Description: A 12 Volt power suppiled designed for
Ron's Modular Burglar Alarm. However, being a popular supply voltage this
circuit will have many other uses as well.
Notes: This Power Supply is suitable for the
Modular Burglar Alarm. However, it has other applications. It is designed to
provide an output of 12-volts, with a current of up to 1-amp. In the event of
mains failure, the back-up battery takes over automatically. When the mains is
restored, the battery recharges. Use a genuine alarm type back-up battery. They
are maintenance-free, and their terminals can be held at 13v8 for many years,
with no ill effects. A smaller or larger capacity battery may be used, without
circuit modification. Use the 2-amp version of the 7805. It needs the larger
heatsink because it has to dissipate a lot of energy, especially when called
upon to recharge a flat battery. This heatsink is at 9v1, and must NOT be
connected to ground. The 7812 never has to dissipate more than 2-watts, so its
heatsink can be smaller.Many of the components, which are shown lying flat on
the board, are actually mounted upright. The links are bare copper wire on the
component side. The heatsinks are folded strips of aluminium, about 2mm thick.
Use a well-insulated panel mounted fuse holder for the mains supply to the
transformer, and fit it with a 1-amp fuse.
