Jednostavni VCO

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ALIGN="bottom" HSPACE="0" VSPACE="0">Izolirano napajanje za LCD DVM</B></U></A></div> <bR> </td> <td valign="top" height=400 BGCOLOR="#FFFFFF" TEXT="#080000"> <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-2650537455752702" crossorigin="anonymous"></script>  <ins class="adsbygoogle" style="display:block" data-ad-client="ca-pub-2650537455752702" data-ad-slot="7117608876" data-ad-format="auto" data-full-width-responsive="true"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script> <bR> <bR> <div> <B><IMG SRC="7e54e9f0.gif" border=0 width="590" height="415" ALT="VCO - naponski upravljan oscilator" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></B></div> <bR> <div>      Ovdje je prikazan jednostavani VCO. Ustvari, ideja je bila kontrolirati frekvenciju oscilatora, ali da <B>potenciometar bude na po volji dugačkim vodovima</B>. Rješenje je jednostavno. Napon sa potenciometra se filtrira sa malim elektrolitskim kondenzatorom (time se miču smetnje) i zatim se prosljedi operacionom pojačalu u mostu. Ono kontrolira i proporcionalno regulira strujni izvor. Struju dovodimo na oscilator sa LMC555 koji je u stanju oscilirati i na 3MHz. Područje regulacije je 1:10 tj. dekada. Izlazni signal je 5V takt malog faktora ispune. Na širinu generiranog impulsa utječe konstanta Cx*220R (onaj na pinovima 6 i 7 LMC555 - minimalno 50R!). Ako faktor ispune treba biti 50%, može se postići djeljenjem frekvencije (sa D bistabilom) na pola. Promjena područja oscilatora se vrši izborom Cx kondenzatora. Koliko je Cx veći toliko je niža frekvencija oscilatora. Cx može biti i nekoliko uF. Međutim, ako se želi imati stabilni takt niže frekvencije, bolje je podijeliti izlazni takt sa djelilom, nego stavljati elektrolitske kondenzatore, koji bi s vremenom mogli promijeniti vrijednost.</div> <bR> <div>      Sklop je primjenjen u generatoru impusa. Dva tranzistora u strujnom izvoru ne unose dodatnu temperaturnu ovisnost jer te promjene kompenzira operaciono pojačalo. LMC555 se napaja sa +5V!.</div> <bR> <bR> <bR> <bR> </td> </tr></table></body>