[sdiy] 3340 oscillator - current limiting resistor equation is wrong?

[Tom Wiltshire]

Ok, so this is why you choose the next value down, rather than the next value up.

Hence 820R not 1K.

Thanks Neil.

Tom

==================
       Electric Druid
Synth & Stompbox DIY
==================

> On 18 Nov 2017, at 20:38, Neil Johnson <neil.johnson71 at gmail.com> wrote:
> 
> Tom,
> 
> If you read the datasheet carefully you see that all the resistor is
> doing is limiting the current for the internal zener diode.  So the
> actual current is not that critical, it just needs to be enough to
> bias the diode into its zener region.  The equation in the datasheet
> suggest this needs to be at least 8mA, more (but not too much) is also
> ok, but less may lead to problems.
> 
> I would go with the E12 series explanation.
> 
> Neil
> 
> On 18 November 2017 at 17:44, Tom Wiltshire <tom at electricdruid.net> wrote:
>> 
>>> On 18 Nov 2017, at 16:20, Florian Anwander <fanwander at mnet-online.de> wrote:
>>> 
>>> On 18.11.17 16:17 , Pete Hartman wrote:
>>>> 
>>>> Could it be as simple as the closest E12 value without going over?
>>>> 
>>> 1k would be much closer to 975R than 820R
>> 
>> I agree, and for a current *limiting* resistor, I’d have thought you wanted a slightly larger value to be on the safe side, rather than a slightly smaller one.
>> 
>> So no-one has ever come across this before?! Seems hard to believe.
>> 
>> I notice both the V3340 and AS3340 data sheets say only “current limiting resistor required for supplies greater than -6V” without actually providing any equation or committing themselves to a figure!!
>> 
>> Tom
>> 
>> ==================
>>       Electric Druid
>> Synth & Stompbox DIY
>> ==================
>> 
>> 
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at synth-diy.org
>> http://synth-diy.org/mailman/listinfo/synth-diy
> 
> 
> 
> -- 
> http://www.njohnson.co.uk