JPH10150766A - Switching regulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress ripple noise contained in the output voltage by eliminating the mutual effect of DC-DC converters. SOLUTION: The regulator comprises DC-DC converters 10, 70 producing output voltages Vo1, Vo2 and the output voltage Vo1 is utilized as an input voltage Vi2 to the DC-DC converter 70. The DC-DC converter 10 comprises a parallel connection of rectifying/smoothing circuit 12, 14 where a rectifying/ smoothing circuit 12 is for the output voltage Vo1 and a rectifying/smoothing circuit 14 for the input voltage Vi2 to the DC-DC converter 70.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching regulator used as a DC constant voltage power supply in general electronic equipment.

[0002]

2. Description of the Related Art Conventionally, in a multi-output switching regulator, when the input voltage is low, or when a buck-boost type circuit is required for the input voltage, etc., there is once a method for improving regulator efficiency and reducing costs. A method of further converting a voltage converted to a convenient voltage has been adopted.
The voltage once converted is often one of the output voltages for cost reduction.

FIG. 3 is a circuit diagram showing such a conventional switching regulator. Hereinafter, description will be made based on this drawing.

A conventional switching regulator has a DC
Having DC converters 50 and 70, obtaining output voltages Vo1 and Vo2 from the DC-DC converters 50 and 70, and converting the output voltage Vo1 of the DC-DC converter 50 to DC-
This is used as the input voltage Vi2 of the DC converter 70. The DC-DC converter 50 is a general one and includes a rectifying / smoothing circuit 52, an inductor 54, a differential amplifier 56, a control circuit 58, a switch element 60, and the like. The rectifying / smoothing circuit 52 is a series circuit including a rectifying diode 521, a resistor 522, and a smoothing capacitor 523. However, the resistor 522 is connected to the smoothing capacitor 5
23 is the internal resistance. The input voltage Vi1 of the DC-DC converter 50 is obtained from the DC voltage power supply 80. DC-
Since the DC converter 70 is a general one, only the control circuit 72, the switch element 74 and the transformer 76 are shown in a simplified form.

[0005]

FIG. 4 is a waveform diagram showing characteristics of a conventional switching regulator. Less than,
A description will be given based on FIG. 3 and FIG.

In a conventional switching regulator, D
For example, when the output power capacity of the C-DC converter 70 is relatively large, as shown in FIG.
Of the input current Ii2 increases. As a result, as shown in FIG. 4, there is a problem that the ripple noise of the output voltage Vo1 of the DC-DC converter 50 increases.

There are the following three causes of the ripple noise generated in the output voltage Vo1. . Voltage drop due to an internal resistance component (resistor 522) included in the smoothing capacitor 523. . A voltage drop that occurs due to a shortage of charge in the smoothing capacitor 523 due to a delay in feedback or the like. . Voltage drop due to internal resistance of inductor 54 and transformer (not shown). These three types of voltage drops depend on the load current, that is, the waveform of the input current Ii2.

[0008]

Therefore, an object of the present invention is to provide a DC-D
In a switching regulator that uses an output voltage of a C converter as an input voltage of another DC-DC converter, it is an object of the present invention to reduce the ripple noise included in the output voltage by eliminating the influence between the DC-DC converters.

[0009]

A switching regulator according to the present invention has a plurality of DC-DC converters, obtains a plurality of output voltages from these DC-DC converters, and obtains an output voltage of a certain DC-DC converter. Is used as an input voltage of another DC-DC converter, one DC-DC converter has a plurality of rectification / smoothing circuits connected in parallel to each other, and these rectification / smoothing circuits are used for an output voltage and another. It is characterized in that it is divided into those for the input voltage of the DC-DC converter.

The rectifying / smoothing circuit naturally has some rectifying element. Therefore, if a plurality of rectifying / smoothing circuits are connected in parallel, these rectifying / smoothing circuits are electrically disconnected from each other by the rectifying elements. Therefore, the influence of the mutual output voltage between the plurality of rectification / smoothing circuits is suppressed.

[0011]

FIG. 1 is a circuit diagram showing one embodiment of a switching regulator according to the present invention. Hereinafter, description will be made based on this drawing. However, in FIG. 1, the same parts as those in FIG. 3 are denoted by the same reference numerals.

The switching regulator of this embodiment has DC-DC converters 10 and 70,
Output voltages Vo1 and Vo2 are obtained from the C converters 10 and 70, and the output voltage Vo1 of the DC-DC converter 10 is used as an input voltage Vi2 of the DC-DC converter 70. The DC-DC converter 10 includes rectifying / smoothing circuits 12 and 14, an inductor 54, a differential amplifier 56,
The control circuit 58 includes a switch element 60 and the like. The rectifying / smoothing circuits 12 and 14 are connected in parallel with each other, and the rectifying / smoothing circuit 12 is for the output voltage Vo1, and the rectifying / smoothing circuit 14 is for the input voltage Vi2 of the DC-DC converter 70. The rectifying / smoothing circuit 12 is a series circuit including a rectifying diode 121, a resistor 122, and a smoothing capacitor 123. The rectifying / smoothing circuit 14 includes the rectifying diode 1
41 is a series circuit of the resistor 41, the resistor 142, and the smoothing capacitor 143. However, the resistors 122 and 142 are internal resistances of the smoothing capacitors 123 and 143. The input voltage Vi1 of the DC-DC converter 10 is obtained from the DC voltage power supply 80. Since the DC-DC converter 70 is a general one, only the control circuit 72, the switch element 74 and the transformer 76 are shown in a simplified form.

The switching regulator of this embodiment is of a boost type. The control circuit 58 of the DC-DC converter 10 feeds back the output voltage Vo1 via the differential amplifier 56, and controls on / off of the switch element 60 so as to keep the output voltage Vo1 constant. DC-DC
The control circuit 72 of the converter 70 feeds back the output voltage Vo2 via a differential amplifier or the like (not shown), and uses a switching frequency sufficiently higher than the switching frequency of the control circuit 58 to switch the output voltage Vo2 so as to keep the output voltage Vo2 constant. The element 74 is on / off controlled.

Since the rectifying / smoothing circuits 12 and 14 are connected in parallel, they are electrically disconnected from each other by the rectifying diodes 121 and 141. Therefore, the output voltages of the rectifying / smoothing circuits 12 and 14, ie, the charging voltages of the smoothing capacitors 123 and 143, hardly affect each other.

FIG. 2 is a waveform diagram showing characteristics of the switching regulator of the present embodiment. Hereinafter, FIGS. 1 and 2
It will be described based on.

The input current Ii2 of the DC-DC converter 70
Output voltage Vo1 of the DC-DC converter 10
As described above, the following three types of ripple noise can be considered. . Voltage drop due to an internal resistance component (resistor 122) included in the smoothing capacitor 123. . A voltage drop caused by insufficient charge of the smoothing capacitor 123 due to feedback delay or the like. . Voltage drop due to internal resistance of inductor 54 and transformer (not shown).

However, since the rectifier / smoothing circuits 12 and 14 are electrically disconnected from each other by the rectifier diodes 121 and 141, the smoothing capacitor 12
Since the charging voltages of 3,143 do not affect each other, the above and the above can be solved. Further, the influence of the internal resistance of the inductor 54 can be almost eliminated by feeding back the output voltage Vo1.

Therefore, the ripple noise generated in the output voltage Vo1 can be substantially caused only by the load current and the charging / discharging current as shown in FIG. DC-DC
Rectifier / smoothing circuit 12 for input voltage Vi2 of converter 70
Also, since the inductor 54 and the switch element 60 are shared, the input voltage Vi2 can obtain a substantially stable value.

It is needless to say that the present invention is not limited to the above embodiment. For example, when the present invention is applied to a transformer type switching regulator, the same operation and effect can be obtained by connecting the secondary side rectification / smoothing circuit in parallel. Also, the switch element 6
Although 0 and 74 are bipolar transistors, they may be field effect transistors or the like.
A diode bridge for full-wave rectification or the like may be used instead of 1,141.

[0020]

According to the switching regulator according to the present invention, in the case where the output voltage of a certain DC-DC converter is used as the input voltage of another DC-DC converter, certain DC-DC converters are connected in parallel with each other. It has a plurality of rectification / smoothing circuits, and these rectification / smoothing circuits are divided into those for output voltage and those for input voltage of other DC-DC converters. It can be in a state of being electrically isolated from each other. Therefore, since the mutual influence of the output voltage between the plurality of rectifying / smoothing circuits can be suppressed, the ripple noise included in the output voltage can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of a switching regulator according to the present invention.

FIG. 2 is a waveform chart showing characteristics of the switching regulator of FIG.

FIG. 3 is a circuit diagram showing a conventional switching regulator.

FIG. 4 is a waveform chart showing characteristics of the switching regulator of FIG. 3;

[Explanation of symbols]

 10, 70 DC-DC converter 12, 14 Rectifying / smoothing circuit 121, 141 Rectifying diode 123, 143 Smoothing capacitor Vo1 Output voltage of DC-DC converter 10 Vi2 Input voltage of DC-DC converter 70

Claims (3)

[Claims] A plurality of DC-DC converters, a plurality of output voltages are obtained from these DC-DC converters, and an output voltage of a certain DC-DC converter is used as an input voltage of another DC-DC converter. In a switching regulator, a certain DC-DC converter has a plurality of rectification / smoothing circuits connected in parallel to each other, and these rectification / smoothing circuits are divided into an output voltage and an input voltage of another DC-DC converter. A switching regulator characterized by being used. 2. The switching regulator according to claim 1, wherein the rectifying / smoothing circuit includes a rectifying unit including a rectifying diode and a smoothing unit including a smoothing capacitor. 3. The switching regulator according to claim 1, wherein said rectifying / smoothing circuit is a series circuit of a rectifying diode and a smoothing capacitor.