[TowerTalk] Ferrites 31 vs. 77 material

[jimlux]

On 11/2/19 2:28 AM, Jim Brown wrote:
> On 11/1/2019 6:40 PM, Roger Parsons via TowerTalk wrote:
>> I would imagine that processing has improved since then, but this must 
>> still be to some extent true.
> 
> You have a vivid imagination. :) I have measured data to prove that. 
> Also see N6RK's post. As luck would have it, I gave a talk to a Silicon 
> Valley club tonight on a very different topic, but afterwards fielded 
> questions about chokes from several engineers who had worked in 
> manufacturing. When I described my work described in an earlier post 
> about dealing with component tolerances, they nodded their heads in 
> agreement.
> 
> My first gig after college was at Motorola, which is where I first 
> learned that a circuit design has to work with every part that gets 
> plugged in to the circuit board, which means that the design has to work 
> with components with tolerances that you can and did buy.
> 


I haven't checked the catalogs, but I'll bet that the tolerances for 
parts intended for general purpose choking and transformers are wider 
than those intended for building inductors.  If a transformer core has a 
higher mu than expected, it still works just fine as a transformer, 
barring issues with loss and/or self resonance.  Likewise, for something 
being used as a lossy choke (as opposed to a resonant choke) you just 
care that the loss is high enough - if it's twice as high as you 
expected that's all the better.

On the other hand, if you're buying inductors for filters or for 
switching power supplies, the core material has to be pretty consistent.

Since there *is* some crossover among applications for cores, you could 
wind up using a poor tolerance core and having it work in a high 
tolerance application, as a prototype.