On Thu, 15 May 2008 19:01:16 -0400, "Doug Bannard" <ve3spf@[EMAIL PROTECTED]
>
wrote:
>
>"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
>
flipper
with the proverbial 'at'
oplink
and, of course, there should then be a "net" after the obligatory
intervening 'dot'
Btw, I also put up another, rather unique, heater circuit you might
find either interesting or amusing. I call it a pulse regulator for
'wrong size' transformers.
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