JPH096441A - Inrush current prevention circuit - Google Patents

Abstract

PURPOSE: To prevent a rush current completely by connecting by thyristor for switching short-circuit or opening of a discharge resistor discharging the charge in a smoothing capacitor for the purpose of smoothing an output waveform in series to the discharge resistor. CONSTITUTION: A DC power supply circuit 50 provided with a rush current prevention circuit is made up of a thyristor 51 connecting in series to a discharge resistor 19 to open the discharge resistor 19 till the voltage across a smoothing capacitor 17 reaches the maximum output voltage Vdmax of rectifier diodes 15a-15d and to connect the discharge resistor 19 when the voltage across the capacitor 17 reaches the maximum output voltage Vdmax and up of a driver 53 controlling ON/OFF of the thyristor 51. Then a switch 33 is used to conduct a current limit resistor 31, and when the output voltage of the smoothing capacitor 17 detected by a comparator 37 exceeds a prescribed value, the thyristor 51 activates the discharge resistor 19 and the switch 33 short circuits the current limit resistor. Thus, a rush current caused by charging the smoothing capacitor 17 is completely prevented when power is applied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power supply circuit for rectifying an AC voltage obtained from an AC power supply and converting the AC voltage into a DC voltage, and in particular, inrush current prevention for preventing inrush power generated immediately after AC power is turned on. Regarding the circuit.

[0002]

2. Description of the Related Art As is well known, in a DC power supply circuit for rectifying an AC voltage obtained from an AC power supply and converting it into a DC voltage, a smoothing capacitor is often used to smooth the output. However, when a smoothing capacitor is used, the smoothing capacitor is charged immediately after the AC power is turned on, so a large current, so-called inrush current flows. Here, a DC power supply circuit that does not prevent the inrush current is shown in FIG. The DC power supply circuit 10 shown in FIG. 5 includes a transformer 11, an AC power supply 13 provided on the primary side of the transformer 11, and a transformer 1.
1. Rectifier diodes 15a to 15d provided on the secondary side of No. 1
And a smoothing capacitor 17 which is provided in parallel on the output side of the rectifier diodes 15a to 15d and smoothes the rectified waveform obtained by the rectifier diodes 15a to 15d, and stabilizes the output of the DC power supply circuit 10 and smooths the capacitor. Discharge resistor 1 for discharging the electric charge charged in 17
9 and.

In the case of this DC power supply circuit 10, an AC power supply 1
Immediately after turning on 3, the inrush current for charging the smoothing capacitor 17 flows. This inrush current increases as the capacity of the smoothing capacitor 17 increases, and therefore causes malfunctions such as disconnection of a fuse provided on the power supply side and interruption of a breaker.

A DC power supply circuit having a circuit for preventing inrush current is shown in FIG. DC power supply circuit 3 shown in FIG.
In addition to the DC power supply circuit 10 shown in FIG. 5, 0 is a current limiting resistor 31 that limits the current flowing to the output side of the rectifying diodes 15a to 15d, a switch 33 that switches between shorting and opening of the current limiting resistor 31, and an output. An output voltage detection resistor 35 for detecting a voltage, an output voltage detected through the output voltage detection resistor 35, and a reference voltage Vre set in advance.
Comparing f with the comparator 37, which outputs an ON signal when the output voltage reaches a set voltage determined by the reference voltage Vref, and outputs an OFF signal when the output voltage does not reach the set voltage. When the ON signal is output, the switch 33 is turned ON to short-circuit and remove the current limiting resistor 31, and when the OFF signal is output from the comparator 37, the switch 33 is turned OFF to make the current limiting resistor 31 conductive. And a power supply 41 for the comparator 37 and the driver 39.

The primary coil of the power source 41 is connected to the primary coil of the transformer 11, and when the AC power source 13 is turned on, the power source 41 is also turned on. In addition, the positive terminals (terminals indicated by white circles) on the power input side of the comparator 37 and the driver 39 are positive terminals of the power source 41 (terminals indicated by white circle).
Further, the minus terminal (terminal indicated by a black circle) on the power input side of the driver 39 is connected to the plus terminal (terminal indicated by a black circle) and the minus terminal (terminal indicated by a black circle) on the output side of the power source 41.

Next, the operation of the DC power supply circuit 30 will be described. Immediately after the AC power supply 13 is turned on, the switch 33 is OF
At F, the smoothing capacitor 17 is charged through the current limiting resistor 31. Therefore, inrush current can be prevented. on the other hand,
In the comparator 37, the output voltage is detected by the output voltage detection resistor 35, and this is compared with the reference voltage Vref. When the output voltage reaches the set voltage determined by the reference voltage Vref preset in the comparator 37, the comparator 37 outputs an ON signal to the driver 39. With this ON signal, the driver 39 turns on the switch 33 to short-circuit and remove the current limiting resistor 31, and the inrush current prevention circuit is released.

[0007]

However, in the conventional DC power supply circuit 30 having the inrush current prevention circuit,
Since the current charged in the smoothing capacitor 17 is discharged by the discharge resistor 19, the voltage value of the smoothing capacitor 17 does not exceed a certain value. Therefore, the smoothing capacitor 17
The switch 33 is turned on in a state in which the smoothing capacitor 17 is not sufficiently charged, and an inrush current flows to try to charge the smoothing capacitor 17 at this time. Therefore, the rectifier diode 1
Maximum output voltage Vdmax of 5a to 15d and smoothing capacitor 1
7 must be equal to the voltage charged. Here, the maximum output voltage Vdm of the rectifier diodes 15a to 15d
Assuming that ax is the resistance value of the discharge resistor 19 and r is the resistance value of the current limiting resistor 31, the voltage Vc of the smoothing capacitor 17 before turning on the switch 33 is Vc = (R / R + r) Vdmax. 1) As shown in the equation (1), the maximum output voltage Vdmax of the rectifying diodes 15a to 15d and the voltage Vc charged in the smoothing capacitor 17 are the resistance value R of the discharge resistor 19.
Are not equal to each other unless they are much larger than the resistance value r of the current limiting resistor 31.

Therefore, the conventional DC power supply circuit 30 having the function of preventing the inrush current has a problem that the inrush current cannot be completely prevented. The present invention has been made in view of the above circumstances, and an object thereof is to provide an inrush current prevention circuit capable of completely preventing an inrush current.

[0009]

In order to achieve the above object, the present invention provides a current limiting resistor for limiting a current supplied from a power source and a short circuit or conduction of the current limiting resistor, for example, an electromagnetic relay, Changeover switches such as a solid state relay, a thyristor, a power transistor, and a GTO, a smoothing capacitor for smoothing an output waveform, a discharge resistor for discharging the electric charge charged in the smoothing capacitor, and a discharge resistor connected in series, Switching between conduction and opening of the discharge resistance, for example, a switching element such as a thyristor or FET, and when the power is turned on, the charging voltage of the smoothing capacitor is detected and turned off until a predetermined value is reached.
When the signal exceeds the predetermined value, a comparator that outputs an ON signal, and when an OFF signal is output from the comparator, the changeover switch causes the current limiting resistor to conduct, and the ON signal is When it is output, the current limiting resistor is short-circuited by the changeover switch. For example, when an OFF signal is output from the changeover switch control circuit such as a driver and the comparator, the discharge resistor is opened by the switch element. When the ON signal is output, the switch element conducts the discharge resistance, and when the power is cut off, the switch element conducts the discharge resistance. For example, a switch element control circuit or a FET including a thyristor. Switch element control consisting of a zener diode, a diode, a photothyristor and a protective resistor It is characterized by comprising a switch element control circuit of the switching element control circuit, comprising a protection circuit or an FET and a Zener diode and a diode and a photo triac resistance.

[0010]

According to the above structure, the changeover switch switches between short-circuiting and conduction of the current limiting resistor, and the switch element is connected in series with the discharge resistor and switches conduction and opening of the discharge resistor. Then, until the output voltage of the smoothing capacitor detected by the comparator when the power is turned on reaches a predetermined value, the discharge resistance is opened by the switching element and the current limiting resistance is made conductive by the changeover switch, and the detection is performed by the comparator. When the output voltage of the smoothing capacitor exceeds a predetermined value, the discharge resistance is made conductive by the switch element and the current limiting resistance is short-circuited by the changeover switch. Therefore, it is possible to completely prevent the inrush current that occurs when the smoothing capacitor is charged when the power is turned on.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing a case where the inrush current prevention circuit of the first embodiment of the present invention is provided in a DC power supply circuit. It should be noted that the same members as those of the DC power supply circuit 10 shown in FIG. 5 and the DC power supply circuit 30 shown in FIG.

As shown in FIG. 1, a DC power supply circuit 50 including the inrush current prevention circuit of the first embodiment is connected in series to a discharge resistor 19 in addition to the DC power supply circuit 30 shown in FIG. The capacitor 17 is a rectifier diode 15a-15
The thyristor 51 that opens the discharge resistor 19 until reaching the maximum output voltage Vdmax of d, and conducts the discharge resistor 19 when reaching the maximum output voltage Vdmax, and this thyristor 5
It is composed of a driver 53 for controlling ON / OFF of 1.

As the smoothing capacitor 17, one that can be charged up to at least the maximum output voltage Vdmax of the rectifying diodes 15a to 15d is used. Further, the plus terminal (terminal indicated by a white circle) on the power input side of the driver 53 is the plus terminal (terminal indicated by a white circle) of the power source 41, and the minus terminal (the terminal indicated by a black circle) on the power input side of the driver 53 is the power source 41. Connected to the negative terminal (the terminal shown by the black circle) on the output side of. Further, the switch 33 may be any switch whose ON / OFF can be controlled by an external signal, for example, an electromagnetic relay, a solid state relay, a thyristor, a power transistor, a GTO, or the like.

Next, the operation of the DC power supply circuit 50 having the inrush current prevention circuit of the first embodiment will be described. First, when the AC power supply 13 is turned on, the power supply 41 is also turned on at the same time, and the comparator 37, the driver 53, and the driver 39 start operating. Immediately after the AC power supply 13 is turned on, the OFF signal is output from the comparator 37 to the driver 39 and the driver 53, so the switch 33 and the thyristor 5 are connected.
Both 1 are kept OFF. Therefore, when the AC power supply 13 is turned on, the current flowing to the secondary side of the transformer 11 charges the smoothing capacitor 17 through the rectifying diodes 15a to 15d and the current limiting resistor 31. At this time, since the discharging resistor 19 is disconnected, the smoothing capacitor 17 can be charged up to the maximum output voltage Vdmax of the rectifying diodes 15a to 15d.

Therefore, if the set voltage for turning on the switch 33 and the thyristor 51 set in the comparator 37 is set to be the same as the maximum output voltage Vdmax of the rectifying diodes 15a to 15d, the smoothing capacitor 17 becomes the rectifying diode 15a.
Since the battery is charged up to the maximum output voltage Vdmax of ˜15d, the inrush current can be completely prevented. If the maximum output voltage Vdmax of the rectifier diodes 15a to 15d is stable and constant, the set voltage may be the same as the maximum output voltage Vdmax, but the maximum output voltage Vdmax of the rectifier diodes 15a to 15d is the internal resistance or the like. If the value becomes lower than the assumed value due to the influence, the switch 33 and the thyristor 51 may not be turned on at all, and therefore the rectifying diode 15
It is set a little lower than the maximum output voltage Vdmax of a to 15d.

Then, in the comparator 37, the output voltage is detected by the output voltage detection resistor 35, and when the set voltage determined by the reference voltage Vref is exceeded, an ON signal is output to the driver 39 and the driver 53. When the ON signal is output from the comparator 37, the driver 39 turns on the switch 33 to short-circuit and remove the current limiting resistor 31, and the driver 5
3 turns on the thyristor 51 to make the discharge resistor 19 conductive. As a result, the DC power supply circuit 50 starts to supply a stable DC current. Also, turn off the AC power supply 13.
When set to, the power supply 41 is also turned off, so the comparator 3
7, the operation of the driver 39 and the driver 53 is also stopped, but the thyristor 51 remains ON until the current becomes zero due to its characteristics. Therefore, the smoothing capacitor 17
The electric charge charged in the electric field is discharged through the discharge resistor 19.

As described above, the DC power supply circuit 50 having the inrush current prevention circuit of the first embodiment has the smoothing capacitor 1 with the discharge resistor 19 opened when the AC power supply 13 is turned on.
Since 7 is charged, it can be charged up to the maximum output voltage Vdmax of the rectifying diodes 15a to 15d, and inrush current can be completely prevented.

The DC power supply circuit 50 having the inrush current prevention circuit of the first embodiment can most easily implement the present invention, but the thyristor 51 has a characteristic that the current flowing therethrough is zero. Since it does not turn off until it becomes, it turns on until the charge stored in the smoothing capacitor 17 is completely discharged.
Will remain. Therefore, when the AC power supply 13 is turned on again before the electric charge charged in the smoothing capacitor 17 is completely discharged, the discharge resistor 19 is not opened, so that the smoothing capacitor 17 is set to the maximum output voltage Vdmax of the rectifying diodes 15a to 15d. unable to charge. Therefore, switch 3
3 will not turn ON at all. Therefore, the first
DC power supply circuit 50 including the inrush current prevention circuit of the embodiment
Is suitable for use when the AC power supply 13 is not turned on again for a predetermined time (at least until the electric charge charged in the smoothing capacitor 17 is completely discharged) after the AC power supply 13 is turned off.

FIG. 2 is a circuit diagram showing a case where the inrush current prevention circuit of the second embodiment of the present invention is provided in the DC power supply circuit. The DC power supply circuit 60 including the inrush current prevention circuit according to the second embodiment has the above-mentioned problem that occurs when the AC power supply 13 is turned on again before the electric charge stored in the smoothing capacitor 17 is completely discharged. It has been resolved. Further, the DC power supply circuit 10 shown in FIG. 5 and the DC power supply circuit 3 shown in FIG.
0 and the same members as those of the DC power supply circuit 50 shown in FIG.

As shown in FIG. 2, the DC power supply circuit 60 having the inrush current prevention circuit of the second embodiment is connected in series with the discharge resistor 19 in addition to the DC power supply circuit 30 shown in FIG. The capacitor 17 is a rectifier diode 15a-15
An FET 61 that opens the discharge resistor 19 until the maximum output voltage Vdmax of d is reached, and conducts the discharge resistor 19 when the maximum output voltage Vdmax is reached, and an ON state of this FET 61.
A driver 63 for controlling ON / OFF, a Zener diode 65 for keeping the FET 61 ON by a Zener voltage when the AC power supply 13 is cut off, and a diode 67.
And a photothyristor 69 for preventing the gate current of the FET 61 from flowing out to the driver 63 when the AC power supply 13 is turned off, protective resistors 71 and 73, and a protective diode 75. The photothyristor 69 is connected to the positive terminal of the power supply 41 via the protection resistor 71,
When the AC power supply 13 is turned on, the photodiode 69a is turned on by the power supply 41, and the FET 61 and its driver 63 are short-circuited.

Next, the operation of the DC power supply circuit 60 having the inrush current prevention circuit of the second embodiment will be described. First, when the AC power supply 13 is turned on, the power supply 41 is also turned on at the same time, and the comparator 37, the driver 63, and the driver 39 start operating. Further, the photothyristor 69 is turned on, and the driver 63 and the FET 61 are short-circuited. here,
When the smoothing capacitor 17 is not charged, the comparator 3
7 outputs an OFF signal, so switch 33 and FET
61 is turned off. Therefore, when the AC power supply 13 is turned on, the current flowing to the secondary side of the transformer 11 charges the smoothing capacitor 17 through the rectifying diodes 15a to 15d and the current limiting resistor 31. At this time, since the discharge resistor 19 is disconnected, the smoothing capacitor 1
7 is the maximum output voltage V of the rectifier diodes 15a to 15d
It is charged up to dmax.

In the comparator 37, the output voltage is detected by the output voltage detection resistor 35, and when the voltage exceeds the set voltage determined by the reference voltage Vref, an ON signal is sent to the driver 39 of the switch 33 and the driver 53 of the thyristor 51. Output. When the ON signal is output from the comparator 37, the driver 39 turns on the switch 33, and the driver 6
3 turns on the thyristor 51. As a result, the stable supply of direct current from the direct current power supply 60 is started.

Next, when the AC power supply 13 is cut off, the power supply 41 is also cut off, so that the operations of the comparator 37, the driver 39 and the driver 53 are also stopped, but the Zener voltage of the Zener diode 65 is applied to the gate of the FET 61. Since the voltage for that amount is applied, the FET 61 remains ON. Therefore, the electric charge charged in the smoothing capacitor 17 is discharged through the discharge resistor 19. At this time, the photothyristor 69 is turned off to prevent the gate current of the FET 61 from flowing out to the driver 63.

Next, when the AC power supply 13 is turned on again, the power supply 41 is turned on at the same time, and the comparator 37, the driver 63 and the driver 39 start operating. Further, the photothyristor 69 is turned on, and the driver 63 and the FE
T61 is short-circuited. Here, when the voltage of the smoothing capacitor 17 has not reached the set voltage determined by the reference voltage Vref of the comparator 37, the comparator 37 outputs an OFF signal to the driver 39 and the driver 63.
T61 is turned off and the inrush current is prevented. vice versa,
When the voltage of the smoothing capacitor 17 reaches the set voltage, the comparator 37 outputs an ON signal to the driver 39 and the driver 63, so that the switch 33 and the FET 61 are turned on.
The inrush current prevention circuit is released.

As described above, the DC power supply circuit 60 equipped with the inrush current prevention circuit of the second embodiment charges the smoothing capacitor 17 with the discharge resistor 19 opened when the AC power supply 13 is turned on. It is possible to charge up to the maximum output voltage Vdmax of 15a to 15d, and it is possible to completely prevent the inrush current. Furthermore, even when the AC power supply 13 is turned on again, the smoothing capacitor 17 can be charged with the discharge resistor 19 opened, and there is no limit to the timing of turning on the AC power supply 13 again, and the smoothing capacitor 17 is always operated according to the voltage of the smoothing capacitor 17. The inrush current prevention circuit can be operated or released.

FIG. 3 is a circuit diagram showing a case where the inrush current prevention circuit of the third embodiment of the present invention is provided in the DC power supply circuit. The DC power supply circuit 80 equipped with the inrush current prevention circuit of the third embodiment discharges the electric charge stored in the smoothing capacitor 17, like the DC power supply circuit 60 equipped with the inrush current protection circuit of the second embodiment. This is a solution to the above-mentioned problem that occurs when the AC power supply 13 is turned on again before it is turned off.
Further, the same members as those of the DC power supply circuit 10 shown in FIG. 5, the DC power supply circuit 30 shown in FIG. 6 and the DC power supply circuit 50 shown in FIG.

The DC power supply circuit 80 having the inrush current prevention circuit of the third embodiment is replaced with the photothyristor 69 of the DC power supply circuit 60 shown in FIG. 2, and when the AC power supply 13 is turned off, the gate current of the FET 61 is changed. The photo triac 81 is provided to prevent the light from leaking to the driver 63. Further, accordingly, the driver 63 is changed to the driver 83, the protection resistor 73 is changed to the protection resistor 85, and the protection diode 75 is removed.

The phototriac 81 is connected to the power source 41 via the protection resistor 71, and is turned on when the AC power source 13 is turned on, and the FET 61 and its driver 6 are connected.
3 shorts. As a result, the DC power supply circuit 80 including the inrush current prevention circuit of the third embodiment operates similarly to the DC power supply circuit 60 including the inrush current prevention circuit of the second embodiment shown in FIG.

Therefore, the DC power supply circuit 80 equipped with the inrush current prevention circuit of the third embodiment is similar to the DC power supply circuit 60 equipped with the inrush current protection circuit of the second embodiment shown in FIG. When the power is turned on, the smoothing capacitor 17 is charged with the discharge resistor 19 opened, so that the maximum output voltage Vdmax of the rectifying diodes 15a to 15d can be charged and the inrush current can be completely prevented. Furthermore, even when the AC power supply 13 is turned on again, the smoothing capacitor 17 can be charged with the discharge resistor 19 opened, and there is no limit to the timing of turning on the AC power supply 13 again, and the smoothing capacitor 17 is always operated according to the voltage of the smoothing capacitor 17. The inrush current prevention circuit can be operated or released.

The application of the DC power supply circuits 50, 60, 80 provided with the inrush current prevention circuits of the first, second and third embodiments is not described, but in both cases, inrush current is generated and
As long as the smoothing capacitor 17 is used, it can be used in any circuit, for example, a gradient magnetic field power supply of a magnetic resonance apparatus (MRI apparatus), a DC power supply circuit of an X-ray CT apparatus, an X-ray diagnostic apparatus, or the like. In this case, it is possible to prevent erroneous operations such as disconnection of the fuse of the power supply unit and interruption of the breaker that occur due to the occurrence of the inrush current. In particular, in a magnetic resonance apparatus (MRI apparatus), an X-ray CT apparatus, and an X-ray diagnostic apparatus, it is desirable that no malfunction occurs immediately before or during observation, but if the inrush current prevention circuit according to the present invention is used, it is possible that Malfunctions can be completely prevented. In addition, the first, second, third
Although the embodiments are described by way of example in which the inrush current prevention circuit of the present invention is provided in the DC power supply circuit, the present invention is not limited to this.
If a rush current is generated and the smoothing capacitor 17 is used, it can be used in other circuits.

Further, in the DC power supply circuit 50 of the first embodiment, the thyristor 51 is used as a switching element, the DC power supply circuit 60 of the second embodiment and the DC power supply circuit 8 of the third embodiment.
In 0, FET61 is used, but not limited to these,
Other switch elements may be used as long as the discharge resistance 19 can be short-circuited when the AC power supply 13 is cut off, and more preferably the discharge resistance 19 can be opened when the AC power supply 13 is turned on again.

Further, in the DC power supply circuit 60 of the second embodiment, when the AC power supply 13 is cut off, the photothyristor 69 is provided in order to prevent the gate current of the FET 61 from flowing out to its driver. Although the power supply circuit 80 uses the phototriac 81, the present invention is not limited to this, and prevents the gate current from flowing out to the driver when the AC power supply 13 is turned on again.
Other elements may be used as long as the ET61 and its driver can be short-circuited.

Further, although the switch 33 is provided on the secondary side of the transformer 11 in the first, second and third embodiments, it may be provided on the primary side of the transformer 11 as shown in FIG. . In this case, the switch 33 can conduct on both the positive side and the negative side, for example, a solid state relay,
It must be a bidirectional switch such as a triac.

[0034]

As described above, according to the present invention, since the switch element is connected in series with the discharge resistor for discharging the electric charge charged in the smoothing capacitor for smoothing the output waveform, the power is turned on / off and It is possible to switch between conduction and opening of the discharge resistor according to the charging voltage of the smoothing capacitor, and it is possible to completely prevent the inrush current that occurs when the smoothing capacitor is charged when the power is turned on.

Further, a switch element is connected in series with a discharge resistor for discharging the charged electric charge in a smoothing capacitor for smoothing the output waveform, and the switch element control circuit causes the switch capacitor to be connected in accordance with the charging voltage of the smoothing capacitor when the power is turned on. Since the short-circuiting and opening of the switch element are controlled and the switch element is short-circuited when the power is cut off, it is possible to completely prevent the inrush current that occurs when the smoothing capacitor is charged when the power is turned on.

Furthermore, a switch element connected in series with the discharge resistor for switching conduction and opening of the discharge resistor and a changeover switch for switching short-circuiting and conduction of the current limiting resistor are provided so that the output voltage of the smoothing capacitor is changed when the power is turned on. The discharge resistance is opened by the switch element and the current limiting resistance is made conductive by the changeover switch until it reaches the predetermined value, and the discharge resistance is made conductive by the switch element when the output voltage of the smoothing capacitor exceeds the predetermined value. At the same time, since the current limiting resistor is short-circuited by the changeover switch, it is possible to completely prevent the inrush current generated when the smoothing capacitor is charged when the power is turned on.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a case where a rush current prevention circuit according to a first embodiment of the present invention is provided in a DC power supply circuit.

FIG. 2 is a circuit diagram showing a case where a rush current prevention circuit according to a second embodiment of the present invention is provided in a DC power supply circuit.

FIG. 3 is a circuit diagram showing a case where a rush current prevention circuit according to a third embodiment of the present invention is provided in a DC power supply circuit.

FIG. 4 is an explanatory diagram when a switch 37 is provided on the primary side of the transformer 11.

FIG. 5 is a circuit diagram showing a DC power supply circuit when inrush current is not prevented.

FIG. 6 is a circuit diagram showing a DC power supply circuit including a conventional inrush current prevention circuit.

[Explanation of symbols]

 10, 30, 50, 60, 80 DC power supply circuit 11 Transformer 13 AC power supply 15 Rectifying diode 17 Smoothing capacitor 19 Discharging resistance 31 Current limiting resistance 33 Switch 35 Output voltage detection resistance 37 Comparator 39, 53, 63, 83 Driver 41 Power supply 51 Thyristor 61 FET 65 Zener diode 67 Diode 69 Photothyristor 71, 73, 85 Protection resistor 75 Protection diode

Claims (3)

[Claims] 1. A rush current preventer characterized in that a switch element for switching between short-circuiting and opening of a discharge resistor for discharging a charge charged in a smoothing capacitor for smoothing an output waveform is connected in series with the discharge resistor. circuit. 2. When the power is turned on, short-circuiting and opening of the switch element are controlled according to the charging voltage of the smoothing capacitor, when the power is shut off, the switch element is short-circuited, and the smoothing capacitor is charged by the discharge resistor. The inrush current prevention circuit according to claim 1, further comprising a switch element control circuit for discharging electric charge. 3. A current limiting resistor for limiting a current supplied from a power supply, a changeover switch for switching between short-circuit removal and conduction of the current limiting resistor, a smoothing capacitor for smoothing an output waveform, and a charge for the smoothing capacitor. And a discharge resistor for discharging the electric charge, which is connected in series with the discharge resistor, and the conduction of the discharge resistor,
A switching element for switching between open and, when the power is turned on, the charging voltage of the smoothing capacitor is detected, and an OFF signal is output until the voltage reaches a predetermined value, and an ON signal is output when the voltage exceeds the predetermined value. When an OFF signal is output from the comparator and the comparator, the current limiting resistor is made conductive by the changeover switch, and when the ON signal is output, the current limiting resistor is short-circuited and removed by the changeover switch. When an OFF signal is output from the changeover switch control circuit and the comparator, the discharge resistance is opened by the switch element, and when an ON signal is output, the discharge resistance is made conductive by the switch element, And a switch element control circuit that conducts the discharge resistance by the switch element when the power is cut off. Inrush current prevention circuit characterized by.