JPH1041797A - Switch circuit with overcurrent detection function - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To protect wiring members and loads. A microcomputer controls on and off of a FET through a drive circuit in accordance with an instruction signal for turning on or off a lamp. The microcomputer 4 also takes in the current I _L flowing through the A / D converter 6 and flowing through the lamp L every predetermined sampling time T _S , and converts the taken current I _L into a known rated current of the lamp L. Compare with value I _R. Then, to start the I _L ≧ I count the energization time T becomes _R, turn off I _L × T FET2 the accumulated value reaches a value S ₀ which is set in advance of the _S. When the detection current I _L is equal to or greater than the preset upper limit value I ₀ (≫I _R ), the microcomputer 4 turns off the FET 2 via the drive circuit 5 immediately.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switch circuit having an overcurrent detection function for controlling on / off of power supply from a power supply to a load.

[0002]

2. Description of the Related Art Countermeasures against short-circuiting of an electric circuit leading to equipment failure or fire have been one of the important issues that have been studied for many years. However, since there are a variety of short-circuiting modes, it has been difficult to realize a countermeasure with a simple configuration that appropriately operates in any of the modes.

Conventionally, fuses have been most frequently used as a measure for protecting devices and electrical wiring against short circuits. The fuse is provided with a metal conductor portion, and when the temperature of the metal conductor portion rises above a set value, the metal conductor portion is blown, and is usually protected by a power supply line to a load or the like. Used in series with a power supply in the electric wiring of the present invention. When an overcurrent flows through the fuse and the temperature of the metal conductor rises above the set value, the metal conductor melts and the power supply through the electric wiring to be protected is cut off. I have.

[0004] On the other hand, conventionally, in order to reduce the weight and thickness of electric products, electronic components mounted thereon have been miniaturized. For example, a switching element for controlling power supply from a power supply to a load and a switching element thereof have been proposed. A switch circuit in which a control circuit for controlling the operation of the element is integrally mounted on a substrate is used. Conventionally, such a switch circuit not only controls the on / off of the switching element, but also detects the occurrence of an abnormality such as overcurrent, overvoltage or overheating, and controls the switching element in response to the abnormality. The one provided with the circuit is used.

[0005]

In the above-mentioned prior art, the fusing of the metal conductor is caused by the accumulation of heat. Therefore, when the ambient temperature is low, the rate of heat accumulation is slow, and the fusing time is long. It is necessary to design the above set value in consideration of derating with respect to temperature.

There are two types of short-circuiting: a case where an overcurrent flows continuously and a case where a pulse-like overcurrent flows intermittently. In the latter case, the heat is more intense than in the former case. Since the accumulation speed becomes slow, there is a possibility that the fusing time may be long or the fusing may not be performed at all even though an overcurrent is flowing. Therefore, it has been difficult to reliably protect devices and electrical wiring using a fuse against intermittently flowing pulse-like overcurrent.

Further, the overcurrent detection in the above-mentioned conventional switch circuit is such that when a current having a level significantly larger than the rated current of the circuit or load is detected, the switching element is immediately turned off to protect the switch circuit from self-protection. This is for the purpose of protection, and does not consider the protection of the wiring member and the load against an overcurrent at a level slightly larger than the rated current of the wiring member and the load between the power supply and the load.

An object of the present invention is to solve the above problem and to provide a switch circuit with an overcurrent detection function capable of reliably protecting a wiring member and a load.

[0009]

According to the present invention, there is provided a semiconductor switching element provided between a load and a power supply, for turning on and off the connection between the load and the power supply in accordance with a control signal input to a control terminal. A switch control means for receiving an instruction signal instructing the operation of the load output from the instruction signal output unit, and outputting a control signal to a control terminal of the semiconductor switching element according to the received instruction signal,
In a switch circuit for controlling power supply from the power supply to the load, current detection means for detecting a load current flowing through the load, and detection of the load current is performed by a wiring between the load and a power supply or an electrical characteristic of the load. And an overcurrent control means for changing the on / off control of the semiconductor switching element when an overcurrent determination condition set in advance is satisfied according to (1).

According to this configuration, when receiving the instruction signal for instructing the operation of the load, which is output from the instruction signal output unit,
A control signal is output to the control terminal of the semiconductor switching element according to the received instruction signal, and the connection between the load and the power supply is turned on and off according to the control signal. When a load current flowing through the load is detected, and the detection of the load current satisfies an overcurrent determination condition set in advance according to a wiring between the load and the power supply or an electrical characteristic of the load, the semiconductor switching element is turned on and off. By changing the control, the passage of an overcurrent exceeding the wiring between the load and the power supply or the electrical characteristics of the load is prevented.

Further, the semiconductor switching element, the switch control means and the overcurrent control means are integrally formed on a substrate.

According to this structure, the semiconductor switching element, the switch control means and the overcurrent control means are integrally formed on the substrate, so that the circuit is downsized and the wiring is simplified.

Further, the current detecting means is further integrally formed on the substrate.

According to this configuration, in addition to the semiconductor switching element, the switch control means, and the overcurrent control means, the current detection means is integrally formed on the substrate, so that
Further, the circuit is downsized and the wiring is simplified.

The overcurrent control means includes a comparing means for comparing the detected load current with a reference current set in advance in accordance with the electrical characteristics, and an energizing means for supplying a current equal to or more than the reference current to the load. Counting means for counting time, wherein the overcurrent determination condition is set using the load current that is equal to or greater than the reference current and the energizing time (claim 4).

According to this configuration, the load current flowing through the load is detected, and the detected load current is compared with a reference current preset according to the wiring or the electrical characteristics of the load. The energization time flowing to the load is counted. When the load current and the energization time that are equal to or greater than the reference current satisfy the overcurrent determination condition, the ON / OFF control of the semiconductor switching element is changed, so that the overcurrent energization time is determined by the wiring between the load and the power supply or the load. Is reliably prevented from being exceeded. As the reference current, the rated current of the wiring or load may be used.

Further, the overcurrent control means determines that an overcurrent determination condition is that a state in which a preset current equal to or higher than the reference current flows to the load for a preset time in accordance with the electric characteristic. And a plurality of overcurrent determination conditions comprising a combination of different set currents and set times in which the set time is shortened as the set current is higher, wherein the comparing means further includes the detected load current and the The count means compares the set currents with each other, and the counting means further counts a conduction time during which a current equal to or more than the set currents flows to the load.

According to this configuration, the load current flowing through the load is detected, and the detected load current is compared with the reference current and each set current. Time is counted. And
The higher the set current is, the shorter the setting time is. Therefore, as the current flowing to the load becomes higher than the reference current, the overcurrent is determined in a short time, so that the overcurrent is determined finely. Energization exceeding the electrical characteristics of the load is reliably prevented.

In the above configuration, the overcurrent control means obtains a product of the current equal to or more than the reference current flowing through the load and the predetermined time every predetermined time, and accumulates the product. And a judging means for judging an overcurrent when the accumulated value reaches a preset value. According to this configuration, when the level of the load current is large, the overcurrent is determined in a short energization time, and when the level of the load current is low, the overcurrent is determined in a long energization time.
The determination of the overcurrent is performed more finely, and the energization exceeding the electrical characteristics of the wiring or the load is reliably prevented.

Further, the overcurrent control means turns off the semiconductor switching element when the overcurrent determination condition is satisfied.

According to this configuration, when the instruction signal for instructing the operation of the load, which is output from the instruction signal output unit, is received,
A control signal is output to the control terminal of the semiconductor switching element according to the received instruction signal, and the connection between the load and the power supply is turned on and off according to the control signal. When a load current flowing through the load is detected, and the detection of the load current satisfies an overcurrent determination condition preset according to a wiring between the load and the power supply or an electrical characteristic of the load, the semiconductor switching element is turned off. This prevents the passage of an overcurrent exceeding the wiring between the load and the power supply or the electrical characteristics of the load.

The overcurrent control means includes a storage means for storing a reference current preset according to the electrical characteristics, and a comparison means for comparing the detected load current with the reference current, When the detected load current is equal to or larger than the reference current, it is determined that the current is an overcurrent (claim 7).

According to this configuration, the reference current preset according to the wiring between the load and the power supply or the electrical characteristics of the load is compared with the detected load current. By being determined to be a current,
Even in the case of an intermittent short-circuit condition rather than a complete short-circuit, the semiconductor switching element is turned off and the overcurrent exceeding the wiring between the load and the power supply or the electrical characteristics of the load is reliably prevented. Becomes

Further, the storage means further stores a high-level reference current having a higher level than the reference current and a preset time, and the overcurrent control means further comprises the switch control means. Means for counting an elapsed time from the time when the semiconductor switching element is turned on by the means, and when the elapsed time is less than the set time, it is determined that an overcurrent occurs when the load current exceeds the high-level reference current. When the elapsed time is equal to or longer than the set time, it is determined that an overcurrent occurs when the load current exceeds the reference current (claim 8).

According to this configuration, the elapsed time from the time when the semiconductor switching element is turned on is counted. Until the preset time elapses from the time when the semiconductor switching element is turned on, if the load current becomes higher than the high-level reference current, an overcurrent occurs. It is determined that the load current is equal to or greater than the reference current after the set time has elapsed from the ON time, so that the load is determined to be an overcurrent. Therefore, there is no possibility that the inrush current is erroneously determined to be an overcurrent.

The storage means further stores a low-level reference current having a lower level than the reference current, and the overcurrent control means further comprises, when the elapsed time is longer than the set time, When the load current is lower than the low level reference current, it is determined that the load current is abnormal (claim 9).

According to this configuration, after a lapse of the set time or more from the ON time, it is determined that the load current is abnormal even when the load current is equal to or lower than the low-level reference current, so that the open state is intermittently opened. Even when an abnormality occurs in the mode, the semiconductor switching element is turned off, so that energization in an abnormal state is reliably prevented.

[0028]

FIG. 1 is a circuit block diagram showing a first embodiment of a switch circuit with an overcurrent detection function according to the present invention. This switch circuit 1 with an overcurrent detection function is:
It constitutes an automobile lamp control circuit for controlling power supply from an automobile battery (power supply) B to a lamp (load) L.
It is called "FET". ) 2, shunt resistor (current detector)
3, a microcomputer 4, a drive circuit 5, and an A / D converter 6, which are integrally formed on a substrate such as a printed circuit board or a semiconductor substrate. Note that the substrate on which the components are arranged may be molded with a synthetic resin or the like.

The FET 2 and the shunt resistor 3 are connected in series between the battery B and the lamp L. The drain of the FET 2 is connected to the positive electrode of the battery B, the source is connected to the shunt resistor 3, and the gate is connected to the drive circuit 5, respectively. When the FET 2 is turned on, a current flows through the lamp L via the shunt resistor 3.

The shunt resistor 3 is a low resistor for converting a current into a voltage. By detecting the voltage between both ends, the current flowing through the lamp L is detected. This shunt resistor 3
Thus, the current can be detected with high accuracy, and a sharp current change can be detected. The A / D converter 6 converts an analog value of the voltage between both ends of the shunt resistor 3 into a digital value and inputs the digital value to the microcomputer 4.

The microcomputer 4 controls on / off of the FET 2 via the drive circuit 5 in response to an externally input instruction signal for turning on or off the lamp L, thereby controlling turning on / off of the lamp L. is there. The drive circuit 5 includes a charge pump or the like that boosts the voltage level of a control signal from the microcomputer 4 and applies a gate signal to the FET 2 according to the control signal of the microcomputer 4 to turn on and off the FET 2.

Further, the microcomputer 4 fetches each (1 sec in this embodiment) of the current I _L which flows in the lamp L predetermined sampling time T _S, which is input via an A / D converter 6, fetched current the I _L is compared with the known rated current I _R of the lamp L. Then, to start the I _L ≧ I count the energization time T becomes _R, turn off I _L × T FET2 the accumulated value reaches a value S ₀ which is set in advance of the _S.

When the detected current I _L is equal to or greater than the preset upper limit I ₀ (≫I _R ), the microcomputer 4 turns off the FET 2 via the drive circuit 5 immediately. When the microcomputer 4 turns off the FET 2 by detecting an overcurrent, the microcomputer 4 outputs a status signal to that effect.

FIG. 2 is a flowchart of the overcurrent detection procedure. When there is a lighting instruction signal for the lamp L, the operation of this routine is started. First, the memory register S is reset to 0 (step S100). Then, when the sampling time T _S has elapsed (YES in step S110), A
The current _IL is taken in from the / D converter 6 (step S
120).

Then, it is determined whether or not I _L ≧ I ₀ (step S130). If I _L ≧ I ₀ (step S13)
0 and YES), immediately turns off FET 2 (step S140), and outputs a status signal (step S140).
150), this routine ends.

On the other hand, if I _L <I ₀ (step S13)
0 NO), whether I _L ≧ I _R is determined (step S
160), if I _L <I _R (N in step S160)
O), and return to step S110.

[0037] In step S160, if I _L ≧ I _R (YES at step S160), S = S + I L × T S
As a product of the memory registers S current I _L and the energization time T _S is accumulated (step S170), then whether S ≧ S ₀ is determined (step S180).

[0038] Then, if the S ≧ S ₀ (step S1
(YES at 80), the process proceeds to step S140, while S <
If it is S ₀ (NO in step S180), it is determined whether there is an instruction signal for turning off the lamp L (step S180).
190), if there is a light-off instruction signal (YES in step S190), this routine ends.

On the other hand, if there is no light-off instruction signal in step S190 (NO in step S190), the process returns to step S120, and the above operation is repeated every sampling time T _S.

As described above, the overcurrent I _{L which} is equal to or higher than the rated current I _R
When the flow, since the accumulated value of the product I _L × T _S of the energization time T _S has to stop the power supply to the lamp L in the preset value S ₀ to become the FET2 off, overcurrent I
When _L-level is low in a relatively long period of energization, when the level of the over current I _L is large in a short time of energization, becomes the energization of the lamp L is stopped, according to the level of overcurrent Power supply stop control can be performed. In addition, it is possible to perform power supply stop control suitable for the withstand current characteristics of the lamp L at the time of overcurrent.

FIG. 3 is a circuit block diagram showing a second embodiment of the switch circuit with an overcurrent detection function according to the present invention. The same members as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In the second embodiment, the switch circuit 1 with an overcurrent detection function includes a Hall sensor (current detection unit) 30 instead of the shunt resistor 3, and an interface (I / F) circuit instead of the microcomputer 4. 40, a current monitoring unit 41, an OR gate circuit 42, and an FET 43. Like the first embodiment, each unit is integrally formed on a substrate such as a printed circuit board or a semiconductor substrate. Incidentally, the rated current I _R of the lamp L is set to 5A.

The Hall sensor 30 is composed of a semiconductor element, and outputs a voltage V proportional to a product I × B of a current I flowing through the semiconductor element and a magnetic flux density B when arranged in a magnetic field having a magnetic flux density B. utilizes the current I _L flowing through the level of the output voltage V to the lamp L is discoverable. The Hall sensor 30 can detect a current with a small size and high accuracy.

The I / F circuit 40 receives an externally input instruction signal for turning on or off the lamp L,
In response to the instruction signal, the on / off of the FET 2 is controlled via the drive circuit 5 to control the lighting and extinguishing of the lamp L.

The current monitoring section 41 includes first to fifth monitoring circuits 41 including a comparator and an on-delay timer.
1 to 415, and each output is an OR gate circuit 4 respectively.
2 inputs. The OR gate circuit 42
Is connected to the gate of the FET 43, the drain of the FET 43 is connected to the gate of the FET 2, and the source of the FET 43 is connected to the ground line.

The current monitoring circuits 411 to 415 take in the current I _L input via the A / D converter 6 every predetermined sampling time T _S (1 second in the present embodiment), and set the high level according to the current level. It outputs a signal. First monitoring circuit 411 starts operating and 100A or more current I _L is input, immediately it outputs a high level signal.

The second monitoring circuit 412 detects the current I of 70 A or more.
_The operation starts when _L is input, and outputs a high level signal when this current input continues for 5 seconds. Third monitoring circuit 41
3 starts operating and 30A or more current I _L is input, outputs a high level signal when the current input is continued for 10 seconds. The fourth monitoring circuit 414 detects the current I _{L of} 10 A or more.
When the current input is continued for 30 seconds, a high level signal is output. Fifth monitoring circuit 41
5 starts operation and 5A above current I _L is input, outputs a high level signal when the current input is continued for 60 seconds.

When a high-level signal is output from at least one of the current monitoring circuits 411 to 415, a high-level signal is output from the OR gate circuit 42 to the gate of the FET 43, thereby turning on the FET 43. And the gate potential of FET2 drops to low,
2 is turned off, and the power supply to the lamp L is cut off.

Table 1 below shows conditions for shutting off the lamp L by the current monitoring unit 41. As shown in Table 1, in accordance with the level of the current I _L which flows in the lamp L, the respective current monitoring circuits 411 to 415, energization of the lamp L is adapted to be shut off.

[0050]

[Table 1]

Next, an operation example 1 will be described with reference to the timing chart of FIG. Upon detection of the current I _L of 15A at t ₁₁ time, the fourth current monitoring circuit 414 and the fifth current monitoring circuit 415 starts operating. When the current flows I _L less 10A or 30A for 30 seconds, the high level signal from the fourth current monitoring circuit 414 is sent to the OR gate circuit 42 at t ₁₂ time, the OR gate circuit 42 FET 43 A high-level signal is output to the gate of. As a result, the FET 43 becomes conductive, the gate potential of the FET 2 drops to low, the FET 2 is turned off, and the current to the lamp L is cut off.

[0052] If t ₂₁ detected at current I _L is 15A, the fourth current monitoring circuit 414 and the fifth current monitoring circuit 41
5 starts operation. If t ₂₁ detected current t ₂₂ time less than 30 seconds from the time I _L is less than 10A (or 5A), the fourth
The operation of the current monitoring circuit 414 is interrupted, and the operation of the fifth current monitoring circuit 415 continues. When the flows t ₂₁ current from the time of more than 5A for 60 seconds I _L, the at t ₂₂ time 5
The high level signal from the monitoring circuit 415 is output from the OR gate circuit 4
2 to the OR gate circuit 42 and the FET 4
A high-level signal is output to the gate of No. 3. As a result, the FET 43 becomes conductive, the gate potential of the FET 2 drops to low, the FET 2 turns off, and the lamp L
Is turned off.

[0053] When the current I _L of less than 10A or more t ₃₁ time and 30A begins to flow, the fourth current monitoring circuit 414 and the fifth
The current monitoring circuit 415 starts operating. 30 from t ₃₁
When detected at t ₃₂ the time of the sub-second current I _L is 85A, further second current monitoring circuit 412 and the third current monitoring circuit 413 starts operating. When over the t ₃₂ time to 5 seconds detected current I _L 70A or more and a state of less than 100A continues,
Since a high-level signal is sent from the second current monitoring circuit 412 to the OR gate circuit 42, the FET 43 becomes conductive, the gate potential of the FET 2 drops to low, and the
2 is turned off, and the power supply to the lamp L is cut off.

[0054] When the current I _L of 50A at t ₄₁ the time begins to flow, the third current monitoring circuit 413～ fifth current monitoring circuit 415
Starts operation. Then, less than 10 seconds from the t ₄₁ time t
₄₂ When the time to detect the current I _L exceeds 100A, immediately since the high level signal from the first current monitor circuit 411 is sent to the OR gate circuit 42, it becomes FET43 is conductive,
The gate potential of the FET2 drops to low, turning off the FET2 and cutting off the current to the lamp L.

[0055] Thus, the current I _L flowing through the lamp L has to turn off the FET2 If determined to be in an overcurrent, can be automatically shut off the power supply to the lamp L. Further, it detects the level of the current I _L, the level of the overcurrent so as to turn off the FET2 in a short energizing time according to increasing and blocks reliably energizing without exceeding the withstand current property of the lamp L Can be.

Note that the present invention is not limited to the first and second embodiments, but can adopt the following modified embodiments (1) to (10). (1) In the first embodiment, as shown by a dashed line in FIG. 1, an input unit 7 including a dip switch and the like is provided, and the microcomputer 4 controls the rated current of the lamp L in accordance with the input to the input unit 7. The value I _R , the set values S ₀ , I ₀ and the like may be arbitrarily set.

(2) In the first embodiment, the FET 2 is turned off when an overcurrent is detected. However, the microcomputer 4 outputs a PWM control signal having a required duty ratio to the drive circuit 5 so that the FET 2 is turned on. ON at the switching frequency of
By turning off, the supply current to the lamp L may be reduced. The switching frequency of the PWM control signal is preferably 100 Hz or more. However, by using the FET 2 as the switching element, it is possible to suitably turn on and off.

(3) In the first and second embodiments, an N-channel field effect transistor is used as a semiconductor switching element. However, a P-channel FET or a bipolar transistor such as an insulated gate bipolar transistor (IGBT) is used. Is also good. Also in these cases, similar to the above-described modification (2), the on / off state is controlled by using the PWM control signal.
By turning off, the current supplied to the lamp L can be reduced.

(4) In the second embodiment, the current monitoring unit 41
Has five current monitoring circuits, but the number of current monitoring circuits may be increased or decreased. By increasing the number of current monitoring circuits and increasing the combination of the current level to be determined and the energizing time until interruption, the interruption characteristic S can be set as shown in FIG.

FIG. 5 is a diagram for explaining a shutoff characteristic S of a lamp L according to the present modification (4). A smoke emission characteristic R indicating a current level at which a load or a wiring member emits smoke is shown together with a fuse blowing as a comparative example. The characteristic F is also shown. In addition,
_Let the rated current of the lamp L be IR. In Figure 5, the detection current I _L when I ₁ ≦ I _L is cut off immediately the power supply. When I ₂ ≦ _IL <I ₁ , the current is cut off at the power-on time T ₁ . When I _R ≦ _IL <I ₃ , the current is cut off at the power-on time T ₂ .

By setting the cutoff characteristic S of the lamp L as shown in FIG. 5, the smoke emission characteristic R of the load and the wiring member can be made closer to the fuse blowing characteristic F. In other words, since the rated current of the wiring member can be reduced to the level of the current that is actually supplied, the diameter of the wire used for the wiring member can be reduced, thereby reducing the weight and cost of the member. Can be reduced.

(5) In the first and second embodiments, a status signal output from the switch circuit 1 with an overcurrent detection function to the outside informs the user of interruption of power supply due to overcurrent from a display unit such as an LCD panel. The notification means may be provided at an appropriate place outside the switch circuit 1 with the overcurrent detection function. As a result, the user can be reliably notified of the current interruption due to the overcurrent.

(6) In the first and second embodiments, instead of the shunt resistor 3 and the Hall sensor 30, the current detecting section includes a resistor connected in series between the FET 2 and the lamp L, And a temperature sensor for detecting the temperature. In this case, the same effect can be obtained with a simple configuration by using a current monitoring unit 4 that monitors a change in current by detecting a change in temperature of the resistor.

(7) The current detector may use a DC current transformer method. In this method, two coils whose winding directions are opposite to each other are arranged so that the electric wire to be measured between the battery B and the lamp L penetrates, and an AC power supply for applying an AC voltage to one of the coils is provided. It is provided with a detection unit for detecting an AC current induced in the other coil when an AC voltage is applied. Since the AC current is proportional to the current flowing through the wire to be measured, the current flowing through the lamp L is reduced. It is intended to be detectable.

Thus, the current detector can be insulated from the electric wire to be measured. The output level can be increased to a desired level by adjusting the winding ratio of the coil. Note that, in this case, a part or the whole of the current detection unit may be provided outside the substrate on which each unit is provided.

(8) The current detecting section may use an AC current transformer method. This is because an electric wire to be measured between the battery B and the lamp L is disposed so that the coil penetrates or is magnetically coupled to the coil, and an alternating current induced in the coil due to a current change such as an inrush current to the lamp L is detected. And a detection unit that performs the operation. In this case, the lamp L
Since the differential waveform of the inrush current to the
The provision of the current monitoring unit that identifies the level of the overcurrent based on the change rate of the current waveform enables the overcurrent to be determined.

(9) In the first and second embodiments, an overvoltage detection unit and a temperature detection unit may be provided integrally on the substrate of the switch circuit 1 with an overcurrent detection function. The overvoltage detection unit is connected to a power supply line from the battery B and detects the presence or absence of an overvoltage.
The temperature detecting section is composed of a thermistor or the like, and detects the ambient temperature to detect the presence or absence of overheating.

(10) In the first and second embodiments, an example in which the present invention is applied to a switch circuit for controlling a lamp as a load has been described. However, the present invention is also applicable to a switch circuit for controlling on / off of a load other than a lamp such as a motor. can do.

Next, a third embodiment will be described. FIG. 6 is a circuit block diagram showing a third embodiment of the switch circuit with an overcurrent detection function according to the present invention.

Switch circuit 11 with overcurrent detection function
Is from the car battery (power supply) B to the lamp (load)
It constitutes a lamp control circuit of an automobile for controlling power supply to the L, and includes an FET 12, a shunt resistor (current detector) 13, a microcomputer 14, a drive circuit 15, and an A / D converter 16.

The FET 12 and the shunt resistor 13 are connected in series between the battery B and the lamp L.
A drain 12 is connected to the positive electrode of the battery B, a source is connected to one end of the shunt resistor 13, a gate is connected to an output terminal of the microcomputer 14 via the drive circuit 15,
The other end of the shunt resistor 13 is grounded via the electric wiring W and the lamp L. With this configuration, when the FET 12 is turned on, power is supplied from the battery B to the lamp L via the shunt resistor 13 and the electric wiring W.

The shunt resistor 13 is a low resistor for converting a current into a voltage. By detecting the voltage between both ends, the load current I _L flowing through the lamp _L is detected. With the shunt resistor 13, the current can be detected with high accuracy, and a sudden current change can be detected. Further, by using a shunt resistor 13 having a small temperature dependency, it is possible to improve current detection accuracy with respect to a change in ambient temperature.

The A / D converter 16 converts an analog value of the voltage between both ends of the shunt resistor 13 into a digital value and inputs the digital value to the microcomputer 14. The drive circuit 15 includes a charge pump that boosts the voltage level of a control signal from the microcomputer 14, and applies a gate signal to the FET 12 in accordance with the control signal from the microcomputer 14 to turn on the FET 12.
It is to turn off.

The microcomputer 14 has a ROM 14a and a RAM
14b, which controls the operation of the lamp control circuit. The RAM 14b temporarily stores data, and the ROM 14a stores preset setting values such as a set time T ₁ , reference currents I ₁ , I ₂ , and I ₃ described later, a control program, and the like. is there.

The set time T ₁ is set in consideration of the duration of the rush current flowing when the lamp L is turned on. Further, the reference currents I ₁ and I ₂ (I ₁ > I ₂ ) are set in consideration of the withstand current characteristics of the electric wiring W (for example, the smoke generation characteristics of the electric wire covering material), and the reference current I ₃ is 0 <I ₃ <is set to a predetermined value that is a I _2.

The microcomputer 14 has the following functions (A) to (F). (A) The turning on and off of the lamp L is controlled by controlling the turning on and off of the FET 12 via the drive circuit 15 in response to an instruction signal for turning on or off the lamp L input from the outside.

(B) It has a function as time counting means for counting an elapsed time T from the time when the FET 12 is switched from off to on. (C) Predetermined sampling time T _S (100 in this embodiment)
Every msec), an input value from the A / D converter 16 is taken in, and a load current IL flowing through the lamp _L is detected.

[0078] (D) is detected by the load current I _L ROM14
It has a function as comparing means for comparing with the reference currents I ₁ , I ₂ , I ₃ stored in a, and as overcurrent judging means for judging whether or not an overcurrent is present based on the comparison result. In this case, when the elapsed time T is less than the set time T _1, the load current I _L is compared with a reference current I _1, I _L ≧
If I ₁ judges that an overcurrent. Further, when the elapsed time T is time above T ₁ configuration, the reference current I _2, I
_3, and if I _L ≧ I ₂ , it is determined that an overcurrent has occurred.
If I _L ≦ I ₃ , it is determined to be abnormal. Where I _L
≦ the case of I ₃ is not necessarily overcurrent, the load current I _L is determined to be abnormal state falls below the reference current I ₃ from a steady level.

(E) It has a function as an overcurrent control means for turning off the FET 12 via the drive circuit 15 when it is determined that an overcurrent or an abnormality has occurred. (F) When it is determined that an overcurrent or abnormality has occurred and the FET 12 is turned off, a status signal to that effect is output.

Next, the operation of the third embodiment will be described with reference to FIGS. FIG. 7 is a flowchart of an overcurrent determination procedure in the third embodiment, and FIGS. 8 and 9 are diagrams each showing an example of an abnormal state.

The FET 12 is turned on by the lighting instruction signal of the lamp L.
When There is turned on the lamp L is lighted, and start this routine, first, the count of the elapsed time T is started (step S200), then it is determined whether or not the set time T ₁ is elapsed (step S210 ), If it has not passed yet (YES in step S210), load current _IL is taken in from A / D converter 16 (step S210).
220).

[0082] Then, if the load current I _L the load current I _L or less than the reference current I ₁ is compared with a reference current I ₁ a captured is determined (step S230), if I _L <I ₁ (step (YES in S230), and returns to step S210. On the other hand, if I _L ≧ I ₁ in step S230 (NO in step S230), it is determined that an overcurrent has occurred, the FET 12 is turned off (step S240), and a status signal is output (step S250). This routine ends.

In step S210, if T ≧ T ₁ , that is, if the set time T _{1 has} elapsed since the lighting of the lamp L (NO in step S210), the counting of the elapsed time T is stopped (step S260), and then the load Current I _L
(Step S270), the load current I _L is compared with the reference currents I ₂ and I ₃ to determine the magnitude (Step S280). If I ₃ <I _L <I ₂ (Step S270) (YES in S280), returning to step S270.

On the other hand, in step S280, I _L ≧
If I ₂ or I _L ≦ I ₃ (N in step S280
O), it is determined that there is an overcurrent or abnormality, and step S24 is performed.
Go to 0.

When an abnormality of the mode shown in FIG. 8 occurs by such a procedure, the set time T ₁ from the turning on of the FET 12 is set.
After the lapse of, at the time t ₁ at which the load current I _L becomes the reference current I ₂ or FET12 is turned off, power supply to the lamp L is interrupted.

As described above, in the case of an abnormality in which a short-circuit state occurs intermittently instead of a complete short-circuit, even if a fuse having a fusing characteristic indicated by a two-dot chain line in the drawing is provided, the temperature rise will not increase. The power supply cannot be cut off because the fuse is not blown because the fuse is slowed down. However, according to the third embodiment, the power supply can be cut off without fail. Can be eliminated, and the electric wiring W and the lamp L can be reliably protected.

When an abnormality of the embodiment shown in FIG. 9 occurs,
After the lapse of the set time T ₁ from the on of FET12,
Load current I _L FET to time t ₂ which is below the reference current I ₃
12 is turned off, and the power supply to the lamp L is cut off.

As described above, in the case of an abnormality in which an open state occurs intermittently, the power supply cannot be cut off because the fuse does not blow because it is not an overcurrent.
According to the third embodiment, it is possible to cut off the power supply by determining that an abnormality has occurred, thereby eliminating the possibility that an arc discharge or the like may occur in the abnormality occurrence portion, and reducing the electric wiring W and the lamp L. Can be reliably protected.

In FIGS. 8 and 9, the dashed lines after the times t ₁ and t ₂ indicate the lamp L according to the present embodiment.
4 shows an abnormal state when the power supply to the power supply is not interrupted.

FIG. 10 is a circuit block diagram showing a fourth embodiment of the switch circuit with an overcurrent detection function according to the present invention. The same members as those in the third embodiment are denoted by the same reference numerals, and description thereof will be omitted. In the fourth embodiment, a Hall sensor (current detection unit) 30 is provided instead of the shunt resistor 13 in the third embodiment.

The Hall sensor 30 utilizes the Hall effect that outputs a voltage V proportional to the product I × B of the magnetic flux density B of the magnetic field and the current I flowing through the semiconductor element when the semiconductor element is placed in a magnetic field. in which the it can be determined and the known current I determined by the battery voltage, and an output voltage V detected by the microcomputer 14, by determining the magnetic flux density B, and the load current I _L which is proportional to the magnetic flux density B.
This Hall sensor 30, it is possible to accurately detect the load current I _L is compact.

According to the fourth embodiment, the microcomputer 14
Perform the same function as in the third embodiment, the same effect can be obtained.

FIG. 11 is a circuit block diagram showing a fifth embodiment of the switch circuit with an overcurrent detection function according to the present invention. The same members as those in the third embodiment are denoted by the same reference numerals, and description thereof will be omitted. The fifth embodiment includes an FET 17, a comparator 18, a constant current circuit 19, and a reference resistor Rref in place of the shunt resistor 13 and the A / D converter 16 in the third embodiment. L is directly connected.

The drain of the FET 17 is connected to the positive terminal of the battery B, the gate is connected to the gate of the FET 12, the source is connected to the input side of the constant current circuit 19, and to one input terminal P of the comparator 18. It is connected.

The other input terminal Q of the comparator 18 is
The output terminal is connected to the source of the FET 12 and the input terminal of the microcomputer 14. Comparator 18
Compares the input terminal P, the input voltage V _P, V _Q to Q, V
A low level signal when the _P ≧ V _Q, and outputs a high level signal when V _P <V _Q. The output side of the constant current circuit 19 is grounded via a reference resistor Rref.

Here, assuming that the ON resistances of the FETs ₁₂ and ₁₇ are R _{DS (on) 12} and R _{DS (on) 17} , respectively,
Is such that R _{DS (on) 12} <R _{DS (on) 17} .
This can be realized by employing an FET having a smaller number of cells than the number of cells of the FET 12. Due to this difference in on-resistance, FET 1
2, that is, a large current can flow through the lamp L.

According to this circuit, since a constant current is supplied to the reference resistor Rref by the constant current circuit 19, the voltage V _P
Becomes a constant value. Therefore, the resistance value of the reference resistor Rref is set so that the value V _Q2 of the voltage V _Q when the load current I _L is I _L = I ₂ is V _Q2 = V _P.

Then, when V _P <V _Q and a high-level signal is input from the comparator 18, the microcomputer 14 determines that an overcurrent has occurred.

[0099] In the fifth embodiment, instead of directly detecting the load current I _L, it is used across the voltage V _Q of the lamp L. Therefore, if V _P <V _Q during the inrush current due to the characteristics of the lamp L, the microcomputer 1
4, an input signal level of discrimination from the comparator 18 is not performed until after the set time T _1, the set time T ₁
May be started after the elapse of.

On the other hand, the reason why the inrush current flows is that the resistance value of the lamp L is low. If V _P <V _Q does not become satisfied by the elapse of the set time T _{1 due to} the characteristics of the lamp L, the microcomputer 14 The elapsed time T is not counted, and the input signal level from the comparator 18 may always be determined.

As described above, according to the fifth embodiment, the load current I _L is compared with the reference current I ₂ by comparing the voltage V _Q across the lamp L with the constant voltage V _P, and V _P < By determining that an overcurrent occurs at V _Q , the same effect as in the third embodiment can be obtained with respect to the abnormality in the mode as shown in FIG.

The present invention is not limited to the above-described third to fifth embodiments, but may employ the following modifications (11) to (14). (11) In the third and fourth embodiments, in FIGS.
As shown by the dashed line, the microcomputer 14 includes an input unit 21 including a dip switch, and the microcomputer 14 can arbitrarily set the values of the reference currents I ₁ , I ₂ , and I ₃ according to the input to the input unit 21. It may be.

(12) In the third to fifth embodiments, an N-channel field-effect transistor is used as a semiconductor switching element. However, a P-channel FET or a bipolar transistor such as an insulated gate bipolar transistor (IGBT) is used. Is also good.

(13) In the third to fifth embodiments, a status signal output from the switch circuit 11 with an overcurrent detection function to the outside is used to notify a user of interruption of power supply due to an overcurrent from a display unit such as an LCD panel. The notification means may be provided at an appropriate place outside the switch circuit 11 with an overcurrent detection function. As a result, the user can be reliably notified of the current interruption due to the overcurrent.

(14) In the third to fifth embodiments, an example in which the present invention is applied to a switch circuit for controlling a lamp L as a load has been described. However, the present invention is not limited to this. It may be a load.

A load that does not generate an inrush current may be used. In this case, the count and the elapsed time T, the comparison of the reference current I ₁ and the load current I _L is not necessary.

[0107]

As described above, according to the present invention,
When the load current flowing to the load is detected and the detection of the load current satisfies the overcurrent determination condition set in advance according to the wiring between the load and the power supply or the electrical characteristics of the load, the on / off control of the semiconductor switching element is performed. Since the change is made, it is possible to prevent an overcurrent that exceeds the electrical characteristics of the wiring or the load from being applied, thereby protecting the wiring and the load against the overcurrent.

Further, by integrally forming the semiconductor switching element, the switch control means and the overcurrent control means on the substrate, it is possible to reduce the size of the circuit and simplify the wiring.

Further, by forming the current detecting means integrally on the substrate, further downsizing of the circuit and simplification of the wiring can be achieved.

Further, by setting an overcurrent judging condition using the energizing time during which a load current equal to or higher than the reference current level flows and the load current, a situation where the energizing time of the overcurrent exceeds the electrical characteristics of the wiring or the load. Can be reliably prevented, whereby the wiring and the load can be surely protected.

Further, the load current flowing to the load is detected, the detected load current is compared with the reference current and a plurality of set currents, and the energizing time during which the reference current and a current equal to or more than each set current flows to the load is counted. By determining the overcurrent using a plurality of overcurrent determination conditions in which the set time is shortened as the set current is higher, the overcurrent can be determined in a finer manner. Can be reliably prevented.

Further, when the load current flowing through the load is detected and the detection of the load current satisfies the overcurrent determination condition set in advance according to the wiring between the load and the power supply or the electrical characteristics of the load, the semiconductor switching element is switched off. By turning off, it is possible to prevent the passage of an overcurrent exceeding the wiring between the load and the power supply or the electrical characteristics of the load.

Also, the reference current preset according to the wiring between the load and the power supply or the electrical characteristics of the load is compared with the detected load current, and when the load current is equal to or more than the reference current, it is determined that an overcurrent occurs. In this case, the semiconductor switching element is turned off and the overcurrent exceeding the electrical characteristics of the load or the wiring between the load and the power supply is reliably prevented even if the short-circuit occurs intermittently instead of completely. can do.

The elapsed time from the ON time of the semiconductor switching element is counted, and it is determined that an overcurrent occurs when the load current becomes higher than the high-level reference current until a preset time elapses from the ON time. However, after a lapse of a set time or more from the on-time, when the load current becomes equal to or more than the reference current, it is determined that an overcurrent occurs. It is possible to prevent erroneous determination that the current is an overcurrent.

Further, after a lapse of a set time or more from the ON point, it is determined that the load current is abnormal even when the load current is equal to or lower than the low-level reference current. Even in such a case, the semiconductor switching element is turned off, so that energization in an abnormal state can be reliably prevented.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing a first embodiment of a switch circuit with an overcurrent detection function according to the present invention.

FIG. 2 is a flowchart of an overcurrent detection procedure.

FIG. 3 is a circuit block diagram showing a second embodiment of a switch circuit with an overcurrent detection function according to the present invention.

FIG. 4 is a timing chart for explaining an operation example 1;

FIG. 5 is a view for explaining a shutoff characteristic of a lamp according to a modification (4).

FIG. 6 is a circuit block diagram showing a third embodiment of a switch circuit with an overcurrent detection function according to the present invention.

FIG. 7 is a flowchart of an overcurrent determination procedure according to a third embodiment.

FIG. 8 is a diagram illustrating an example of an abnormal state.

FIG. 9 is a diagram showing another example of the mode of the abnormal state.

FIG. 10 is a circuit block diagram showing a fourth embodiment of a switch circuit with an overcurrent detection function according to the present invention.

FIG. 11 is a circuit block diagram illustrating a switch circuit with an overcurrent detection function according to a fifth embodiment of the present invention.

[Description of Signs] 1 Switch circuit with overcurrent detection function 2 FET (semiconductor switching element) 3 Shunt resistor (current detection means) 30 Hall sensor (current detection means) 4 Microcomputer (switch control means, overcurrent control means) 40 I / F circuit (switch control means) 41 current monitoring unit (overcurrent control means) 411 to 415 first current monitoring circuit to fifth current monitoring circuit 42 OR gate circuit (overcurrent control means) 43 FET (overcurrent control means) Reference Signs List 5 drive circuit 6 A / D converter 11 switch circuit with overcurrent detection function 12 FET 13 shunt resistor 14 microcomputer 15 drive circuit 16 A / D converter 17 FET 18 comparator 19 constant current circuit B battery (power supply) L lamp (load) ) Rref reference resistance

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Hoshino 1-7-10 Kikuzumi, Minami-ku, Nagoya City, Aichi Prefecture Inside Harness Research Institute, Inc. (72) Inventor Motonori Kido 1 Kikuzumi, Minami-ku, Nagoya City, Aichi Prefecture 7-7-10 Harness Research Institute, Inc. (72) Inventor Miya ▲ Saki ▼ Junyuki 1-7-10 Kikuzumi, Minami-ku, Nagoya-shi, Aichi Harness Research Institute, Inc.

Claims (9)

[Claims] A semiconductor switching element provided between a load and a power supply for turning on and off a connection between the load and the power supply in response to a control signal input to a control terminal; Switch control means for receiving an instruction signal instructing the operation of the load to be controlled and outputting a control signal to a control terminal of the semiconductor switching element in accordance with the received instruction signal, and controlling power supply from the power supply to the load. Current detection means for detecting a load current flowing through the load, and detecting the load current by an overcurrent determination condition preset according to a wiring between the load and a power supply or an electrical characteristic of the load. And an overcurrent control means for changing on / off control of the semiconductor switching element. Switch circuit. 2. The switch circuit according to claim 1, wherein said semiconductor switching element, said switch control means, and said overcurrent control means are integrally formed on a substrate. 3. The switch circuit with an overcurrent detection function according to claim 2, wherein said current detection means is further integrally formed on said substrate. 4. The overcurrent control means includes: a comparison means for comparing the detected load current with a reference current set in advance according to the electrical characteristics; A counting means for counting time, wherein the overcurrent determination condition is set using the load current and the energization time that are equal to or greater than the reference current. 2. The switch circuit with an overcurrent detection function according to 1. 5. The overcurrent control means according to claim 1, wherein a condition in which a preset current equal to or higher than the reference current flows through the load continues for a preset time in accordance with the electrical characteristic. And, having a plurality of overcurrent determination conditions consisting of a combination of different set current and set time shortened the set time as the set current is higher,
The comparing means further compares the detected load current with each of the set currents, and the counting means further counts a conduction time during which a current equal to or more than each of the set currents flows through the load. 5. The switch circuit with an overcurrent detection function according to claim 4, wherein: 6. The switch circuit with an overcurrent detection function according to claim 1, wherein said overcurrent control means turns off said semiconductor switching element when said overcurrent determination condition is satisfied. 7. The storage device according to claim 1, wherein the overcurrent control unit stores a reference current preset according to the electrical characteristics.
7. A comparison means for comparing the detected load current with the reference current, wherein when the detected load current is equal to or more than the reference current, it is determined that the current is an overcurrent. Switch circuit with overcurrent detection function as described. 8. The storage means further stores a high-level reference current having a higher level than the reference current, and a preset time, and the overcurrent control means further comprises: the switch control means. Means for counting an elapsed time from the time when the semiconductor switching element is turned on by the means, and when the elapsed time is less than the set time, it is determined that an overcurrent occurs when the load current exceeds the high-level reference current. 8. The switch circuit with an overcurrent detection function according to claim 7, wherein when the elapsed time is equal to or longer than the set time, when the load current is equal to or higher than the reference current, it is determined that an overcurrent occurs. . 9. The storage means further stores a low-level reference current having a lower level than the reference current, and the overcurrent control means further comprises: when the elapsed time is equal to or longer than the set time. 9. The switch circuit with an overcurrent detection function according to claim 8, wherein when the load current is equal to or lower than the low level reference current, it is determined that the load current is abnormal.