A New Modulation Mode Of Switching Power Supply Design

Switching power supply, named from the adjustment of the regulator control functions of the device which always works in switch-mode in power supply. It has the advantages of small size, light weight, low power consumption, low noise, high integration, good reliability and other characteristics. It is widely used in various fields of automation and control, LED lighting, digital products and medical equipment.This thesis based on an overview of the switching power supply and control circuit, designed off-line single-chip AC/DC switching power supply chip. The chip maximum output current limit is250mA, and the operating frequency of132KHz, the maximum withstand voltage700V, and pulse width modulation (PWM) and pulse skip modulation (PSM), and over-current, over-temperature, under-voltage and self-restart protections.This thesis focuses on the feedback loop modulation system in the chip control system. It uses a combination of PWM and PSM modulation mode and current mode control and specifically related to the chip within the three sub-modules:the current limit comparator, enable/under-voltage (EN/UV) circuit and oscillator. The current limit comparator and another sub-module current limit state machine work together to achieve the current control mode, and generate the PWM control signal, and also limit the maximum output current value. Enable/under-voltage circuit detects the external feedback signal to produce the PSM control signal. Oscillator through the comparator and differential pair to produce a stable clock signal, which is not only the clock signal of the low-voltage digital circuit blocks, but also is modulated by the PWM and PSM signals and eventually be used to control the power device on or off. In this paper these three sub-circuits were the detailed analysis and simulation, and give the simulation waveforms, and verify the correctness and feasibility of the circuit design.Finally, according to the layout design rules, design the layouts of the above three sub-modules and the overall circuit layout.