Development Of High Efficiency And Low Cost Laboratory Power Supply Based On Electronic Transformer

Laboratory power supply, i.e., adjustable DC voltage-stabilized power supply used in laboratory. It is an indispensable basic instrument in electronic laboratory, the status of its performance can directly influence the results of experiments and it is tend to face complex and changeable experimental environment, such as over-current, short circuit, sudden power cut, etc. Thus, laboratory power supply has certain requirements for voltage regulation, load regulation, anti-overload ability, output voltage ripple, efficiency, etc. While traditional laboratory power supply is not only poor in anti-interference and efficiency, but also big volume, heavy weight, high cost, which is not suitable for mass usage in school laboratories. In allusion to the problems above, this thesis proposes a high efficiency and low cost laboratory power supply design scheme based on electronic transformer.Firstly, in order to improve the Power Factor, conversion efficiency and anti-overload ability, reduce the volume of power supply, this thesis, which is based on Active Power Factor Correction (APFC) technology and electronic transformer principle, designed an electronic transformer which is provided with the function of APFC. This electronic transformer contains a DC link. Among them, the process of AC/DC is a Boost type APFC circuit, adopts the NCP1200which has simple structure and self-powered function as the control chip. The process of DC/AC/DC is a half-bridge type electronic transformer based on IR2155.Secondly, in order to realize the adjustability of both output voltage and protective current, this thesis designed a Buck type convertor with double feedback control loop. The main circuit of this convertor adopts simple peripheral circuit and low cost L4960as the control chip. It makes use of the method of resistance sampling method and principle of differential amplifier and comparator to design sampling circuit and feedback control circuit.Finally, in order to further reduce the voltage regulation, load regulation and output ripple, this thesis also designed a constant current discharge load and a low dropout dynamic filter. Moreover, this thesis designed a display circuit by using module design so as to further reduce the volume of power supply and enhance the display accuracy.This thesis has made a prototype of laboratory power supply and has conducted a comprehensive test. Actual test data indicated that the Power Factor of the laboratory power supply based on electronic transformer reached over0.98, the efficiency reached more than82%, and the output voltage ripple is only7mV, in addition, it reduced the volume and weight and decreased the cost compared to the traditional laboratory power supply.