On Thu, 15 May 2008 15:54:44 -0400, "Doug Bannard" <ve3spf@[EMAIL PROTECTED]
>
wrote:
>
>"flipper" <flipper@[EMAIL PROTECTED]
> wrote in message
>news:rj3p24pftvlhtc0rq52fs49e4te0e5aibv@[EMAIL PROTECTED]
>> I've been toying with the idea of building a tube phono preamp and
>> using DC heaters but, as you all probably noticed from my last few
>> projects, I want to power the thing with a wallwart. That presented
>> the regulator drop out problem so I whipped up a '0V dropout'
>> regulator.
>>
>> Thought I remembered seeing others discuss that same issue (like
>> converting an existing amp with 12.6V transformer) so I posted the
>> schematic to my website in case anyone is interested.
>>
>> http://flipperhome.dyndns.org
>>
>> Not fancy and it doesn't have soft start but that could be easily
>> added.
>>
>> I haven't built it yet but spice says the sucker should regulate to
>> better than 100uV ripple, which should be ridiculously good for a
>> heater.
>
>This will work just fine although, as you said on your webpage, you may
need
>to do a little compensation if there's any tendency towards instability.
Depending on how fast you looked I found an error. hehe
I added a tickler resistor from the unregulated Vin to the zener diode
to ensure the opamp turns the MOSFET on at start up. Otherwise the
circuit might not start.
You could just power the zener from there if you don't mind the
increased output ripple to a few mV <rolling eyes>.
Of course, stick a big cap under the resistor, with a reverse reset
diode across it, and you get 'soft start'.
>I've built many of these in the past, except that my particular versions
use
>a bipolar transistor and a TL431 in place of your zener and opamp.
I'd be interested to see a schematic because I can't visualize it from
the brief description. Sounds almost like a conventional series pass
NPN regulator.
>
>Best Regards : Doug Bannard
>
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