battery power indicator circuit
battery power indicator circuit
(OP)
I am trying to find most efficient way to detect the voltage of a battery without drawing too much power from it(as that would defeat the purpose).I have seen some comparator circuits which do that but they all used zener(power wastage). Is there another way or better way to do it? Thanks





RE: battery power indicator circuit
Do you need continuous monitoring, or is once a month (day year, millisec?) good enough.
How accurate?
A switched circuit using relays would eliminate drain when you are not monitoring.
Relays may be low reliability, FET's may do.
A high Z bridge set to near whee you expect the voltage to be could be a very low drain (and possibly a charge instead of a drain) possibility.
Do you need to know the voltage, or do you need a trip point indicator? If all you need is a trip point, what latency can you afford? Within an hour or a few seconds?
Without further information a guess would be a timed relay to a beridge with an accurate monitor. This solution could be much more expensive than you need, so better requirements can produce more cost effective solutions.
RE: battery power indicator circuit
TTFN
RE: battery power indicator circuit
RE: battery power indicator circuit
RE: battery power indicator circuit
RE: battery power indicator circuit
To build something similar, all you need is a very low power op amp or comparator and a voltage reference from somewhere. A voltage divider of high value resistors, and some hysteresis, and bingo !
RE: battery power indicator circuit
Or check Maxim or TI - both have battery management
IC's which might be used for the purpose. Some have
"sleep" modes (i.e., very low current drain) if you
have a way to control it from your embedded MPU.
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RE: battery power indicator circuit
If your micro is running directly off battery (no regulator, we are talking cheap here) and you have an LED indicator, enable the LED for a very short time and read the LED voltage into an A/D input that references the micro's power supply. The LED will maintain a fairly constant voltage at only a few milliamps (much less than a zener) so as your battery voltage drops the constant voltage off the LED will give a higher reading. Pass this through a look up table and you have a fairly accurate (I vaguely remember about 5%) battery monitor that consumes much less power than a zener circuit.
RE: battery power indicator circuit
RE: battery power indicator circuit
RE: battery power indicator circuit
RE: battery power indicator circuit
One caveat on my non-regulator technique - watch out for the micro's operating voltage. This initial design had a PIC18 and with fresh batteries we ran it above the specified voltage (5.5V) but well below the absolute maximum voltage (7.5V). Unfortunately the EEPROM had intermittent failures in this range so we ended up discharging the battery packs slightly before shipping until we could get a design tweak in place :-(.