What voltage?

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2camjohn

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I have a circuit which has two voltage regulators, one at 3.3V and one at 8V.

I am free to run my PIC16f628a (smt) of either of them.

Which option would be better? 3.3 or 8.0V??
Why?

Thanks
John
 
2camjohn said:
I have a circuit which has two voltage regulators, one at 3.3V and one at 8V.

I am free to run my PIC16f628a (smt) of either of them.

Which option would be better? 3.3 or 8.0V??
Why?

Try consulting the datasheet!, max/min specs are near the back - 8V is likely to be far too high, and I would suggest using a 16LF628 if running off 3.3V (although it may just scrape in the spec for an 16F628).
 
well, isn't 8v outside the maximum operating voltage range of the PIC? I think that would narrow it down rather quickly :lol:

oops, nigel beat me to it. In any case, you could run it off 8v with a 5v regulator, but that's a waste of power if you can run it on 3.3v instead. (linear regulators are inefficient)
 
Thanks guys

I have just checked the datasheet and cant find the minimum and maximum voltages.

Oh well its running fine off 8V now, so I will leave it like that.
 
Chapter 17 'electrical specifications' in the 16f628a datasheet

Max voltage : 6.5 Volt ! !

You are killing it at 8 Volt, it may run now but it's unlikely to be happy and will soon die :?
 
Oops, thanks Exo:

When I read evandudes post it said to me "well 8V ISNT outside the maximum operating voltage range of the PIC". He is actually saying it IS outside the maximum rating.

I cant see in chapter 17 where it says what the minimum voltage is?



I will try 3.3V and see what happens...


John
 
I believe 3.3v is okay for a regular 16F, however as nigel said you're much better off going to a 16LF (low-voltage version) instead, they are good down to a couple volts.

whatever the case, I'd say try it and see
 
2camjohn said:
I cant see in chapter 17 where it says what the

Page 140 - 141
chapter 17.2 for LF, 17.3 for normal operation
3.0V is minimum
 
I saw that but I cant imagine my pic will run off -0.3V


Im guessing that is more to do with what is safe to put into your PIC, rather than the minimum voltage it will run off.



Ill give 3.3V a go anyway.
Thanks guys.
 
Actually there is another way how to run PIC from 8V and 3,3V simultaneously (in case you don't need ground to be common).
Because 8-3.3=4.7V you can run the PIC with VDD connected to 8V and VSS connected to 3.3V and the PIC will run just fine.
 
In this situation, the clock(crystal) frequency is an important part of the choice.

With just over 3V you shouldn't run higher than 12MHz according to the data sheet.

So, using 8V with a 5V regulator can allow you to run it at max. 20MHz.

It's your choice, I reckon it is only an additional 78L05 regulator, the size of a transistor.
 
Someone Electro said:
I guy ran an PIC16F84 at 38Mhz and it ran fine whithout an single problem.
Yes, it's easy to overclock them, but nobody can guarantee it will run fine and errorless :lol:
 
Jay.slovak said:
Actually there is another way how to run PIC from 8V and 3,3V simultaneously (in case you don't need ground to be common).
Because 8-3.3=4.7V you can run the PIC with VDD connected to 8V and VSS connected to 3.3V and the PIC will run just fine.


Great Idea!

However I am using the PIC to control devices which are running on the 8V and 3.3V power rails.


Would this be possible with the PIC wired up as you have described?

Thanks alot
John
 

I am using the internal 4mhz osc so I should be fine with that!
 
The guy that overclocked it to 38Mhz made it do an loop.He tested it for 2 houres runing that.It didnt make not one error in that time.

That means that the chanses of making an error are more than 70 200 000 000 to 1 (thats how many instructions it was suposed to make in 2 houres)

I wodner if you can overclock an dsPIC to 200Mhz (they ware suposed to run at "only" 120Mhz)

Oh and dont forget to disable the Brown out reset of you run it at 3.3 V (Or it will keep reseting your PIC)

Well i run PICs of an single litium cell and it works fine.
 
Unfortunatelly no, atleast not directly. But if you use a realy or optocoupler then yes...
 
Right,

Well that would mean extra components, something that I am trying to cut down on.

Thanks for the idea though.


I will redesign the board so that the PIC runs off the 3.3V regulator. And disable the brown out protection.



Thanks
John
 
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