Urgent!!!..PIC resets when changing to battery backup...Help

[sajeev]

HI
I am using PIC16f72 to buil a time sceduler with battery backup for pic which is running on 32khz crystall.I am using timer0 to generate the 1second relay.I am using a 3.6v NiCd battery backup for the pic.But when it changes from5v to 3.6 v battery mode the pic resets.Why?I dissabled brown out detedt in config word.Is there any thing I have to do to avoid this problem??

 

[vamanan]

Have you measured the change over time ?. Is there any high value capacitor in the battery circuit which is making any delay in change over?. Can you share the change over circuit you are using ?. I am also using the same battery back up for many application with PIC microcontroller. I didnt face any [problem there.

 

[sajeev]

Re: Urgent!!!..PIC resets when changing to battery backup...

Have you measured the change over time ?. Is there any high value capacitor in the battery circuit which is making any delay in change over?. Can you share the change over circuit you are using ?. I am also using the same battery back up for many application with PIC microcontroller. I didnt face any [problem there.

I used the circuit given below


I have added 1000uf before the 1n4oo7 diode,ie at the o/p of 7805 regulator

 

[master_picengineer]

Hi,
Naturally the Pic resets when supply falls to 3.7v or 3.5 v . To avoid this problem, you can configurate the PIC to work in the low battery mode. Untill 3 v PIC will not resets.

 

[sajeev]

Re: Urgent!!!..PIC resets when changing to battery backup...

Hi,
Naturally the Pic resets when supply falls to 3.7v or 3.5 v . To avoid this problem, you can configurate the PIC to work in the low battery mode. Untill 3 v PIC will not resets.

How to do that plz expalin.Is there any such option for pic16f72?

Added after 24 minutes:

I checked the voltages at pins :MCLR=4.1v,Vdd pin 4.4v
When I swith on/off the board then it resets.I added capacitors of .1u and .01u to the regulator.But no change...

 

[PaulHolland]

Re: Urgent!!!..PIC resets when changing to battery backup...

Make sure that the voltage on the MCLR pin never does go above VCC on the PIC otherwise it will give a latch-up and resets .. VCC on a pic16f72 can be from 2V upto 6V with no problem so ignore the comments from people regarding 4 or 3.5V !.
Maybe increase 4K7 to 33K !

 

[rachid77]

Re: Urgent!!!..PIC resets when changing to battery backup...

Hi,
Naturally the Pic resets when supply falls to 3.7v or 3.5 v . To avoid this problem, you can configurate the PIC to work in the low battery mode. Untill 3 v PIC will not resets.

hello
ok sir your idea is very good...
thanks

 

[sajeev]

Re: Urgent!!!..PIC resets when changing to battery backup...

Hi
I checked the circuit in another location.Then there was no problem at all.So I think its problem with the supply line.Supply regulation is done using 7805 and .1, .01, .001uf ,1000uf capacitors......Still sometimes ...between 20 on/off swiching of the board one reset will occur.