Thanks Kai for your warning,

I will put the entire development of power supply
1. My current power supply
(Dont know by whom & when it was designed)
is linear power supply having 17VAC input (Transformer O/P) rectified and then


Now in this circuit the battery charging of 6V/10Ah battery was done through 7809's O/P, in addition the 7809s were getting 17VAC as I/P and getting very hot and some times use to burst as if the mains I/P at the I/P of thetransformer is 230V then the transformer gives 17VAC O/P but if the mains AC is 280V then the trans. O/P goes high and hence the I/P of the 7809 also.

Now I have modified the circuit by routing the 7809 i/p through the 7812, but another problem is 7812 (TO-3) can support only 1A and now it is suppose to supply to
Two 7809
One 78R05
and its own o/p of 12V for two relays.
We thought of increasing the current capacity of 7812 by putting TIP121 accross its i/o & o/p but are not very sure of the idea neither we have any formula for making any calculations.


Now since the supply conditions in INDIA (Other than METROS) can be from 110V AC to 290-295V AC so finally we desided the have an SMPS.

We went for an SMPS with Device 1 - TOP247Y
O/P1. 5V/3A with 1% Regulation of SMPS
O/P2. 5V/4A with 5% regulation as SMPS can give only
one O/P tightly regulated and 55 was ok for the
application with that power i/p.
O/P3. 12V/2A for 3 Relays and may be any additional
circuit.

And for battery charging we had 7V/1A charger with a TINY switch
(Bothe the devices are from PI - Power Integration)

And we wanted to have the battery back up for only O/P1 i.e. 5V/3A (1%Regulation one) as in absence of power only control card keypad and display was suppose to function and motors and solenoids were never going to operate as mains is not there.

But the UPS function was bit problematic for only O/P1 as the battery is of 6V and the O/P voltage to be backedup is 5V.

If we give backup to other devices then the motors will not run but the relays may operate and even if we take care of the relay activation through the program in power down condition still the other circuit or ICs will keep on draining the battery which will altemately result in less backup time.

I know there are many conditions but
can there be a solution satisfying most of the conditions?

Sachin