[time-nuts] Thunderbolt? (re simple gpsdo.) >> capacitors

shalimr9 at gmail.com shalimr9 at gmail.com
Fri Jan 6 02:19:16 UTC 2012


I have used that trick also for HV supplies when leakage through a capacitor (typically the capacitor used to compensate the HV divider used for regulation) exposed to 10 or 20kV is hard to eliminate.

At the time, I did not know it had already been invented...

Didier KO4BB


Sent from my BlackBerry Wireless thingy while I do other things...

-----Original Message-----
From: "Poul-Henning Kamp" <phk at phk.freebsd.dk>
Sender: time-nuts-bounces at febo.com
Date: Thu, 05 Jan 2012 22:49:55 
To: Discussion of precise time and frequency measurement<time-nuts at febo.com>
Reply-To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) >> capacitors

In message <CAL8XPmO76XuTETZC=33_v2YWuJGcw8gCvtTDHyae6E4MFb18=g at mail.gmail.com>
, Azelio Boriani writes:

>I have googled extensively trying to find something about the dual
>capacitor method of reducing the leakage current... nothing found. Please,
>can you indicate anything for me to learn more?

It is very simple:

R1 charges C1 to the DC potential and therefore C2 sees
(almost) no DC voltage, which means (almost) no leakage
current.  C2 is still a capacitor for any AC or dV component.
	
I belive I picked this trick up from a datasheet or app-note relating
to precision voltage references.

Poul-Henning

>> [Some op-amp]  >-+-----R2-----+-->
>>                  |            |
>>                  |          ----- C2
>>                  |          -----
>>                  |    ____    |
>>                  +---|____|---+
>>                        R1     |
>>                               |
>>                             -----  C1
>>                             -----
>>                               |
>>                              GND

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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