DC/DC converter, control circuit thereof, power supply, power adapter and electronic apparatus using the same

摘要

A control circuit of a DC/DC converter having a transformer, a switching transistor, and a detector includes: a feedback terminal receiving a feedback voltage corresponding to an output voltage of the DC/DC converter; a current detection terminal receiving a detection voltage generated in the detection resistor; a conversion circuit configured to amplify, attenuate and/or level-shift at least one of the feedback voltage and the detection voltage, wherein a gain and/or a shift of the conversion circuit are variable; and a gain controller configured to control the gain and/or the shift of the conversion circuit.

主权项

1. A control circuit of a DC/DC converter including a transformer having a primary winding and a secondary winding, a switching transistor disposed on a current path of the primary winding of the transformer, and a detection resistor connected to the switching transistor, the control circuit comprising:
a feedback terminal receiving a feedback voltage corresponding to an output voltage of the DC/DC converter; a current detection terminal receiving a detection voltage generated in the detection resistor; a conversion circuit configured to amplify, attenuate and/or level-shift at least one of the feedback voltage and the detection voltage, wherein a gain and/or a shift of the conversion circuit are variable; a pulse modulator configured to generate a pulse signal pulse-modulated such that the output voltage of the DC/DC converter approaches a target value, based on the feedback voltage and the detection voltage passed through the conversion circuit; a driver configured to drive the switching transistor based on the pulse signal; a burst control circuit configured to control a switching period during which the switching transistor is switched and a stop period during which the switching transistor is fixed to switching-OFF; and a gain controller configured to control the gain and/or the shift of the conversion circuit, wherein the gain controller sets the conversion circuit to a first state in which a gain of the conversion circuit is a first gain under normal conditions, set the conversion circuit to a second state in which the gain of the conversion circuit is a second gain greater than the first gain when the feedback voltage is decreased to a predetermined first threshold, set the conversion circuit to a third state in which the gain of the conversion circuit is a third gain greater than the first gain and smaller than the second gain during a predetermined period when the feedback voltage is increased to a second threshold greater than the first threshold, and, thereafter, returns the conversion circuit to the first state.