JPH03218254A - Surge preventing circuit in input circuit for switching power supply - Google Patents

Abstract

PURPOSE:To prevent surge current by catching the surge current, upon turn ON of an AC power supply, as the charging current for a smoothing capacitor and then operating a relay by means of a relay circuit having an auxiliary coil, during rising process of the capacitor charging voltage, thereby short- circuiting a limiting resistor. CONSTITUTION:Upon connection of an AC power supply E between AC source terminals U, V, a current limited by a limiting resistor R1 flows through a rectifying circuit D1 and the rectified current causes charging voltage rise of a smoothing capacitor C1 thus actuating a switching control circuit 1. A voltage is induced in an auxiliary coil N2 and rectified/smoothed through a diode D2 and a capacitor C2 in a relay circuit containing the auxiliary coil N2. When the voltage U rises upto the responsive voltage of a relay X, the relay X is excited to close the contact (x) thereof thus blocking surge current.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inrush prevention circuit in an input circuit of a switching power supply.

[Conventional technology]

Conventionally, as shown in FIG. 2 of the attached drawings, an AC power terminal U
, V, a limiting resistor 11 short-circuited by a contact 10' of a relay 10, a diode 12, a resistor 13, and the relay 10 are connected in series, and a delay circuit consisting of a smoothing capacitor 14 and a resistor 15 is connected to the relay 10. 16 are connected in parallel, a rectifier circuit 17 is connected to the rectifier circuit 17, an output transformer 18 and a smoothing capacitor 19 are connected in parallel, and a switching control circuit @2 is connected to the primary coil of the output transformer 18.
Switching element 2 that is ON/OFF controlled by 0
1 are connected in series, and when AC power supply E is connected to AC power supply terminals U and V, inrush current is prevented by delaying the activation of relay 10 by delay circuit #I16 and closing its contact 10'. An inrush prevention circuit in an input circuit of a switching power supply having such a configuration is known.

[Problem to be solved by the invention]

However, according to the above-mentioned conventional ellipse, the constant voltage of the excitation coil of the relay is limited depending on the input voltage, which limits the selection of relays, and there is a risk that the relays will become expensive. As the delay circuit capacitor deteriorates,
There were defects such as loss of anti-intrusion effect.

[Means to solve the problem]

The present invention provides an inrush prevention circuit in an input circuit of a switching power supply, which aims to eliminate the conventional drawbacks, and supplies AC power to a rectifier circuit via a limiting resistor, and also supplies the control resistor to the control resistor by a relay. a circuit that connects a smoothing capacitor to the rectifier circuit and supplies its output to an output transformer through a switching element; an auxiliary coil is provided in the output transformer; and a relay is actuated by the induced voltage of the auxiliary coil. It is characterized by being constructed from a relay circuit. Preferably, the relay circuit comprises a relay and a capacitor connected in parallel to the auxiliary coil via a diode, and further comprises a resistor connected in series to the relay.

[For production]

When the AC power is input, a current limited by the limiting resistor flows into the rectifying circuit, charging the smoothing capacitor, and in the process of increasing the charging potential, the switching element is activated by the switching control circuit. It operates ON and OFF, and an intermittent current flows through the primary coil of the output transformer.

Then, a voltage is induced in the auxiliary coil corresponding to the turns ratio between the primary coil and the auxiliary coil, and this induced voltage is rectified and smoothed by the diode and the capacitor and applied to the relay. .

Therefore, by setting the applied voltage equal to the constant line voltage of the excitation coil of the relay, the relay is activated by the induced voltage and its contacts short-circuit the limiting resistor, thereby achieving prevention of inrush current. Ru.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to FIG. 1 of the accompanying drawings.

Between AC power supply terminals U and V, there is a contact χ of relay X, which will be described later.
A resistor R1 which is short-circuited by the rectifier circuit D1 is connected in series with the rectifier circuit D1. An output transformer T and a smoothing capacitor C1 are connected in parallel to the output side of the rectifier circuit D1,
A switching element 01 whose ON and OFF states are controlled by a switching control circuit 1 is connected in series to the primary coil N of this output transformer T, as in the conventional case.

The output transformer T is provided with an auxiliary coil N2, and a relay X having a capacitor Q and a resistor R2 connected to the auxiliary coil N2 via a diode is connected in parallel to form a relay circuit.

When the AC power supply E is connected between the AC power supply terminals U and V, a current that is not limited by the limiting resistor R1 flows into the rectifier circuit D1, and the DC current is smoothed and the charging potential of the capacitor C1 increases. , In the process, the switching control circuit 1 is activated, and thereby the switching element Q is turned on and off, and an intermittent current flows through the primary coil N, of the output transformer T, so that the primary coil N, and the auxiliary coil N2 The auxiliary coil N2 corresponds to the winding ratio of
A voltage is induced at point a, and this induced voltage is rectified and smoothed by a diode in the relay circuit including the auxiliary coil N2 and a capacitor G, and the potential Va at point a at this time is N
, Vato v1 N1 However, v1 is the primary side voltage of the output transformer T.

Therefore, if the voltage applied to the excitation coil of relay When the relay X is energized, its contacts χ close, thereby achieving prevention of inrush current.

〔Effect of the invention〕

As described above, according to the present invention, the inrush current when an AC power source is input is captured as the charging current of the smoothing capacitor, and in the process of increasing the charging voltage of the capacitor, the relay circuit including the auxiliary coil operates the relay. Because it is an elliptical configuration that short-circuits the limiting resistor, there is no risk of it being affected by capacitor flaking or deterioration, and it is possible to reliably prevent inrush current, as well as to prevent the output transformer's primary coil and auxiliary coil from By selecting the winding ratio and the value of the resistor connected in series with the relay, it is possible to use a relay with any constant voltage, which has the advantage of being economical.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a conventional circuit diagram. R1...limiting resistance D1...rectifier circuit CI,
C2...Smoothing capacitor 1...Switching control circuit Q1...Switching element X...Relay T...Output 1 Herance N2...Auxiliary coil χ...Contact ■...Tiode

Claims (1)

[Claims] 1. A circuit that supplies AC power to a rectifier circuit through a limiting resistor and short-circuits the control resistor using a relay, a smoothing capacitor connected to the rectifier circuit, and whose output is connected to a switching element. An inrush prevention circuit in an input circuit of a switching power supply, characterized in that it is comprised of a circuit for supplying a voltage to an output transformer, and a relay circuit in which an auxiliary coil is provided in the output transformer and a relay is actuated by the induced voltage of the auxiliary coil. 2. An inrush prevention circuit in an input circuit of a switching power supply according to claim 1, wherein the relay circuit comprises a relay and a capacitor connected in parallel to the auxiliary coil via a diode. 3. An inrush prevention circuit for an input circuit of a switching power supply according to claim 2, comprising a resistor connected in series to the relay.