Greetings,
I'm looking at powering a tiny PIC from 4 AA batteries, but the max voltage rating on the PIC is 5.5V. Looking at the nominal voltage for fresh AA batteries, the total voltage should be a max of ~6.5V. So I need to drop this a bit for the time when the batteries are fresh and I immediately think of using a diode or two in series with the voltage line.
The thing is, thinking further along, this micro is going to spend the vast majority of its life in sleep, drawing only 0.5-1.5uA. (Active mode will draw 1.5mA max) At this current level, for all the diode curves I've examined so far anyway, the diodes won't be dropping their nominal .7V-1V, but only .15 - .25V, which puts me with only a .3V-.5V drop for a pair.
I also don't want to add in a constant current drain resistor to hold the drop at a certain level since this is supposed to be a long-life battery monitor circuit that will remain powered even when the main device is switched off.
My intuition says this might still be okay since the voltage limitation is likely not to cause damage until a significant current is being drawn and when a significant current is drawn, the voltage will drop back down into the nominal range. But I'm not at all certain of this, so I'm here seeking opinions or experience on this.
Thanks for any help or insight,
Mike
I'm looking at powering a tiny PIC from 4 AA batteries, but the max voltage rating on the PIC is 5.5V. Looking at the nominal voltage for fresh AA batteries, the total voltage should be a max of ~6.5V. So I need to drop this a bit for the time when the batteries are fresh and I immediately think of using a diode or two in series with the voltage line.
The thing is, thinking further along, this micro is going to spend the vast majority of its life in sleep, drawing only 0.5-1.5uA. (Active mode will draw 1.5mA max) At this current level, for all the diode curves I've examined so far anyway, the diodes won't be dropping their nominal .7V-1V, but only .15 - .25V, which puts me with only a .3V-.5V drop for a pair.
I also don't want to add in a constant current drain resistor to hold the drop at a certain level since this is supposed to be a long-life battery monitor circuit that will remain powered even when the main device is switched off.
My intuition says this might still be okay since the voltage limitation is likely not to cause damage until a significant current is being drawn and when a significant current is drawn, the voltage will drop back down into the nominal range. But I'm not at all certain of this, so I'm here seeking opinions or experience on this.
Thanks for any help or insight,
Mike