FLYBACK CONVERTER OUTPUT CURRENT EVALUATION CIRCUIT AND EVALUATION METHOD

摘要

An output current calculating circuit for a flyback converter operating under CCM and DCM is disclosed. The off current value ION and the blanking current value ILEB flowing through a sensing resistor are calculated using a detection module and are summed together using a current summing unit. A voltage converted from the sum value of the off current value IOFF and the blanking current value ILEB is transmitted through an output stage in a predetermined time ratio of a cycle with the duty cycle determined by a logic control unit, in which the logic control unit controls the output stage to receive the voltage converted from sum current in a predetermined time period of each cycle, and prevents the output stage to receive the voltage converted from sum current in the remaining time other than such predetermined time period of each cycle.

主权项

1. An output current calculation circuit for a flyback converter comprises:
a detection module detecting a primary current flowing through a sensing resistor connected in series with a primary winding, wherein at a moment a main switch controlling on or off of the primary winding is turned off by a control signal, the detection module detects an off current value IOFF flowing through the sensing resistor, and at a moment an active state of a leading-edge blanking signal used for shielding an initial spike of the primary current ends, the detection module detects a blanking current value ILEB flowing through the sensing resistor; a sample and hold latch storing information related to the off current value IOFF and the blanking current value ILEB; a current summing unit summing the off current value IOFF and the blanking current value ILEB; an output stage transmitting a voltage converted from a sum current of the off current value IOFF and the blanking current value ILEB according to a predetermined ratio in each cycle; and a logic control unit controlling the output stage only to transmit the voltage converted from the sum current within a predetermined time period in each switching cycle.