JP7373767B2 - Overload detection circuit - Google Patents

Description

The present invention relates to an overload detection circuit, and particularly to an overload detection circuit for an electric circuit mounted on a vehicle.

Conventionally, various protection circuits have been proposed for protecting electrical circuits from overloads such as overvoltages and overcurrents applied to input terminals of electrical equipment.

For example, Patent Document 1 discloses an overload protection circuit in which a power Zener diode, a diode, and a history recording circuit are connected in parallel between input terminals of an electric circuit.

When a voltage with a polarity opposite to normal is applied between the input terminals, the power Zener diode and the diode short-circuit the input terminals in a so-called reverse connection state to protect the electric circuit. Further, when an overvoltage is applied between the input terminals, the voltage clamping effect of the Zener diode protects the electrical circuit by preventing a voltage higher than the breakdown voltage from being applied to the electrical circuit.

For example, a history recording circuit is used in which a plurality of serially connected bodies of Zener diodes and fuses or bonding wires are prepared and these are connected in parallel. The breakdown voltages of the respective Zener diodes are set to be different from each other, and are set stepwise to voltages at which it is desired to leave a history before and after the breakdown voltage of the power Zener diode. If an overvoltage higher than the breakdown voltage of the power Zener diode is applied between the input terminals, the fuse or bonding wire will blow depending on the magnitude of the overvoltage. When an electrical circuit is recovered at the time of a failure, it is possible to easily determine what level of overvoltage was occurring by investigating which fuse has blown.

Japanese Patent Application Publication No. 2007-053876

However, in the conventional configuration disclosed in Patent Document 1, a power Zener diode that functions as a protection circuit for an electric circuit, and the diode and the history recording circuit are connected in parallel. For this reason, when an overvoltage is applied, the history recording circuit itself is protected, and the overvoltage level may not be reliably detected.

Furthermore, although it is possible to detect the level of overvoltage when it is applied, it has not been possible to detect the level of voltage applied in a reversely connected state.

The present invention has been made in view of the above, and an object thereof is to provide an overload detection circuit capable of detecting the presence or absence of overvoltage and its level with a simple configuration.

In order to achieve the above object, an overload detection circuit according to the present invention is an overload detection circuit connected between a high potential side input terminal and a low potential side input terminal of an electric circuit. a Zener diode whose cathode is connected to the potential side input terminal; a capacitor connected to the anode of the Zener diode and the low potential side input terminal; and between the anode of the Zener diode and the low potential side input terminal. at least a plurality of resistors each connected in parallel with the capacitor, each of the plurality of resistors has at least one of a resistance value and a rated power, and each of the plurality of resistors has a resistance value and a rated power of at least one of the same. The diode further includes a diode, at least one of which is different from the other and electrically connected to the high potential side input terminal and the low potential side input terminal, the cathode of the diode being connected to the high potential side input terminal, and the anode of the diode being connected to the high potential side input terminal. The diodes are electrically connected to the low potential side input terminals, the diodes are connected in parallel with the capacitor, the cathodes of the diodes are connected to the anodes of the Zener diodes, and the anodes of the diodes are connected to the low potential side input terminals. It is characterized by being connected to each .

According to this configuration, the overload detection circuit can be easily configured. Additionally, in the event of a malfunction in an electrical circuit, by checking which of the multiple resistors has been burnt out or partially melted, it is possible to determine whether or not an overload has been applied to the electrical circuit, as well as the level of overload. can be detected.

Furthermore, it is possible to detect a reverse connection state in which a negative voltage is applied between the high potential side input terminal and the low potential side input terminal of the electric circuit.

According to the overload detection circuit of the present invention, the presence or absence of overvoltage and its level can be reliably detected with a simple configuration. Further, a reverse connection state can be detected.

FIG. 1 is a schematic configuration diagram of an overload detection circuit according to Embodiment 1 of the present invention. FIG. 3 is a diagram showing an example of a temporal change in voltages applied to a Zener diode and first to third resistors. FIG. 2 is a schematic configuration diagram of an overload detection circuit according to Embodiment 2 of the present invention. FIG. 3 is a schematic configuration diagram of another overload detection circuit.

Hereinafter, embodiments of the present invention will be described in detail based on the drawings. The following description of preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its applications, or its uses.

(Embodiment 1)
[Configuration of overload detection circuit]
FIG. 1 shows a schematic configuration diagram of an overload detection circuit according to this embodiment. terminal) 22.

The inverter circuit 20 is mounted on a vehicle, and a DC voltage from a battery (not shown), in this case +12V, is applied to a power supply voltage terminal 21, and a GND terminal 22 is connected to the GND potential. The inverter circuit 20 receives the DC voltage of the battery and converts it into an AC voltage having a desired frequency and voltage value.

The overload detection circuit 10 includes a Zener diode ZD, a capacitor C, and first to third resistors R1, R2, and R3, and is mounted on the vehicle like the inverter circuit 20. Furthermore, as described later, the overload detection circuit 10 also has a function as an overvoltage protection circuit.

The Zener diode ZD has a cathode connected to the power supply voltage terminal 21 and an anode connected to the GND terminal 22.

The capacitor C is connected in series with the Zener diode ZD, with one end connected to the anode of the Zener diode ZD, and the other end connected to the GND terminal 22.

The first to third resistors R1, R2, and R3 are connected in series with the Zener diode ZD and in parallel with the capacitor C, respectively. That is, one end of each of the first to third resistors R1, R2, and R3 is connected to the anode of the Zener diode ZD, and the other end of each is connected to the GND terminal 22.

Further, the breakdown voltage of the Zener diode ZD is set to 27V, that is, a value obtained by adding a slight margin to the voltage doubled of the DC voltage of the battery. The capacitance of capacitor C is set to 10 μF. Furthermore, the resistance values of the first to third resistors R1, R2, and R3 are set to the same value, and are set to 1Ω in this embodiment. On the other hand, the rated powers of the first to third resistors R1, R2, and R3 are set to be different from each other. The rated power of the first resistor R1 is set to 0.1W, the rated power of the second resistor R2 is set to 0.125W, and the rated power of the third resistor R3 is set to 0.5W. However, these values are not particularly limited, and may be changed as appropriate depending on the specifications of the voltage range applied to the inverter circuit 20. For example, if the power source such as a battery is 24V, a +24V DC voltage is applied to the power supply voltage terminal 21. In this case, the breakdown voltage of the Zener diode ZD is set to be 53V, that is, a value obtained by adding a slight margin to the double voltage of the DC voltage of the battery. The capacitance of capacitor C is set to 20 μF. Furthermore, the resistance values of the first to third resistors R1, R2, and R3 are each set to 1Ω. On the other hand, the rated power of the first resistor R1 is set to 0.1W, the rated power of the second resistor R2 is set to 0.125W, and the rated power of the third resistor R3 is set to 0.5W.

Note that since the first to third resistors R1, R2, and R3 are connected in parallel with each other, their combined resistance value is lower than their respective resistance values. In this embodiment, the combined resistance value is approximately 0.3Ω. As will be described later, when a positive overvoltage equal to or higher than the breakdown voltage of the Zener diode ZD is applied to the power supply voltage terminal 21, a current flows through each of the first to third resistors R1, R2, and R3, causing a voltage drop. In other words, the potential of the power supply voltage terminal 21 rises with respect to the GND potential. Therefore, it is necessary to set the combined resistance value so that the potential of the power supply voltage terminal 21 does not exceed the allowable maximum input voltage of the inverter circuit 20. In other words, the combined resistance of the first to third resistors R1, R2, and R3 is such that the difference between the potential difference between the power supply voltage terminal 21 and the GND terminal 22 and the breakdown voltage of the Zener diode ZD is equal to or less than a predetermined value. The value is set.

Next, the operation of the overload detection circuit 10 will be explained.

For example, when a positive overvoltage higher than the breakdown voltage of the Zener diode ZD is applied to the power supply voltage terminal 21, the Zener diode ZD becomes conductive and current flows. Further, the voltage between the anode and cathode of the Zener diode ZD is clamped to the breakdown voltage.

When the applied overvoltage changes greatly over time, for example, when the overvoltage is applied transiently, the current flowing through the Zener diode ZD flows into the GND terminal 22 via the capacitor C. Therefore, no overvoltage is applied inside the inverter circuit 20, and the inverter circuit 20 is protected. Further, substantially no current flows through the first to third resistors R1, R2, and R3.

On the other hand, when the time change of the applied overvoltage is small, the current flowing through the Zener diode ZD flows through the first to third resistors R1, R2, and R3, respectively. Therefore, electric power is consumed in each of the first to third resistors R1, R2, and R3. This will be explained using FIG. 2.

FIG. 2 shows an example of a time change in the voltage applied to the Zener diode ZD and the first to third resistors R1, R2, R3. In this example, the Zener diode ZD and the first to third resistors R1, R2, Consider the case where the applied voltage V applied to the series connection body with R3 is a constant value Va until time t1, rises to Vc at time t1, then continuously decreases, and returns to the original value Va at time t2. . Further, Va is the DC voltage of the battery (=+12V), and Vb is the breakdown voltage of the Zener diode ZD.

As mentioned above, the voltage across the Zener diode ZD is clamped to the breakdown voltage Vb, and the voltage exceeding this is equally applied to each of the first to third resistors R1, R2, and R3, causing current to flow. . At this time, the amount of power Pi consumed by the resistor Ri is expressed in the form shown in equation (1). Further, Pi corresponds to the area of the hatched part shown in FIG.

Pi=∫{(V-Vb) ² /Ri}dt...(1)

here,
Pi: power consumption at the i-th resistor (i is an integer from 1 to 3) Ri: resistance value of the i-th resistor.

As is clear from FIG. 2 and equation (1), the power consumption of each of the first to third resistors R1, R2, and R3 exceeds the above-mentioned rated power and also exceeds the allowable value of each resistor. Then, the resistor burns out or partially melts. Here, the allowable value of the resistor is the actual value due to the material of the resistor. This actual value depends on the individual resistor since the resistor's specifications exceed the guaranteed rated power. In this embodiment, since the rated power of the first resistor R1 is the smallest, first the first resistor R1 burns out or partially melts. Also, if the power consumption of the second resistor R2 and the third resistor R3 exceeds the rated power, these resistors will burn out or partially melt. Note that while current is flowing through any of the first to third resistors R1, R2, and R3, the voltage clamping effect of the Zener diode ZD is exhibited, and the voltage inside the inverter circuit 20 exceeds a predetermined value, in this case. No voltage higher than +24V is applied. In other words, the overload detection circuit 10 protects the inverter circuit 20 from overvoltage exceeding a predetermined value.

Note that if all the resistors burn out, overvoltage will be applied to the series connection of Zener diode ZD and capacitor C, but unless capacitor C causes dielectric breakdown and current does not flow, overvoltage will not flow inside the inverter circuit 20. Applied directly.

If an overvoltage of a predetermined value or more is applied to the inverter circuit 20, the inverter circuit 20 may fail. If it is found that a problem has occurred in the inverter circuit 20, check the state of the overload detection circuit 10, especially whether any of the first to third resistors R1, R2, and R3 is burnt out or partially melted. By checking, it is possible to know whether an overvoltage of a predetermined value or more is applied between the power supply voltage terminal 21, which is an input terminal of the inverter circuit 20, and the GND terminal 22. Additionally, the level of overvoltage can be estimated by checking which resistors are burnt out or partially melted.

[Effects etc.]
As explained above, the overload detection circuit 10 according to the present embodiment has a power supply voltage terminal (high potential side input terminal) 21 and a GND terminal (low potential side input terminal) 22 of the inverter circuit 20 (electric circuit). connected between.

The overload detection circuit 10 includes a Zener diode ZD whose cathode is connected to a power supply voltage terminal 21, a capacitor C connected between the anode of the Zener diode ZD and the GND terminal 22, and a capacitor C connected between the anode of the Zener diode ZD and the GND terminal 22. It includes at least first to third resistors R1, R2, and R3 each connected in parallel with a capacitor C between them. The first to third resistors R1, R2, and R3 have different rated powers.

By configuring the overload detection circuit 10 in this way, the overload detection circuit 10 can be configured easily. In addition, if a problem occurs in the inverter circuit 20, it is possible to determine whether an overload has been applied to the inverter circuit 20 by checking which of the first to third resistors R1, R2, and R3 has been burnt out or partially melted. Whether or not, the level of overload can also be reliably detected.

Further, even if an overvoltage of a predetermined value or higher, in this case, a voltage of +24V or higher is applied to the inverter circuit 20, if any of the first to third resistors R1, R2, and R3 is in a conductive state, , the potential difference between the power supply voltage terminal 21 and the GND terminal 22 is clamped to about the breakdown voltage of the Zener diode ZD. This can prevent a voltage of +24 V or more from being applied inside the inverter circuit 20, and can suppress damage to the inverter circuit 20.

Furthermore, according to the present embodiment, it is possible to detect a reverse connection state in which a negative voltage is applied between the power supply voltage terminal 21 and the GND terminal 22. Furthermore, the inverter circuit 20 can be protected. These will be further explained.

As is clear from FIG. 1, when a negative voltage is applied between the power supply voltage terminal 21 and the GND terminal 22, the GND terminal 22 has a higher potential than the power supply voltage terminal 21. Therefore, a forward bias voltage is applied to the Zener diode ZD, and a current flows from the GND terminal 22 to the power supply voltage terminal 21 through the first to third resistors R1, R2, R3 and the Zener diode ZD, and the inverter circuit No negative voltage is applied inside 20. Therefore, the inverter circuit 20 is protected.

Further, the value of the current flowing from the GND terminal 22 to the power supply voltage terminal 21 is determined by the forward resistance value of the Zener diode ZD and the combined resistance value of the first to third resistors R1, R2, and R3. As described above, when this current value exceeds a predetermined value, the first resistor R1, which has the lowest rated power among the first to third resistors R1, R2, and R3, begins to burn out or partially melt. .

Therefore, even when a negative voltage is applied between the GND terminal 22 and the power supply voltage terminal 21, it is difficult to determine whether any of the first to third resistors R1, R2, and R3 is burned out or partially melted. By checking, it is possible to know whether the applied negative voltage is equal to or higher than a predetermined value. Furthermore, by checking which resistors are burnt out or partially melted, the level of the applied negative voltage can be estimated.

Further, according to the present embodiment, first to third resistors R1, R2, and R3 are connected in series with the Zener diode ZD that protects the inverter circuit 20 from overvoltage. As a result, the first to third resistors R1, R2, and R3 themselves are protected by the Zener diode ZD, and the conventional problem of not being able to detect the presence or absence of overvoltage or the level of overvoltage does not occur.

The first to the third Preferably, a combined resistance value of resistors R1, R2, and R3 is set.

By doing so, the potential of the power supply voltage terminal 21 does not exceed the allowable maximum input voltage of the inverter circuit 20, and the inverter circuit 20 can be protected even when an overvoltage is applied.

Further, as described above, the inverter circuit 20 and the overload detection circuit 10 are each mounted on the vehicle.

A battery is generally used as a power source for supplying electric power to electrical equipment in a vehicle. A battery outputs a DC voltage determined by its performance.

However, with the recent progress in electrification of vehicles, the number of electrical devices installed in vehicles has increased, and the range of voltage and current used by each device has also expanded. For this reason, multiple batteries are often connected in series to generate higher voltage.

However, as such high voltages are applied to a plurality of electrical devices and the number of connections between the electrical circuits mounted on these devices increases, it becomes difficult to design connections between the electrical circuits. For this reason, an overvoltage higher than the allowable input voltage may be applied to the electrical circuit due to insufficient confirmation of the specifications of each device or a design error in the connection between electrical devices.

According to the present embodiment, it is possible to protect the inverter circuit 20 from such overvoltage, and even if some kind of malfunction occurs in the inverter circuit 20, it is possible to determine whether or not an overload has been applied to the inverter circuit 20, and whether or not the overload has occurred. The level can be easily detected.

(Embodiment 2)
FIG. 3 shows a schematic configuration diagram of an overload detection circuit according to this embodiment, and FIG. 4 shows a schematic configuration diagram of another overload detection circuit. In addition, in FIGS. 3 and 4, the same parts as in Embodiment 1 are given the same reference numerals and detailed explanations are omitted.

The configuration according to this embodiment shown in FIG. 3 differs from the configuration shown in Embodiment 1 in that it includes a diode Di connected to a power supply voltage terminal 21 and a GND terminal 22. The cathode and anode of the diode Di are connected to the power supply voltage terminal 21 and the GND terminal 22, respectively.

By configuring the overload detection circuit 10 as shown in FIG. 3, in a reverse connection state where a negative voltage is applied between the GND terminal 22 and the power supply voltage terminal 21, the diode Di becomes forward biased, and the diode Di becomes Current also flows. By appropriately adjusting the forward resistance value of the diode Di, the combined resistance value of the Zener diode ZD, and the first to third resistors R1, R2, and R3, the first to third resistors R1, R2, and R3 can be adjusted. Current can be passed from the GND terminal 22 to the power supply voltage terminal 21 without burning out or partially melting.

As a result, as shown in the first embodiment, even if a negative voltage is applied between the GND terminal 22 and the power supply voltage terminal 21, the negative voltage is not applied inside the inverter circuit 20, and the inverter circuit 20 can be protected.

Further, even if a negative voltage is applied, the first to third resistors R1, R2, and R3 are not burnt out or partially melted, so that the overload detection circuit 10 can be continuously operated. Thereby, positive overvoltage applied between the GND terminal 22 and the power supply voltage terminal 21 can be reliably detected.

Note that if the absolute value of the negative voltage is large and the diode Di is disconnected, depending on the current flowing through the first to third resistors R1, R2, R3, the consumption in the first to third resistors R1, R2, R3 may The amount of power may exceed the respective rated power. In this case, the first to third resistors R1, R2, and R3 may be burnt out or partially melted, but the inverter circuit 20 is reliably protected. Also, by checking whether any of the first to third resistors R1, R2, and R3 is burnt out or partially melted, it is possible to know whether the applied negative voltage is equal to or higher than a predetermined value. be able to. Furthermore, by checking which resistors are burnt out or partially melted, the level of the applied negative voltage can be estimated.

In addition, as shown in FIG. 4, the arrangement of the diode Di within the overload detection circuit 10 may be changed. In this case, the diode Di is connected in parallel with the capacitor C and the first to third resistors R1, R2, and R3. Further, the cathode of the diode Di is connected to the anode of the Zener diode ZD, and the anode of the diode Di is connected to the GND terminal 22.

In this way, even if a negative voltage is applied between the GND terminal 22 and the power supply voltage terminal 21, the negative voltage is not applied inside the inverter circuit 20, and the inverter circuit 20 can be protected. In addition, by appropriately adjusting the forward resistance value of the diode Di and the combined resistance value of the first to third resistors R1, R2, and R3, the first to third resistors R1, R2, and R3 can be burnt out or A current can be passed from the GND terminal 22 to the power supply voltage terminal 21 without partially melting it. Furthermore, positive overvoltage applied between the GND terminal 22 and the power supply voltage terminal 21 can be reliably detected.

(Other embodiments)
In the first embodiment, the first to third resistors R1, R2, and R3 have the same resistance value, but are set to have different rated powers. However, the present invention is not particularly limited to this, and for example, the rated power may be the same, but the resistance values may be different from each other. Further, both the resistance value and the rated power may be different from each other. It is sufficient that the difference between the rated power and the amount of power consumed when overvoltage is applied is different for each resistor. By doing so, it is possible to reliably detect whether an overload has been applied to the inverter circuit 20 and the level of the overload.

Further, the number of resistors provided in the overload detection circuit 10 is not limited to three, but may be more than this, or may be two. By increasing the number of resistors, the circuit scale increases slightly, but it becomes possible to evaluate the overvoltage level in more detail.

Further, in the first and second embodiments, an example was shown in which the overload detection circuit 10 is connected to the inverter circuit 20, but the overload detection circuit 10 is connected to an electric circuit other than the inverter circuit 20. may have been done.

Further, the voltage applied to the power supply voltage terminal 21 of the inverter circuit 20 is not limited to +12V or +24V, and may be changed as appropriate depending on the specifications, connection state, etc. of the battery constituting the power supply. For example, a voltage of +48V may be applied to the power supply voltage terminal 21. In that case, it is preferable that the breakdown voltage of the Zener diode ZD is set to more than twice this voltage, about 100V or more. If it is difficult to set with a single Zener diode ZD, a plurality of Zener diodes ZD may be connected in series.

The overload detection circuit of the present invention can reliably detect the presence or absence of overvoltage and its level with a simple configuration, and is useful when applied to electric circuits installed in on-vehicle equipment.

C Capacitor Di Diode R1 First resistor R2 Second resistor R3 Third resistor ZD Zener diode 10 Overload detection circuit 20 Inverter circuit 21 Power supply voltage terminal (high potential side input terminal)
22 GND terminal (low potential side input terminal)

Claims (4)

An overload detection circuit connected between a high potential side input terminal and a low potential side input terminal of an electric circuit,
a Zener diode whose cathode is connected to the high potential side input terminal;
a capacitor connected to the anode of the Zener diode and the low potential side input terminal;
At least a plurality of resistors each connected in parallel with the capacitor between the anode of the Zener diode and the low potential side input terminal,
Each of the plurality of resistors is different from each other in at least one of resistance value and rated power,
further comprising a diode electrically connected to the high potential side input terminal and the low potential side input terminal,
A cathode of the diode is electrically connected to the high potential input terminal, an anode of the diode is electrically connected to the low potential input terminal, and
the diode is connected in parallel with the capacitor,
An overload detection circuit characterized in that a cathode of the diode is connected to an anode of the Zener diode, and an anode of the diode is connected to the low potential side input terminal. The overload detection circuit according to claim 1,
the electrical circuit so that the difference between the potential difference between the high potential side input terminal and the low potential side input terminal and the breakdown voltage of the Zener diode is equal to or less than a predetermined value when an overload is applied to the electric circuit; An overload detection circuit characterized in that a composite resistance value of a plurality of resistors is set. The overload detection circuit according to claim 1 or 2 ,
It is characterized by being configured such that it is possible to detect whether an overload is applied to the electric circuit and the level of overload by checking which of the plurality of resistors is burnt out or partially melted. Overload detection circuit. The overload detection circuit according to any one of claims 1 to 3 ,
An overload detection circuit, wherein the electric circuit and the overload detection circuit are each mounted on a vehicle.

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