Re: TI-H: SPinTerface build question
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Re: TI-H: SPinTerface build question
Bryan Rittmeyer wrote:
> I should probably take another look at the schematic, however, a 7805
> can handle about an amp on a heatsink and is probably overkill for a
> SPinTerface... if the idea is small size, why not use a (harder to find
> but much cheaper) 78L05 which comes in a TO-92 package? But even
> a 78L05 will not cut it...
I noticed that. This thing is HUGE! 35V input voltage? 1A output
current? I don't think this is needed. I'm not big in electronics
(yet) but this sure doesn't seem like the smallest thing we can use.
> The problem is that the spec sheet for most 7805s states that the part
> has a 2.0-2.5 volt "dropout." This means that the part will not operate
> correctly on anything less than 7-8 volts -- This is required overhead.
> Now, if you are powering the 7805 with 6 volts... which would work,
> in theory, you are essentially encouraging sporadic operation. I haven't
> gotten a clean 5 volts out of a normal 7805 with less than about 9
> volts.
That sounds right. But then how come Rich can somehow expect us all to
get 5 volts in the troubleshooting section of his page? Did he verify
it on his calc?
> like a cow avoids a butcher) However, if you flip through the
> DigiKey or Mouser catalog you'll find no shortage of very low dropout
> 5V TO-92 package regulators (an SMT version of one of these is probably
> what the calculator itself uses)
So can I just swap regulators and that will solve the problem? Or is
there additional wiring involved?
THanks for clearing this up for me.
Tony
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