JP2812345B2 - Capacitor charging circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitor charging circuit capable of smoothly charging a capacitor even when a power supply voltage fluctuates.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram showing a conventional example of a capacitor charging circuit. In FIG. 2, the AC power output from the AC power supply 2 is converted into DC power by a rectifier 5 configured by a diode bridge connection, and when this DC power is supplied to a load 7, the DC power output from the rectifier 5 is Since the pulsation includes the ripple, a large-capacity smoothing capacitor 6 is connected to the DC output side of the rectifier 5 to absorb the ripple and smooth the DC power supplied to the load 7. However, when the AC power supply 2 is directly connected to the rectifier 5 to activate the rectifier 5, an extremely large charging current enters the smoothing capacitor 6, so that the rectifier 5 is damaged by an overcurrent or a voltage drop due to the inrush current. Inconveniences such as adversely affecting other loads connected to the AC power supply 2 occur. Therefore, a parallel connection circuit of the current limiting resistor 3 and the short-circuit contactor 4 is connected between the AC power supply 2 and the rectifier 5, and the current limiting resistor 3 is inserted (that is, the short-circuit contactor 4 is open). When the capacitor voltage detected by the capacitor voltage detector 11 rises to the value set by the charge switching voltage setting device 12 while limiting the current, the short-circuit contactor 4
And the current limiting resistor 3 is short-circuited. Thus AC power supply 2
Is applied to the smoothing capacitor 6 to complete the charging.

[0003]

Since the output voltage of the power supply generally fluctuates due to a change in the load or a change in the circuit power factor, the load can be operated without any problem even if the power supply voltage fluctuates slightly. ing. Here, the power supply voltage is often set to a range of ± 15% of the rated voltage (that is, 85% to 115% of the rated voltage) as an allowable voltage fluctuation range. Incidentally, in the conventional circuit shown in FIG. 2, when the AC power supply 2 is at the rated voltage, the charge switching voltage setting device 12
Is set to 95% of the rated voltage, for example.
If the output voltage of the AC power supply 2 drops to the lower limit of the allowable fluctuation range, that is, 85% of the rated voltage, the comparator 13 does not operate, and the current limiting resistor 3 is connected to the circuit. , That is, the state where the charging of the smoothing capacitor 6 is not completed is continued. Such inconvenience can be solved by setting the set value of the charge switching voltage setting device 12 to a value lower than the allowable lower limit value of the voltage fluctuation. However, when the short-circuit contactor 4 is closed and the current-limiting resistor 3 is short-circuited, The charging voltage of the smoothing capacitor 6 is low,
The output voltage of the current limiter becomes large, which causes a problem that a large charging current enters the smoothing capacitor 6 at the moment when the current limiting resistor 3 is short-circuited. In particular, the rush current becomes extremely large when the output voltage of the AC power supply 2 rises to near its allowable upper limit (115% of the rated voltage).

Accordingly, an object of the present invention is to provide a capacitor charging circuit in which a capacitor is first charged via a current limiting resistor and then the current limiting resistor is short-circuited. To be able to do it.

[0005]

In order to achieve the above object, a capacitor charging circuit according to the present invention comprises: a power supply whose output voltage fluctuates within an allowable range; a capacitor connected to and charged by the power supply; And a resistor inserted between the capacitor, short-circuit means for short-circuiting the resistance, capacitor voltage detection means for detecting the terminal voltage of the capacitor,
Charge switching voltage setting means for setting a charge switching voltage;
A power supply voltage detecting means for detecting a voltage of the power supply in a capacitor charging circuit comprising a comparator for issuing a resistance short-circuit command to the short-circuit means when the capacitor voltage reaches a charge switching voltage, and And a charge switching voltage changing means for changing a charging switching voltage set value to be given to the comparator, wherein the charge switching voltage changing means includes a first voltage setting means for setting a lower limit value of an allowable voltage of the power supply as a set value; A first calculating unit calculates a deviation between the set value of the first voltage setting unit and the output voltage value of the power supply.
Adding means, a second voltage setting means for setting a value obtained by subtracting a constant value from an allowable voltage lower limit value of the power supply, and a set value of the second voltage setting means and an addition operation result of the first adding means. And second adding means for adding.

[0006]

According to the present invention, charging of a capacitor is started via a current limiting resistor, and when the capacitor voltage rises to a charge switching voltage, the current limiting resistor is short-circuited and the entire output voltage from a power supply is applied to the capacitor. If the power supply voltage fluctuates in the capacitor charging circuit that completes the charging of the capacitor, the charge switching voltage is changed in response to this voltage fluctuation, so that the incomplete charging state continues or the current-limiting resistor is short-circuited. This is to avoid a problem that sometimes a large charging current enters.

[0007]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. An AC power supply 2, a current limiting resistor 3, a short-circuit contactor 4, a rectifier 5, and a smoothing capacitor 6 shown in the circuit of this embodiment. , Load 7, capacitor voltage detector 11, and comparator 1
The name, application, and function of 3 are the same as those of the conventional circuit described above with reference to FIG.

The circuit shown in FIG. 1 includes an instrument transformer 21 for detecting the output voltage of the AC power supply 2 and a power supply voltage detector 22. The detected voltage is switched by charging. It is provided to the voltage changing circuit 20. When the output voltage of the AC power supply 2 fluctuates, the charge switching voltage applied to the comparator 13 also changes in conjunction with the voltage fluctuation, so that the ratio of the charge switching voltage to the power supply voltage when the current limiting resistor 3 is short-circuited is substantially constant. Value.

In the embodiment shown in FIG. 1, the difference between the output voltage of the AC power supply 2 output from the power supply voltage detector 22 and the voltage set by the first voltage setting device 23 is calculated by the first adder 24. However, the set value of the first voltage setter 23 is selected as the lower limit of the allowable voltage fluctuation range of the AC power supply 2. For example, if the rated voltage of the AC power supply 2 is 200 volts, the first voltage setting device 23 sets K × 200 × 0.85 = 229.5 volts (where the value of the constant K is 1.35 in the case of three-phase full-wave rectification). I do. Therefore, when the output voltage of the AC power supply 2 is at the lower limit of the allowable fluctuation range, the operation result of the first adder 24 is zero, but when the output voltage of the AC power supply 2 is at the upper limit of the allowable fluctuation range, K × ( The first adder 24 outputs 81 volts (1.15 × 200−0.85 × 200) = 81 volts.

The set value of the second voltage setting unit 26 is
A value obtained by subtracting a certain value from the lower limit value of the allowable voltage fluctuation range is set. Assuming a constant value of 10 volts, this setting is 1.
35 x 200 x 0.85-10 = 219.5 volts. The result obtained by adding the set value of the second voltage setter 26 and the addition operation result of the first adder 24 obtained via the blocking diode 25 by the second adder 27 is given to the comparator 13.
Therefore, the comparator 13 supplies the current limiting resistor 3 to the short-circuit contactor 4.
(That is, the result of the addition operation of the second adder 27) is 0 + 219.5 = 219.5 volts when the output voltage of the AC power supply 2 is 85% of the rated value, and this output voltage (2
00 x 0.85 x 1.35 = 229.5 volts).
81 when the output voltage of AC power supply 2 is 115% of the rated value.
+ 219.5 = 300.5 port and this output voltage (200 ×
1.15 x 1.35 = 310.5 volts). That is, even if the output voltage of the AC power supply 2 fluctuates, the ratio of the voltage at which the short-circuit contactor 4 operates to the output voltage is substantially constant.

[0011]

According to the present invention, a capacitor charging circuit which first charges a capacitor via a current limiting resistor, then short-circuits the current limiting resistor and completes charging. By providing a charge switching voltage change circuit so that the ratio of the capacitor voltage to the power supply voltage at the time when the resistor is short-circuited is always constant, the current-limiting resistor is not short-circuited and the charging incomplete state continues, or the current-limiting resistor Can prevent the inconvenience of inrush of a large charging current when short-circuiting the capacitor, so that the effect of smoothly charging the capacitor can be obtained. Effects such as avoiding adverse effects can also be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional example of a capacitor charging circuit.

[Explanation of symbols]

 2 AC power supply 3 Current limiting resistor 4 Short circuit contactor 5 Rectifier 6 Smoothing capacitor 11 Capacitor voltage detector 12 Charge switching voltage setting device 13 Comparator 20 Charge switching voltage change circuit 21 Instrument transformer 22 Power supply voltage detector 23 First voltage setting Unit 24 first adder 25 blocking diode 26 second voltage setting unit 27 second adder

Claims (1)

(57) [Claims] A power supply whose output voltage fluctuates within an allowable range;
A capacitor connected to and charged by the power supply, a resistor inserted between the power supply and the capacitor, short-circuit means for short-circuiting the resistance, capacitor voltage detection means for detecting a terminal voltage of the capacitor, and a charge switching voltage And a comparator for issuing a resistance short-circuit command to the short-circuit means when the capacitor voltage reaches the charge-switching voltage, wherein a power supply voltage for detecting an output voltage of the power supply is provided. Detecting means; and charging switching voltage changing means for changing a charging switching voltage set value to be applied to the comparator in response to the change in the power supply voltage, wherein the charging switching voltage changing means sets an allowable voltage lower limit value of the power supply. A first voltage setting means to be a set value, and a bias between the set value of the first voltage setting means and an output voltage value of the power supply. , A second voltage setting means for setting a value obtained by subtracting a constant value from the lower limit of the allowable voltage of the power supply, and a setting value of the second voltage setting means and the first adding means. And the second addition means for adding the result of the addition operation of the second addition means. If the terminal voltage of the capacitor reaches the addition operation result of the second addition means, the comparator issues a resistance short-circuit command to the short-circuit means. Characteristic capacitor charging circuit.