JP2001045650A - Power supply controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely protect three terminal switching element and a load, even if the three terminal switching element is driven by means of a drive pulse whose duty is fine. SOLUTION: When a temperature sensor detects the temperature of not less than a prescribed temperature of a three terminal switching element QF, an overheating disconnection switching element QS becomes an on-state and a voltage applying means 201 continuously applies voltage equivalent to a drive voltage to a control terminal TG. While a drive voltage is applied to the control terminal TG according to the detection of the temperature of not less than a prescribed temperature, a holding means 122 holds the on-state of the overheating interruption switching element QS.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply control device, and more particularly to a power supply control device having a three-terminal switching element for controlling on / off of a power supply from a DC power supply such as a vehicle battery to a load. .

[0002]

2. Description of the Related Art Generally, in a vehicle, a power supply from a vehicle-mounted battery as a first DC power supply is distributed to various parts of the vehicle via a power MOSFET as a three-terminal switching element and a power supply line covered with an insulating film. Is being supplied to a load. The above-described power line is routed along the vehicle body in an engine room or the like that is constantly vibrating. At this time, if the power line is located close to the corner of the vehicle body, the power line is intermittently connected to the corner due to vibration. When the contact lasts for a long period of time, the coating of the power supply line is gradually cut off by the corners of the vehicle body, so that the internal conductor is exposed, albeit minutely.

When the exposed portion of the power supply line comes into contact with the vehicle body, a dead short or a rare short circuit occurs in the power supply line, and when an overcurrent flows, the power MOSFET or the power supply line is overheated and is thermally destroyed. Become like Therefore, in order to prevent such a situation from occurring, a configuration as shown in FIG. 3 is conventionally known.

In FIG. 1, a power supply voltage VB from a vehicle-mounted battery 101 includes a resistor RE and a power MOSFET QF.
And a load S such as a headlight or a drive motor of a power window through a drain D as a power supply side terminal and a source S as a load side terminal. The drive circuit DR as a drive voltage generating means includes an NPN transistor Q5 whose supply is supplied with a charge pump output voltage VP (= VB + 10 [V]) obtained by boosting the power supply voltage VB, and a collector connected to the emitter of the transistor Q5. Done N
It has a PN transistor Q6, and a contact point between the emitter of the transistor Q5 and the collector of the transistor Q6 is connected to a gate TG as a control terminal of the power MOSFET QF via an internal resistor RG.

When a signal instructing driving of the load 102 is inputted from the external switch C1, the driving circuit DR turns on the transistor Q5 and turns off the transistor Q6 to drive the charge pump output voltage VP. A voltage is applied to the gate TG of the power MOSFET QF to turn on the power MOSFET QF.

On the other hand, the drive circuit DR includes an external switch C
When there is no signal input from 1, the transistor Q5 is turned off and the transistor Q6 is turned on to stop applying the drive voltage to the gate TG of the power MOSFET QF and turn it off.

Further, the above-mentioned power MOSFET QF
Includes an internal resistance RG, a temperature sensor 121, a temperature detection FET Q11, a holding circuit 122 as holding means,
FET for thermal shutdown as switching element for thermal shutdown
It is formed in the same chip with QS, and the chip has three terminals of a gate TG, a drain D and a source S. The temperature sensor 121 is composed of four series diodes, and the four diodes have a greater negative temperature dependency than the resistor R32. Further, the temperature sensor 122 is attached to the power MOSFET QF for mounting, and
The temperature of QF is detected.

The holding circuit 122 includes a pair of MOSFETs Q14 in which a MOSFET Q14 and a gate and a drain are cross-coupled.
It is basically composed of OSFETs Q12, Q13 and load resistors R34, R35. Since the load resistance R34≪the load resistance R35, the holding circuit 122 is an asymmetric flip-flop.

The overheat shutoff FET QS is a power MOSF
The drain is connected to the gate TG of the ETQF, and the source is connected to the source S. When turned on, the gate TG and the source S are short-circuited to forcibly turn off the power MOSFET QF. The Zener diode ZD1 is used to keep the voltage between the gate TG and the source S at 12 [V] and apply a high-pass when an overcurrent is applied to the gate TG.

The operation of the power supply control device having the above configuration will be described below. Power MOSFET by drive circuit DR
When the drive voltage is output to the gate TG of the QF, the power M
When the temperature of the OSFET QF is low, the temperature sensor 121
The divided voltages of the four diodes constituting
Since the temperature is equal to or higher than the threshold of the ETQ11, the temperature detection FET Q11 is turned on. Therefore, the temperature detection FE
The drain voltage of TQ11 becomes L level and MOSFE
TQ14 is turned off.

When the MOSFET Q14 is off,
Since the MOSFET Q12 is off, the Q13 is on, and the drain of the MOSFET Q13, which is the output of the holding circuit 122, is at the L level, the overheat cutoff FET QS is kept off. Therefore, the power MOSFET QF
Is not short-circuited between the gate TG and the source S, and the power MOSFET QF is turned on and off in accordance with the drive voltage applied to the gate TG.

In addition, the power MO
If the temperature of the SFET QF rises above a predetermined temperature,
Since the voltages of the four diodes constituting the temperature sensor 121 drop below the threshold of the temperature detection FET Q11, the temperature detection FET Q11 is turned off. Therefore, the drain voltage of the MOSFET Q11 becomes H level, and the MOSFET Q14 is turned on. MOSFET Q
When the MOSFET 14 is ON, the MOSFET Q12 is ON and the MOSFET Q13 is OFF.
QS is turned on, the gate TG and the source S of the power MOSFET QF are short-circuited, and the temperature is lowered by being controlled to the cut-off state.

As described above, when the temperature rises and the MOSFET Q12 forming the holding circuit 122 changes from off to on, the load resistance R34≪the load resistance R35. The voltage applied to both diodes drops, and the temperature detection FE
It is below the threshold of TQ11. For this reason, even if the temperature of the power MOSFET QF decreases and the resistance of the diode rises again, the divided voltage of the diode does not exceed the threshold value.
Is never turned on. Next, when the application of the driving voltage is stopped, the MOSFET Q
12, Q13 and Q14 are turned off, and the holding of the cutoff state is reset. Therefore, once the power MOSFET QF is turned off, the holding circuit 122 turns on the overheat cutoff FET QS even if the temperature of the power MOSFET QF decreases while the drive voltage is applied to the gate TG by the drive circuit DR. It works to maintain the state and the interruption state.

[0014]

By the way, the load 102
When a lamp load is used, dimming of the lamp load is performed by applying a drive pulse having a voltage corresponding to the drive voltage to the gate TG of the power MOSFET QF and controlling the duty of the drive pulse. However, the power M of the conventional power supply control device described above
When the OSFET QF is turned on / off by a drive pulse whose duty is controlled, even if the holding state of the overheat cutoff FET QS is held by the holding circuit 122, if the temperature of the power MOSFET QF decreases, the holding circuit 122 FE for overheating cutoff
The holding of the ON state of TQS is reset, and the power MOSFET QF is turned on again at the rise of the next drive pulse.

For this reason, the power MOSFET QF repeatedly turns on and off.
A rush current higher than usual flows through the SFET QF, the power supply line, the load, and the like, and the power MOSFET QF receives electric stress for a long time, leading to thermal destruction. In order to prevent such a situation from occurring, a power supply control device as shown in FIG. 4 has been considered.

This power supply control device includes a lamp load 10
2 is a circuit for controlling the power supply of the vehicle-mounted battery 101 to the power supply 2, and a drive pulse whose duty is controlled is input to the gate TG of the power MOSFET QF by the drive circuit DR in order to perform dimming of the lamp load 102. In this figure, parts that are the same as in FIG. 3 are given the same reference numerals, and detailed descriptions thereof are omitted. In the figure, the power MOSF
The ETQF is connected to a temperature sensor 121, a holding circuit 122, and an overheat cutoff FET QS (not shown).

Also, the vehicle-mounted battery 101 and the power MOS
The shunt resistor RS provided between the FET QF and the FET QF is a low resistor for converting the load current IF flowing through the power MOSFET QF into a voltage. By detecting the voltage between both ends, the load current IF flowing through the lamp load 102 is detected. You. Both ends of the shunt resistor RS are connected to the +
The differential amplifier 41 is connected to the input terminal and the negative input terminal, and outputs a voltage corresponding to the load current IF.

The output of the differential amplifier 41 is amplified by an amplifier 42 and then output from an A / D converter 4 in a microcomputer 43.
4 is converted to a digital value. An instruction signal S1 instructing the microcomputer 43 to drive the lamp load 102 from an external switch C1, and a dimming voltage V1 obtained by dividing the voltage VA by a resistor R1 and a variable resistor R2 for adjusting the brightness of the lamp load 102. Is input. When the instruction signal S1 is input, the microcomputer 44 outputs a control pulse S2 having a duty corresponding to the dimming voltage V1 adjusted by the variable resistor R2 to the drive circuit DR. The drive circuit DR uses the charge pump output voltage boosted by the charge pump circuit 45 in response to the output of the control pulse S2 output from the microcomputer 43 as a drive pulse and uses the power MOSFET QF
To the gate TG.

Further, the microcomputer 43 takes in the value of the load current IF every predetermined sampling time TS, and when the taken-in load current IF is 0 and the control pulse S1 is output, the microcomputer 43 detects the temperature of the power MOSFET QF. Rises to determine that overheating has been interrupted, and the control pulse S2
Stop output of When the output of the control pulse S2 is stopped, the drive pulse output by the drive circuit DR is stopped, so that the cutoff state of the power MOSFET QF is maintained thereafter. That is, once the temperature rises and the power MOSFET
When the TQF is cut off, no drive pulse is output thereafter, so that the power MOSFET QF does not repeat on / off and does not lead to thermal destruction.

However, in the above-described conventional example, the load current IF is fetched for each sampling time TS, and the power MOSFET is controlled by the state of the control pulse S2 when the load current IF is fetched.
It was determined whether or not the QF was overheated. For this reason, if sampling is performed at an interval equal to or more than １ ／ of the H period of the control pulse (= H period of the drive pulse), the sampling during the L period of the control pulse S2 may be repeated, and the power MOSFET QF It is not possible to reliably determine whether or not the overheat interruption has been performed.

In order to reliably determine that the power MOSFET QF has been overheated, it is necessary to perform sampling at intervals equal to or less than 1/2 of the H period of the control pulse S2. However, there is a limit in shortening the sampling time TS, and when the power MOSFET QF is driven on and off by a drive pulse with a fine duty, it cannot be reliably detected that overheating has been performed, and the power There is a problem that protection of the MOSFET QF and the load cannot be reliably performed.

Therefore, the present invention pays attention to the above-mentioned problems, and reliably protects the three-terminal switching element and the load even when the three-terminal switching element is driven by a driving pulse with a fine duty. It is an object to provide a power supply control device that can perform the control.

[0023]

According to the first aspect of the present invention,
A three-terminal provided between a first DC power supply and a load, the power supply-side terminal connected to the first DC power supply, the load-side terminal connected to the load, and a control terminal to which a drive voltage is applied A switching element, drive voltage generating means for applying the control terminal, and generating the drive voltage for turning on the three-terminal switching element by turning on the power supply side terminal and the load side terminal; A temperature sensor for detecting a temperature, and the three-terminal switching element is forcibly turned off by short-circuiting between the control terminal and the load terminal by turning on in response to detection of a temperature equal to or higher than a predetermined temperature by the temperature sensor. A switching element for overheating cut-off, and the switching element for overheating cut-off while a drive voltage is applied to the control terminal in response to detection of a temperature equal to or higher than the predetermined temperature. A power supply control device comprising: a holding unit that holds an ON state; and a voltage corresponding to the drive voltage is applied to the control terminal after the overheat switching device short-circuits the control terminal and the load-side terminal. And a voltage applying means for continuously applying the voltage.

According to the first aspect of the present invention, when the drive pulse whose duty is controlled is generated by the drive voltage generating means, and the on / off control of the three-terminal switching element is performed by the drive pulse, the three-terminal switching by the temperature sensor is performed. In response to the detection of the temperature equal to or higher than the predetermined temperature of the element, the holding circuit holds the overheat cutoff switching means in the on state while the drive pulse is being applied, and holds the cutoff state of the three-terminal switching element. When the three-terminal switching element is turned off and the temperature decreases, the holding of the overheat cut-off switching element by the holding means is released with the falling of the driving pulse, and the three-terminal switching element is turned on at the next rising of the driving pulse. Then 3
Although the terminal switching element repeatedly turns on and off, once the voltage applying means short-circuits between the control terminal and the load side terminal by the overheating switching means,
Since the voltage corresponding to the drive voltage is continuously applied to the control terminal, even if the drive pulse falls, the holding of the ON state of the overheat cutoff switching element by the holding means is not released, and at the rise of the next drive pulse. The three-terminal switching element does not turn on. Therefore, the three-terminal switching element does not repeatedly turn on and off. Moreover, since the voltage application unit continues to apply the voltage to the control terminal in response to the short circuit between the control terminal and the load side terminal, there is no need to monitor the on / off state of the drive pulse.

According to a second aspect of the present invention, the voltage applying means is provided between a second DC power supply and the control terminal,
The overheat cutoff switching element short-circuits between the control terminal and the load-side terminal, and when the potential of the load-side terminal becomes a negative potential equal to or less than a predetermined value, keeps the on-state and the second The power supply control device according to claim 1, further comprising a first switching element that continuously applies a voltage corresponding to the drive voltage from a DC power supply to the control terminal.

According to the second aspect of the present invention, when the three-terminal switching element is turned off due to the wiring inductance of the power supply line connecting the three-terminal switching element and the load, a back electromotive force is generated and the potential of the load terminal becomes a negative potential. Becomes When the overheating cutoff switching element is in the off state, when the load side terminal has a negative potential equal to or less than a predetermined value, a bias is applied between the control terminal and the load side terminal, and a voltage corresponding to the drive voltage is applied to the control terminal. As a result, the three-terminal switching element conducts, and the load-side terminal does not become a negative potential below a predetermined value,
When the overheat cutoff switching element is on,
Since the control terminal and the load-side terminal are short-circuited, even if the load-side terminal has a negative potential equal to or lower than a predetermined value, the three-terminal switching element cannot conduct, and the negative potential advances to be lower than the predetermined value. Therefore, the first switching element keeps the ON state after the overheating cutoff switching element short-circuits the control terminal and the load side terminal and the potential of the load side terminal becomes a negative potential equal to or less than a predetermined value. Then, the voltage corresponding to the drive voltage is continuously applied from the second DC power supply, so that the three-terminal switching element, the temperature sensor, the holding means, and the overheat cutoff switching element are formed together, and the three-terminal switching element has A drive pulse is provided only by providing a voltage applying means between the load side terminal and the control terminal without increasing the number of terminals of a protection chip for protecting a three-terminal switching element or the like when driven by a drive voltage. And protection of a three-terminal switching element and the like when driven.

According to a third aspect of the present invention, the voltage applying means is provided between the load-side terminal and ground, and when the load-side terminal has a negative potential equal to or less than a predetermined value, the voltage is applied from the ground. A first bias circuit that generates a bias voltage by flowing a current to a load-side terminal; and a first bias circuit that is provided between the second DC power supply and the load-side terminal, and that is provided by a bias voltage generated by the first bias circuit. A second switching element that is turned on; and a second switching element that is provided between the second DC power supply and the second switching element, and is turned on from the second DC power supply to the load-side terminal when the second switching element is turned on. A second bias circuit that generates a bias voltage that causes a current to flow to turn on the first switching element;
A third bias circuit that is provided between the first switching element and the load-side terminal, and that generates a bias voltage that keeps the second switching element on while the first switching element is on; 3. The power supply control device according to claim 2, wherein:

According to the third aspect of the present invention, when the load terminal has a negative potential equal to or less than a predetermined value, the first bias circuit generates a bias voltage by flowing a current from the ground to the load terminal. The second switching means is turned on by the bias voltage generated by the first bias circuit, and the second bias circuit causes a current to flow from the second DC power supply to the load side terminal when the second switching element is turned on, so that the first bias circuit is turned on. , A bias voltage for turning on the switching element is generated. While the first switching element is on, the third bias circuit eliminates the back electromotive force due to the wiring inductance and the current flows from the second DC power supply to the load-side terminal even if the load-side terminal is not at a negative potential below a predetermined value. To generate a bias voltage that keeps the second switching element on. That is, once the first switching element is once turned on, the current continues to flow from the second DC power supply to the load side terminal, and the second switching means continues to be turned on by the bias voltage generated by the third bias circuit. For this reason, once the first switching element is once turned on, the first switching element keeps its own on state and continues to apply the voltage from the second DC power supply to the control terminal. Therefore, it is not necessary for the comparator to detect that the load-side terminal has become equal to or lower than the predetermined potential, and for the flip-flop circuit to hold the ON state of the first switching means, thereby simplifying the circuit configuration.

According to a fourth aspect of the present invention, there is provided the power supply control device according to the third aspect, wherein the second DC power supply has a lower voltage than the first DC power supply.

According to the fourth aspect of the present invention, since the second DC power supply has a lower voltage than the first DC power supply, the control terminal and the load-side terminal are short-circuited when the overheat cutoff switching means is off. Otherwise, when a malfunction occurs and a voltage is applied from the second DC power supply to the control terminal by the voltage applying means, the control terminal and the load side terminal are not short-circuited and the second DC Since the three-terminal switching element is turned on by the voltage from the power supply, the potential of the load terminal becomes equal to the voltage of the first DC power supply, and the potential of the load terminal becomes higher than the potential of the second DC power supply. The current flowing from the DC power supply to the load-side terminal is stopped, the first and second switching elements are turned off, and the application of voltage from the voltage applying means to the control terminal is stopped. Therefore, even when the voltage application unit applies a voltage to the control terminal due to a malfunction, the application of the voltage can be automatically canceled.

According to a fifth aspect of the present invention, the power supply control device according to the fourth or fifth aspect is mounted on a vehicle.
5. The power supply control device according to claim 3, wherein when the first DC power supply is a vehicle-mounted battery, the second DC power supply is supplied with power from the vehicle-mounted battery via an ignition switch. 6. Exists.

According to the fifth aspect of the present invention, since the second DC power supply is supplied from the vehicle-mounted battery via the ignition switch, the voltage application state is maintained by the voltage application means by turning off the ignition switch. Is reset. Therefore, it is not necessary to newly provide a means for resetting the voltage applying means.
When the ignition switch is turned off, the holding of the applied state is released, and when the ignition switch is turned on, power can be supplied to the load again.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A power supply control device according to the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of a power supply control device according to the present invention. This power supply control device includes a vehicle-mounted battery 101 for the lamp load 102.
For controlling the power supply of the power MOSFET QF.
Drive pulse whose duty is controlled is applied to the drive circuit D
It is input by R. In the figure, the same reference numerals are given to the same parts as those of the related art described above with reference to FIG. 3, and the detailed description thereof will be omitted.

In the figure, as described in the above-mentioned conventional example, the FET QA with the overheat cutoff function is a power MOSFET QF.
Temperature sensor 121, temperature detection FET Q11,
The holding circuit 122 and the overheating cutoff FET QS are provided in the same chip, and the chip has three terminals of a gate G, a drain D, and a source S. The FET QA with an overheat cutoff function is a chip used for protection of the power MOSFET QF and the like when driven by a drive voltage.

The voltage application circuit 201 functions as voltage application means, and the overheat cutoff FET QS is connected to the power MOSFET.
After the short circuit between the gate TG and the source S of the ETQF, a voltage corresponding to the drive voltage is continuously applied to the gate TG.

In the voltage application circuit 201, a first power supply is provided between a DC power supply VCC as a second DC power supply and the gate G.
PNP transistor Tr as switching element
1 is provided. When the transistor Tr1 is turned on, the DC power VCC is applied to the gate G. Source S
Diode D21, bias resistor R22, diode D23 and zener diode ZD
A first bias circuit 21 having 24 is provided.
In the first bias circuit, when the potential of the source S becomes a negative potential equal to or lower than a predetermined value and a voltage equal to or higher than a predetermined voltage is applied to both ends of the Zener diode D24, the ground → the Zener diode ZD24 → the diode D23 → the bias resistor R2
A current flows in the order of 2 → diode D21 → source S to generate a bias voltage across the bias resistor R22.

A second power supply is provided between the DC power source VCC and the source S.
NPN transistor Tr as switching element
2 is provided, and the emitter and the collector of the transistor Tr2 are connected via a bias resistor R22.

Further, the DC power supply VCC and the transistor Tr
2 and a bias resistor R26, a resistor R2
5 is provided.
When the transistor Tr2 is turned on, the second bias circuit 22 is connected to the DC power supply VCC → the bias resistor R26 → the resistor R2.
5 and a bias voltage is generated at both ends of the bias resistor R26. Further, the above-described transistor T
The emitter-collector of r1 is connected via a bias resistor R26.

A third bias circuit 23 having resistors R27 and R29, a bias resistor R22 and a diode D21 is provided between the base of the transistor Tr1 and the source S. When the transistor Tr1 turns on, the DC power supply V
CC → between emitter and base of transistor Tr1 → resistor R27 → R29 → bias resistor R22 → diode D2
A current is caused to flow in the order of 1 to generate a bias voltage across the bias resistor R22.

Based on the circuit configuration of the power supply control device described above, the principle used by the power supply control device of the present embodiment will be described with reference to FIG. Generally in vehicles, power MOSFE
The TQF is provided in a junction box on the right side of the driver's seat. For this reason, the power supply line connecting the load such as the tail lamp located at the rear of the vehicle away from the junction box and the power MOSFET QF becomes extremely long. In such a case, the power supply from the vehicle-mounted battery 101 to the load 102 is conceptually represented as shown in FIG. 3, and the power supply line connecting the power MOSFET QF and the load 102 has a wiring inductance L0 and a wiring resistance R0. Will have.

Accordingly, the temperature is low and the overheating cutoff FET QS
Is off, when the drive pulse output from the drive circuit DR is stopped and the power MOSFET QF is turned off from on, a back electromotive force is generated by the wiring inductance L0, and the source S of the power MOSFET QF has a negative potential.
When this source S has a negative potential of 3 V or more, the power MOSF
The gate TG-source S of the ETQF is biased, and as a result, conduction is established between the drain D and the source S of the power MOSFET QF, and power is supplied from the vehicle-mounted battery 101,
The negative potential of the source S does not advance by 3 V or more.

On the other hand, the power M
The temperature of the OSFET QF rises and the overheating cutoff FET QS
Is turned on, and the power MOSFET QF is forcibly turned off, a back electromotive force is generated by the wiring inductance L0, and the source S has a negative potential as in the case described above. However, when the overheat is cut off, the overheat cutoff FET
Since the gate TG and the source S are short-circuited by the QS, the power MOSFET Q
F cannot be conducted, and the source S drops to a negative potential of 3 V or less determined by the wiring inductance L0. In this case, the negative potential of the source S is usually -10 to -40 V.

That is, when the power MOSFET QF is turned off during the L period of the drive pulse from the drive circuit DR, the source S has a negative potential of about 3 V, and the power MOSFET QF is forcibly turned off by the overheat cutoff FET QS. When this is done, the potential becomes a negative potential of -10 to -40 V. Therefore, the voltage application circuit 201 is configured to continue applying a voltage corresponding to the drive voltage to the gate TG after the source S becomes lower than the predetermined potential.

As described above, since the voltage application circuit 201 continues to apply the voltage corresponding to the drive voltage to the gate TG after the source S becomes equal to or lower than the predetermined potential, the number of terminals of the FET QA with the overheat cutoff function is reduced. Voltage application circuit 201 between the gate TG and the source S without increasing the voltage
Power MOSFE by the driving pulse.
Since it is possible to cope with protection of the power MOSFET QF and the like when the TQF is driven, the cost can be reduced.

Next, the operation of the power supply control device shown in FIG. 1 will be described below. Power MOSFET QF is normally turned on and off by a drive pulse from drive circuit DR applied to gate TG. The duty of the drive pulse is controlled by a microcomputer (not shown), and the smaller the duty of the drive pulse, the darker the lamp load 102 becomes. At this time, the power MO
When the temperature of the SFET QF rises, the overheating cutoff FET Q
S is turned on, the gate TG and the source S are short-circuited, and the power MOSFET QF is forcibly turned off.
When the power MOSFET QF is forcibly turned off, as described above, the source S is turned to a negative potential to a value determined by the wiring inductance L0, and becomes a negative potential equal to or lower than a predetermined value.

When the source S has a negative potential equal to or less than a predetermined value,
A voltage equal to or higher than a predetermined voltage is applied to both ends of the Zener diode ZD24, and ground → Zener diode ZD24 →
Diode D23 → bias resistor R22 → diode D
Current flows in the order of 21 → source S.

When a current flows through the bias resistor R22, a bias voltage is generated across the bias resistor R22, and the transistor Tr2 is turned on by the bias voltage. When the transistor Tr2 is turned on, a current flows from the DC power supply VCC in the order of the bias resistor R26 → the resistor R25 → the emitter of the transistor Tr2, and a bias voltage is generated across the bias resistor R22. The transistor Tr1 is turned on by this bias voltage.

When the transistor Tr1 provided between the DC power supply VCC and the gate TG is turned on, the DC power supply VCC is applied to the gate TG, and the DC power supply VCC → the emitter-base of the transistor Tr1 → the resistor R27 →
The current continues to flow in the order of R29 → bias resistor R22 → diode D21, and a bias voltage is generated across the bias resistor R22 to keep the transistor Tr2 on. The third bias circuit 23 generates a bias voltage that keeps the transistor Tr2 on by flowing a current from the DC power supply VCC to the source S even when the back electromotive force due to the wiring inductance is eliminated and the source S is not at a negative potential equal to or less than a predetermined value. I do. That is, once the transistor Tr1 is turned on, the transistor Tr1 keeps its on state and continues to apply the voltage from the power supply voltage VCC to the gate TG.

As described above, after the power MOSFET QF is forcibly cut off by the overheat cutoff FET QS, the power supply voltage V is applied to the gate TG by the voltage application circuit 201.
Since the CC is continuously applied, even if the drive pulse falls, the holding state of the overheat cutoff FET QS by the holding circuit 122 is not released, and the power MOSFET QF may be turned on at the next rise of the drive pulse. Absent. Therefore, since the power MOSFET QF does not repeatedly turn on and off, the protection of the power MOSFET QF and the load can be reliably performed even when the power MOSFET QF is driven by a drive pulse with a fine duty.

Further, if the DC power supply VCC is used so that VCC <VB, a malfunction occurs when the overheating cutoff FET QS is off and the gate TG and the source S are not short-circuited, and the voltage application circuit 201 When the direct current power supply VCC is applied to the gate TG, the power MOSFET Q has no short circuit between the gate TG and the source S.
When F is turned on and the potential of the source S becomes equal to the power supply voltage VB, and the power supply voltage VB = the potential of the source S> the power supply voltage VCC, the DC power supply VCC → the emitter-base of the transistor Tr1 → the resistance R27 → R29 → bias. Resistance R2
2 → Diode D21 and DC power supply VCC → Bias resistor R26 → Resistor R25 → Base of transistor Tr2−
The current flowing between the emitters stops and the transistor Tr1
And Tr2 are turned off, and the application of the voltage from the voltage application circuit 201 to the gate TG is stopped. Therefore, even when the voltage application circuit 201 applies a voltage to the gate TG due to a malfunction, the application of the voltage can be automatically released, so that the reliability can be improved. .

Further, if the DC power supply VCC is supplied with power from the vehicle-mounted battery 101 via the ignition switch, the holding of the voltage application state by the voltage application circuit 201 is reset by turning off the ignition switch. Therefore, needless to say, it is not necessary to newly provide a unit for resetting the voltage application circuit 201.
When the ignition switch is turned off, the holding of the applied state is released, and when the ignition switch is turned on, power can be supplied to the load again, so that usability can be improved.

In the above-described embodiment, when the source S has a negative potential equal to or less than a predetermined value, it is determined that the gate TG and the source S have been short-circuited by the overheating interruption FET QS. The voltage applied to the gate is monitored, and if the gate is at the H level, the overheat cutoff FET QS is turned on and the gate TG-source S
It may be determined that a short circuit has occurred. Also in this case, since it is not necessary to monitor the on / off state of the drive pulse, even when the power MOSFET QF is driven by a drive pulse with a fine duty, the power M
The protection of the OSFET QF and the load can be reliably performed.

In the above embodiment, the transistors Tr1, Tr2, the first, second and third bias circuits 2
The voltage corresponding to the drive voltage has been continuously applied to the gate TG after the source S has become a negative potential equal to or less than a predetermined value by using the comparators 1, 22, and 23. When the potential is detected, the transistor Tr1 is turned on and, for example, the holding circuit 1 is turned on.
The on state of the transistor Tr1 may be maintained by a flip-flop circuit having the same configuration as that of the transistor 22.
However, in this case, since the comparator and the flip-flop circuit are used, the configuration becomes complicated and the cost becomes high.

[0054]

As described above, according to the first aspect of the present invention, the holding of the ON state of the overheat cutoff switching element by the holding means is not released even if the drive pulse falls, Does not turn on at the rise of the drive pulse. Therefore,
The three-terminal switching element does not repeatedly turn on and off. Moreover, since the voltage applying means continues to apply a voltage to the control terminal in response to a short circuit between the control terminal and the load side terminal,
Because it does not monitor the on / off state of the drive pulse,
A power supply control device capable of reliably protecting the three-terminal switching element and the load even when the three-terminal switching element is driven by a fine drive pulse can be obtained.

According to the second aspect of the present invention, the three-terminal switching element, the temperature sensor, the holding means, and the overheat switching element are formed together, and the three-terminal switching element has three terminals. In the case of driving by a drive pulse only by providing a voltage applying means between the load side terminal and the control terminal without increasing the number of terminals of a protection chip for protecting a three-terminal switching element and the like when driven by voltage, Since it is possible to protect the terminal switching element and the like, it is possible to obtain a power supply control device with a reduced cost.

According to the third aspect of the present invention, it is not necessary for the comparator to detect that the load-side terminal has become equal to or lower than the predetermined potential and to hold the ON state of the first switching means by the flip-flop circuit. Since the configuration can be simplified, a power supply control device with reduced cost can be obtained.

According to the fourth aspect of the present invention, even when the voltage applying means applies a voltage to the control terminal due to a malfunction, the application of the voltage can be automatically canceled.
A power supply control device with improved reliability can be obtained.

According to the fifth aspect of the present invention, it is not necessary to newly provide a means for resetting the voltage applying means, and the holding of the applied state is released by turning off the ignition switch, and the load is again turned on by turning on the ignition switch. Can be supplied to the power supply control device, a power supply control device with improved usability can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a power supply control device according to the present invention.

FIG. 2 is an explanatory diagram for explaining a principle used by the power supply control device according to the embodiment;

FIG. 3 is a diagram illustrating an example of a power supply control device including a conventional three-terminal switching element.

FIG. 4 is a diagram illustrating an example of a power supply control device including a conventional three-terminal switching element.

[Explanation of symbols]

101 vehicle-mounted battery (first DC power supply) 102 load D drain (power supply terminal) S source (load side terminal) TG gate (control terminal) QF power MOSFET (three terminal switching element) DR drive circuit (drive voltage generation means) 121 Temperature sensor QS Overheat cutoff FET (overheat cutoff switching element) 122 Holding circuit (holding means) 201 Voltage applying circuit (voltage applying means) VCC DC power supply (second DC power supply) Tr1 transistor (first switching element) Reference Signs List 21 first bias circuit Tr2 transistor (second switching element) 22 second bias circuit 23 third bias circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) AX32 AX37 AX44 AX64 BX16 CX22 CX28 DX13 DX22 DX53 DX54 EX01 EX02 EX04 EX06 EX11 EY01 EY05 EY12 EY13 EY17 EY21 EZ07 EZ10 EZ23 EZ31 EZ57 FX04 FX05 FX06 FX33 FX35 FX38 GX01

Claims (5)

[Claims] A control provided between a first DC power supply and a load, wherein the power supply terminal to which the first DC power supply is connected, the load side terminal to which the load is connected, and a drive voltage are applied. A three-terminal switching element having a terminal, a drive voltage generating means for applying the control terminal, and generating the drive voltage for turning on the three-terminal switching element by conducting the power supply side terminal and the load side terminal; A temperature sensor for detecting the temperature of the three-terminal switching element, and forcibly turning on in response to the detection of a temperature equal to or higher than a predetermined temperature by the temperature sensor to short-circuit the control terminal and the load-side terminal to force the three terminal A switching element for switching off the overheat, and a switch for overheating interrupting while a drive voltage is applied to the control terminal in response to detection of the temperature equal to or higher than the predetermined temperature. A power supply control device comprising: a holding unit configured to hold an on state of the switching element; wherein when the overheat cutoff switching element short-circuits between the control terminal and the load-side terminal, the control terminal corresponds to the drive voltage. A power supply control device, further comprising: voltage applying means for continuously applying a voltage. 2. The voltage application means is provided between a second DC power supply and the control terminal, and the overheat cutoff switching element short-circuits between the control terminal and the load-side terminal, so that the load A first switching element that keeps an on state and continues to apply a voltage corresponding to the drive voltage from the second DC power supply to the control terminal after the potential of the side terminal becomes a negative potential equal to or less than a predetermined value. The power supply control device according to claim 1, further comprising: 3. The voltage applying means is provided between the load-side terminal and ground, and when the load-side terminal has a negative potential of a predetermined value or less, a current is applied from the ground to the load-side terminal. A first bias circuit for generating a bias voltage by flowing the current, and a second switching circuit provided between the second DC power supply and the load-side terminal, the second switching circuit being turned on by the bias voltage generated by the first bias circuit. Element, provided between the second DC power supply and the second switching element, and when the second switching element is turned on, a current flows from the second DC power supply to the load-side terminal, A second bias circuit for generating a bias voltage for turning on a first switching element; and a first switching element provided between the first switching element and the load-side terminal. 3. The power supply control device according to claim 2, further comprising: a third bias circuit that generates a bias voltage that keeps the second switching element on while the switch is on. 4. The power supply control device according to claim 3, wherein the second DC power supply has a lower voltage than the first DC power supply. 5. The power supply control device according to claim 4, wherein the power supply control device is mounted on a vehicle, and when the first DC power supply is a vehicle-mounted battery, the second DC power supply includes an ignition switch. The power supply control device according to claim 3, wherein power is supplied from the on-vehicle battery via the power supply.