Design And Implementation Of High-speed Acquisition Circuit Of Dc Power Tester

With the rapid development of science and technology,when people enjoy the comfort and convenience brought by electronic equipment,designers are facing the problem of how to efficiently and accurately test the performance of power supply.The DC power supply tester uses electronic measurement technology to automatically test multiple output parameters such as the DC power supply’s voltage regulation accuracy,ripple voltage,inrush current,and load regulation rate,providing a reliable DC power supply test solution for power supply designers.As the core component of the DC power supply tester,the signal acquisition circuit is responsible for collecting the output voltage and current signals of the DC power supply and performing preliminary calculation processing.The extremely high acquisition speed is conducive to discovering the details in the waveform,and accuracy and bandwidth are also the key to improving the performance of the tester.This paper studies and designs a high-speed acquisition circuit applied to a DC power tester.The main research contents are as follows:1.After comparing several commonly used high-speed high-current and voltage acquisition methods,selected a resistor shunt and a resistor-capacitor voltage divider to collect current and voltage signals.Two sampling resistors with low temperature drift of 0.1Ω and 0.1mΩ are selected to complete the collection of current signals in two ranges of 2.5A,DC ~ 20 MHz and 250 A,DC ~ 1MHz.The influence of the wiring method of the sampling resistor and the distribution parameters of the circuit are analyzed and optimized,and the generation mechanism and suppression method of common mode noise in the circuit are analyzed;a resistance-capacitance voltage divider with 200 times attenuation ratio is designed to complete the acquisition of voltage signals in the range of 200 V,DC~20MHz,and optimized design for the influence of parasitic capacitance in the circuit on amplitude flatness.2.Designed a general signal conditioning circuit to condition the collected voltage and current signals.Its main components are: a program-controlled gain amplifier composed of multi-stage amplifier circuits and analog switches built with multiple sets of op amps;a voltage-controlled voltage source type second-order low-pass filter with adjustable multi-stop frequency through an analog switch switching resistor;Input drive circuit composed of subtractor and single-ended-to-differential circuit designed to meet ADC input conditions.3.Analyzed the ADC’s key parameter requirements and selected a pipelined ADC with 200 Msps sampling rate and 14 Bit resolution for analog-to-digital conversion.The influence of sampling clock jitter on ADC signal-to-noise ratio performance is analyzed,Finally,a phase-locked loop is selected as a low-jitter sampling clock generator.4.Regarding the digital processing part,a simple selection analysis of main controllers which include FPGA and ARM is carried out,and DDR3 and FSMC are selected as the data storage and high-speed communication interface of the digital processing system.In addition,a complete collection circuit power management module was designed through power integrity analysis,and the isolation technology of GPIO,USB and network port was analyzed and designed.Finally,after detailed testing and verification,the measurement accuracy of this acquisition circuit reached 0.1% of reading + 0.1% of range,and the maximum bandwidth of voltage and current measurement reached 20 MHz,meeting expected index requirements.