JP2017229170A - Inrush current prevention circuit and abnormality detection method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inrush current prevention circuit capable of detecting connection abnormality at a relay contact, using a simple configuration.SOLUTION: An inrush current prevention circuit provided in a load drive circuit for performing power variable drive on a load comprises: a limit resistor for limiting inrush current at the time of starting the load drive circuit; a relay including a relay contact connected in parallel to the limit resistor; and a control circuit for performing power variable drive on the load. The control circuit executes: initial drive processing (S30) that at the time of starting the load drive circuit, drives the load for a predetermined period after a power supply voltage increases to a predetermined voltage, using power that decreases the power supply voltage by a predetermined amount in the case that the power is supplied via the limit resistor; determination processing (S40) that determines whether or not the power supply voltage has decreased by the predetermined amount during the initial drive processing; and abnormality determination processing (S50) that when it is determined by the determination processing that the power supply voltage has decreased by the predetermined amount, determines connection abnormality of the relay contact.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an inrush current prevention circuit provided in a load drive circuit that drives a load by changing supplied power.

  A conventional inrush current prevention circuit is disclosed in Patent Document 1, for example. Patent Document 1 discloses an inrush current prevention circuit including a resistor provided in a current path to a compressor motor as a load and a relay contact connected in parallel to the resistor. In this case, at the start of energization of the compressor motor, the relay contact is turned off for about 2 seconds and the smoothing capacitor is charged through a resistor to prevent the inrush current from flowing into the smoothing capacitor. After about 2 seconds, the relay contact is turned on, and the compressor motor is energized through the relay contact.

JP 2001-56170 A

  However, in the conventional inrush current prevention circuit, when the relay contact is functioning normally, although desired power can be supplied to the load via the relay contact, dust or the like adheres to the relay contact, When a failure occurs in the connection of the relay contact, there is a possibility that the load cannot be controlled in a desired control form. Therefore, there has been a demand for a technique for detecting a connection abnormality of a relay contact with a simple configuration in an inrush current prevention circuit having such a resistor and a relay contact.

  The technology disclosed in the present specification has been completed based on the above circumstances, and an inrush current prevention circuit and an inrush current prevention circuit capable of detecting a relay contact connection abnormality with a simple configuration. An abnormality detection method is provided.

  The inrush current prevention circuit disclosed in the present specification is an inrush current prevention circuit provided in a load drive circuit that drives a load with variable power, and is connected in series to a power supply line that supplies a drive current to the load. A limiting resistor for limiting an inrush current at the start of the load driving circuit; a smoothing capacitor connected between the power supply line and the ground line on the load side of the limiting resistor; and a relay connected in parallel to the limiting resistor A relay that includes a contact and closes the relay contact when a power supply voltage that is a charging voltage of the smoothing capacitor increases to a predetermined voltage, and supplies the drive current to the load via the relay contact; and the power supply voltage And a control circuit that variably controls the load, and the control circuit is configured such that when the load driving circuit is activated, the power supply voltage is: An initial driving process for driving the load with a predetermined amount of power when the load is supplied via the limiting resistor after increasing to a predetermined voltage, and during the initial driving process. A determination process for determining whether or not the power supply voltage has decreased by the predetermined amount, and an abnormality for determining that the relay contact is abnormal when the determination process determines that the power supply voltage has decreased by the predetermined amount. And a determination process.

According to this configuration, by performing the initial driving process at the time of starting the load driving circuit, when the relay contact is not normally closed, a current flows through the power supply line via the limiting resistor, and a voltage drop due to the limiting resistor occurs. . At that time, due to the discharge of the smoothing capacitor, the charging voltage of the smoothing capacitor, that is, the power supply voltage is lowered. Therefore, by appropriately setting the predetermined amount of power supply voltage drop and the power to reduce the power supply voltage by a predetermined amount when supplied via the limiting resistor, the power supply voltage is determined by the initial drive process and the determination process. When a predetermined amount of decrease is determined, an abnormality of the relay contact can be detected. At that time, the abnormality detection can be performed with the existing circuit configuration. That is, no additional circuit configuration for detecting an abnormality is required. Therefore, it is possible to detect a connection abnormality of the relay contact with a simple configuration.
Here, “relay contact connection abnormality” includes connection abnormality due to the relay contact itself due to dust and the like, and connection abnormality due to relay malfunction. In addition, the “predetermined period”, “predetermined amount of power supply voltage decrease”, and “power that decreases the power supply voltage that reaches the predetermined voltage when supplied via the limiting resistor” are the resistance of the limiting resistor. Based on the value or the like, the value is determined in advance by experiments or the like in relation to each other.

In the inrush current prevention circuit, the voltage detection circuit is a voltage dividing circuit that detects a divided voltage obtained by dividing the power supply voltage, and the inrush current prevention circuit further includes the divided voltage and a reference voltage. In comparison, the control circuit includes a comparison circuit that generates a comparison signal, and the control circuit executes the determination process based on the comparison signal during the initial drive process, and the divided voltage decreases to less than the reference voltage. The abnormality determination process may be executed when the comparison signal indicating that the error has occurred is received.
According to this configuration, the predetermined amount of decrease in the power supply voltage for detecting the relay contact connection abnormality can be appropriately set according to the abnormality detection state, based on the set value of the reference voltage. For example, the predetermined amount of reduction can be set small by setting the reference voltage to a value with a small difference from the divided voltage of the power supply voltage in the steady state. On the other hand, by setting the reference voltage to a value having a large difference from the divided voltage, the predetermined amount of decrease can be set large.

In the inrush current prevention circuit, the control circuit may execute a notification process for notifying the abnormality of the relay contact when executing the abnormality determination process.
According to this configuration, it is possible to prompt the user to take countermeasures by notifying the user of abnormality of the relay contact.

In the inrush current prevention circuit, the load is a motor that is driven at least at a high speed and a low speed as the variable power drive, and the control circuit is configured to perform the predetermined operation at the start-up in the initial drive process. During the period, the motor may be driven at the high speed.
According to this configuration, when the load is a motor, it is possible to drive at high power by driving at high speed. As a result, the amount of decrease in the power supply voltage when the relay contact is abnormal can be increased, and the abnormality detection of the relay contact is facilitated.

  An abnormality detection method for an inrush current prevention circuit disclosed in the present specification is a method for detecting an abnormality in an inrush current prevention circuit provided in a load drive circuit that drives a load with variable power, and the inrush current prevention circuit The circuit is connected in series to a power supply line that supplies a drive current to the load, and a limiting resistor that limits an inrush current at the time of starting the load driving circuit, and on the load side of the limiting resistor, the power supply line and the ground line A smoothing capacitor connected in between, and a relay contact connected in parallel to the limiting resistor, the relay contact is closed when a power supply voltage that is a charging voltage of the smoothing capacitor increases to a predetermined voltage, and the relay A relay for supplying the drive current to the load via a contact, and an abnormality detection method for the inrush current prevention circuit includes the power supply when the load drive circuit is activated. An initial driving step of driving the power supply with a predetermined amount of power when the load is supplied via the limiting resistor after the voltage has increased to the predetermined voltage; and the initial driving. A determination step of determining whether or not the power supply voltage has decreased by a predetermined amount during the process, and a determination that the relay contact is abnormal when it is determined in the determination step that the power supply voltage has decreased by the predetermined amount An abnormality determination step.

  In the abnormality detection method for the inrush current prevention circuit, the load is a motor that is driven at least at a high speed and a low speed as the power variable drive, and the initial drive step includes the predetermined period, The motor may be driven at the high speed.

  According to the inrush current preventing circuit of the present invention, it is possible to detect an abnormal connection of the relay contacts with a simple configuration.

The block diagram which shows the structure of the motor drive circuit provided with the inrush current prevention circuit which concerns on this invention Flow chart showing detection procedure of relay contact abnormality Schematic time chart showing operation of inrush current prevention circuit when relay is abnormal Schematic time chart showing the operation of the inrush current prevention circuit when the relay is normal

An embodiment according to the present invention will be described with reference to FIGS.
1. Configuration of Motor Drive Circuit In this embodiment, the motor drive circuit 1 is provided in an ice making machine and drives a variable speed (variable power) fan motor 50 that cools the condenser of the ice making machine as a load. In the present embodiment, the fan motor 50 is, for example, an inverter built-in type three-phase DC brushless motor.

The motor drive circuit 1 drives the fan motor 50 by changing the rotational speed of the fan motor 50 (hereinafter simply referred to as “speed”) according to the ambient temperature. When the ambient temperature is low, for example, it is driven at a low speed of 600 r / min. When the ambient temperature is high, for example, it is driven at a high speed of 1200 r / min, and at an intermediate temperature, for example, at a medium speed of 900 r / min. To drive. Normally, the power consumption increases as the speed of the fan motor 50 increases. In other words, the motor drive circuit 1 drives the fan motor 50 in a variable manner. The motor drive circuit 1 is an example of a load drive circuit.
In the present embodiment, the fan motor 50 is driven at a low speed, a medium speed, and a high speed, and is at least driven at a low speed and a high speed. That is, it is assumed that the power usage area of the fan motor 50 is almost the entire power variable range, but the power usage area is not limited to this. For example, the power usage area may be only a low power area lower than the intermediate power of the power variable range. In this case, the fan motor 50 is only driven at a low speed.

  The motor is not limited to a fan motor that cools the condenser, and may be, for example, a pump motor of an ice maker, a compressor motor of a refrigerator, a stirring motor of a beer dispenser, or the like. Further, the load driving circuit is not limited to the motor driving circuit. For example, the load driving circuit may be a heater driving circuit that drives a hot wire heater that is a load with variable power, or may be a lamp driving circuit that drives a lamp that is a load with variable power. There may be. In short, the load driving circuit may be a circuit that variably drives the load.

  As shown in FIG. 1, the motor drive circuit 1 includes a power supply circuit 10, an inrush current prevention circuit 20, and a microcomputer board (hereinafter referred to as “microcomputer board”) 30. Note that the configuration is not limited to the configuration shown in FIG. 1. For example, the power supply circuit 10 and the microcomputer board 30 may be provided in one control board.

  As shown in FIG. 1, the power supply circuit 10 includes a power switch SW1, a diode bridge DB1, a limiting resistor 21, a smoothing capacitor C1, a voltage dividing circuit 22, a comparator 23, a relay 24, a DC / DC converter 11, and a low-pass filter 12. , And photocouplers (PC1-PC3).

  The power switch SW1 is a switch for turning on / off the power circuit 10. The power circuit 10 is activated when the power switch SW1 is turned on, and the operation of the power circuit 10 is performed when the power switch SW1 is turned off. Stopped.

  In the present embodiment, the diode bridge DB1 rectifies an AC voltage of 100V. The limiting resistor 21 is connected in series to a power supply line Ls that supplies a drive current to a fan motor (hereinafter simply referred to as “motor”) 50 in the subsequent stage of the diode bridge DB1, and the inrush current when the power switch SW1 is turned on is connected. Restrict.

  The smoothing capacitor C1 is connected between the power supply line Ls and the ground line Lg after the limiting resistor 21, that is, on the motor 50 side. The smoothing capacitor C1 smoothes the rectified AC voltage and generates a DC power supply voltage of about 140 V for driving the fan motor 50. The DC / DC converter 11 converts a DC power supply voltage of 140V into a control DC voltage Vc of 15V.

  The relay 24 includes a relay contact 24a connected in parallel to the limiting resistor 21, and closes the relay contact 24a when the power supply voltage Vs that is the charging voltage of the smoothing capacitor C1 increases to the steady power supply voltage Vss. In the present embodiment, the steady power supply voltage Vss is, for example, DC 140V.

  The voltage dividing circuit 22 includes two voltage dividing resistors R1 and R2, and divides the power supply voltage Vs by the voltage dividing resistors R1 and R2 to generate the divided voltage Vdv. The voltage dividing circuit 22 is an example of a voltage detection circuit that detects the power supply voltage Vs, and indirectly detects the power supply voltage Vs.

  The divided voltage Vdv is input to an inverting input terminal of a comparator (an example of a “comparison circuit”) 23. On the other hand, a reference voltage Vref generated by dividing the control DC voltage Vc by the resistors R3 and R4 is input to the non-inverting input terminal of the comparator 23.

  The comparator 23 compares the divided voltage Vdv and the reference voltage Vref to generate a comparison signal Scom. When the divided voltage Vdv is smaller than the reference voltage Vref, the comparison signal Scom becomes a logic high level, and when the divided voltage Vdv is equal to or higher than the reference voltage Vref, the comparison signal Scom becomes a logic low level.

  When the comparison signal Scom is at a logic high level, the PNP transistor Q1, which is a switch transistor, is not turned on. Therefore, the relay 24 is not excited, and the relay contact 24a is in an open state. This corresponds to a period in which the charging voltage of the smoothing capacitor C1 is low immediately after activation of the motor drive circuit 1 (specifically, the power supply circuit 10) in which the power switch SW1 is turned on, from time t0 to time t1 in FIG. It corresponds to a period. During this period, the smoothing capacitor C1 is charged through the limiting resistor 21. This prevents an inrush current from flowing into the smoothing capacitor C1 when the motor drive circuit 1 is started. Thereby, the smoothing capacitor C1 is protected from the inrush current.

  On the other hand, when the comparison signal Scom is at a logic low level, the PNP transistor Q1 is turned on. As a result, the relay 24 is energized, and the relay contact 24a is closed and becomes conductive. This state corresponds to a period in which the charging of the smoothing capacitor C1 is completed and the charging voltage reaches a predetermined steady power supply voltage Vss, and corresponds to a period after time t1 in FIG.

  The comparison signal Scom is supplied from the collector of the PNP transistor Q1 to the microcomputer board 30 through the photocoupler PC1 as a charge signal Sch with inverted logic. That is, when the charging signal Sch is at a logic high level, the charging completion state of the smoothing capacitor C1 is indicated (see FIG. 4).

  The photocoupler PC2 receives a PWM (pulse width modulation) signal for generating the speed command signal Ssc from the microcomputer board 30. The low-pass filter 12 converts the PWM signal into a speed command signal Ssc that is an analog voltage. The speed command signal Ssc is supplied to the motor 50 and used for speed control of the motor 50. The photocoupler PC3 supplies a rotation pulse signal Srp, which is supplied from the motor 50 and indicates the rotation speed of the motor 50, to the microcomputer board 30.

The microcomputer board 30 includes a CPU 31, a ROM 32, an LED 33, a timer 34, a power supply circuit (not shown), and the like.
The CPU 31 performs variable speed control of the motor 50. Here, the CPU 31 is an example of a “control circuit”, and the speed variable control is an example of “power variable control”. At that time, the CPU 31 calculates the rotation speed (speed) of the motor 50 based on the rotation pulse signal Srp, and changes the pulse width of the PWM signal so that the speed of the motor 50 becomes a predetermined speed. I do. The control circuit is not limited to the CPU, and may be, for example, an ASIC (Application Specific Integrated Circuit).

Further, the CPU 31 executes each process related to abnormality detection of an inrush current prevention circuit, which will be described later, specifically, abnormality detection of the relay contact 24a according to a program stored in the ROM 32.
The ROM 32 stores various programs executed by the CPU 31. When the abnormality of the relay contact 24a is detected, the LED 33 displays the abnormality. The timer 34 measures time when the CPU 31 executes various programs.

  In the present embodiment, the inrush current prevention circuit 20 is configured by a limiting resistor 21, a smoothing capacitor C1, a voltage dividing circuit 22, a comparator 23, a relay 24, a CPU 31, and the like, among the configurations of the motor drive circuit 1.

2. Inrush Current Prevention Circuit Abnormality Detection Processing Next, with reference to FIGS. 2 to 4, the inrush current prevention circuit abnormality detection processing (abnormality detection processing method) executed by the CPU 31 in accordance with the program stored in the ROM 32. explain. It is assumed that the power supply (not shown) of the microcomputer board 30 is started up before the power switch SW1 is turned on, and the CPU 31 is in an operating state.

  If the power switch SW1 of the power supply circuit 10 is turned on at time t0 in FIG. 3 (step S10 in FIG. 2), the CPU 31 in step S20 based on the charging signal Sch (inverted signal of the comparison signal Scom), It is determined whether or not the divided voltage Vdv has reached or exceeded the reference voltage Vref.

  When it is determined that the divided voltage Vdv has not reached the reference voltage Vref or higher (corresponding to the period from time t0 to time t1 in FIGS. 3 and 4), the CPU 31 stands by. On the other hand, when it is determined that the divided voltage Vdv has reached or exceeded the reference voltage Vref (corresponding to the time t1 in FIGS. 3 and 4), the CPU 31 performs a PWM signal for high speed operation (a PWM with a large duty ratio) in step S30. Signal) is generated, and the motor 50 is driven at a high speed (high speed driving), for example, at 1200 r / min for a predetermined period K1 (period from time t1 to time t3 in FIG. 4), for example, for 2-3 seconds. That is, the process of step S30 for operating the motor 50 at a high speed is as follows: “Initial driving for driving the power supply voltage that has reached a predetermined voltage when the load is supplied via a limiting resistor for a predetermined period by a predetermined amount of power. This is an example of “processing or initial driving process”.

  Next, in step S40, the CPU 31 determines whether or not the divided voltage Vdv has decreased below the reference voltage Vref based on the charging signal Sch. Here, the process of step S40 corresponds to a “determination process” and a “determination process”. That is, in the process of step S40, whether the power supply voltage Vs has decreased by a predetermined amount ΔV (here, the difference voltage between the steady power supply voltage Vss and the power supply voltage Vs corresponding to the reference voltage Vref) during the initial drive process. Whether or not is determined based on the charging signal Sch. Here, since the charging signal Sch is an inverted signal of the comparison signal Scom, and the comparison signal Scom is a signal based on the divided voltage Vdv, the charging signal Sch is a signal based on the divided voltage Vdv. Therefore, it can be determined whether or not the power supply voltage Vs has decreased by a predetermined amount ΔV based on the charging signal Sch. At this time, in this embodiment, the predetermined amount ΔV corresponds to a difference between the divided voltage Vdv corresponding to the steady power supply voltage Vss and the reference voltage Vref. For example, the predetermined amount ΔV may be a difference between the divided voltage Vdv corresponding to the steady power supply voltage Vss and another voltage different from the reference voltage Vref.

  Note that the predetermined amount ΔV of the decrease in the predetermined period K1 and the power supply voltage Vs is determined in advance in this embodiment based on the resistance value of the limiting resistor 21 and the like when the motor 50 is operated at a high speed of, for example, 1200 r / min. It is determined by experiment etc. However, the present invention is not limited to this, and conversely, for example, the predetermined amount ΔV may be determined first, and the rotational speed of high-speed operation at which the predetermined amount ΔV is obtained may be determined. That is, “predetermined period K1”, “resistance value of limiting resistor 21”, “value of voltage dividing resistors R1 and R2,” “predetermined amount ΔV of decrease in power supply voltage Vs”, and “rotation speed during initial drive processing ( The electric power) etc. may be determined in advance by experiments or the like in relation to each other in accordance with the state of abnormality detection of the relay. At that time, the order of determining each value is arbitrary.

  When it is determined that the divided voltage Vdv has decreased below the reference voltage Vref (YES: corresponding to time t2 in FIG. 3), in step S50, the CPU 31 has a poor connection of the relay contact 24a, that is, the relay contact 24a. It is determined that an abnormal connection has occurred (corresponding to “abnormality determination process” and “abnormality determination step”). Then, the CPU 31 stops the generation of the PWM signal to stop the rotation of the motor 50 and, for example, generates an abnormal signal Sa (see time t2 in FIG. 3), turns on the LED 33 by the abnormal signal Sa, and relay contacts Is notified to the user (corresponding to “notification process”).

  Note that the "relay contact abnormality" here is that the relay 24 is normally excited and the relay contact 24a moves, but the connection abnormality due to poor conduction due to dust or the like adhering to the relay contact 24a, Connection abnormality in which the moving operation of the relay contact 24a is not performed due to the 24 excitation operation failure.

  Further, when the abnormality notification is performed when the abnormality of the relay contact is determined, the rotation of the motor 50 is not necessarily stopped. Further, the method for notifying the abnormality of the relay contact is not limited to this. For example, the abnormality may be displayed on the LCD by characters or the like. Further, when the rotation of the motor 50 is stopped when the relay contact abnormality is determined, the abnormality notification need not be performed.

  On the other hand, if it is determined in step S40 that the divided voltage Vdv has not decreased below the reference voltage Vref (NO), the CPU 31 determines in step S60 whether or not the predetermined period K1 of high-speed operation has elapsed, for example. The determination is made based on the measurement of the timer 34.

  If it is determined that the predetermined period K1 has not elapsed (NO), the process returns to step S40. On the other hand, if it is determined that the predetermined period K1 has elapsed (YES: corresponding to time t3 in FIG. 4), the CPU 31 determines in step S70 that the connection of the relay contact 24a is normal and performs normal PWM control, that is, Start normal rotation speed control.

  Note that the order of the processes shown in FIG. 2 is merely an example, and can be changed as appropriate. For example, the process may proceed to step S60 after step S30, and then the process of step S40 may be performed. That is, it may be determined whether or not the power supply voltage Vs has dropped by a predetermined amount after the high-speed operation in the predetermined period K1 ends. In this case, if YES is determined in step S40, the process proceeds to step S50. If NO is determined, the process proceeds to step S70.

3. Effects of the present embodiment In the present embodiment, when the load driving circuit 1 is started, that is, when the power switch SW1 of the power supply circuit 10 is turned on, the power supply voltage Vs reaches a predetermined value (140 V in the present embodiment) (FIG. 3 and after time t1 in FIG. 4), the high-speed operation process S30 (initial drive process) is forcibly performed. Accordingly, when the relay contact 24a is not normally closed, a larger current flows through the power supply line Ls through the limiting resistor 21 than in the medium speed operation, and the limiting resistor 21 causes a larger voltage than in the medium speed operation. A descent occurs. At that time, due to the discharge of the smoothing capacitor, the charging voltage of the smoothing capacitor, that is, the power supply voltage Vs is greatly reduced compared to the medium speed operation or the like. Therefore, the abnormality of the relay contact 24a can be detected by appropriately setting the predetermined amount ΔV of the decrease in the power supply voltage Vs for abnormality detection. At that time, the abnormality detection can be performed with the circuit configuration of the existing inrush current prevention circuit 20 by the control process according to the program of the CPU 31. That is, no additional circuit configuration for detecting an abnormality is required. Therefore, it is possible to detect a connection abnormality of the relay contact 24a with a simple configuration.

  At this time, in the present embodiment, the predetermined amount ΔV of the decrease in the power supply voltage for detecting the connection abnormality of the relay contact 24a is set based on the set value of the reference voltage Vref of the comparator 23 as the abnormality detection status, for example, the detection speed. It can set suitably according to etc. For example, by setting the reference voltage Vref to a value with a small difference from the divided voltage Vdv of the power supply voltage Vs in the steady state, the predetermined amount of decrease ΔV can be set small. On the other hand, by setting the reference voltage Vref to a value having a large difference from the divided voltage Vdv of the power supply voltage Vs in the steady state, the predetermined amount of decrease ΔV can be set large.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention, and further, within the scope not departing from the gist of the invention other than the following. Various modifications can be made.

  (1) In the above embodiment, the voltage detection circuit is configured by the voltage dividing circuit 22 that indirectly detects the power supply voltage Vs. However, the present invention is not limited to this. The voltage detection circuit may be configured by a circuit that directly detects the power supply voltage Vs. In this case, the amount of decrease in the power supply voltage Vs when the abnormality of the relay contact 24a is detected can be calculated from the difference between the steady power supply voltage Vs and the voltage detection signal and compared with the predetermined decrease amount ΔV.

  (2) In the above embodiment, the example in which the motor 50 is operated at high speed (high power driving) at 1200 r / min in the initial driving process of step S30 has been described, but the present invention is not limited thereto. For example, when the motor 50 is used in a low power range that is low within the variable power range, it is operated at an operation speed that is higher than the normal power consumption in the low power range, for example, 800 r / min in the initial drive process. You may make it do. In short, in the initial driving process, when the motor 50 (load) is supplied via the limiting resistor 21 for a predetermined period K1, it may be driven with power that reduces the power supply voltage Vs by a predetermined amount ΔV. At that time, “predetermined period K1”, “resistance value of limiting resistor 21”, “predetermined amount ΔV of decrease in power supply voltage Vs”, “rotational speed (power)”, and the like depend on the state of abnormality detection of the relay. This is determined in advance through experiments or the like. Note that the voltage drop at the limiting resistor 21 is proportional to current, in other words, power. For this reason, the power in the initial driving process is advantageously higher in the power variable region to be used as in the present embodiment.

  (3) In the above embodiment, the inrush current prevention circuit is applied to the motor drive circuit 1 that drives the fan motor 50 that cools the condenser of the ice making machine. However, the inrush current prevention circuit of the present invention is not limited to this. Application is not limited to this. The inrush current prevention circuit according to the present invention can be applied to any load driving circuit that drives a load with variable power.

DESCRIPTION OF SYMBOLS 1 ... Motor drive circuit (load drive circuit), 20 ... Inrush current prevention circuit, 21 ... Limit resistance, 22 ... Voltage dividing circuit, 23 ... Comparator, 24 ... Relay, 24a ... Relay contact, 31 ... CPU, C1 ... Smoothing capacitor

Claims (6)

An inrush current prevention circuit provided in a load drive circuit for driving a load with variable power,
A limiting resistor connected in series to a power supply line for supplying a driving current to the load, and limiting an inrush current at the time of starting the load driving circuit,
On the load side of the limiting resistor, a smoothing capacitor connected between the power line and the ground line,
A relay contact connected in parallel to the limiting resistor, the relay contact is closed when a power supply voltage, which is a charging voltage of the smoothing capacitor, increases to a predetermined voltage, and the drive is driven to the load via the relay contact A relay for supplying current;
A voltage detection circuit for detecting the power supply voltage;
A control circuit that variably controls the power of the load,
The control circuit includes:
At the time of starting the load driving circuit, after the power supply voltage has increased to the predetermined voltage, when the load is supplied through the limiting resistor for a predetermined period, the power is reduced by a predetermined amount. Initial driving process to drive,
A determination process for determining whether the power supply voltage has decreased by the predetermined amount during the initial drive process;
An inrush current preventing circuit that executes an abnormality determination process that determines that the connection of the relay contact is abnormal when it is determined in the determination process that the power supply voltage has decreased by the predetermined amount. In the inrush current prevention circuit according to claim 1,
The voltage detection circuit is a voltage dividing circuit that detects a divided voltage obtained by dividing the power supply voltage,
The inrush current prevention circuit further includes:
A comparison circuit that compares the divided voltage with a reference voltage to generate a comparison signal,
The control circuit performs the determination process based on the comparison signal during the initial drive process, and receives the comparison signal indicating that the divided voltage has decreased below the reference voltage. An inrush current prevention circuit that executes abnormality determination processing. In the inrush current prevention circuit according to claim 1 or claim 2,
The control circuit is an inrush current prevention circuit that executes a notification process of notifying the abnormality of the relay contact when executing the abnormality determination process. In the inrush current prevention circuit according to any one of claims 1 to 3,
The load is a motor driven at least at a high speed and a low speed as the variable power drive,
The control circuit is an inrush current prevention circuit that drives the motor at the high speed for the predetermined period at the start-up in the initial driving process. A method for detecting an abnormality of an inrush current prevention circuit provided in a load drive circuit for driving a load with variable power,
The inrush current prevention circuit is
A limiting resistor connected in series to a power supply line for supplying a driving current to the load, and limiting an inrush current at the time of starting the load driving circuit,
On the load side of the limiting resistor, a smoothing capacitor connected between the power line and the ground line,
A relay contact connected in parallel to the limiting resistor, the relay contact is closed when a power supply voltage, which is a charging voltage of the smoothing capacitor, increases to a predetermined voltage, and the drive is driven to the load via the relay contact A relay for supplying current,
The abnormality detection method of the inrush current prevention circuit is as follows:
When the load driving circuit is activated, the power supply voltage is reduced by a predetermined amount when the load is supplied through the limiting resistor for a predetermined period after the power supply voltage has increased to the predetermined voltage. An initial driving process to drive;
A determination step of determining whether the power supply voltage has decreased by the predetermined amount during the initial driving step;
An abnormality detection method for an inrush current prevention circuit, comprising: an abnormality determination step for determining that the connection of the relay contact is abnormal when it is determined that the power supply voltage has decreased by the predetermined amount in the determination step. In the abnormality detection method of the inrush current prevention circuit according to claim 5,
The load is a motor driven at least at a high speed and a low speed as the variable power drive,
The method for detecting abnormality of an inrush current preventing circuit, wherein the initial driving step includes driving the motor at the high speed for the predetermined period at the time of starting.

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