Design Of High-power Digital Source-meter System

Digital Source Meter is a kind of comprehensive instrument with functions of voltage source,current source,voltage measurement and current measurement.It is widely used in power semiconductor testing,optoelectronic device research,transistor verification and so on.At present,the domestic digital source meter market is monopolized by foreign companies,but imported digital source meters are expensive and have high maintenance costs.Therefore,the research on digital source meters has great market value and strategic significance.The main research contents of this subject are as follows:（1）Aiming at the defects of crossover distortion and difficult control of the fourquadrant DC regulated power supply based on MOS tube,this paper adopts the power amplifier as the voltage-stabilizing element to realize the function of the four-quadrant source.By designing a cascaded power amplifier circuit,the system achieves a maximum current output capacity of 20 A,which achieves the high safety and convenience control effect of the regulated power supply,and reduces the complexity of hardware and the difficulty of debugging.（2）Aiming at the defects of slow response and high CPU occupancy rate of software regulated power supply output,this paper adopts hardware PI controller as the control unit,so that the voltage/current source output has the characteristics of high resolution and high accuracy.The principle of the hardware PI controller is simple and easy to implement.By setting the resistance-capacitance parameters,the steady-state error and dynamic response performance of the power supply output can be easily adjusted.（3）In view of the characteristics of the digital source meter with many functions and high hardware cost,this paper designs a large number of hardware modules with functional reusability,which greatly reduces the use of chips and saves production costs.The specific performance is: the signal conditioning output is used as the sampling signal and the feedback signal at the same time;the DAC output can be used as the output control quantity or limit control quantity;the PI controller is used for the output regulation of the voltage source or the current source;the I/V conversion is used for the current source and the ammeter.electrical signal conversion.By reusing function modules,hardware resource consumption and debugging workload are reduced,and control logic is simplified.After testing and verification,the high-power digital source meter designed in this paper can work in four quadrants;the maximum output power is 200 W,the maximum voltage is 40 V,and the maximum current is 20A;the source/measurement resolution index reaches 0.01% of the full scale;the source/measurement accuracy The specification reaches 0.05% of full scale.At the same time,the system has remote protection and voltage limiting/current limiting protection functions to protect the system itself and external loads.