"flipper" <flipper@[EMAIL PROTECTED]
> wrote in message
news:1d6p24pg7kc5cvbpcvsn2dk1ltk252av4h@[EMAIL PROTECTED]
> 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
Send me your email address and I'll be happy to scan in a schematic and
send
it to you.
Best Regards : Doug Bannard
|
