| Switch Mode Power Supply(SMPS) has been widely used in the fields of consumer electronics,communication,electrical and energy as its advantages of high efficiency,small size and high control precision. With the rapid development of modern information industry and widely used in portable electronic devices, SMPS exhibits a broad market prospect.In this paper a Current Mode PWM DC/DC converter has been designed for portable applications powered from one cell Li-ion or three cell NiCd batteries. The device with an adjustable output voltage from Vin to 12V is able to deliver up to 1.2A. The device has a built-in 1.2MHz oscillator which reduces component size by allowing a small inductor and capacitor. It uses synchronous rectification to increase efficiency, thermal shutdown protection and under voltage lockout protection are plus.Many functional blocks have been designed,simulated and optimized, including the bandgap reference circuit, the LDO regulator, the error amplifier, the PWM comparator, the current sensing circuit, the oscillator, the slope compensation circuit , under voltage lockout protection and thermal shutdown protection.
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