return circuit includes a transistor Tr having an emitter connected to the output terminal on the power supply battery 10 side, a base connected to the input terminal on the switch SW1 side via the resistor R0, and a resistor Tr connected in series between its collector and ground. R1, R3, R2
A diode D1 for passing a current flowing through the resistor R1 to the (+) terminal side of the comparator CMP1;
And a diode D2 for passing the current flowing through the comparator CMP1 to the (-) terminal side of the comparator CMP1. The resistance value of the resistor R1 is
When the switch SW1 is turned on and the transistor Tr1 is turned on, the potential V1 at the connection point of the resistors R1 and R3 is about 60 to 80% of the battery, and the potential of the source SA is the resistor R5.
Is set to a value larger than the voltage V3 (the potential on the cathode side of the diode D1), which is reduced by the voltage drop in the above.

Also, the ON / OFF counting circuit 4
The capacitor C is charged each time the gate is turned off during the on / off operation of the main thermal FET QA of this embodiment. The capacitor C is charged only when VDS is at the Hi level in an AND manner while the gate is off, and is not charged when the gate is continuously on or continuously off.

Next, the operation and operation of the power supply control system for a vehicle-mounted power supply according to the present embodiment having the above configuration will be described.

First, a large flow of the operation of the present apparatus is limited around the first power supply control device 1 at the output node 20 when an overcurrent occurs on the downstream side of the power supply line 11. When an overcurrent occurs on the upstream side of the power supply line 11, the overcurrent is limited by the second power supply control device 1 on the upstream side. Such power supply line 1
Even if an overcurrent is generated in any part of the entire line, the overcurrent is limited and controlled to reduce waste of power supply and realize power saving.

Therefore, the electrical components 12, 13,
It is assumed that any one or more of the fourteen switches 14 are turned on by selecting the corresponding switches SW1, SW2, and SW3 at the switch node 30. This switch-on signal v3 is sent to the microcomputer 15 built in the output node 20 via the multiplex transmission line 16. Based on the switch-on signal v3 received from the switch node 30, the microcomputer 15 sends an operation-on signal to one or a plurality of target first power supply control devices 1 to start up.

At the same time, the ON signal v of the selected switch
3 is input from the multiplex transmission line 16 to the determination circuit 17,
In response to the switch-on signal v3, the determination circuit 17 turns on / off the corresponding one of the transistors Tr1, Tr2, Tr3. Assume that the transistor Tr
Assuming that some of the transistors 1, Tr2 and Tr3 are turned on, the combined values of some of the corresponding resistance values R1, R2 and R3 change, and the threshold value of the current changes. The threshold value is determined each time according to the ON operation state of such transistors Tr1, Tr2, Tr3. Each time the determination circuit 17 changes the threshold value, it is stored in memory as the “current limit value” of the upstream second power supply control device 1 and performs reference control.

Therefore, when an abnormality such as an overcurrent due to a short circuit or an undercurrent (open) occurs on the downstream side of this state, one of the corresponding first power supply control devices 1 in the output node 20 or A plurality controls such abnormalities by the control as described above.

On the other hand, the above-mentioned abnormality which has occurred on the downstream side is also sent from the microcomputer 15 to the upstream determination circuit 17 as a signal. That is, one of the upstream first power supply control devices 1
An abnormal signal v1 (or v2) such as an overcurrent is sent from one or more devices to the microcomputer 15, and the microcomputer 15 returns the abnormal signal to the multiplex transmission line 16 and sends it to the upstream determination circuit 17. The determination circuit 40 operates to compare the received abnormal signal from the microcomputer 15 with a previously stored current limit value and change the threshold value. That is, the current limit value in the second power supply control device 1 on the upstream side is reduced to the current level of the abnormal signal, and the power supply level is reduced.

Therefore, in the second power supply control device 1 on the upstream side, the power supply can be turned off in response to the abnormality that has occurred on the downstream side, and despite the occurrence of an abnormality such as overcurrent on the downstream side. Power consumption can be reduced by cutting off the flow of useless current. At the same time, the judgment circuit 1
7 can send an operation signal to a warning lamp 18 to give a warning by lighting or blinking.

Next, when an abnormality such as an overcurrent due to a short circuit or an undercurrent occurs on the upstream side, the following operation is performed.

For example, when an abnormality due to a short circuit occurs at any part on the upstream side, the three first power supply control devices 1 at the downstream output node 20 are normally in the operation ON state. , Load electrical components 12, 13,
14 is in an open state when the power supply from the upstream side is turned off.

The three first power supply control devices 1 are electric components 1
The open state of each of the loads 2, 13, and 14 is detected, and the detection signal is sent to the microcomputer 15 as an open signal v2. When the microcomputer 15 receives the open signal v2 indicating that all of the electrical components 12, 13, and 14 are in the open state, the microcomputer 15 determines that the "short circuit" has occurred on the upstream side, and multiplexes the control signal v4 based on the determination. The signal is sent to the determination circuit 17 via the line 16. The determination circuit 17 sends the control signal v4 from the microcomputer 15 as a command signal v5 to the drive circuit 2 in the second power supply control device 1 on the upstream side to turn off the operation. By such an operation, the power supply line 11 can be protected from a short circuit generated on the upstream side.

Since the microcomputer 15 can determine the number of the electrical components 12, 13, 14 that have become open, the number of open components is sent to the determination circuit 17 via the multiplex transmission line 16. The determination circuit 17 turns on the corresponding one of the transistors Tr1, Tr2 and Tr3 based on the received open number, and sets the resistance values R1, R2 and R3.
Are synthesized and changed. As a result, a current limit value corresponding to an electrical component that is not open and is in a normal operation state can be set.

[0045]

As described above, the power supply control system for a vehicle-mounted power supply according to the present invention provides an overcurrent abnormality due to a short circuit and an undercurrent due to an open circuit over the entire power supply line from the power supply to a plurality of loads. By detecting the occurrence of an abnormality and judging the abnormality, it is possible to save power without flowing useless current from the power supply, and it is also effective in protecting equipment.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a power supply control system for a vehicle-mounted power supply according to the present invention.

FIG. 2 is a circuit diagram showing a configuration of first and second power supply control devices arranged upstream and downstream of a power supply line in the present embodiment.

FIG. 3 is a block diagram illustrating a configuration of a conventional power supply system.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 first and second power supply control device 2 drive circuit 10 battery power supply 11 power supply line 12, 13, 14 electrical component (load) 15 microcomputer (electronic control device) 16 multiplex transmission line 17 determination circuit 18 warning lamp 20 output node 30 switch nodes

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H03K 17/08 H03K 17/08 CF term (Reference) 5G004 AA04 AB02 BA03 BA04 BA05 CA01 CA02 DA02 DA04 DC04 DC14 EA01 FA01 GA02 5G013 AA02 AA09 BA01 CA10 5J055 AX12 AX31 AX64 BX16 CX22 CX23 CX25 CX28 DX13 DX22 DX53 DX54 DX73 DX83 EX02 EX04 EX06 EX11 EX24 EY01 EY10 EY12 EY13 EY17 EY21 EZ07 EZ39 EZ55 FX57 EZ55 FX57

Claims (4)

[Claims] An output node connected to a power supply line from a power supply to a plurality of loads; and an output node provided by the number of the plurality of loads, the current flowing downstream from the output node to each load. A plurality of first switching devices including a semiconductor switch device for limiting and outputting an abnormal signal due to an excessive current or an excessive current of a current flowing on the downstream side thereof to be loaded on a multiplex transmission line.
A power supply control device, which is basically composed of the same circuit as the first power supply limiting device, is connected to the power supply line on the upstream side up to the output node, and is output from the first power supply limiting device. One second power supply control device for cutting power flowing upstream of the power supply line based on each information including an abnormal signal from a multiplex transmission line; and a corresponding number of turning on / off the load. A switch node that outputs an on / off signal of each of the switches, puts it on the multiplex transmission line, and sends it to the first power supply control device; and an on / off of the switch by the multiplex transmission line. Each time a signal is received, a current threshold value of the second power supply control device is calculated and stored, and the stored current threshold value is stored in the first power supply control device. By changing each time to match the current value of the abnormal signal sent from the device, when the changed current threshold value is exceeded, the second power supply control device is turned off to supply power from the power supply. And a determination circuit for interrupting the power supply at a level lower than the rated current. 2. An output node for sending a switch on / off signal received from the switch node via the multiplex transmission line to a corresponding one of the loads via the first power supply control device. A microcomputer which sends a control signal to the multiplex transmission line to indicate the abnormal current value based on an abnormal detection signal due to an excessive current or an excessive current sent from the first power supply control device and sends the control signal to the determination circuit; The power supply control system for a vehicle-mounted power supply according to claim 1, further comprising an electronic control device comprising: 3. A main semiconductor switch element comprising a field effect transistor connected to a power supply line from the power supply to the load, the first and second power supply control devices comprising: a main semiconductor switch element; A first reference circuit connected in parallel with the switch element to generate a reference voltage for detecting an excessive current flowing through the power supply line, and output an abnormality detection signal due to the excessive current to the electronic control device; A reference voltage for detecting an undercurrent flowing in the power supply line, being connected in parallel to the main semiconductor switch element, and outputting an abnormality detection signal due to the undercurrent to the electronic control device; 4. The power supply control system for a vehicle-mounted power supply according to claim 3, further comprising: two reference circuits. Tem. 4. A current threshold value of the second power supply control device is set by combining an arbitrary number of resistance values that are turned on among a plurality of transistors connected in series by an on / off signal from the determination circuit. 4. The power supply control system for a vehicle-mounted power supply according to claim 1, wherein the power supply control system is changeable.