Control circuit of switch power supply and method thereof

Abstract

The invention discloses a control circuit of a switch power supply and a method thereof. The method comprises the following steps: a constant-current control module generates and outputs a control signal for controlling an output current of the switch power supply according to feedback information on a pin FB and a pin CS, adjusts a power-on duty ratio of a power transistor, and adjusts an output current IO of a power supply system as a constant value; a constant-current precision compensation module adjusts a circuit calculation parameter of the constant-current control module and a sampling and holding module according to the feedback information on the pin FB and the pin CS, so that the output constant-current precision is not influenced by the change of a working mode and / or the change of an input condition; a timer determines a moment when the voltage VFB on the pin FB reaches a peak value; and a pressure control oscillator adjusts the switching frequency of a power transistor according to a control signal outputted by the constant-current control module and an output signal of the timer, so that the switch power supply works at a QR mode or a CCM mode, and when the output voltage is changed, the QR mode is kept unchanged or the current continuous depth of the CCM mode is kept similar.

Description

technical field [0001] The invention relates to a control circuit of a switching power supply and a method thereof, which are suitable for a power supply management integrated circuit system and belong to the technical field of power semiconductors. Background technique [0002] The output current of a flyback switching power supply can be expressed as: in, is the turns ratio of the primary and secondary sides of the transformer, I PRI_PK is the peak value of primary current during transformer excitation, I PRI_O is the initial value of primary current during transformer excitation, T D is the transformer degaussing time, T P is the single switching cycle time of the flyback switching power supply. This expression can also be expressed as: Among them, R CS is the resistance value of the primary side current detection resistor, V CS_PK R for the transformer excitation period CS The peak value of the voltage across the terminal, V CS_O R for the transformer excita...

AI Technical Summary

Problems solved by technology

[0008] To sum up, the above working method not only increases the design cost of control circuit pins and power system, but also has disadvantages such as large output current difference between working modes, low input voltage adjustment rate, and poor constant current accuracy.

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