JPH0530650A - Inrush current preventing circuit - Google Patents

Abstract

PURPOSE:To provide an inrush current preventive circuit for various electric appliances in which inrush current is blocked when an AC input is applied intermittently and the inrush current is suppressed easily and positively. CONSTITUTION:The inrush current preventive circuit comprises two inrush current preventing resistors 1, 2, a switch circuit 3, and a section 10 for detecting a rectified voltage and controlling the switch circuit 3. Resistances of the resistors 1, 2 are set so that an inrush current can be suppressed even if an AC voltage is applied when the voltage of a capacitor 5 is 0V and the ratio of the resistances is set to that the AC input voltage divided by the resistors 1, 2 will provided a detection voltage thus suppressing the inrush current easily and positively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inrush current prevention circuit used in a power supply circuit.

[0002]

2. Description of the Related Art An example of a conventional inrush current prevention circuit will be described below with reference to the drawings. FIG. 5 shows a conventional inrush current prevention circuit diagram. As shown in FIG. 5, as components, 1 is a resistor, 2 is a switch circuit, 3 is a control circuit, 4 is a rectifying diode, and 5 is a capacitor.

The operation of the inrush current prevention circuit configured as described below will be described below. When no alternating current is input, the control circuit 3 turns off the switch circuit 2. When an alternating current is input, the resistance 1 suppresses the inrush current. When an alternating current is input and the capacitor 5 is charged, the control circuit 3 turns off the switch circuit 2 to suppress the loss in the resistor 1.

[0004]

However, in the above-mentioned configuration, when the control circuit malfunctions when the AC input is intermittently applied and the switch circuit is turned on while the voltage of the rectifying capacitor is discharged, the resistance is reduced. Since it is short-circuited by the switch circuit, the impedance becomes small and inrush current flows. Further, the circuit design is difficult and complicated in order to prevent the control circuit from malfunctioning when the AC input is intermittently applied.

In view of the above problems, the present invention provides a rush current prevention circuit that reliably suppresses the rush current at the time of AC input.

[0006]

In order to achieve the above-mentioned object, the present invention has two resistance ratios obtained from the ratio of the residual voltage and the input voltage when the detection voltage or the AC input is intermittently applied. By using the inrush current prevention resistor, the inrush current can be surely suppressed even when the AC input is intermittently applied. The two resistance values may be set so that the inrush current is suppressed when the switch circuit is off and the voltage of the rectifying capacitor is OV, and when the switch circuit is on and the voltage of the rectifying capacitor is the detection voltage or the residual voltage. . When the resistors are connected in series, the inrush current is controlled by the total impedance of the two resistors in the state of the capacitor voltage OV, and the ratio of the two resistors is the resistance voltage division of the input voltage is the detection voltage or the residual voltage. It may be set so that it becomes a voltage.

With the above structure, the voltage detection control is
This is performed by direct detection of the rectified voltage or detection of a transformer output voltage that converts a switching power supply output voltage having an arbitrary line regulation characteristic in the subsequent stage or a primary input voltage into a low voltage.

[0008]

According to the present invention, when the detected voltage or the residual voltage is smaller than the voltage (resistance divided voltage of the input voltage) obtained from the two resistance ratios, the switch circuit is turned off and the impedance of the line rises due to the above structure. The current is small. When the voltage is high, the switch circuit is turned on and the impedance of the line becomes small, but the inrush current is small because the voltage is charged in the capacitor. Therefore, when the AC input turns on immediately after turning off, even if the switch circuit does not turn off, the inrush current is small as long as the residual voltage is equal to or higher than an arbitrary voltage.

In the voltage detection control, when a switching power supply is connected in the subsequent stage, the switch circuit can be controlled by detecting the voltage by using the regulation characteristic of the input voltage of the power supply.

Further, by performing the voltage detection control with the output voltage of the transformer for converting the primary side input into a low voltage, the detection circuit can be operated with a low power supply voltage, which facilitates the circuit design.

[0011]

(Embodiment 1) An inrush current prevention circuit according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a circuit diagram of an inrush current prevention circuit according to one embodiment of the present invention. As shown in FIG. 1, as components, 1 is a resistor, 2 is a resistor, 3 is a switch circuit, 4 is a rectifying diode, 5 is a capacitor, 6 is a resistor, 7 is a resistor,
Reference numeral 8 is a reference voltage, 9 is a comparator, and 10 is a voltage detection unit, which includes resistors 6 and 7, a reference voltage 8 and a comparator 9.

The operation of the inrush current prevention circuit configured as described above will be described. When no alternating current is input, no voltage is applied to the capacitor 5 and the voltage detection unit 10 turns off the switch circuit 3. When the alternating current is input, the switch circuit 3 is off, so the inrush current is small. The resistors 6 and 7 and the reference voltage 8 are determined so that the voltage detection control unit 10 turns on the switch circuit 3 when the voltage exceeds the ratio of the resistors 1 and 2 of the input voltage.
When the voltage of the capacitor 5 exceeds the detection voltage, the switch circuit 3 is turned on and the loss in the resistor 2 disappears. When the switch circuit 3 is turned on, no rush current flows because the capacitor 5 is charged with voltage. When the AC input disappears, the voltage of the capacitor 5 drops, and even when AC is input again when the voltage is equal to or higher than the detection voltage, the rush current does not flow because the voltage remains in the capacitor 5. When the voltage of the capacitor 5 drops below the detection voltage, the switch circuit 3 is turned off, and no inrush current flows even if the switch circuit 3 is input again. The values R1 and R2 of the resistors 1 and 2 are such that R1 + R2 can suppress the inrush current when the switch circuit off-capacitor 5 is at the voltage OV, and the ratio of R1 and R2 is the input voltage R1.
And the voltage divided by R2 becomes the detection voltage. As described above, according to the present embodiment, the two resistors, the switch circuit connected in parallel to one of the two resistors, the two resistors for controlling the resistor, and the voltage detection control unit for performing detection with the voltage determined by the input voltage are provided. Thus, the inrush current can be surely suppressed.

(Second Embodiment) The second embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a circuit diagram of an inrush current prevention circuit showing a second embodiment of the present invention. In FIG. 2, resistors 1, 2,
The switch circuit 3, the diode 4, the capacitor 5, the resistors 6 and 7, the reference voltage 8, and the comparator 9 have the same configuration as in FIG. The difference from the configuration of FIG.
1, a resistor 12, a capacitor 13, a buffer 14, a transformer 15, a rectifying diode 16, a capacitor 17, and a capacitor 18 are provided. The voltage detection control unit 19 includes resistors 6, 7, 12, a reference voltage 8, a comparator 9, a diode 11, capacitors 13, 18, and a buffer 14.

The operation of the inrush current prevention circuit configured as described above will be described below. The operations of the resistors 1 and 2 and the switch circuit 3 are the same as those in the first embodiment. The difference is the operation of the voltage detection controller 19 will be described. The voltage detection detects the voltage of the capacitor 17 output from the transformer 15. The capacitor 18 detects the change in the detection voltage. Only the ON operation of the switch circuit 3 is delayed by the diode 11, the resistor 12, the capacitor 13, and the buffer 14 for a predetermined time. When alternating current is input, the voltage of the capacitor 17 rises through the transformer 15 and the diode 16. This rise is detected by the capacitor 18 and delayed for a certain period of time to turn on the switch circuit. When the AC input disappears, the voltage of the capacitor 17 drops, the voltage is detected through the capacitor 18, and the switch circuit 3 is turned off. The detection voltage is a transformer 1 that converts AC input into low voltage.
5, the voltage of the detection circuit is low and the design is easy. Further, in this case, the relationship between the voltages of the capacitor 5 and the capacitor 17 is different when rising and when falling, so the voltage value and the voltage change are detected, and the switch circuit 3 is controlled by delaying the voltage for a certain period only when it is on. . The residual voltage remaining in the capacitor 5 when the switch circuit 3 is turned off is used as the detection voltage of the first embodiment to determine the values of the resistors 1 and 2. In this way, the inrush current can be suppressed by the resistors 1 and 2 during AC input. The rush current is suppressed by the resistor 1 even when an alternating current is input while the residual voltage remains in the capacitor 5 and the switch circuit is turned on. As described above, by detecting the output of the transformer that converts the AC input into a low voltage, the detection voltage and the circuit voltage are lowered, so that the circuit design becomes easier, and the change in the voltage is detected and the switch circuit 3 is turned on for a certain period of time. By delaying the detection voltage, the switch circuit can be reliably controlled even from a place other than the capacitor 5, and the inrush current can be suppressed.

(Third Embodiment) A third embodiment of the present invention will be described below with reference to the drawings. FIG. 3 is a circuit diagram of an inrush current prevention circuit showing a third embodiment of the present invention. In FIG. 3, 1 and 2 are resistors, 3 is a switch circuit, 4 is a diode, and 5 is a capacitor. The above is the same as the configuration of FIG. The difference from the configuration of FIG. 1 is that the voltage detection control section is eliminated, the switching power supply 20 is connected to the latter stage, and the output circuit controls the switch circuit.

The operation of the inrush current prevention circuit configured as described above will be described below. As the input regulation characteristic of the switching power supply, the regulation characteristic is deteriorated and the output voltage is lowered when the input voltage is lower than a certain value as shown in FIG. The voltage is detected by this regulation characteristic, and the switch circuit 3 is controlled by the output voltage. The threshold voltage of the regulation characteristic corresponds to the detection voltage of the first embodiment. In general, a switching power supply is often connected in the subsequent stage, and by providing the switching power supply with the above characteristics, the voltage detection control unit is not necessary and the switching circuit 3 is controlled using the switching power supply output voltage. I can do things.

[0019]

As described above, according to the present invention, two resistors are connected to an AC input line, and a switch circuit is connected in parallel to one of the resistors, and a detection voltage determined by the two resistance ratios and the input voltage is applied. By controlling the switch circuit by the voltage detection unit provided therein, the inrush current can be surely suppressed even if the AC input becomes continuous.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an inrush current prevention circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of an inrush current prevention circuit according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram of an inrush current prevention circuit according to a third embodiment of the present invention.

FIG. 4 is a regulation characteristic diagram for the switching current input of FIG.

FIG. 5 is a circuit diagram of a conventional inrush current prevention circuit.

Claims (5)

[Claims] 1. An inrush current preventing resistor connected in series to an AC input line, a switch circuit connected in parallel with one of the resistors, a rectified voltage is detected, and two input voltages are connected in series. An inrush current prevention circuit that has a voltage detection control circuit that controls the switch circuit with a detection voltage that is determined by the voltage divider of the resistor. 2. The inrush current prevention circuit according to claim 1, further comprising a transformer that changes the primary side AC input to a low voltage, a circuit that rectifies the transformer output, and a voltage detection control circuit that detects the rectified voltage. 3. The inrush current prevention circuit according to claim 2, wherein the voltage detection control circuit detects the voltage value and the amount of change in the voltage and has a delay in the switch circuit ON operation. 4. A switching power supply circuit having a rectified voltage as an input and causing a voltage drop when the regulation characteristic is rapidly deteriorated at a certain input voltage or less, and a switch circuit is controlled by the switching power supply output voltage. Inrush current prevention circuit. 5. An inrush current prevention resistor connected in series to an AC input line, and a switch circuit in which one resistor is connected in parallel, one resistor and a switch circuit are connected in series, and the other. 2. The inrush current prevention circuit according to claim 1, wherein the one resistor is connected in parallel.