JPH02307326A - Rush current preventing circuit for power unit - Google Patents

Abstract

PURPOSE:To prevent a rush current by detecting terminal voltage of a smoothing capacitor to charge it and AC side voltage of a main rectifier and controlling an electric charge of the capacitor and electrification of the coil of a relay for short-circuiting a current limiting resistor. CONSTITUTION:When a main switch 1 is closed, a main rectifier 2 is actuated, and charging of a capacitor 3 is started through a current limiting resistor 4. While AC side voltage of the main rectifier 2 is rectified by diodes 12 with the current limiting resistor 4 short-circuited through a smoothing circuit, and steady operation is performed. When the main switch 1 is turned off, the AC side voltage of the main rectifier 2 is decreased to zero to instantaneously discharge the capacitor 3, and a condition, prepared for a restart, is obtained by opening a contact 5-2 in a relay to insert the current limiting resistor 4 in series to a circuit of the smoothing capacitor 3. Thus even when the main switch is reclosed in a short time after it is turned off, a rush current can be prevented by surely resetting the circuit for short-circuiting the current limiting resistor.

Description

Detailed Description of the Invention (1) Purpose of the Invention [Field of Industrial Application] The present invention relates to a power supply device, particularly a power supply device that supplies direct current to a control device for a servo motor used in machine tools, robot devices, etc. It is used for.

[Prior Art] Figure 2 is a circuit diagram showing the concept of a conventional power supply device, in which a three-phase 220V commercial power supply is supplied to a main rectifier 2 via a main switch 1, and converted to direct current. The ripple is reduced by a smoothing capacitor 3 via a current limiting resistor 4 and supplied to the control device from an eleventh terminal, and a relay coil 5- is connected to the terminal of the smoothing capacitor 3 via a resistor 6.
1 is connected, the a contact 5-2 of the relay is connected to both ends of the current limiting resistor 4, and the diode 7 is connected to the coil 5 of the relay.
This is a device that absorbs a back electromotive force of -1.

In the figure, when the main switch 1 is turned on, the current limiting resistor 4 charges the smoothing capacitor 3 with the output voltage of the main rectifier 2, so a large inrush current flows, which may damage the main rectifier and the smoothing capacitor. This is intended to limit the damage to the main parts and prevent damage to the main parts.

However, if the current-limiting resistor 4 is left inserted, inrush current can be prevented, but the voltage drop across the current-limiting resistor 4 is large, resulting in disadvantages such as increased loss and voltage fluctuation. Therefore, if a contact 5-2 of the relay is provided at both ends of the current-limiting resistor 4, and the coil 5-1 of this relay is connected to the terminal of the smoothing capacitor 3 via the resistor 6, immediately after the main switch 1 is turned on, the contact 5-2 of the relay is Since the contact 5-2 is open, the smoothing capacitor 3 is charged via the current limiting resistor 4, so inrush current is prevented, and when the terminal voltage of the smoothing capacitor 3 reaches a certain value, the a contact 5-2 of the relay is charged. is closed and the current limiting resistor 4 is short-circuited,
This has the effect of reducing voltage drop, reducing loss, and reducing voltage fluctuations.

When the main switch 1 is turned OFF to stop the main rectifier 2 and the smoothing capacitor 3 is sufficiently discharged and the terminal voltage becomes below the relay operating voltage, the relay's a contact 5-2 is opened and the current limiting resistor 4 is inserted into the circuit. Therefore, when the main switch 1 is turned on again, the same operation as described above is performed to prevent inrush current and enable safe startup.

[Problems to be Solved by the Invention] However, when the main switch is turned off and then turned on again, the a contact of the relay is closed and the current limiting resistor is shorted, so a large inrush current may flow, causing the relay to This causes the problem of welding the a-contact.

This problem can occur not only when the main switch is opened or closed, but also when a momentary power outage occurs.

The present invention solves the problems in the prior art as described above,
To obtain an inrush current prevention circuit in which no inrush current flows even if a main switch is turned on again immediately after being turned off.

(2) Structure of the invention [Means to solve the problem] In order to solve the above problem in the present invention.

a first means for detecting the terminal voltage of the smoothing capacitor and charging the capacitor; a second means for detecting the AC side voltage of the main rectifier; and a third means for controlling the electric charge of the capacitor by the output of the second means. This is achieved by a configuration in which energization of a coil of a relay that short-circuits a current-limiting resistor is controlled by the above means and a fourth means controlled by the electric charge of the capacitor.

[Function] After the terminal voltage of the smoothing capacitor reaches a predetermined level by the first means, the capacitor starts charging, and when the capacitor voltage reaches a certain level, the fourth means closes the a contact of the relay. The configuration is such that the current limiting resistor is short-circuited by the second means, and the charge of the capacitor is controlled by the third means depending on the presence or absence of the AC side voltage of the main rectifier detected by the second means, and if there is no AC side voltage, the capacitor circuit is short-circuited. Even if the main switch is turned on again, the fourth means cannot operate until the voltage of the capacitor reaches a certain level, so even in the case of a momentary power outage, etc. The capacitor is instantly discharged, and the current limiting resistor is not short-circuited until the capacitor is charged when restarting, preventing inrush current.

[Embodiment] FIG. 1 is a circuit diagram of a power supply device equipped with an inrush current prevention circuit embodying the present invention, and the same parts as those in the prior art shown in FIG. 2 are given the same reference numerals and their explanation will be omitted.

In the figure, a first Zener diode 9, a resistor 10, and a capacitor 11 are connected in series and connected to the terminal of a smoothing capacitor 3, and when the terminal voltage of the smoothing capacitor 3 exceeds the Zener voltage of the first Zener diode 9, The first means is configured to start charging the capacitor 11 via the resistor 10, and the AC side voltage of the main rectifier 2 is connected to the diode 1.
2 is connected to the base of the transistor 13 via a rectifying and smoothing circuit, and connected to the collector of the transistor 13 via a resistor 14 from another power source 15, and the transistor 16
and second means connected to the base of the transistor 18, the collector of the transistor 16 being connected via a resistor to the terminals of the capacitor 11, the terminals of the capacitor 11 being connected via a second Zener diode 17 to the base of the transistor 18. 3
and a fourth means in which the collector of the transistor 18 is connected to the terminal of the smoothing capacitor 3 via the relay coil 5-1 and a resistor.

To explain the operation of the illustrated circuit, when the main switch 1 is turned on, the main rectifier 2 operates, the smoothing capacitor 3 is charged via the current limiting resistor 4, the terminal voltage rises, and the smoothing capacitor 3
When the terminal voltage of the first Zener diode 9 exceeds the Zener voltage of the first Zener diode 9, the capacitor 11 starts charging via the resistor 10.

- The AC side voltage of the oyster rectifier 2 is rectified by the diode 12, and current flows through the smoothing circuit to the base of the transistor 13, turning the transistor 13 on, so the transistor 16 turns off.

The voltage of the capacitor 11 is connected to the second Zener diode 17
When the Zener voltage of transistor 1 is exceeded through the resistor,
A current flows through the base of the transistor 8, turning on the transistor 18, energizing the relay coil 5-1, and closing the relay's a contact 5-2.

The current limiting resistor 4 is short-circuited and the operation becomes steady.

When the main switch 1 is turned off, the AC side voltage of the main rectifier 2 becomes zero, so the transistor 13 is turned off, and the transistor 16 is turned on, instantly discharging the charge in the capacitor 11, and turning off the transistor 18, so the relay The a contact 5-2 is opened and the current limiting resistor 4 is inserted in series with the circuit of the smoothing capacitor 3 to prepare for restart.

FIG. 3 shows an oscillogram of the operating state of an embodiment. In the figure, the AC side voltage of the main rectifier 2, the terminal voltage of the smoothing capacitor 3, the current of the current limiting resistor 4, and the current of the relay coil 5-1 are recorded, respectively, and the main switch 1 is turned on at timing 1. When this happens, the current in the current limiting resistor 4 rises to the limiting value and then decreases, and the terminal voltage of the smoothing capacitor 3 rises. After about 0.35 seconds, the coil 5-1 of the relay turns on and the current limiting resistor 4 decreases. 4 current becomes zero. Next, when the main switch 1 is turned off at timing 2, the current in the relay coil 5-1 becomes zero, and the terminal voltage of the smoothing capacitor 3 slowly decreases.

Even if the main switch 1 is turned on again at timing 3 before the terminal voltage of the smoothing capacitor 3 has decreased sufficiently, the current in the current limiting resistor 4 is within the limit value, and inrush current is reliably prevented.

[Effects of the Invention] Since the inrush current prevention circuit of the power supply device according to the present invention has the above-described configuration, the circuit that short-circuits the current limiting resistor can be reliably restored even if the main switch is turned on again in a short time after being turned off. This has the effect of preventing inrush current.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing the configuration of an inrush current prevention circuit of a power supply device according to the present invention, and Fig. 2 is a circuit diagram of a conventional inrush current prevention circuit of a power supply device according to the present invention. It is an oscillogram showing the operating state of the inrush current prevention circuit of the power supply device. Explanation of symbols 1... Main switch, 2... Main rectifier, 3... Smoothing capacitor, 4... Current limiting resistor, 5-1... Relay coil, 5-2... Relay a Contact, 6,10.14・
··resistance. 7.12...Diode, 9.17...Zener diode, 11...Capacitor, 13,16.18.
...transistor, 15...other DC power supply.

Claims (1)

[Claims] This is applied to a power supply device that rectifies commercial power and supplies DC current to a control device such as a motor through a smoothing circuit.A current limiting resistor is inserted between the main rectifier and a smoothing capacitor, and the current limiting resistor is In an inrush current prevention circuit configured to have a contact A of a relay interposed at both ends, a coil of the relay connected to a terminal of a smoothing capacitor, and a terminal voltage of the smoothing capacitor detected to control energization of the current limiting resistor. a first means for detecting the terminal voltage of the capacitor and charging the capacitor;
a second means for detecting the AC side voltage of the main rectifier; a third means for controlling the electric charge of the capacitor of the first means by the output of the second means; and a fourth means for controlling the electric charge of the capacitor of the first means by the output of the second means. An inrush current prevention circuit for a power supply device, characterized in that the circuit controls energization of the coil of the relay by means.