Flyback Chip Switching Power Supply Chip Research And Design

From the 90's, switching power supply began to be used in electronics, communications, medical and some other fields, low power, low cost, high efficiency switching power supply becomes the main direction of circuit design. The core of circuit design in switching power supply is the control IC, control IC was widely used for many advantages, such as low cost, high efficiency, simple external circuit and high integration, etc.This thesis is mainly from the project'the chip design of power supply'of microelectronics of the University of Electronic Science and Technology of China. We mainly focus on the research and design of the control IC of the off-line fly-back switching power supply.This paper researches the fundamental of the external circuit of the tiny-switch, the fundamental of chip and the design of the sub-block of this chip. This chip adopts the current mode and introduces frequency jittering to reduce EMI. The bypass/ multi-function pin (BP) of the chip connected to an external capacitor to provide energy to the internal control circuitry. In order to control the circuit, the chip will detect and control the pin voltage. This chip has auto-restart function in short circuit and the line under voltage detection, which can greatly save the cost of components. In addition, this chip is different from the traditional PWM modulation, it uses a simple on/off to adjust the output voltage, so that it need loop compensation on longer. This article also designs and analysis the major sub-block of this chip, such as reference, enable/under-voltage, over-thermal protection, current limit comparator and so on.