JPH0327721A - Inrush current limit circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an inrush current limiting circuit used, for example, in a power supply device for an AC servo driver.

BACKGROUND OF THE INVENTION FIG. 2 is a block diagram of a conventional inrush current limiting circuit. In Fig. 2, 1 is an AC power supply, 2 is a rectifier circuit connected to the AC power supply 1, 3 is a smoothing capacitor, 4 is a motor drive circuit connected to both ends of the smoothing capacitor 3, 5 is a synchronous motor, and 6 is a A current limiting resistor connected between the rectifier circuit 2 and the smoothing capacitor 3, 7 a relay that short-circuits the current limiting resistor 6, 8 a DC/DC converter, 9 a motor control circuit, and 10 a base drive circuit. It is.

FIG. 3 shows the relay drive power supply voltage and the base drive circuit 10 power supply voltage.

The operation of the inrush current limiting circuit configured as above will be described below.

First, the inrush current generated when the power is turned on is limited by the current limiting resistor 6. Thereafter, as the input voltage increases, when the relay drive power supply voltage output from the DC/DC converter reaches the relay operating voltage (approximately 80% of the rated value), the relay turns on and short-circuits the current limiting resistor 6.

Also, when the power is turned off, the relay drive power supply voltage reaches the relay open voltage (approximately 10% of the rating) and the relay opens (
OFF).

Problems to be Solved by the Invention However, the conventional inrush current limiting circuit shown in FIG. 2 had the following problems.

After the power supply operation enters steady state, the power supply momentary O
In the case of FF and ON, the inrush current limiting operation may not be performed sufficiently.

The reason for this is that the operating voltage of a relay is generally lower than the voltage at the start of operation (approximately 80% of the rating) and the voltage at the time of opening (approximately 1% of the rating).
0%) is very low. Furthermore, since the drive power for the relay 7 is input directly from the DC/DC converter 8, it takes time for the drive power voltage for the relay 7 to drop because the charge accumulated in the smoothing capacitor 3 remains after the power is turned off. Therefore, when the power is turned on again (ON) while the relay 7 is not opened, that is, the drive power supply voltage of the relay 7 has not reached the relay open voltage, the inrush current is not sufficiently limited. Therefore, there was a problem of wear and welding of the contacts of the power switch.

The present invention solves the above-mentioned problems, and the present invention solves the above-mentioned problems.
FF. The purpose of the present invention is to provide an inrush current limiting circuit that can operate reliably even when the inrush current is turned on.

Means for Solving the Problems To achieve this object, the present invention provides a relay drive circuit disposed between a relay that short-circuits a current limiting resistor and a DC/DC converter that drives this relay, The circuit configuration is such that the relay is controlled by the output signal from this drive circuit.

According to the above structure, the relay is opened (OFF) when either the input power supply detection signal or the low voltage detection signal outputs "0", and both of the signals output "1". When this happens, the relay is activated (ON).

As shown in Figure 3, the low voltage detection value VL is set near the bending point of the relay drive power supply voltage and the base drive circuit power supply voltage, and when the main power supply voltage drops (lower than the low voltage detection value VL), the low voltage is detected. The detection circuit stops the motor when outputting "0" from "1" to protect the system. In addition, the input power supply detection circuit outputs a "1" signal when the input power is ON, an "O" signal when the input power is OFF, and outputs an "O" signal when the input power is turned ON.
The motor is stopped when the signal is output to protect the system.

Embodiment FIG. 1 shows a block diagram of an inrush current limiting circuit in an embodiment of the present invention.

In Figure 1, 1 is an AC power supply, 2 is a rectifier circuit, 3 is a smoothing capacitor, 4 is a motor drive circuit, 5 is a synchronous motor, 6 is a current limiting resistor, 7 is a relay 8 is a DC/DC
The converter, 9 is a motor control circuit, and 10 is a base drive circuit, which are the same as in the conventional example. 11 is a relay drive circuit, 12 is an input power supply detection circuit that detects ON/OFF of the input power supply, and 13 is a low voltage detection circuit that detects a voltage drop in the main power supply.

The operation of the inrush current limiting circuit configured as described above will be described below.

The inrush current generated when the power is turned on is passed through the current limiting resistor 6.
The output signal of the input power supply detection circuit 12 outputs "1" at the same time as the power is turned on.

After that, as the main current voltage increases, the low voltage detection value V
．． ．． When the voltage reaches the above level, the output signal of the low voltage detection circuit 13 becomes “
1", and the relay drive circuit 11 detects that both of the output signals are "1", and the relay 7 is activated (ON) L.
to short-circuit the current limiting resistor 6.

After the power is turned off, the output signal of the input power supply detection circuit is “O”
is output instantaneously, and the relay drive circuit 11 detects it and opens the relay 7 (OFF).

As described above, according to this embodiment, when the input power is turned ON and OFF,
By detecting the detection signals generated from the input power supply detection circuit that detects F and the low voltage detection circuit that detects the voltage drop of the main power supply and controlling the short-circuit and opening of the relay, when the input power is first turned on, As shown, the relay activation time is delayed by T time compared to the conventional method, and the inrush current can be limited even when the power is turned off and turned on instantaneously.

Effects of the Invention As described above, the present invention controls a relay using a combination of an input power supply detection signal and a low voltage detection signal, thereby limiting the inrush current from the time the power is first turned on, and also enables instantaneous OFF of the power supply. Even in the case of ON, it is possible to realize an excellent circuit that can sufficiently perform the rush current limiting operation.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an inrush current limiting circuit according to an embodiment of the present invention, Fig. 2 is a block diagram of a conventional inrush current limiting circuit, and Fig. 3 is a diagram showing relay drive voltage and input-output characteristics of a rectifier circuit. FIG. 3 is a diagram showing a relationship between low voltage setting values vL. 1... AC power supply, 2... Rectifier circuit, 3
... Smoothing capacitor, 4 ... Motor drive circuit, 6 ... Current limiting resistor, 7 ...
...Relay, 8...D C/DC converter, 9...Motor control circuit 11...Relay drive circuit, 12...Input power supply detection circuit , 13
...Low voltage detection circuit.

Claims (2)

[Claims] (1) A rectifier circuit connected to an AC power source, a motor drive circuit connected to the output end of this rectifier circuit, a smoothing capacitor connected in parallel to this drive circuit, and a motor drive circuit connected between this smoothing capacitor and the rectifier circuit. A motor control circuit and a relay drive circuit are connected to the output of a DC/DC converter connected to the output end of the rectifier circuit, and the relay drive circuit has a current limiting resistor and a relay that short-circuits the resistor. An inrush current limiting circuit configured to short-circuit or open a relay depending on the output. (2) The relay drive circuit is configured to turn on and off the input power supply.
2. The inrush current limiting circuit according to claim 1, wherein the relay is short-circuited or opened by detecting a detection signal generated from an input power supply detection circuit that detects a voltage drop in the output voltage of the smoothing capacitor and a low voltage detection circuit that detects a voltage drop in the output voltage of the smoothing capacitor.