low voltage detector & interrupt

[banh]

Please find below "slightly" modified circuit that ensures that the battery is charged when the +12V supply is present, regardless of the state of the "MCU output" pin (picture1), and "simplified" circuit with NPN (picture2) ..

Regards,
IanP

Hi IanP,
in your picture 1 (using PNP & NPN), when 12V is off the battery is always supplying to the regulator (via 200Ohm & diode), regardless of the state of the MCU output !

In your circuit in Figure 2 (using only NPN), because the battry negative terminal is conected to Collector, the current is not flowing for Collector to Emitter, but in the reverse direction! Is there any problem with this?

Added after 1 hours 12 minutes:

now i think of another way:
no more battery, and use only 1 12V power source (see attached circuit).

when the main switch is open -> NMI handler will start running and turn on the NPN, which will turn on the PNP. At this time 12V is supplied again, the MCU keeps on running, does necessary backup and finally turn off the NPN to shutdown its own.

Any comment on this circuit?

 

[IanP]

The circuit with PNP-NPN needs another diode in series with 200Ω resistor - to cut-off direct path between battery and the voltage regulator, the other circuit may also need small change here or there; after all they were just concepts ..

As far as you new circuit - without battery - is concerned, you may face some problems when voltage drops to fast and microcontroller doesn't have enough time to do whatever it needs to do and shut itself down ..

Maybe you can re-consider PNP-NPN circuit with diode+200Ω ..

Regards,
IanP

 

[dnarenderreddy]

hi i got the same problem as yours, i need to write the data in ram into a serial eeprom attached. can u give me the circuit you used

thanks
narender

Added after 1 hours 13 minutes:

hi,

but i think battery will become bulky for my application,
how much size will a 9 volts NiMH battery be. and what will be its size.
i just want back up for vey small time less than a minute. the battery capacity (AH)should be very small.
i think lead acid battery will not suit my application(wall hanging energy meter).

is there any other battery which will be small in size and provide me 9 volts .

awaiting
your


thank you
narender