JP2001327161A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circuit structure capable of increasing output voltage holding time at an instantaneous power failure without enlarging a switching power supply. SOLUTION: This switching power supply supplies DC voltage obtained by rectifying and smoothing voltage generated at the secondary winding P2 of a converter transformer 5 with a diode 6 and an electrolytic capacitor 7, to a load by means of the switching operation of a converter circuit. A plurality of electric double-layer capacitors 9, 10 and a resistor 11 are connected to the electrolytic capacitor 7 in parallel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art FIG. 2 shows a conventional switching power supply circuit. The holding time t of the output voltage during an instantaneous power failure is determined by the capacity of an electrolytic capacitor 7 and the resistance of a load 8. Is very small in microfarads (μF), so the retention time t is very short.

[0003]

(Equation 1)

In order to increase the holding time, it is necessary to connect a large number of electrolytic capacitors 7 in parallel, so that a large area is required for installation, and the size of the switching power supply must be increased. .

[0005]

Because of the above problems, the switching power supply is not increased in size, that is, without increasing the number of electrolytic capacitors and connecting them in parallel, the capacitance value is increased, There has been a demand for a circuit configuration that extends the holding time of the output voltage during a power failure.

[0006]

The present invention solves the above-mentioned problems. As shown in FIG. 1, a series circuit of an electric double layer capacitor 9, 10 and a resistor 11 is connected in parallel with an electrolytic capacitor 7. By doing so, the electric charge stored in the electric double-layer capacitors 9 and 10 is discharged to the load 8 via the resistor 11 at the time of an instantaneous power failure, thereby increasing the holding time. That is, in the switching power supply which supplies a load with a DC voltage obtained by rectifying and smoothing the voltage generated in the secondary winding P2 of the converter transformer 5 by the diode 6 and the electrolytic capacitor 7 by the switching operation of the converter circuit, In parallel with the capacitor 7,
A plurality of electric double-layer capacitors 9, 10 and a resistor 11
Is a switching power supply.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in the circuit diagram of the switching power supply of FIG. 1, a series circuit of electric double layer capacitors 9, 10 and a resistor 11 is used in parallel with an electrolytic capacitor 7. Since the resistor 11 functions as a charging current limiting resistor, the voltage of the electric double layer capacitor gradually rises, but the voltage of the electrolytic capacitor 7 connected in parallel rises immediately.
A specified voltage can be instantaneously supplied to the load, and the electric double-layer capacitor is charged in a short time after charging the electrolytic capacitor 7. Further, once charged, even if the switching power supply is not applied to converter transformer 5 due to an instantaneous power failure, the falling speed of the supply voltage to load 8 becomes slow. Since the present invention is configured as described above, the voltage rises promptly by the electrolytic capacitor 7, and the charge time of the electric double layer capacitors 9, 10 greatly increases the holding time according to the following equation. Can be.

[0008]

(Equation 2)

The capacitance value of the electrolytic capacitor 7 is about 470 to 1000 μF when the output specification is 5 V and 100 mA. On the other hand, the capacity of the electric double layer capacitor is 4
Since 7 to 100F can be selected, substituting the capacitance values into [Equation 1] and [Equation 2] gives the following equations, respectively.

[0010]

(Equation 3)

[0011] Comparing the two equations of [Equation 3], t ₁ and t ₂
Is given by [Equation 4], and the circuit of the present invention can extend the holding time of the conventional circuit by 50,000 times.

[0012]

(Equation 4)

[0013]

FIG. 1 is a circuit diagram of a switching power supply according to the present invention, and FIG. 4 is a circuit diagram of a conventional example. FIG.
FIG. 5 shows the power switch 1 in FIGS. 1 and 4, respectively.
The output voltage Vo is the voltage of the electrolytic capacitor 7, and the output voltage Vo is the voltage of the electrolytic capacitor 7, and the output voltage Vo of the embodiment shown in FIG. FIG. 7 shows a comparison between the two. The resistor 11 of the circuit of the present invention shown in FIG. 2 is used for limiting the charging current because the electric double-layer capacitors 9 and 10 have a high capacity. The rise time of the electric double-layer capacitor is as shown in FIG. 7, the output voltage to the load 8 shows the rising characteristic of FIG. 7 due to the electrolytic capacitor 7, so that no design problem occurs. When the switching voltage is not generated in the converter transformer 5 due to the momentary power failure, the circuits of the present invention and the conventional example are equivalently shown in FIGS. 3 and 6, respectively, and the falling characteristic of the supply voltage to the load 8 is shown in FIG. As a result, the fall time becomes significantly longer than in the conventional example. That is, 5
5V → 4.75V under V, 0.1A load condition
Table 1 shows the retention time until the lower limit (-5%).
It can be seen that the holding time is greatly improved by the present invention.

[0014]

[Table 1]

Here, the electrolytic capacitor 7 470 μF electric double-layer capacitor 9 47F electric double-layer capacitor 10 47F The resistance of the resistor 11 was set to 1Ω, and the resistance of the load 8 was set to 0.13Ω.

[0016]

As described above, by adopting the circuit configuration of the present invention in which a plurality of electric double layer capacitors and resistors are connected in parallel with the electrolytic capacitor, the fall time of the output voltage at the momentary power failure of the switching power supply is obtained. Can be lengthened, and the output voltage holding time can be greatly lengthened.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a current flowing to a secondary side when a power switch is turned on in FIG.

FIG. 3 is an equivalent circuit diagram of a secondary circuit when oscillation of the converter is stopped in FIG. 1;

FIG. 4 is a circuit diagram of a conventional switching power supply.

FIG. 5 is a diagram showing a current flowing to a secondary side when a power switch is turned on in FIG.

FIG. 6 is an equivalent circuit diagram of a secondary circuit when oscillation of the converter is stopped in FIG. 4;

FIG. 7 is a diagram comparing the rising characteristics of the secondary side output voltage when the power switch is turned on between the embodiment according to the present invention and the conventional example.

FIG. 8 shows the rising characteristics of the electric double-layer capacitor when the power switch is turned on in FIG.

FIG. 9 shows the falling characteristics of the secondary output voltage when the oscillation of the converter is stopped in the example and the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC input voltage 2 Rectifier circuit 3 Input electrolytic capacitor 4 Converter circuit 5 Converter transformer 6 Rectifier diode 7 Electrolytic capacitor 8 Load 9, 10 Electric double layer capacitor 11 Resistance 12 Power switch P1 Primary winding P2 Secondary winding

Claims (1)

[Claims] A switching power supply for supplying a DC voltage obtained by rectifying and smoothing a voltage generated in a secondary winding of a converter transformer by a diode and an electrolytic capacitor to a load by a switching operation of a converter circuit, wherein the electrolytic capacitor Characterized in that a plurality of electric double-layer capacitors and resistors are connected in parallel with the switching power supply.