Design Of The Current Detecting Circuit In BUCK DC-DC Converter

The rapid development of the large-scale integration (LSI) brings forth the increasingly smaller electronics, which in turn accelerates the flourishing of portable electronics. Meanwhile the growing new features and capacities make electronics more and more complex, and this poses even greater challenges to power supply, which serves as the core of the operation of electronics. The DC-DC converters, characterized by high efficiency and low power, have won an irreplaceable position in the electronics market. Thus it is of great significance to try to study and improve the performance of DC-DC converters.Apart from satisfying the requirements of power supply products, power supplies have to be protected in each and every way. Among all the protection measures, over-current protection is one of the most desirable one for many DC-DC converters against the accidental damages as a result of overload or short circuit. And current detecting is the key of over-current protection. After analyzing the advantages and disadvantages of the traditional detecting measures, this paper proposes to work out a current detecting circuit of high performance and suitable for the BUCK DC-DC converter in current-control-mode in order that it could detect the current in time and protect the chip effectively.The first part of this paper introduces the background and significance of this research; the second part comes to discuss some kinds of current sensing circuits. After that, on the basis of the prior knowledge, we successfully scheme out an over-current protection circuit which includes a current sensing circuit and a current limiting circuit. The principle of current sensing is as follows: if one input of differential amplifier is connected to power elements, the input voltage at the other end would be equal to that at the matching point. This paper uses a folded cascade operational amplifier for current sensing, and a telescopic cascade operational amplifier for current limiting.Circuits designed by CMOS technology have their competitive advantages-even smaller element size, faster speed of MOSFETs, low power consumption and low cost. So this circuit is manufactured by normal 0.6μm CMOS technology. The Hspice simulation results proved the feasibility and reliability of the circuit. And finally this circuit can also be used in the current detecting of the BOOST DC-DC converter and BUCK-BOOST DC-DC converter.