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</o:shapelayout></xml><![endif]--></head><body lang=FR-CA link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Thank you René.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>This is what I was looking for..<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>JP<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-CA style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=FR style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>De :</span></b><span lang=FR style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> Synth-diy [mailto:synth-diy-bounces@synth-diy.org] <b>De la part de</b> René Schmitz<br><b>Envoyé :</b> 3 juillet 2020 07:24<br><b>À :</b> synth-diy@synth-diy.org<br><b>Objet :</b> Re: [sdiy] XR2206 temeperature stability within +/- 5%<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p>Hi Jean-Pierre and all,<o:p></o:p></p><p>On 02.07.2020 17:09, Jean-Pierre Desrochers wrote:<o:p></o:p></p><p class=MsoNormal style='margin-bottom:12.0pt'>> I need a pure sine wave generator adjustable from 10Hz to 60Hz at > around 5v peak. The adjusted frequency should stay stable within +/- > 5% temperature wise. The project inside metal enclosure could have > temp of up to around +40deg C. I have a bunch of XR2206 VCO IC on > hand to use. I wonder if the best capacitor to be used here would be > A polystyrene type for temperature stability.. (??) I'll use 1% metal > film resistors for the rest of circuit.. <br><br>The 2206 datasheet gives you a hint to the best value of the resistor for optimum temperature stability. <o:p></o:p></p><p>There is a graph of frequency variation vs resistance and temperature. (Figure 9) From that we can conclude that the <o:p></o:p></p><p>optimum is somewhere between 4k and 200k.<o:p></o:p></p><p class=MsoNormal style='margin-bottom:12.0pt'><br>Now with your desired range, lets put 60Hz at the top and use 10k, this gives with 1/RC -> 1.65uF.<o:p></o:p></p><p>Practically you'd choose 1.5u or even lower and raise the resistor value somewhat. Distortion is best at about 30k. <o:p></o:p></p><p>As long as you stay near that corridor. <o:p></o:p></p><p class=MsoNormal style='margin-bottom:12.0pt'><br><br>As for the dielectric, I'd say your requirements are rather modest, and can easily be met.<br><br><br><br>For a ball park figure:<br><br><a href="https://en.wikipedia.org/wiki/Film_capacitor#Frequency_and_temperature_changes_in_capacitance">https://en.wikipedia.org/wiki/Film_capacitor#Frequency_and_temperature_changes_in_capacitance</a><o:p></o:p></p><p>The basic properties of some of the films used for film caps. (Ceramics COG or NP0 may <o:p></o:p></p><p>work, but large values might not be available. Some other films exist, but are not given in the plot.)<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p>You can see that PP and PPS have excellent properties.<o:p></o:p></p><p><br>At 60Hz you don't have to worry much about inductance, frequency or other effects either.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p>Polystyrene and Polycarbonate were once the best choice for timing caps, but afaik are out of <o:p></o:p></p><p>production. And it is difficult to find a PS cap in that capacitance range anyway.<o:p></o:p></p><p class=MsoNormal style='margin-bottom:12.0pt'><br><br>But even PET and PEN would be well within 2% over a practical 0..70°C range.<br><br>If your enclosure narrows this temperature range by shielding it from the environment, it may even help.<br><br><o:p></o:p></p><p>So you can make this with cheap and easy to get polyethylene caps. You'd have to confirm with the <o:p></o:p></p><p>datasheet of the cap chosen of course. <o:p></o:p></p><p><o:p> </o:p></p><p>The largest contributors are the chip with worst below 1% and the cap with 2%. Metal film resistors <o:p></o:p></p><p>would add a mere 100-200ppm and are a good choice. <o:p></o:p></p><p class=MsoNormal style='margin-bottom:12.0pt'><br><br><br>Best,<br><br> René<br><br><br>--<br><a href="mailto:synth@schmitzbits.de">synth@schmitzbits.de</a><br><a href="http://schmitzbits.de">http://schmitzbits.de</a><o:p></o:p></p></div></body></html>