SWITCHING POWER SUPPLY

摘要

The switching element is turned ON and OFF according to when the current flowing through the inductance element becomes equal to zero and according to an amplified error voltage between the output voltage and a target output voltage. More particularly, the OFF time of the switching element is calculated, and when the OFF time is less than a prescribed value, the ON time of the switching element is increased. Moreover, the amount by which the ON time of the switching element is increased is reduced if the error voltage if greater than a prescribed value.

主权项

1. A switching power supply, comprising:
a switching element that, when turned ON, forms a current path between terminals of an input power source through an inductance element; a voltage output circuit that, when the switching element is turned OFF, rectifies and smooths a current obtained from the inductance element in order to generate an output voltage; an error amplifier that generates an error voltage representing a difference between the output voltage and a prescribed target output voltage; a zero current detection circuit that determines that the current flowing through the inductance element has decreased to zero when the current flowing through the inductance element has decreased to less than a prescribed reference value; a ramp voltage generation circuit that starts generating a ramp voltage each time the switching element is turned ON; an ON/OFF control circuit that turns the switching element ON each time the zero current detection circuit detects zero current and subsequently turns the switching element OFF when the ramp voltage generated by the ramp voltage generation circuit exceeds the error voltage; an OFF time detection circuit that monitors an OFF time of the switching element; an ON time increasing circuit connected to the ramp voltage generation circuit, the ON time increasing circuit comparing the OFF time of the switching element as monitored by the OFF time detection circuit with a prescribed value and, when the OFF time of the switching element is less than said prescribed value, causing the ramp voltage generated by the ramp voltage generation circuit to change in such a way as to increase the ON time of the switching element; and an ON time increase reduction circuit that determines whether the input power source is a relatively low voltage system or a relatively high voltage system, and that reduces an amount by which the ON time of the switching element is increased by the ON time increasing circuit when the input power source is determined to be the relatively low voltage system.