Jinx wrote:
>> LT1173-5 to give me 5 V to power the PIC16F887
>>     
>
> Is that the best choice ?
>
> http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1042,C1033,P
> 1468,D1808
>
> The introduction in the pdf says
>
> "The device can deliver 5V at 80mA from a 3V input in step-up mode"
>
> although ambiguously in Table 1 further down says 90mA (min) with
> a 47uH inductor. Perhaps I've become cynical of mftr's claims. They
> may be stating the maximums, I don't know. Seems a long way from
> the 160mA you were aiming at though
>
>   
He only intends to run the PIC of the 5V, the LED's go straight off the 
battery (at whatever V that may be). Of course, this is also inefficient 
for power conservation because his current-limiting resistors will not 
produce the desired light output for most of the battery life-cycle 
(either too much or too little depending on the cell voltage....). If he 
uses 260Ohm to get 5mA through the 1.7Vf Red LED at 3V (when the cells 
are fresh), then, when the cells are half-depleted, at 1.2V each, the 
LED current will be only 2.7mA, and when the cells are dead (at say 
1.0V), the current will be only 1.15mA

I see that as being a major design issue with his 'prototype'. The LED's 
need a constant supply voltage for the life of the cells.

Of course, he could use Lithium AA cells, and get much more consistent 
output....

Rolf

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