Pwm Dc / Dc Step-down Transformation Of Ic Research And Design

Power supply is an indispensable part in application electronic equipments such as TV, computer and portable communication equipments, which is the fundamental requirement for normal operation. Switch mode power supply, with its compact volume, small weight, high efficiency and good line regulation, has been widely applied in most of electronic fields. The core of switch mode power supply is integrated IC control system. Its high integration level, quality-price ratio and efficiency make it become the major candidate for application power design.A new type of voltage-mode and pulse-width-mode controller is designed in this thesis. Its operation frequency is 1.38MHz, with an integration of a power MOSFET whose breakdown voltage is up to 50V. The allowable input voltage ranges from 2.7V to 5.5V and its output voltage can be programmed between -2V and -15V, additionally, the output current is in a 200mA range in typical application. To avoid the poor efficiency of the PWM control scheme at light load, a skip-cycle-mode operation is introduced that allows system's efficient operation at the light load. Furthermore, the building blocks in system are elegantly designed to give the result of low power dissipation. Over-voltage protection module, over-current protection module, under voltage protection module is also integrated in the system. Consequently, an integrate switch mode power supply with high efficiency and good reliability can be realized by the controller with very few external parts.The fundamental principle of monolithic voltage-mode switching regulator is firstly introduced in this thesis, which is followed by a comparison between voltage-mode and current-mode converters where the pros and cons of both converters are discussed in detail; next, the global system architecture is proposed upon the design requirements and sub-block circuits are also introduced that focuses on several essential sub-blocks such as AMP, WAVE, PWM control, PSC, OSC and VREF. Finally, all sub-circuits and the whole chip circuit are simulated by Hspice whose results indicate that the circuit function and performance have perfectly satisfied the design requirements.