Switch power device and electronic device using said switch power device

Abstract

A switching power supply device, comprising: a turn-off circuit (5) for turning off a first switching element (Q1) in a conduction state; according to a feedback signal from an output voltage detection circuit (3), when the load is lighter, the The control circuit (4) of the control circuit (6) controls the off-period the longer the turn-on delay of the switching element (Q1) is. The off-period control circuit (6) is provided in series between the feedback coil (N3) and the control terminal of the first switching element (Q1), and has a second circuit that controls ON / OFF based on a feedback signal from the output voltage detection circuit. 2 The switching element is the transistor (Q3). When the load is lighter, the switching frequency can be reduced, and the power consumption at light load can be reduced.

Description

technical field [0001] The invention relates to a switching power supply device and an electronic device using the switching power supply device. Background technique [0002] In recent years, in printers and facsimiles, for example, there has been an increasing demand for reducing power consumption during standby, that is, when no printing work is being performed. One of the demands is to reduce the power consumption of a power supply unit used in a printer or a facsimile when it is in standby, that is, under a light load. [0003] However, in general RCC switching power supply devices, the switching frequency increases as the load becomes lighter, and the switching loss increases. If this situation is not changed, it is impossible to reduce power consumption at light loads. [0004] In contrast, Japanese Unexamined Patent Publication No. 7-67335 discloses a switching power supply device for reducing the power consumption of an RCC switching power supply device under light...

AI Technical Summary

Problems solved by technology

[0005] However, in the switching power supply device disclosed in Japanese Patent Laid-Open No. 7-67335, there is also a problem that the switching frequency cannot be significantly reduced at light loads only by limiting the switching frequency to a certain frequency. Therefore, the power consumption cannot be greatly reduced

[0006] In addition, there is also the problem that the switching frequency cannot change with the sharp change of the load

For example, if it is set so that the switching frequency changes greatly between light load and heavy load, then when the load changes sharply from light load to heavy load, the switching frequency cannot follow the change of load, which may cause output reduction or power failure. power outage

Therefore, there is a problem that the switching frequency cannot be significantly reduced even at light load

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