<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">It looks to me there's something we're not understanding (or misunderstanding) here. There's no way a capacitor that is spec'd to 35V loses 90% of its capacitance by 35V. That simply wouldn't be *useful*.<div><br></div><div>What does this specification and that graph *really* mean?</div><div><br></div><div>T.</div><div><br><div><br><div><div><div>On 5 Apr 2017, at 18:20, cheater00 cheater00 <<a href="mailto:cheater00@gmail.com">cheater00@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><p dir="ltr">The effect is much more dramatic than you say, and it seems to be easily achievable. Here's a post by <a href="mailto:evilterrance@hotmail.com">evilterrance@hotmail.com</a> on the Electronics 101 mailing list:</p><p dir="ltr">> how about losing 80% of their capacitance by the time you are only halfway to their voltage rating? Look at the graph in the upper right:<br>
> <br>
> <a href="https://product.tdk.com/info/en/documents/chara_sheet/C1608X5R1V225K080AC.pdf">https://product.tdk.com/info/en/documents/chara_sheet/C1608X5R1V225K080AC.pdf</a><br>
><br>
> That +-10% tolerance? Only counts to ONE volt. To be fair, that is an X5R...but look up your favorite X7R cap and check that DC bias curve. Disappointing.</p>
<br><div class="gmail_quote"><div dir="ltr">On Wed, 5 Apr 2017 17:25 Gordonjcp, <<a href="mailto:gordonjcp@gjcp.net">gordonjcp@gjcp.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">On Wed, Apr 05, 2017 at 03:04:19PM +0000, cheater00 cheater00 wrote:<br class="gmail_msg">
> Hi guys,<br class="gmail_msg">
> I've recently been reminded that ceramic caps (eg x5r) will only adhere to<br class="gmail_msg">
> their rating up to 1V, and will then start losing capacitance as you go<br class="gmail_msg">
> beyond. So effectively a DC bias could create a voltage controlled filter<br class="gmail_msg">
> just like that, with no semiconductors. I wonder, has anyone tried this?<br class="gmail_msg">
<br class="gmail_msg">
Not significantly. I guess if you biased them up to a few kV you could get a couple of femtofarads of a swing out of it.<br class="gmail_msg">
<br class="gmail_msg">
Bear in mind that varicap diodes actually have a practical method of operation where the gap between semiconductor layers varies with bias voltage, and need about 30V to get a couple of pF out of them.<br class="gmail_msg">
<br class="gmail_msg">
--<br class="gmail_msg">
Gordonjcp MM0YEQ<br class="gmail_msg">
<br class="gmail_msg">
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