JPH0197131A - Switching power circuit - Google Patents

Abstract

PURPOSE:To prevent the breakdown of parts by limiting a rush current through directly detecting an AC input current. CONSTITUTION:When an AC input current from an AC input 23 is small, the detected value of an AC input current detection circuit 2 becomes small, a comparison circuit 3 judges the AC input current to be below a prescribed value, and a resistance short-circuiting circuit 4 short-circuits an AC input current-limiting resistance 5. When the AC input current increases to reach said prescribed value, the resistance short-circuiting circuit 4 is opened contrary to said operation. Therefore, the AC current-limiting resistance 5 works on a rush current flowing directly after the AC input switch 1 is turned ON, and a smoothing capacitor 7 is charged via a rectifier 6. When the AC input current is below the prescribed value, the AC current-limiting resistance 5 is short- circuited.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a switching power supply circuit.

[Conventional technology]

A conventional switching power supply circuit has a configuration as shown in FIG.

That is, the conventional switching power supply circuit shown in FIG. 2 includes an AC input switch 1, a current limiting resistor 12, a rectifier 6, a smoothing capacitor 7, and a switching control circuit 8.
, a switching transformer 16 , a secondary circuit 10 , a triac 18 , a diode 19 , resistors 20 and 21 , and a capacitor 22 .

Immediately after turning on the AC input switch 1, turn on the AC input switch 2.
A large current flows from the capacitor 3 to charge the smoothing capacitor 7. This is called an inrush current, and in this example, this inrush current is limited by a current limiting resistor 12 to prevent damage to components.

However, to prevent this, a triac 18 is connected. When the smoothing capacitor 7 is charged, the switching control circuit 8 starts operating and a voltage is induced in the auxiliary winding of the switching transformer 16. This induced voltage turns on the triac 18 and short-circuits the current limiting resistor 12. In this way, the current limiting resistor 12 is prevented from burning out.

[Problem that the invention seeks to solve]

However, in the above-mentioned conventional switching power supply circuit, the triac remains ON when the switching control circuit is operating, so if the AC input switch is turned ON within a short period of time when it is OFF, the triac remains ON.
Since no FF' occurs and an unlimited rush current flows, there is a drawback that connected parts may be damaged.

[Means for solving problems]

The switching power supply circuit of the present invention includes an AC input current limiting resistor, an AC input current detection circuit, a comparison circuit that compares a detected value of the AC input current detection circuit with a specified value, and a and a resistor shorting circuit that shorts the AC input current limiting resistor.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

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

The switching power supply circuit shown in FIG. 1 includes an ACC input switch color, an AC input current limiting resistor 5, an AC input current detection circuit 2, and a comparison circuit that compares the detected value of the AC input current detection circuit 2 with a standard value. 3, a resistor shorting circuit 4 that shorts the AC input current limiting resistor 5 based on the comparison result in the comparison circuit 3, a rectifier 6, a smoothing capacitor 7, a switching control circuit 8, a switching transformer 9,
It is configured to include a secondary circuit IO.

Next, the operation of the embodiment shown in FIG. 1 will be explained in detail with reference to the drawings.

When the AC input current from AC human power 23 is small, A
The detected value of the C input current detection circuit 2 becomes smaller, the comparison circuit 3 determines that the AC input current is less than a specified value, and the resistor shorting circuit 4 shorts the AC input current limiting resistor 5.

If the AC input current increases and reaches the specified value,
In contrast to the above operation, the resistive short circuit 4 becomes open.

Therefore, the AC current limiting resistor 5 acts on the inrush current immediately after turning on the AC input switch 1, and when the smoothing capacitor 7 is charged via the rectifier 6 and the AC input current becomes less than the specified value, the AC current The limiting resistor 5 is short-circuited.

〔Effect of the invention〕

The switching power supply circuit of the present invention directly detects and limits the AC input current, so even if the AC input switch is turned 0N10FF at any timing, the inrush current can be limited, thereby preventing component damage. effective.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional example. 1...AC input switch, 2...A
C input current detection circuit, 3... Comparison circuit, 4...
... Resistor short circuit, 5 ... AC input current limiting resistor, 6 ... Rectifier, 7 ... Smoothing capacitor, 8 ... Switching control circuit, 9
, 16... Switching transformer, 10...
... Secondary circuit, 12 ... Current limiting resistor, 1
8...Triac, 19...Diode, 20.21...Resistor, 22...
Capacitor, 23...AC input. Agent Patent Attorney Oto Uchihara

Claims (1)

[Claims] an AC input current limiting resistor, an AC input current detection circuit,
A switching power supply circuit comprising: a comparison circuit that compares a detection value of the AC input current detection circuit with a specified value; and a resistance shorting circuit that shorts the AC input current limiting resistor based on the result of the comparison circuit. .