JP7396240B2 - Overcurrent protection circuit - Google Patents

Description

The present disclosure relates to overcurrent protection circuits.

A circuit including a power source and a load that receives power from the power source is sometimes provided with an overcurrent protection circuit that prevents overcurrent from flowing through the power source or the load due to short circuits or the like. For example, Patent Document 1 discloses an output overcurrent protection device for an arc welding power source. On the other hand, control devices such as control panels and switchboards are often provided with circuit protectors that protect loads by tripping electrical circuits when overcurrent occurs.

Japanese Patent Application Publication No. 4-220172

The output overcurrent protection device for an arc welding power source disclosed in Patent Document 1 is useful for protecting the arc welding power source. However, in control equipment such as control panels and distribution boards, when the overcurrent protection device that prevents power supply failures is activated, the output current from the power supply does not rise to a value sufficient to operate the circuit protector, and the circuit The protector may not work. In order to protect the power supply, load, etc. circuits in the event of an overcurrent, it is necessary not only to adopt a means to cut off the output current, but also to adjust the output current to a level that does not cause the power supply, load, etc. circuits to fail. is also useful.

An object of the present invention is to provide an overcurrent protection circuit that can reduce the risk of failure of circuits such as power supplies and loads.

An overcurrent protection circuit according to one aspect of the present disclosure includes:
An overcurrent protection circuit for protecting a load driven by DC power output from a DC power supply circuit,
The overcurrent protection circuit is
a current detection unit that detects an output current flowing from the DC power supply circuit to the load;
a threshold setting section that sets a predetermined threshold for the output current;
a timer unit that measures an overcurrent period when the output current exceeds the threshold;
a control unit that controls the DC power supply circuit so that when the output current exceeds the threshold, the output current becomes equal to or less than the threshold;
The threshold setting section changes the threshold to a set value smaller than the threshold when the overcurrent period exceeds a predetermined time period.

According to the overcurrent protection circuit according to the present disclosure, it is possible to reduce the risk of failure of circuits such as a power supply and a load.

FIG. 1 is a circuit diagram showing a configuration example of a power supply system according to a first embodiment of the present disclosure. 2 is a graph showing an example of the operation of the overcurrent protection circuit of FIG. 1. FIG. 2 is a graph schematically showing the relationship between the output current of the ACDC converter of FIG. 1 and time during a period including an overcurrent period. FIG. 2 is a circuit diagram showing a configuration example of a power supply system according to a second embodiment of the present disclosure. 5 is a graph showing an example of the operation of the overcurrent protection circuit shown in FIG. 4. FIG. FIG. 3 is a circuit diagram showing a configuration example of a power supply system according to a third embodiment of the present disclosure. 7 is a graph showing an example of the operation of the overcurrent protection circuit shown in FIG. 6;

Hereinafter, embodiments of an overcurrent protection circuit according to the present disclosure will be described with reference to the accompanying drawings. In the following embodiments, the same or similar components are given the same reference numerals.

1. First embodiment 1-1. Configuration example 1-1-1. Overall Configuration Example FIG. 1 is a circuit diagram showing a configuration example of a power supply system 100 according to a first embodiment of the present disclosure. The power supply system 100 includes an AC power supply 1 , an ACDC converter 2 , a circuit protector 3 , and an overcurrent protection circuit 4 . Power supply system 100 supplies power to load L.

AC power supply device 1 supplies AC power to ACDC converter 2 . For example, the AC power supply device 1 is a commercial power supply. Alternatively, the AC power supply device 1 may include a DC power supply device and an inverter circuit that converts direct current supplied from the DC power supply device into alternating current.

ACDC converter 2 generates DC power using AC power supplied from AC power supply device 1 . The output voltage of the ACDC converter 2 is Vo (see FIG. 2). The ACDC converter 2 is an example of a "DC power supply circuit" of the present disclosure. The DC power supply circuit is, for example, a DC stabilized power supply circuit or a DC non-stabilized power supply circuit. Although not shown, the ACDC converter 2 includes, for example, a transformer such as a transformer that transforms the voltage of AC power supplied from the AC power supply 1, a rectifier circuit that converts the AC power into DC power, and a rectifier circuit that converts the voltage of the AC power supplied from the AC power supply 1. This is a transformer-type circuit that includes a smoothing circuit that smoothes the applied voltage. The ACDC converter 2 may be configured with a switching type circuit that controls on/off of a switching element using control means such as PWM (Pulse Width Modulation) control.

The circuit protector 3 is an overcurrent protection device that protects the load L by tripping the electric circuit when an overcurrent occurs due to a failure such as a short circuit. Circuit protector 3 is arranged between ACDC converter 2 and load L, for example.

The overcurrent protection circuit 4 is a circuit for protecting the load L from overcurrent such as short circuit current. The overcurrent protection circuit 4 is an example of the "first overcurrent protection circuit" of the present disclosure, and the circuit protector 3 is an example of the "second overcurrent protection circuit" of the present disclosure. The overcurrent protection circuit 4 includes a current detection section 41 , a current-voltage conversion circuit 42 , a threshold setting section 43 , a comparator 44 , a control signal transmission circuit 45 , and an ACDC converter control section 46 .

Current detection section 41 detects the output current output from ACDC converter 2 . For example, the current detection section 41 is a shunt resistor. Current detection section 41 is arranged, for example, between ACDC converter 2 and load L. The current-voltage conversion circuit 42 is a circuit that converts the output current output from the ACDC converter 2 into a voltage. The current-voltage conversion circuit 42 may include an amplifier that amplifies the converted voltage. The current-voltage conversion circuit 42 outputs the converted voltage V _DET to the non-inverting input terminal of the comparator 44 .

The threshold setting section 43 is a circuit that sets a predetermined threshold for the output current. In the example shown in FIG. 1, the threshold setting unit 43 outputs the threshold voltage Vth as an example of such a threshold. Details of the threshold setting section 43 will be described later.

The comparator 44 is a comparison circuit that compares the output current output from the ACDC converter 2 and the threshold value set by the threshold value setting section 43, and outputs an output signal indicating the comparison result. In the example shown in FIG. 1, comparator 44 includes a non-inverting input terminal, an inverting input terminal, and an output terminal. A voltage V _DET output from the current-voltage conversion circuit 42 is input to a non-inverting input terminal of the comparator 44 . The threshold voltage Vth output from the threshold setting section 43 is input to the inverting input terminal of the comparator 44 . The comparator 44 compares the voltage V _DET input to the non-inverting input terminal and the voltage Vth input to the inverting input terminal, and outputs an output voltage indicating which one is greater. For example, the comparator 44 outputs a High (H) level signal when V _DET > Vth, that is, when there is an overcurrent, and outputs a Low (L) level signal when V _DET ≦Vt. . Conversely, the comparator 44 may output an L level signal when V _DET >Vth, and output an H level signal when V _DET ≦Vt. However, the present disclosure is not limited thereto, and the comparator may compare the magnitude of two input currents, for example.

The control signal transmission circuit 45 is a circuit that transmits the output signal of the comparator 44 to the ACDC converter control section 46. For example, the control signal transmission circuit 45 is a photocoupler. If a photocoupler is used as the control signal transmission circuit 45, the preceding circuit of the control signal transmission circuit 45 and the ACDC converter control unit 46, which is the subsequent circuit, can be insulated. However, the present disclosure is not limited thereto, and the control signal transmission circuit 45 is one that electrically connects a front-stage circuit of the control signal transmission circuit 45 and an ACDC converter control section 46 that is a rear-stage circuit to transmit signals. It may be.

The ACDC converter control unit 46 controls the output current of the ACDC converter 2 based on the signal input from the comparator 44 via the control signal transmission circuit 45. For example, the ACDC converter control unit 46 controls the output current by controlling the output voltage of the ACDC converter 2. As an example of such control, when the output current output from the ACDC converter 2 exceeds the threshold set by the threshold setting unit 43, the ACDC converter control unit 46 controls the output current to exceed the threshold value set by the threshold setting unit 43. The ACDC converter 2 is controlled as follows. For example, the ACDC converter control unit 46 performs feedback control on the ACDC converter 2 so that the output current becomes equal to a threshold value. In the example of FIG. 1, the ACDC converter control unit 46 performs feedback control of the ACDC converter 2 so that V _DET =Vth. ACDC converter control unit 46 is an example of a “control unit” of the present disclosure.

1-1-2. Configuration Example of Threshold Setting Unit In FIG. 1, the threshold setting unit 43 includes a reference voltage power supply 431, a voltage attenuation circuit 432, a voltage attenuation value setting circuit 433, and a timer circuit 434. The reference voltage power supply 431 is a constant voltage source that outputs a predetermined reference voltage V1.

The voltage attenuation circuit 432 is, for example, a circuit that divides the reference voltage V1 and attenuates the reference voltage V1. In the example shown in FIG. 1, voltage attenuation circuit 432 includes a resistor R1 and a resistor R2 connected in series with resistor R1. One end of the resistor R1 is connected to the reference voltage power supply 431, and the other end is connected to one end of the resistor R2 at the connection point A. The other end of resistor R2 is grounded. Connection point A is connected to the inverting input terminal of comparator 44. Voltage attenuation circuit 432 outputs threshold voltage Vth from connection point A to the inverting input terminal of comparator 44.

The voltage attenuation value setting circuit 433 is a circuit for setting the attenuation value or degree of attenuation of the reference voltage V1 by the voltage attenuation circuit 432. The voltage attenuation value setting circuit 433 includes a resistor R3 and a switching element Q1 connected in series between the connection point A and the ground voltage. The switching element Q1 switches between connection (on) and non-connection (off) between the switching element Q1 and the ground voltage according to the output signal voltage of the timer circuit 434. The switching element Q1 is, for example, a transistor such as a MOSFET (metal-oxide-semiconductor field-effect transistor) or a bipolar transistor. In the illustrated example, the switching element Q1 is a MOSFET, and the output terminal of the timer circuit 434 is connected to the gate of the switching element Q1. The gate of the MOSFET is an example of a control terminal of the switching element of the present disclosure. However, the present disclosure is not limited thereto, and the switching element Q1 may be a mechanical switch.

When the threshold voltage Vth at the connection point A when the switching element Q1 is on and off is Vth(ON) and Vth(OFF), respectively, the relationship of Vth(ON)<Vth(OFF) holds.

The above Vth (OFF) and Vth (ON) can be set to desired values by changing the circuit design such as changing the number of resistors.

The timer circuit 434 is a circuit that measures the overcurrent period when the output current exceeds a threshold value. The timer circuit 434 is an example of a "timekeeping section" of the present disclosure. The timer circuit 434 measures the time period (overcurrent period) during which the output signal of the comparator 44 is an H level signal (or an L level signal) representing overcurrent. Timer circuit 434 turns on switching element Q1 when the overcurrent period exceeds a predetermined period _tth . The timer circuit 434 turns off the switching element Q1 when the initial state and the overcurrent period do not exceed a predetermined period _tth .

As described above, when the overcurrent period exceeds the predetermined period _tth , the switching element Q1 is turned on and the resistor R3 is grounded, so that the threshold voltage Vth at the connection point A becomes Vth( OFF) to Vth(ON). In this way, when the overcurrent period exceeds the predetermined period _tth , the threshold setting unit 43 sets the threshold voltage Vth(OFF) to the set value Vth(ON), which is smaller than the threshold voltage. ).

The timer circuit 434 is realized, for example, by a delay circuit included in the S809xxC series manufactured by ABLIC Inc.

1-2. Operation Example FIG. 2 is a graph showing an operation example of the overcurrent protection circuit 4 of FIG. 1. The horizontal axis of the graph in FIG. 2 represents the output current of the ACDC converter 2, and the vertical axis represents the output voltage of the ACDC converter 2. In FIG. 2, I _R represents the rated current of the load L.

The graph shown by the solid line in FIG. 2 shows the output current-output voltage characteristics in the initial period of the overcurrent period. The "initial period" represents the time period from time t0 at which overcurrent occurs to time t1 thereafter. For example, the predetermined period t _th in the above-described timer circuit 434 is designed so that t _th =t1-t0.

On the other hand, the graph shown by the dashed line in FIG. 2 shows the output current-output voltage characteristic in the overcurrent period after time t1. FIG. 3 is a graph schematically showing the relationship between the output current of the ACDC converter 2 and time t during a period including the overcurrent period as described above. In FIG. 3, time t=0 represents the time when ACDC converter 2 starts supplying power to load L.

(Initial period)
An example of the operation of the overcurrent protection circuit 4 in the initial period will be described with reference to FIGS. 1 to 3. As shown in the solid line portion of FIG. 2 and FIG. 3, if a short circuit occurs in the load L at time t0 and an overcurrent flows through the load L, the ACDC converter control unit 46 controls the ACDC converter 2 to Let the output current be the first threshold current I _th1 . The first threshold current I _th1 is designed to be, for example, 170% of the rated current I _R. A specific example of this operation is as follows.

In FIG. 1, a current detection unit 41 detects the output current flowing from the ACDC converter 2 to the load L, and a current-voltage conversion circuit 42 converts the detected current into a voltage V _DET . Comparator 44 compares V _DET and threshold voltage Vth (OFF) output from threshold setting section 43 and outputs an output voltage indicating which one is larger. For example, when V _DET >Vth (OFF), that is, when there is an overcurrent, the comparator 44 outputs an H level signal indicating the overcurrent. Next, control signal transmission circuit 45 transmits an H level signal indicating overcurrent to ACDC converter control section 46 . The ACDC converter control unit 46 controls the ACDC converter 2 to reduce the output current so that V _DET =Vth (OFF). The threshold setting unit 43 is designed so that V _DET =Vth (OFF) when the output current reaches the first threshold current I _th1 . Therefore, the ACDC converter control unit 46 controls the ACDC converter 2 so that the output current becomes the first threshold current I _th1 .

With the above configuration, the overcurrent protection circuit 4 can prevent a current exceeding the first threshold current I _th1 from flowing to the load L, and can protect the load L from overcurrents such as short circuit current. can.

Further, for example, the circuit protector 3 is selected or designed so as to cut off the current supply to the load L by the ACDC converter 2 when the first threshold current I _th1 flows through the circuit protector 3. Therefore, the current control by the overcurrent protection circuit 4 does not prevent the circuit protector 3 from interrupting the current. In this way, the overcurrent protection circuit 4 not only protects the load L by reducing the output current, but also operates the circuit protector 3 in an overcurrent state to more reliably protect the load L.

(period after initial period)
After the initial period has elapsed, at time t1, the ACDC converter control unit 46 controls the ACDC converter 2 to set the output current to the second threshold current I _th2 . The second threshold current I _th2 is designed to be, for example, 110% of the rated current I _R. A specific example of this operation is as follows.

As mentioned above, the timer circuit 434 measures the overcurrent period. Timer circuit 434 turns on switching element Q1 when the overcurrent period exceeds a predetermined period _tth . As a result, the threshold voltage Vth at the connection point A changes from Vth (OFF) to Vth (ON). The ACDC converter control unit 46 controls the ACDC converter 2 to reduce the output current so that V _DET =Vth (ON). The threshold setting unit 43 is designed so that V _DET =Vth (ON) when the output current reaches the second threshold current I _th2 . Therefore, the ACDC converter control unit 46 controls the ACDC converter 2 so that the output current becomes the second threshold current I _th2 .

With the above-described configuration, the overcurrent protection circuit 4 changes the output current to the second threshold, which is smaller than the first threshold current I _th1 , when the overcurrent period exceeds the predetermined period t _th . The value current I _th2 can be changed. As a result, the overcurrent protection circuit 4 prevents a current that greatly exceeds the rated current I _R from flowing to the load L, even if the circuit protector 3 is not present or does not operate due to a failure. Risks such as heat generation in the internal circuit and failure of the ACDC converter 2 can be reduced.

1-3. Effects, etc. As described above, the overcurrent protection circuit 4 includes the current detection section 41, the threshold setting section 43, the timer circuit 434, and the ACDC converter control section 46. Current detection section 41 detects the output current flowing from ACDC converter 2 to load L. The threshold setting section 43 sets a predetermined threshold for the output current. Timer circuit 434 times the overcurrent period when the output current exceeds the threshold. The ACDC converter control unit 46 controls the ACDC converter 2 so that the output current is equal to or less than the threshold value when the output current exceeds the threshold value. The threshold setting unit 43 changes the threshold to a set value smaller than the threshold when the overcurrent period exceeds a predetermined time period t _th .

With this configuration, the overcurrent protection circuit 4 prevents a current exceeding the threshold set by the threshold setting section 43 from flowing into the load L, and reduces the risk of failure of the load L, ACDC converter 2, etc. can be reduced. In addition, the overcurrent protection circuit 4 sets a high threshold value when the overcurrent period is less than or equal to a predetermined time period _tth , and sets the threshold value to a high value when the overcurrent period exceeds the predetermined time period _tth . Change the setting value to a value smaller than the threshold value. As a result, when the overcurrent period is less than or equal to a predetermined time period t _th , the circuit protector 3 provided inside the load L or between the ACDC converter 2 and the load L is operated to ensure that the load is L can be protected.

The ACDC converter control section 46 may control the ACDC converter control section 46 so that the output current becomes equal to the threshold value during the overcurrent period.

In addition to the above-mentioned effects, by performing such feedback control, the overcurrent protection circuit 4 can temporally stabilize the output current.

A description will be given of how the overcurrent protection circuit 4 can operate the circuit protector 3 to more reliably protect the load L. The overcurrent protection circuit included in the power supply itself not only limits the output current when an overcurrent occurs, but also reduces the output voltage (dropping) depending on the load condition such as impedance during overload. There are many things to do. Furthermore, overcurrent protection circuits are also known that cause the power supply to perform an intermittent operation in which the output is switched on and off intermittently when the voltage falls below a predetermined standard.

When an intermittent operation type overcurrent protection circuit is adopted, it is difficult to control the on-time during intermittent operation and the peak current during on-time using an inexpensive circuit. Therefore, it is difficult to reliably trip the circuit protector during the on-time. An intermittent operation type overcurrent protection circuit may not be able to start up if there is capacity on the load side.

An overcurrent protection circuit that continues to flow a constant current when an overcurrent occurs is easier to design to reliably trip a circuit protector than an intermittent operation type. However, if the threshold current at which the circuit protector trips is set to a large value, there is a risk of heat generation in the internal circuit of the load L, failure of the ACDC converter 2, etc. when an overcurrent occurs. Therefore, a circuit protector with a large tripping threshold current cannot be used.

On the other hand, the overcurrent protection circuit 4 is not of an intermittent operation type, but is a type of circuit that continues to flow a constant current, but when the overcurrent period is less than a predetermined time period _tth , the threshold value is set high. , when a predetermined time period t _th is exceeded, the threshold value is changed to a set value smaller than the threshold value. As a result, when the overcurrent period is less than or equal to a predetermined time period t _th , the circuit protector 3 provided inside the load L or between the ACDC converter 2 and the load L is operated to ensure that the load is L can be protected. By operating in this manner, the overcurrent protection circuit 4 also prevents a current exceeding the threshold set by the threshold setting section 43 from flowing to the load L, and protects the load L, the ACDC converter 2, etc. The risk of circuit failure can be reduced. The overcurrent protection circuit 4 can achieve the above effects with an inexpensive circuit.

2. Second Embodiment FIG. 4 is a circuit diagram showing a configuration example of a power supply system 200 according to a second embodiment of the present disclosure. Overcurrent protection circuit 204 of power supply system 200 of FIG. 4 differs from overcurrent protection circuit 4 of power supply system 100 of FIG. 1 in the following points. That is, the threshold setting section 243 of the overcurrent protection circuit 204 in FIG. 4 includes a resistor R4, a switching element Q2, and a diode in addition to the configuration of the threshold setting section 43 of the overcurrent protection circuit 4 in FIG. D1 and a Zener diode D2.

Resistor R4 is connected in series with switching element Q2 between connection point A and ground voltage. The switching element Q2 is, for example, a transistor such as a MOSFET or a bipolar transistor, but is not limited thereto, and may be a mechanical switch.

The anode of the diode D1 is connected to the output terminal of the timer circuit 434, and the cathode is connected to the gate of the switching element Q2. The anode of the Zener diode D2 is connected to the gate of the switching element Q2, and the cathode is connected to the + side output terminal (voltage Vo) of the ACDC converter 2.

FIG. 5 is a graph showing an example of the operation of the overcurrent protection circuit 204 shown in FIG. When the graph of FIG. 5 is compared with the graph showing the operation example of the overcurrent protection circuit 4 of FIG. 2, it shows a current-voltage characteristic different from the current-voltage characteristic shown in FIG. 2 when the output voltage is Vz or less. Here, Vz is the Zener voltage of the Zener diode D2.

Specifically, in the initial period of the overcurrent period, when the output voltage of ACDC converter 2 is lower than Vz, both switching elements Q1 and Q2 are off. The threshold voltage Vth (OFF, OFF) at the connection point A in this case has the highest value. The threshold setting unit 243 is designed so that V _DET =Vth (OFF, OFF) when the output current reaches the third threshold current I _th3 . Therefore, the ACDC converter control unit 46 controls the ACDC converter 2 so that the output current becomes the third threshold current I _th3 .

In the initial period of the overcurrent period, when the output voltage of ACDC converter 2 is higher than Vz, switching element Q1 is off and switching element Q2 is on. In this case, the threshold voltage Vth (OFF, ON) at the connection point A has an intermediate value lower than Vth (OFF, OFF). The threshold setting unit 243 is designed so that V _DET =Vth (OFF, ON) when the output current reaches the fourth threshold current I _th4 . Therefore, the ACDC converter control unit 46 controls the ACDC converter 2 so that the output current becomes the fourth threshold current I _th4 that is smaller than the third threshold current I _th3 .

After the initial period of the overcurrent period has elapsed, both switching elements Q1 and Q2 are turned on by the output from the timer circuit 434, regardless of whether the output voltage of the ACDC converter 2 is lower than or equal to Vz. In this case, the threshold voltage Vth (ON, ON) at the connection point A has a minimum value lower than Vth (OFF, ON). The threshold setting unit 243 is designed so that V _DET =Vth (ON, ON) when the output current reaches the fifth threshold current I _th5 . Therefore, the ACDC converter control unit 46 controls the ACDC converter 2 so that the output current becomes the fifth threshold current I _th5 which is smaller than the fourth threshold current I _th4 .

As described above, when the output voltage of the ACDC converter 2 is less than or equal to the predetermined voltage Vz, the threshold setting unit 243 sets the initial value of the threshold value so that the output voltage of the ACDC converter 2 is lower than the predetermined voltage Vz. It is set to a value I _th3 that is larger than the value I _th4 that is set when it is large.

With this configuration, the output current can be precisely designed according to the output voltage of the ACDC converter 2. For example, in a relatively safe case where the output voltage is Vz or lower, by setting the initial value of the threshold to a large value I _th3 , the circuit protector 3 can be operated. Therefore, the load L and/or the ACDC converter 2 can be protected more reliably.

3. Third Embodiment FIG. 6 is a circuit diagram showing a configuration example of a power supply system 300 according to a third embodiment of the present disclosure. Overcurrent protection circuit 304 of power supply system 300 of FIG. 6 differs from overcurrent protection circuit 4 of power supply system 100 of FIG. 1 in the following points. That is, the threshold setting section 343 of the overcurrent protection circuit 304 in FIG. 6 includes a voltage attenuation value setting circuit 433a in place of the voltage attenuation value setting circuit 433 in the threshold setting section 43 in FIG. The voltage attenuation value setting circuit 433a in FIG. 6 includes an NTC (Negative Temperature Coefficient) thermistor T in place of the resistor R3 in the voltage attenuation value setting circuit 433 in FIG.

The NTC thermistor T is an example of the "temperature detection section" of the present disclosure. The temperature detection section is not limited to the NTC thermistor T, but may be a PTC (Positive Temperature Coefficient) thermistor or a CTR (Critical Temperature Resistor) thermistor.

FIG. 7 is a graph showing an example of the operation of the overcurrent protection circuit 304 shown in FIG. The graph in FIG. 7 is compared with the graph showing the operation example of the overcurrent protection circuit 4 in FIG. 2 in that the changed threshold current after the initial period of the overcurrent period is smaller as the temperature T becomes higher. different. In the example shown in FIG. 7, the sixth threshold current I _th6 represents the threshold current when the temperature T is 25° C. after the initial period of the overcurrent period (switch Q1 is on). There is. The sixth threshold current I _th6 is designed to be, for example, 110% of the rated current I _R. Further, in the example shown in FIG. 7, the seventh threshold current I _th7 is the threshold current when the temperature T is 100° C. after the initial period of the overcurrent period has elapsed (switch Q1 is on). represents. The seventh threshold current I _th7 is designed to be, for example, 80% of the rated current I _R.

The NTC thermistor T is placed, for example, near a component, circuit, etc. that generates heat when current flows therethrough. The NTC thermistor T is placed near, for example, adjacent to, for example, heat-sensitive components, circuits, and the like. The NTC thermistor T is placed, for example, near internal wiring, a capacitor, etc. of the ACDC converter 2.

With this configuration, the overcurrent protection circuit 304 reduces the set value of the threshold current after the initial period of the overcurrent period has elapsed according to the temperature T, and reduces heat generation in the circuits forming the power supply system 300. I can do it. Thereby, failures due to heat in the circuits forming the power supply system 300 can be prevented.

(Modified example)
Although the embodiments of the present disclosure have been described in detail above, the above descriptions are merely illustrative of the present disclosure in all respects. Various improvements and modifications can be made without departing from the scope of this disclosure. For example, the following changes are possible. In addition, below, the same code|symbol is used regarding the same component as the said embodiment, and description is abbreviate|omitted suitably about the point similar to the said embodiment. The following modifications can be combined as appropriate.

In FIG. 1, an example has been described in which the overcurrent protection circuit 4 according to the first embodiment of the present disclosure includes the current-voltage conversion circuit 42 that converts the output current output from the ACDC converter 2 into voltage. In this example, the comparator 44 compares the voltage V _DET converted by the current-voltage conversion circuit 42 and the threshold voltage Vth output from the threshold setting section 43 . In this example, the ACDC converter control unit 46 performs feedback control on the ACDC converter 2 so that V _DET =Vth. However, the overcurrent protection circuit 4 according to the present disclosure is not limited to the above example, as long as it controls the ACDC converter 2 so that the output current is equal to or less than a threshold value. For example, the overcurrent protection circuit 4 may not include the current-voltage conversion circuit 42. In this case, the ACDC converter control section 46 of the overcurrent protection circuit 4 may control the output current detected by the current detection section 41 so that it becomes equal to or less than a predetermined threshold value.

Further, in the example of FIG. 1, the current detection unit 41 is connected to the - side output terminal of the ACDC converter 2, but the present disclosure is not limited to this, and the current detection unit 41 is connected to the + side output terminal of the ACDC converter 2. may be connected to.

Furthermore, in the example of FIG. 1, the voltage V _DET output from the current-voltage conversion circuit 42 is input to the non-inverting input terminal of the comparator 44, and the threshold voltage output from the threshold setting unit 43 is input to the inverting input terminal. It has been explained that Vth is input. However, the comparator 44 may adjust the output signal based on whether or not V _DET exceeds Vth, and the present disclosure is not limited thereto. For example, even if the voltage V _DET output from the current-voltage conversion circuit 42 is input to the inverting input terminal of the comparator 44 and the threshold voltage Vth output from the threshold setting section 43 is input to the non-inverting input terminal, good.

1 AC power supply device 2 ACDC converter (DC power supply circuit)
3 circuit protector 4,204,304 overcurrent protection circuit 41 current detection section 42 current voltage conversion circuit 43,243,343 threshold setting section 44 comparator 45 control signal transmission circuit 46 control section 46 converter control section 100,200, 300 Power supply system 431 Reference voltage power supply 432 Voltage attenuation circuit 433, 433a Voltage attenuation value setting circuit 434 Timer circuit (timekeeping section)
R1, R2, R3, R4 Resistor Q1, Q2 Switching element T NTC thermistor

Claims (6)

An overcurrent protection circuit for protecting a load driven by DC power output from a DC power supply circuit,
The overcurrent protection circuit is
a current detection unit that detects an output current flowing from the DC power supply circuit to the load;
a threshold setting section that sets a predetermined threshold for the output current;
a timer unit that measures an overcurrent period when the output current exceeds the threshold;
a control unit that controls the DC power supply circuit so that when the output current exceeds the threshold, the output current becomes equal to or less than the threshold;
The threshold setting unit is an overcurrent protection circuit that changes the threshold to a set value smaller than the threshold when the overcurrent period exceeds a predetermined time period. The overcurrent protection circuit according to claim 1, wherein the control unit controls the DC power supply circuit so that the output current becomes equal to the threshold value during the overcurrent period. The overcurrent protection circuit according to claim 1 or 2, wherein the threshold setting section changes the initial value of the threshold according to the output voltage of the DC power supply circuit. The threshold setting section sets the initial value of the threshold when the output voltage of the DC power supply circuit is below a predetermined voltage, and sets the initial value of the threshold when the output voltage of the DC power supply circuit is higher than the predetermined voltage. The overcurrent protection circuit according to claim 3, wherein the overcurrent protection circuit is set to a value larger than the set value. The overcurrent protection circuit further includes a temperature detection section that detects the temperature of the DC power supply circuit or the overcurrent protection circuit,
The overcurrent protection circuit according to any one of claims 1 to 4, wherein the threshold setting section changes the set value according to the temperature detected by the temperature detection section. The overcurrent protection circuit according to claim 5, wherein the threshold value setting section decreases the set value as the temperature detected by the temperature detection section increases.

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