單片機開(kai)關方式 控制開(kai)關電源三種方式
時間：2018-07-25 來源：未(wei)知
單片機開關(guan)方式(shi)(shi) 控制開關(guan)電源三種方式(shi)(shi)
在(zai)單片機控(kong)制(zhi)開(kai)關(guan)電(dian)(dian)源(yuan)上，單片機控(kong)制(zhi)開(kai)關(guan)電(dian)(dian)源(yuan)可以從輸(shu)出功率的控(kong)制(zhi)中(zhong)得到多種(zhong)控(kong)制(zhi)方(fang)式。
其一是單片(pian)機輸出(chu)一個電(dian)(dian)(dian)(dian)壓(ya)(ya)(經DA芯片(pian)或PWM方(fang)式(shi)),用作電(dian)(dian)(dian)(dian)源(yuan)的基準(zhun)電(dian)(dian)(dian)(dian)壓(ya)(ya).這種(zhong)方(fang)式(shi)僅(jin)僅(jin)是用單片(pian)機代替了(le)原來的基準(zhun)電(dian)(dian)(dian)(dian)壓(ya)(ya),可以用按鍵輸入電(dian)(dian)(dian)(dian)源(yuan)的輸出(chu)電(dian)(dian)(dian)(dian)壓(ya)(ya)值,單片(pian)機并(bing)沒有加入電(dian)(dian)(dian)(dian)源(yuan)的反(fan)饋(kui)環,電(dian)(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)(dian)路并(bing)沒有什么改動.這種(zhong)方(fang)式(shi)最簡單.
其(qi)二是單片(pian)機擴展AD,不斷(duan)檢測電源(yuan)的輸(shu)出電壓,根(gen)據電源(yuan)輸(shu)出電壓與(yu)設定值之差,調整DA的輸(shu)出,控(kong)制PWM芯片(pian),間接控(kong)制電源(yuan)的工作.這種方(fang)式單片(pian)機已加入到電源(yuan)的反饋(kui)環(huan)中,代替原來的比較放(fang)大環(huan)節,單片(pian)機的程序要(yao)采用比較復雜的PID算法.
其(qi)三是(shi)單片機(ji)擴展AD,不斷檢(jian)測(ce)電(dian)源(yuan)的(de)輸出(chu)電(dian)壓,根據電(dian)源(yuan)輸出(chu)電(dian)壓與設定(ding)值(zhi)之差,輸出(chu)PWM波(bo),直接控制電(dian)源(yuan)的(de)工作.這種方式(shi)單片機(ji)介入電(dian)源(yuan)工作最(zui)多.
第三種(zhong)方(fang)式是最(zui)徹底的單(dan)片機(ji)(ji)控制開關(guan)電(dian)源,但對單(dan)片機(ji)(ji)的要求也(ye)最(zui)高.要求單(dan)片機(ji)(ji)運算速度快,而且(qie)能夠輸出足(zu)夠高頻率的PWM波.這(zhe)樣(yang)的單(dan)片機(ji)(ji)顯然價格也(ye)高.
DSP類(lei)單片機速(su)度夠高,但目(mu)前(qian)價格也很高,從成本(ben)考慮,占電源成本(ben)的比例太大,不宜采用(yong).
廉(lian)價單(dan)片(pian)(pian)(pian)機中,AVR系列最快,具有PWM輸出,可以(yi)考慮(lv)采用.但AVR單(dan)片(pian)(pian)(pian)機的工作(zuo)頻率(lv)仍不夠高(gao),只能是(shi)勉強(qiang)使用.下面我們(men)具體計算一下AVR單(dan)片(pian)(pian)(pian)機直接控制開關(guan)電源工作(zuo)可以(yi)達到什么水(shui)平.
AVR單(dan)片機中,時(shi)鐘頻(pin)率(lv)(lv)最高(gao)為16MHz.如果(guo)PWM分(fen)(fen)辨(bian)率(lv)(lv)為10位(wei),那么PWM波的頻(pin)率(lv)(lv)也就(jiu)是開關(guan)(guan)(guan)電源(yuan)的工作頻(pin)率(lv)(lv)為16000000/1024=15625(Hz),開關(guan)(guan)(guan)電源(yuan)工作在(zai)這個頻(pin)率(lv)(lv)下(xia)顯然(ran)不夠(在(zai)音頻(pin)范圍(wei)內).那么取PWM分(fen)(fen)辨(bian)率(lv)(lv)為9位(wei),這次開關(guan)(guan)(guan)電源(yuan)的工作頻(pin)率(lv)(lv)為16000000/512=32768(Hz),在(zai)音頻(pin)范圍(wei)外,可以用,但距離現代開關(guan)(guan)(guan)電源(yuan)的工作頻(pin)率(lv)(lv)還(huan)有一定距離.
不過(guo)必須(xu)注意,9位(wei)分(fen)(fen)辨(bian)率是(shi)說(shuo)功率管(guan)導(dao)通-關斷(duan)這個周(zhou)期中,可以分(fen)(fen)成512份(fen),單就導(dao)通而(er)言,假定占空比為0.5,則(ze)只(zhi)能分(fen)(fen)成256份(fen).考(kao)慮(lv)到(dao)(dao)脈沖寬度(du)與電(dian)源的輸出(chu)并(bing)非線性關系,需要至少再打個對折,也就是(shi)說(shuo),電(dian)源輸出(chu)最多只(zhi)能控制(zhi)到(dao)(dao)1/128,無論負載變化還是(shi)網電(dian)源電(dian)壓變化,控制(zhi)的程度(du)只(zhi)能到(dao)(dao)此為止(zhi).
還(huan)要(yao)(yao)注意,上面(mian)所述(shu)(shu)只有(you)一個PWM波,是單端工作.如果(guo)要(yao)(yao)推挽工作(包括半橋),那就(jiu)需要(yao)(yao)兩個PWM波,上述(shu)(shu)控制精度(du)還(huan)要(yao)(yao)減(jian)半,只能控制到(dao)約1/64.對要(yao)(yao)求不高(gao)的電(dian)(dian)源(yuan)例如電(dian)(dian)池充(chong)電(dian)(dian),可以滿足(zu)使用要(yao)(yao)求,但對要(yao)(yao)求輸出(chu)精度(du)較(jiao)高(gao)的電(dian)(dian)源(yuan),這就(jiu)不夠了(le).
綜上(shang)所述,AVR單(dan)片(pian)機(ji)只能很勉強地使用(yong)在直接控制PWM的方式(shi)中.
