Research On Outside Adjustable Current Limiting Type CC/CV DC-DC Converter

The DC-DC converter system, which is usually used in the electronic system as a constant currentsource or a constant voltage source, can convert the DC voltage or current into the other controllable DCvoltage or current at different level. With the increasing requirements for the various electronic products,the constant-current sources or voltage sources with single function are difficult to meet the requirements ofthe different systems.The DC-DC converter system with the function of single output only can be used as a constantcurrent source or a constant voltage source, so it gradually unable to meet the application requirements ofthese electronic products. The DC-DC converter system with constant current or constant voltage not onlyprovides a stable output voltage, also limits the current accurately. Hence, the DC-DC converter system canmeet the different needs of application conditions, and has received considerable attention. However, mostof the DC-DC converter systems have many disadvantages such as the complex structure, the poor stabilityand the high costs, which limit the further applications in the actual engineering.To solve the problems above, a new scheme of the outside adjustable current limiting type CC/CVDC-DC converter system is proposed. The system consists of the outside adjustable current limiting circuit,the current error amplifier circuit, the voltage amplification circuit, the saw-tooth generating circuit and thelogic drive circuit. The critical load resistance value depends on the output current and voltage of thesystem. When the output load is less than the critical value, the system can operate in constant current mode,and the system can operate in constant voltage mode when the output load is greater than the critical value.By means of some experiments, when the CC is1A, the CV is3.3V and the external adjustableresistance changes from40KΩ to120KΩ, the functions of CC, CV and outside adjustable current limitingfor the system are verified with UMC0.35μm CDMOS process. The experimental results show that thecritical value of load resistance is3.3Ω. When the load resistance RL<3.3Ω, the system operates in CCmode, and the system operates in constant voltage mode when the load resistance RL>3.3Ω. Furthermore,the current limiting value of the system is decreasing gradually varied with the outside adjustable resistanceincreasing gradually.