| With the development of electric and communication technology, portable power is increasingly becoming the most important application area for power semiconductor integrated circuits. Small form factor, high efficiency and low cost are the most desired features for portable power ICs.A new type high efficiency synchronous step-up DC/DC converter for hand-held device is designed in this thesis. It works in the PFM (Pulse Frequency Modulating) mode, and its switching frequency can up to 500 KHz. It offers a built-in synchronous rectifier that reduces size and cost by eliminating the need for an external Schottky diode and improves overall efficiency by minimizing losses. The on-resistance of the synchronous rectifier is as low as 0.4?.It has a very high efficiency even in the light load thanks to its low quiescent supply current. The chip can be widely used in MP3 player, PDA, digital camera, cells phone and portable products etc.This thesis first introduces the basic theory of switching power supply. The operating theory of this circuit has been demonstrated. The operating principle and simulation analysis about band gap reference, self-biased current source, one shot circuit, hysteresis comparator, and current-limit circuit have been particularly expounded in this thesis. At last the whole circuit is simulated and shows that the desired functions and performances are achieved. |
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