Control circuit and switching power supply unit

Abstract

A control circuit controls a switching element in a switching power supply unit. The control circuit includes: a controller connected to the switching element; a signal generating circuit connected to the input part of the controller; a reference voltage source connected to the signal generating circuit; and a comparator having a first input terminal to which an output voltage is input from the switching power supply unit, a second input terminal to which a comparison signal is input from the signal generating circuit, and an output terminal connected to the signal generating circuit and to the input part of the controller.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a control circuit and a switching power supply unit.[0003]2. Description of the Related Art[0004]Ripple injection non-linear control in which a comparator is used is known as a method of controlling a switching power supply unit (see U.S. Pat. Nos. 6,147,478 and 7,202,642).[0005]In the circuit illustrated in FIG. 9 that is used in ripple injection hysteresis control described in U.S. Pat. No. 6,147,478, a comparison voltage Vfb input to the non-inverted input terminal of a comparator 106 becomes a first voltage, which is at a high level, when an output Sp from the comparator 106 is high and becomes a second voltage, which is at a low level, when the output Sp from the comparator 106 is low. A difference between the first voltage and the second voltage is a hysteresis width. An alternating-current component obtained by integrating the output voltage from the comparator 106 or a voltage in...

AI Technical Summary

Benefits of technology

The control circuit enhances responsiveness and resistance to switching noise, ensuring stable operation even at high frequencies and maintaining a sufficient phase margin, independent of output voltage ripple.

Problems solved by technology

However, the conventional technology is problematic in that, since an output voltage feedback circuit loop in U.S. Pat. No. 6,147,478 has low-pass characteristics due to resistors 107h and 107g and a capacitor 107i, a response to a rapid change in an output load is slow.

This may lead to the possibility that switching noise causes a malfunction.

It is also difficult to assure a phase margin, which is an important index related to stability control.

Another problem is that there is a dependency on an output voltage ripple of the converter.

A problem in U.S. Pat. No. 7,202,642 is that, although malfunctions caused by switching noise generated when the power switch is turned on can be reduced, malfunctions caused by switching noise generated when the power switch is turned off are still problematic.

Another problem is that, since a fixed-time trigger, which is turned on during a fixed time, is used and a response cannot be returned in the fixed time, so a response to a rapid change in an output load is slow.

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