AVR-Chat

Talk about unregulated supply voltages...

Have you looked at a switchmode regulator like the MC34063, Alexandre?  
Some, like the '063, will withstand up to 50 volt supply voltages and 
won't cost a lot to build...perhaps a couple of bucks for parts and some 
assembly time, but it depends upon how critical your circuit is.  You 
could set your regulator output for something less than your minimum 
input voltage, like 4 volts, and then you'd be good to go.  Build up a 
prototype and check to see how it behaves.

Doesn't the bandgap reference get fed by a constant current source?  
That being the case, the supply voltage shouldn't make that much 
difference so long as it's kept within the parameters specified for your 
controller.  Look at the reference variation with supply voltage 
specification in your datasheet.  It should tell you if you can maintain 
8 bit accuracy.


REB


Alexandre Guimaraes wrote:

> 
>Hi,
> 
>	I have an application where a simple and cheap zener regulator with
>emitter follower would be my best ( cheap) option for powering a Atmega168
>with the AD converter using the internal 1.1 volts reference. As the input
>voltage range is way to big, from about 5 volts up to 40 volts, the
>regulation will not be too good because the zener current will vary too
>much.
> 
>	I did not find any references if I will get into trouble varying the
>supply at the AVR in the range of 3 to 5 volts. Does anyone have references
>or opnions about this ? Would the AD suffer from those variations in supply
>voltage even using the internal bandgap as a reference ? I just need 8 bit's
>out of the AD...
> 
>	I would appreciate any insight. I always try to make the power
>supply as stable as possible and letting it out to the microcontroller with
>such a big variation feels really weird to me... But I looked around all I
>could and did not find anywhere saying that I could not do it with a micro
>that is specified for this full range !
> 
>	Thanks in advance...
> 
>Best regards,
>Alexandre Guimaraes
>  
>


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