Analysiz And Design Of Current Sensing Technique

With the rapid growth of market of portable communication and the increasing demand for consumer electronic equipment, the lifetime of battery in portable system has become a focus of academic and commercial concern. Therefore, great effort has been made to develop high efficiency, low voltage and low power consumption circuit recently years. It is well-known that current-mode buck converter takes the advantages of automatic over-current protection, better stability and faster dynamic responses compared with the voltage-mode control. Therefore many different current-sensing schemes have been developed and implemented to sense the inductor current .One of our works is to design an integrated high performance low voltage current sensing circuit , based on the traditional current sensing circuit, to sense the inductor current in fixed PWM control mode.The traditional fixed PWM control technique tends to prove a satisfactory efficiency level when the DC-DC converter is driving a heavy load with an output current at or near the converter's rated maximum. However, when the load decreases to a moderate or light level, the efficiency of the converter also decreases; it's because the switching components continue to be toggled at the same fixed frequency, while the converter provides less output current. Therefore, when load decrease to light load, the system transitions from fixed PWM mode to pulse skipping mode, where we design a current sensing amplifier based on R_ds sense technique to monitor the current of power FET .When the monitored current decrease to a level, the power FET is closed to shorten the duration time of work by another control closed loop. This is another main work of this paper. Two control modes, two control closed loops and two current sensing techniques maintain the high efficiency level of DC-DC converter over a wider output current range than can be achieved with fixed PWM control. The first section includes the significant of the current mode DC-DC converter. Current traditional current sensing techniques, principle and the problem they are facing are addressed in section II. The design idea of the work in paper and the comparison with current circuit are described in section III .the schematic and it's simulation result of high-performance DC-DC converter with the current sensing circuits we present are showed in section IV. The significance and existed problem are discussed in the last section..