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

[Neil Johnson]

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