【正文】 S52 the entire system uses a singlechip microputer control ponents, preferences current value data will be sent to the D / A converters (MAX531), the hardware circuit for the constant transformation of DC output, but not using the basic temperature drift Concord Manganin resistor Silk as a sophisticated sampling resistor. Performance is better than the ordinary use of the FET transistor as a constant current source of major ponents, highpower transistors as expanding the main circuit device, the bination of threeterminal regulators and the multifilter makes the whole system a performance boost levels to achieve a highprecision constant current source purposes. Output voltage of the system to conduct realtime sampling, through the A / D converters with sampling to MCU users to set limit values to pare pressure to control the output voltage. At the same time, the keyboard control and realized the value of output current and voltagelimiting values can be preset, stepping adjustment, the current signal and the output voltage signal can be directly figures show that the function, and realtime monitoring of the output voltage, such as overvoltage alarm function. In the past pared to DC current source, the design of a highprecision constant current source, simple structure and work stability, and easy to operate, low cost, with a payload capacity, and other advantages.Key words: Current source AT89S52MCU MAX531 MAX187 III / 51目錄摘要 ............................................................I前言 ............................................................1第一章 系統(tǒng)結(jié)構(gòu)及功能介紹 .......................................2 系統(tǒng)工作原理概述 ...........................................2 系統(tǒng)的特點(diǎn)和使用 ...........................................2 系統(tǒng)的特點(diǎn) .............................................2 系統(tǒng)的使用說明 .........................................3第二章 設(shè)計(jì)方案 .................................................4 方案比較 ...................................................4 整體方案 ...............................................4 方案一 ...............................................4 方案二 ...............................................5 方案三 ...............................................5 恒流源方案 .............................................6 方案一 ..............................................6 方案二 ..............................................6 方案三 ..............................................7 最終選用方案 ...............................................7第三章 硬件系統(tǒng)設(shè)計(jì) .............................................8 系統(tǒng)硬件基本組成 ...........................................8 各模塊單元電路設(shè)計(jì) ........................................8 電源電路 ...............................................8 擴(kuò)流電路 ...............................................9 電路的優(yōu)點(diǎn). .......................................9 電路工作原理 .....................................10 恒流電路 ..............................................10 采樣電路 ..............................................11 系統(tǒng)主要芯片介紹 ..........................................12 AT89S52 單片機(jī) .......................................12 MAX531...............................................12 MAX187...............................................13 AT24C16..............................................14IV / 51第四章 軟件設(shè)計(jì) ................................................18 概述 ......................................................18 主程序結(jié)構(gòu) ................................................18 各模塊子程序設(shè)計(jì)原理 ......................................20 MAX531 工作原理 ......................................20 MAX187 工作原理 ......................................20 鍵盤掃描原理 .........................................21 LCD 12864 顯示 .......................................22第五章 系統(tǒng)調(diào)試 ................................................23 硬件設(shè)計(jì)要點(diǎn) ..............................................23 共地問題 ..............................................23 采樣電阻選擇 ..........................................23 D/A 及 A/D 電路處理 ...................................24第六章 數(shù)據(jù)測試及分析 ..........................................25 輸出電流測試 ...........................................25 步進(jìn)電流測試 ...........................................26 工作時(shí)間測試 ............................................27 負(fù)載阻值變化測試 ........................................28 輸出電壓值測試 ..........................................29第七章 結(jié)束語 ..................................................31參考文獻(xiàn) .......................................................32附錄 ...........................................................33一、 系統(tǒng)電路原理圖： ........................................33圖 系統(tǒng)電源原理圖 .......................................33圖 系統(tǒng)恒流源電路原理圖 .................................33圖 系統(tǒng)單片機(jī)最小系統(tǒng)原理圖 .............................34圖 系統(tǒng) D/A、A/D 原理圖 ..................................34圖 系統(tǒng)顯示電路及存儲電路 ...............................35二、系統(tǒng)部分程序設(shè)計(jì) .........................................352．1 MAX531 子程序 .........................................352．2 MAX187 子程序 .........................................362．3 鍵盤掃描子程序 ........................................372．4 AT24C16 子程序 ........................................382．5 LCD12864 子程序 .......................................42致謝 ...........................................................451 / 51前言隨著電子技術(shù)的發(fā)展、數(shù)字電路應(yīng)用領(lǐng)域的擴(kuò)展，現(xiàn)今社會，產(chǎn)品智能化、數(shù)字化已成為人們追求的一種趨勢，設(shè)備的性能、價(jià)格、發(fā)展空間等備受人們的關(guān)注，尤其對電子設(shè)備的精密度和穩(wěn)定度最為關(guān)注。同時(shí)通過鍵盤的控制,實(shí)現(xiàn)了輸出電流值和限壓值可預(yù)置，可步進(jìn)調(diào)整、輸出的電流信號和電壓信號可直接數(shù)字顯示的功能，并具有輸出電壓實(shí)時(shí)監(jiān)控限壓報(bào)警并自動降低輸出電流等功能。采用性能優(yōu)于普通晶體管的場效應(yīng)管作為恒流源的主要部件，大功率晶體管作為擴(kuò)流電路的主要器件，結(jié)合三端穩(wěn)壓管和多層濾波使得整個(gè)系統(tǒng)性能提升了一個(gè)層次，從而實(shí)現(xiàn)了高精度恒流源的目的。I / 51摘要本文介紹了一種開環(huán)智能數(shù)控直流電流源的設(shè)計(jì)原理和實(shí)施方案，該方案采用 D/A（MAX531）轉(zhuǎn)換器、運(yùn)算放大器等器件來控制場效應(yīng)管導(dǎo)通狀態(tài)的原理，達(dá)到了輸出恒流的目的。整個(gè)系統(tǒng)采用 AT89S52 單片機(jī)作為主控部件，將預(yù)置電流值數(shù)據(jù)送入 D/A 轉(zhuǎn)換器（MAX531） ，經(jīng)硬件電路變換為恒定的直流輸出，同時(shí)采用基本沒有溫度漂移的康錳銅電阻絲作為精密采樣電阻。系統(tǒng)還對輸出電壓進(jìn)行實(shí)時(shí)采樣，通過 A/D 轉(zhuǎn)換器采樣回單片機(jī)與用戶給定的限壓值進(jìn)行比較，從而監(jiān)控了輸出電壓。與以往的直流恒流源相比，此次所設(shè)計(jì)的恒流源具有精度高、結(jié)構(gòu)簡單、工作穩(wěn)定、操作方便、成本低廉、帶負(fù)載能力強(qiáng)等優(yōu)點(diǎn)。性能好的電子設(shè)備，首先離不開穩(wěn)定的電源，電源穩(wěn)定度越高，設(shè)備和外圍條件越優(yōu)越，那