JP2012217271A - Power supply device and power supply method - Google Patents

Abstract

A power supply device and a power supply method including an overcurrent protection circuit that can be realized at a low cost by reducing the number of components.
A timer circuit outputs a cut-off signal when receiving an overcurrent signal Sc output from a comparison circuit 5 continuously for a predetermined time. When the control circuit 7 receives the cutoff signal S output from the timer circuit 6, the control circuit 7 stops outputting the control signal to the charge pump circuit 8. Thereby, the voltage application to the gate terminal of the switching element 1 is eliminated, and the switching element 1 is shut off.
[Selection] Figure 1

Description

  The present invention relates to a power supply device and a power supply method, and more particularly to a power supply device and a power supply method having a function of protecting an electrical component mounted on a wire harness or a vehicle from an overcurrent.

  2. Description of the Related Art A fuse is provided in a power supply device that supplies electric power to an electrical component mounted on a vehicle via a wire harness in order to protect the wire harness and the electrical component from burning due to overcurrent. In an overcurrent protection circuit using a fuse, when an overcurrent occurs, the fuse is blown to protect the circuit, so it is necessary to perform maintenance (maintenance) such as replacement of the blown fuse. For this reason, the installation place of the overcurrent protection circuit using the fuse is limited, and it is necessary to install the fuse in a place where it can be easily replaced. As a result, the degree of freedom in designing the wiring harness layout is reduced (for example, an optimal harness design cannot be performed and the harness routing increases). Further, in the conventional power supply apparatus, a relay is often used as a switching element, but there is a problem that the size and heat generation of parts are large, leading to an increase in the size of the apparatus. In addition, an appropriate wire diameter is selected in consideration of the protection characteristics of the overcurrent protection circuit, but there is a problem that the wire diameter of the wire increases due to large deterioration and variation of the fuse over time. It was.

  Therefore, in recent years, an overcurrent protection circuit using a transistor element instead of a fuse or a relay has been proposed (see Patent Document 1). This overcurrent protection circuit has a transistor element connected between the power supply and electrical components, and determines whether or not an overcurrent has occurred based on a voltage change between the source electrode and drain electrode of the transistor element To do. When the overcurrent protection circuit determines that an overcurrent has occurred, the transistor element is turned off to cut off the connection between the power supply and the electrical component, thereby protecting the electrical component from overcurrent in a nondestructive manner. To do. According to such an overcurrent protection circuit, it is not necessary to prepare transistor elements even when an overcurrent occurs. Therefore, the power supply device including the overcurrent protection circuit using the transistor element has a high degree of freedom in the wiring harness layout without being limited in installation location. In addition, the size of the device can be reduced by reducing fuses and reducing the size and loss of transistor elements. Furthermore, it is possible to select an electric wire with a smaller wire diameter (reducing the electric wire diameter) by suppressing aging deterioration, variation, and the like as compared with the fuse.

  By the way, the curve (it is also called overcurrent limit characteristic) which shows the smoke generation characteristic of an electric wire is represented by a graph as shown, for example in FIG. In FIG. 5, the horizontal axis indicates the time for flowing current through the electric wire, and the vertical axis indicates the current flowing through the electric wire. The solid line shows the relationship between the time and current when the wire covering material smokes. Since it takes time until the heat is transmitted to the covering material after the current is passed, smoke does not reach even if the current is large at the beginning of the current flow. Here, the equilibrium limit current I1 shown in FIG. 5 is a value that allows the current to flow in a thermal equilibrium state in which the heat generated by the current flows and the heat dissipation are balanced. This equilibrium limit current I1 is determined by the wire material, wire diameter (wire size), and the like. In the overcurrent limit characteristic curve, a region where the time is smaller than the time t1 corresponding to the equilibrium limit current I1 and the current is smaller than the characteristic curve is referred to as a transient region. Further, the region where the time is longer than time t1 and the current is smaller than the characteristic curve is referred to as a thermal saturation region. In this heat saturation region, there is a current I2 that allows a current to continue to flow without reaching smoke. The current I2 is a current such that the broken line indicating the current value does not intersect the characteristic curve even if time elapses.

JP 2009-142146 A

  Here, the power supply device including the overcurrent protection circuit needs to determine the overcurrent and cut off the current so that the protection target does not burn out. This overcurrent determination requires a higher accuracy. In addition, it is required that the determination accuracy of occurrence of overcurrent is high. If the determination accuracy is low, a design margin including an overcurrent generation determination error must be set in the design of the protection target. As a result, for example, in the case of an electric wire, there is a design restriction such that the diameter has to be increased excessively, and for example, problems such as difficulty in miniaturization occur.

  In Patent Document 1, the determination accuracy is improved by simulating an overcurrent limit characteristic (particularly, a transient region) using a CR time constant circuit. However, the number of wires to be protected by the overcurrent protection circuit is large, and the number of components of the CR time constant circuit is increased, resulting in an increase in mounting space. In particular, since the heat capacity is small for a thin wire, an overcurrent protection circuit simulating the overcurrent limit characteristic (particularly the transient region) by the CR time constant circuit is not necessary.

  The present invention has been made in view of the above, and an object of the present invention is to provide a power supply device and a power supply method including an overcurrent protection circuit that can be realized at a low cost by reducing the number of components.

  In order to solve the above-described problems and achieve the object, a first aspect of a power supply device according to the present invention is provided with a switching element capable of interrupting a current supplied from a power supply to a load, and supplied to the load. A current detection circuit for detecting a current and outputting a sense current; a comparison circuit for outputting an overcurrent signal when the sense current is equal to or greater than a predetermined overcurrent determination threshold; and an input of the overcurrent signal for a predetermined time A timer circuit that outputs a cut-off signal when input continuously, and a predetermined power supply signal that is output when a load control signal is input from the outside, while the power supply signal is output when the cut-off signal is input from the timer circuit. An overcurrent protection circuit comprising one or more overcurrent protection circuits, and the switching element conducts a current supplied to the load when the power supply signal is input, The current supplied to the load is cut off when the overcurrent signal is continuously input for the predetermined time or more in the timer circuit.

  In another aspect of the power supply apparatus according to the present invention, the predetermined time is determined based on an overcurrent limit characteristic of an electric wire connected from the switching element to the load.

  In another aspect of the power supply apparatus according to the present invention, the switching element and the current detection circuit are configured by a single IPS (intelligent power switch) element, and the voltage of the power source is monitored and this is determined. And a voltage monitoring unit that outputs the cutoff signal to each of the control circuits of the one or more overcurrent protection circuits.

  In another aspect of the power supply apparatus according to the present invention, the IPS element provided in each of the one or more overcurrent protection circuits monitors the voltage of the power supply and individually sets a cutoff threshold value for each of the IPS elements. Voltage monitoring means for stopping the switching element in the IPS element when lowered to below, the cutoff threshold used in the monitoring device is the maximum cutoff threshold set individually for the IPS element. Is set.

  A first aspect of a power supply method according to the present invention includes a switching element capable of interrupting a current supplied from a power supply to a load, a current detection circuit that detects a current supplied to the load and outputs a sense current, A comparator circuit that outputs an overcurrent signal when the sense current is equal to or greater than a predetermined overcurrent determination threshold, and a timer that outputs the overcurrent signal when the sense current is input continuously for a predetermined time An overcurrent protection circuit comprising: a circuit; and a control circuit that outputs a predetermined power supply signal when a load control signal is input from the outside, and that interrupts the power supply signal when the cutoff signal is input from the timer circuit. A power supply method using a power supply device including one or more, wherein the timer circuit outputs a cut-off signal to the control circuit when the overcurrent signal is continuously input for the predetermined time or more. Thus, the power supply signal output from the control circuit is interrupted, and the current that conducts the switching element is interrupted.

  In another aspect of the power supply method according to the present invention, the switching element and the current detection circuit are configured by a single IPS (intelligent power switch) element. When the voltage drops below the cutoff threshold, the cutoff signal is output to the control circuit of each of the one or more overcurrent protection circuits.

  According to the present invention, it is possible to realize a power supply device and a power supply method including an overcurrent protection circuit with a simple configuration and a low cost by reducing the number of components. In particular, for a thin wire having a small heat capacity, the transient region in the overcurrent limit characteristic is small, so that the effectiveness is increased.

FIG. 1 is a block diagram showing the configuration of the power supply apparatus according to the first embodiment of the present invention. FIG. 2 is a diagram illustrating a cutoff characteristic realized by using the timer circuit of the first embodiment. FIG. 3 is a schematic diagram showing operating characteristics of an overcurrent protection circuit equipped with an IPS element. FIG. 4 is a block diagram showing the configuration of the power supply apparatus according to the second embodiment of the present invention. FIG. 5 is a diagram illustrating an example of an overcurrent limit characteristic of an electric wire.

  Hereinafter, embodiments of a power supply device and a power supply method according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. In the drawings, the same or corresponding elements are denoted by the same reference numerals as appropriate.

(First embodiment)
FIG. 1 is a block diagram showing the configuration of the power supply apparatus according to the first embodiment of the present invention. As shown in FIG. 1, a power supply device 100 includes a switching element 1, a current detection circuit 2, an I / V conversion circuit 3, a voltage dividing resistor circuit 4 (4a, 4b), a comparison circuit 5, and a timer. One or more overcurrent protection circuits 101 (101-1 to 101-N) including a circuit 6, a control circuit 7, and a charge pump circuit 8 are provided.

  The switching element 1 is an n-channel MOSFET. The switching element 1 has a drain terminal connected to a power source (battery) having a voltage + B, and a source terminal connected to a DC load 10 such as a motor via an electric wire W. The gate terminal of the switching element 1 is connected to the charge pump circuit 8.

  The current detection circuit 2 detects the load current IL flowing into the DC load 10 via the switching element 1 by measuring the voltage between the drain terminal and the source terminal of the switching element 1. Furthermore, the current detection circuit 2 outputs a sense current Is at a constant ratio (for example, 1/1000) with respect to the detected load current IL. The output sense current Is is converted into a sense voltage Vs by the I / V conversion circuit 3.

  The comparison circuit 5 is a comparator composed of an operational amplifier and has two input terminals. The sense voltage Vs converted by the I / V conversion circuit 3 is input to one input terminal, and the other input terminal is cut off. An overcurrent determination voltage (overcurrent determination threshold) Vref corresponding to the threshold is input. The overcurrent determination voltage Vref is set to a predetermined voltage by dividing the voltage by the resistors 4a and 4b of the voltage dividing resistor circuit 4. Then, the sense voltage Vs and the overcurrent determination voltage Vref are compared, and when the sense voltage Vs becomes larger than the overcurrent determination voltage Vref, an overcurrent signal Sc is output.

  The timer circuit 6 outputs the interruption signal S when the overcurrent signal Sc output from the comparison circuit 5 is continuously received for a predetermined time. In addition, the predetermined time depends on the wire diameter of the electric wire W, and the predetermined time is set longer as the wire diameter increases.

The control circuit 7 receives the cutoff signal S output from the timer circuit 6. A load control signal (power supply signal) C for driving the DC load 10 from the outside is also input.
When the DC load 10 is driven, a control signal is output to the charge pump circuit 8. The charge pump circuit 8 boosts the control signal (about 5 V) from the control circuit 7 and outputs the boosted voltage (about 10 to 12 V) to the gate terminal of the switching element 1 to make the switching element 1 conductive. .

Further, when the cut-off signal S is input to the control circuit 7, even if the load control signal C is received, the cut-off signal S has priority, and the output of the control signal to the charge pump circuit 8 is stopped. It becomes. When the control signal is stopped, no voltage is applied to the gate terminal of the switching element 1 and the switching element 1 is cut off.
Note that the comparison circuit 5, the timer circuit 6, and the control circuit 7 are preferably constituted by digital circuits. Such a digital circuit makes it possible to flexibly support various power supply devices.

  The interruption characteristics realized using the timer circuit 6 of this embodiment are shown in FIG. 2 in comparison with the overcurrent limit characteristics of various electric wires. The horizontal axis in FIG. 2 indicates the time for passing a current through the electric wire W, and the vertical axis indicates the current through the electric wire. Moreover, the dotted line has shown the smoke generation characteristic (W1-W3) of various electric wires, and the continuous line has shown the interruption | blocking characteristic Sd of this Embodiment. Note that the smoke generation characteristics of W1 to W3 respectively simulate wire diameters of 3 sq, 0.5 sq, and 0.2 sq as wire types.

  As shown in FIG. 2, by using the timer circuit 6, the overcurrent protection circuit 101 can be realized with a simple configuration that does not use the CR time constant circuit. In particular, for thin wires with a small heat capacity, the transient region in the overcurrent limit characteristic is small as shown by W3, so that the interruption characteristic Sd realized using the timer circuit 6 can be substituted, and the number of parts is large. There is no need for a high cost CR time constant circuit. Furthermore, since the timer circuit can be easily changed for a predetermined time depending on the setting, it can be adapted to various power supply devices.

(Second Embodiment)
A power supply device and a power supply method according to the second embodiment of the present invention will be described below.
In recent years, an IPS (intelligent power switch) element in which the functions of the switching element 1, the current detection circuit 2, and the charge pump circuit 8 are integrated into an IC has been developed. The IPS element usually has a self-protection function so that the element does not become too hot. As part of this self-protection function, there is a voltage monitoring function for monitoring the supply voltage supplied to the IPS element. When the supply voltage to the IPS element decreases, the switching element 1 is shut down (cut off), whereby the IPS element Is protecting. The cutoff threshold (Vth) of the voltage monitoring function varies depending on the application and specification of the overcurrent protection circuit.

  In the present embodiment, an IPS element in which the switching element 1 and the like are integrated into an IC is used. A plurality of overcurrent protection circuits mounted on a vehicle have various uses and specifications, and a plurality of overcurrent protection circuits are supplied with power from a single battery. Here, when the cutoff threshold values (Vth) of the IPS elements provided in each of the plurality of overcurrent protection circuits are different, the operation as shown in FIG. 3 occurs, which may cause a problem.

FIG. 3 shows the operating characteristics of an overcurrent protection circuit equipped with an IPS element. The horizontal axis in FIG. 3 indicates the elapsed time, and the vertical axis indicates the battery supply voltage + B.
When the supply voltage + B from the battery decreases due to deterioration of the battery or the like, the overcurrent protection circuit in which the cutoff threshold (Vth) of the IPS element is set high (for example, 5 V) is shut down by the voltage monitoring function of the IPS element. (Operation at point a in FIG. 3). On the other hand, other overcurrent protection circuits equipped with IPS elements whose cutoff thresholds are set lower (for example, 3.5 V) will maintain their operation without shutting down. Since some of the overcurrent protection circuits are shut down, the load on the battery is greatly reduced, so that the supply voltage of the battery temporarily returns (increases) (operation at point b in FIG. 3). Then, when the battery supply voltage returns (increases) to the shut-off threshold taking hysteresis into account, the overcurrent protection circuit that has been shut down can return to the normal state, and thus the shutdown operation is canceled (FIG. 3). Operation at point c). When the overcurrent protection circuit that has been shut down returns to the normal state, the load that receives the supply of voltage from the battery increases again, and thus the supply voltage of the battery decreases again. Hereinafter, there is a risk of repeating the operation from the point a to the point c.

  The operation of repeating point a to point c is generally called a hunting operation, and the electric wire is repeatedly heated, the heat repeatedly heated is accumulated, and the electric wire is disconnected. If configured, it becomes a big problem.

  The power supply apparatus and the power supply method according to the present embodiment are made to solve this problem, and have a configuration as shown in FIG. FIG. 4 is a block diagram showing the configuration of the power supply apparatus 200 according to the second embodiment. In FIG. 1, a plurality of overcurrent protection circuits 101 are displayed in an overlapping manner, but in FIG. 4, a plurality of overcurrent protection circuits 201 (201-1 to 201-N) are displayed in a vertical row. FIG. 4 shows a state where a plurality of overcurrent protection circuits 201-1 to 201-N are supplied with a voltage + B from one battery. Each operation of the overcurrent protection circuit 201 is as shown in FIG.

  In the power supply apparatus 200 of this embodiment, the IPS element 20 is mounted on each of the overcurrent protection circuits 201, and the switching element 1, the current detection circuit 2, and the charge pump circuit 8 are integrated in the IPS element 20. Yes. The IPS element 20 further includes a voltage monitoring unit 21 that monitors a decrease in the supply voltage + B from the battery. That is, the voltage monitoring means 21 monitors the supply voltage + B from the battery, and shuts down the IPS element 20 when it falls below the cutoff threshold Vth. The value of the cutoff threshold Vth may be different for each IPS element 20 of the overcurrent protection circuit 201. As an example, in FIG. 4, the cutoff threshold Vth of the IPS element 20 of the overcurrent protection circuit 201-1 is 3.5V, The cutoff threshold Vth of the IPS element 20 of the overcurrent protection circuit 201-2 is 5V, the cutoff threshold Vth of the IPS element 20 of the overcurrent protection circuit 201-N is 4V, and the like.

  The power supply apparatus 200 of this embodiment is provided with one voltage monitoring unit 202 for N overcurrent protection circuits 201-1 to 201-N. The voltage monitoring unit 202 inputs and monitors the voltage + B of the power supplied to each IPS element 20, and when detecting that the voltage + B has dropped below a predetermined cutoff threshold Vth0, N overcurrent protections A cutoff signal S ′ for shutting off the IPS element 20 is output to each control circuit 7 of the circuits 201-1 to 201-N. When the cutoff signal S ′ is input to the control circuit 7, the control circuit 7 stops outputting the control signal to the charge pump circuit 8. As a result, no voltage is applied to the gate terminal of the switching element 1, and the switching element 1 is cut off.

  The cutoff threshold Vth0 used in the voltage monitoring unit 202 is preferably matched with the highest voltage among the cutoff thresholds Vth used in the IPS elements 20 of the overcurrent protection circuits 201-1 to 201-N. Thus, when the IPS element 20 having the highest cutoff threshold Vth reaches a condition for shutting down, not only the IPS element 20 but also the IPS element 20 mounted in the other overcurrent protection circuit 201 is shut down at the same time. . The voltage dividing resistor circuit 4, the comparison circuit 5, the timer circuit 6, and the control circuit provided in each of the N overcurrent protection circuits 201-1 to 201-N can be configured by one ASIC. The voltage monitoring unit 202 can also be formed by the same ASIC.

  According to the power supply device 200 of the present embodiment, all the other IPS elements 20 are shut down simultaneously with the IPS element 20 that has reached the first shutdown condition, so that hunting as illustrated in FIG. It disappears. As a result, the electric wire can be safely protected without being heated. In the present embodiment, a single monitoring unit 202 can be configured to shut down the IPS elements 20 of all overcurrent protection circuits 201 connected to the power supply of voltage + B. Alternatively, it is also possible to provide a monitoring unit 202 for each block unit classified according to usage, etc., and to configure each monitoring unit 202 to shut down the IPS element 20 of the overcurrent protection circuit 201 in the block. .

  Note that the description in the present embodiment shows an example of the power supply device and the power supply method according to the present invention, and the present invention is not limited to this. The detailed configuration and detailed operation of the power supply device and the power supply method in the present embodiment can be changed as appropriate without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 Switching element 2 Current detection circuit 3 I / V conversion circuit 4 Voltage dividing resistor circuit 5 Comparison circuit 6 Timer circuit 7 Control circuit 8 Charge pump circuit 10 DC load 20 IPS element 21 Voltage monitoring means 100, 200 Power supply devices 101, 201 Overcurrent protection circuit 202 Voltage monitoring unit

Claims (6)

A switching element capable of interrupting a current supplied from a power source to a load;
A current detection circuit for detecting a current supplied to the load and outputting a sense current;
A comparison circuit that outputs an overcurrent signal when the sense current is equal to or greater than a predetermined overcurrent determination threshold;
A timer circuit that inputs the overcurrent signal and outputs a cut-off signal when it is continuously input for a predetermined time; and
A control circuit that outputs a predetermined power supply signal when a load control signal is input from the outside, and shuts off the power supply signal when the shut-off signal is input from the timer circuit. ,
The switching element supplies a current supplied to the load when the power supply signal is input, and is supplied to the load when the timer circuit continuously inputs the overcurrent signal for the predetermined time or more. A power supply device that cuts off the current. The power supply device according to claim 1, wherein the predetermined time is determined based on an overcurrent limit characteristic of an electric wire connected from the switching element to the load. The switching element and the current detection circuit are configured by one IPS (intelligent power switch) element, and when the voltage of the power source is monitored and falls below a predetermined cutoff threshold, the one or more overcurrents The power supply apparatus according to claim 1, further comprising a voltage monitoring unit that outputs the cutoff signal to each control circuit of a protection circuit. The IPS element provided in each of the one or more overcurrent protection circuits monitors the voltage of the power source, and when the voltage drops below an individually set cutoff threshold, the switching element in the IPS element is Has voltage monitoring means to stop,
The power supply apparatus according to claim 3, wherein a maximum value of a cutoff threshold value individually set for the IPS element is set as the cutoff threshold value used in the monitoring device. A switching element capable of interrupting a current supplied from a power source to a load, a current detection circuit for detecting a current supplied to the load and outputting a sense current, and when the sense current is equal to or greater than a predetermined overcurrent determination threshold A comparator circuit that outputs an overcurrent signal to the input circuit, a timer circuit that outputs the cutoff signal when the overcurrent signal is input and continuously input for a predetermined time, and a predetermined power source when a load control signal is input from the outside A power supply method by a power supply device comprising one or more overcurrent protection circuits, comprising: a control circuit that outputs a supply signal while cutting off the power supply signal when the cutoff signal is input from the timer circuit. ,
When the timer circuit continuously inputs the overcurrent signal for the predetermined time or longer, the timer circuit outputs a cut-off signal to the control circuit to cut off the power supply signal output from the control circuit, thereby turning on the switching element. A power supply method characterized by cutting off a current to be generated. The switching element and the current detection circuit are configured by one IPS (intelligent power switch) element,
6. The power supply according to claim 5, wherein the power supply voltage is monitored, and when the voltage drops below a predetermined cutoff threshold, the cutoff signal is output to each of the control circuits of the one or more overcurrent protection circuits. Supply method.

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