JP2002369513A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide circuitry for prolonging the operating time of a switching circuit in an instantaneous interruption, without increasing the size of a capacitor installed in a switching power supply. SOLUTION: A series circuit of a second smoothing capacitor 9 and a resistor 7 is connected, in parallel with a first smoothing capacitor 6 in a rectifying and smoothing circuit on the primary side of a converter transformer 10; the anode of a diode 8, connected in parallel with the resistor 7, is connected with the positive pole of the second smoothing capacitor 9; and the cathode is connected with the positive pole of the first smoothing capacitor 6 and one end of the primary winding 15; and the other end of the primary winding 15 is connected with the negative pole of the second smoothing capacitor 9 via an FET 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply provided with a measure against an instantaneous power failure.

[0002]

2. Description of the Related Art FIG. 5 is a circuit diagram of a conventionally used switching power supply. In order to extend the operation time of a switching circuit at the moment of an AC input momentary power failure, it is necessary to increase the capacity of a smoothing capacitor 3. However, it is necessary to increase the size as the capacity of the capacitor 3 increases. For example, in the case of a capacitor of φ35, it is necessary to use a capacitor of φ51 which is one rank higher, so that there is a problem that the material cost is increased, the size of parts is increased, and the mounting area is increased.

[0003]

Due to the above-mentioned problems, there has been a demand for a circuit configuration for extending the operation time of the switching circuit at the time of an instantaneous power failure without increasing the size of the capacitor.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and has a small-capacity first smoothing capacitor smaller in size than the large-sized, large-capacity smoothing capacitor 3 of the prior art shown in FIG. 6 and a second smoothing capacitor 9 having a smaller size and a smaller capacity are connected in parallel as shown in FIG. 1 to reduce the mounting area of the capacitor and reduce the ripple current. Things. That is, a series circuit of a second smoothing capacitor 9 and a resistor 7 is connected in parallel with the first smoothing capacitor 6 of the rectifying / smoothing circuit on the primary side of the converter transformer 10, and a diode 8 connected in parallel to the resistor 7 is connected. The anode is connected to the positive electrode of the second smoothing capacitor 9, and the cathode is connected to the positive electrode of the first smoothing capacitor 6 and one end of the primary winding 15.
Is connected to the negative electrode of the second smoothing capacitor 9 via the FET 11.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A series circuit of a second smoothing capacitor 9 and a resistor 7 is connected in parallel with a first smoothing capacitor 6 of a rectifying / smoothing circuit on the primary side of a converter transformer 10,
The anode of the diode 8 connected in parallel with the resistor 7 is connected to the second
The cathode is connected to the positive electrode of the first smoothing capacitor 6 and one end of the primary winding 15, and the other end of the primary winding 15 is connected to the negative electrode of the second smoothing capacitor 9 via the FET 11. Connected to. With the configuration described above, the mounting area of the smoothing capacitor can be reduced, and the switching operation time at the time of an instantaneous power failure can be maintained long.

[0006]

FIG. 1 is a basic circuit diagram of a switching power supply according to the present invention. When the AC input is turned on, as shown in FIG. 2, the second smoothing capacitor 9 is slowly charged through the resistor 7, but the first smoothing capacitor 6 is rapidly charged, and the charging time characteristics of both are smoothed. Is as shown in FIG.
During the steady operation of the switching power supply, the input current to the switching circuit 4 is mainly supplied from the first smoothing capacitor 6 and almost not supplied from the second smoothing capacitor 9 as shown in FIG. The life of the smoothing capacitor 9 is not shortened. When the AC input is off,
As shown in FIG. 4, the voltage is discharged from the first smoothing capacitor 6 to the switching circuit 4, and when the voltage drops, the voltage is discharged from the second smoothing capacitor 9 via the diode 8. The input capacitor capacitance of the circuit 4 is the sum of the first smoothing capacitor 6 and the second smoothing capacitor 9. Accordingly, the discharge time characteristics are as shown in FIG. 7, and the voltage drop time from 140 V to 50 V is one rank higher than that of the embodiment of the present invention using the first smoothing capacitor 6 and the second smoothing capacitor 9. Compared with the conventional example using the large smoothing capacitor 3, the result is almost the same. Here, the relationship between the smoothing capacitor 3 according to the conventional example and the first smoothing capacitor 6 and the second smoothing capacitor 9 according to the embodiment is represented by the following equation.

[0007]

(Equation 1)

[0008] Even if the first smoothing capacitor 6 is opened in the abnormal test, the charging current to the second smoothing capacitor 9 is limited by the resistor 7, so that most of the current flows through the switching circuit 4. Since the current flowing through the capacitor 9 becomes very small, there is no problem such as the explosion-proof valve of the capacitor 9 being operated. Therefore, the second smoothing capacitor 9 can sufficiently function as an auxiliary capacitor. FIGS. 8A and 8B show the mounting shapes of the first smoothing capacitor 6 and the second smoothing capacitor 9 used in the circuit of the present invention on the substrate, and FIGS. 9A and 9B show conventional shapes. 3 shows the mounting shape of the capacitor 3 of the circuit. In each figure,
(A) is a plan view and (b) is a side view. In addition, in the switching power supply according to the embodiment of FIG. 1, the capacity of the first smoothing capacitor 6 at the time of input is smaller than that of the conventional smoothing capacitor 3 of FIG. Power restart time is also reduced. Ratings (capacitance / voltage), shape and dimensions, mounting area of the capacitors used in the embodiment and the conventional example, 140 V → 50 V when AC input is off
Fall time, circuit restart time when AC input is off → on,
The following table shows that the circuit of the present invention has smaller parts and dimensions, a smaller mounting area, a shorter circuit restart time, and a lower cost than the conventional circuit. be able to. Note that the capacitance ratio of the second capacitor to the first smoothing capacitor 6 is
As a result of investigating a reduction in the mounting area, a reduction in the restart time, and a reduction in the cost, the range of 1/10 to 1/2 is appropriate.

[0009]

[Table 1]

[0010]

As described above, according to the switching power supply of the present invention, the area occupied by the capacitor mounted on the switching power supply can be reduced, the restart time of the circuit is shortened, and the cost is reduced. it can.

[Brief description of the drawings]

FIG. 1 is a basic circuit diagram of a switching power supply according to the present invention.

FIG. 2 is a diagram showing a flow of a charging current to a capacitor when an AC input is turned on in the circuit diagram of FIG. 1;

FIG. 3 is a diagram showing a current flow during a steady operation in the first circuit diagram.

FIG. 4 is a diagram showing a flow of a discharge current of a capacitor when an AC input is turned off in the circuit diagram of FIG. 1;

FIG. 5 is a basic circuit diagram of a conventional switching power supply.

FIG. 6 is a diagram showing a time characteristic of a charging voltage of a capacitor when an AC input is turned on in the circuit diagram of FIG. 1;

FIG. 7 is a diagram showing a time characteristic of a discharge voltage of a capacitor when an AC input is turned off according to the present invention.

FIGS. 8A and 8B are diagrams in which first and second capacitors are mounted on the switching power supply substrate of the present invention, wherein FIG. 8A is a plan view and FIG. 8B is a side view.

9A and 9B are diagrams in which a capacitor is mounted on a conventional switching power supply board, wherein FIG. 9A is a plan view and FIG. 9B is a side view.

[Explanation of symbols]

 Reference Signs List 1 AC input 2 Rectifier circuit 3 Smoothing capacitor 4 Switching circuit 5 Load 6 First smoothing capacitor 7 Resistance 8 Diode (primary side) 9 Second smoothing capacitor 10 Converter transformer 11 FET 12 Control circuit 13 Diode (secondary side) 14 Smoothing capacitor (secondary side) 15 Primary winding 16 Auxiliary winding 17 Secondary winding 18 Substrate

Continuation of the front page F term (reference) 5G015 FA16 GA04 HA16 JA60 5H730 AA16 BB23 BB43 BB52 CC01 DD04 EE02 EE07 XX02 XX14 ZZ12

Claims (1)

[Claims] 1. A series circuit of a second smoothing capacitor and a resistor is connected in parallel with a first smoothing capacitor of a rectifying / smoothing circuit on a primary side of a converter transformer, and an anode of a diode connected in parallel with the resistor is connected to a first resistor. The cathode was connected to the positive electrode side of the second smoothing capacitor and the positive electrode of the first smoothing capacitor and one end of the primary winding, and the other end of the primary winding was connected to the negative electrode of the second smoothing capacitor via the FET. A switching power supply characterized in that: