Build This Simple Power Supply For Your Intruder Alarm Project

This power supply is designed for the Modular Burglar Alarm but is suitable for various applications. It delivers a 12-volt output with a maximum current of 1 amp. In case of a mains failure, the backup battery activates immediately, and when mains power is restored, the battery recharges automatically. The 7805 voltage regulator requires a larger heatsink due to significant energy dissipation, especially during the recharging of a depleted battery. Its heatsink is connected to the 9V1 point and must not be grounded. The 7812 regulator does not exceed a dissipation of 2 watts, allowing for a smaller heatsink. Many components depicted lying flat on the board are actually mounted vertically. The links are made of bare copper wire located on the component side of the board. The heatsinks are fabricated from folded strips of aluminum, approximately 2mm thick. A well-insulated panel-mounted fuse holder should be used for the mains supply to the transformer, fitted with a 1-amp fuse. A genuine alarm-type backup battery is recommended, as they are maintenance-free and can maintain a terminal voltage of 13.8V for many years without significant degradation. Their life expectancy is around five years; however, they may not recover well from deep discharges. Users have the option to utilize batteries of varying capacities.

This power supply circuit is designed to provide reliable voltage regulation and backup power for alarm systems, ensuring continuous operation even during power interruptions. The primary output voltage of 12V is achieved using voltage regulators, specifically the 7805 and 7812, which are configured to maintain stable voltage levels under varying load conditions.

The 7805 voltage regulator is responsible for supplying a consistent output voltage, and its larger heatsink is crucial for dissipating heat generated during operation, particularly when the backup battery is being charged. The heatsink must be carefully positioned to avoid grounding, which could lead to circuit malfunction. The 7812 regulator, which operates at lower power levels, is equipped with a smaller heatsink, thus optimizing space on the circuit board.

Component orientation is an important aspect of the design, as many components are mounted vertically to save space and improve airflow around the heatsinks. The use of bare copper wire for links on the component side enhances conductivity while minimizing potential issues with solder joints.

The inclusion of a panel-mounted fuse holder with a 1-amp fuse is a safety feature that protects the transformer and associated circuitry from overcurrent situations. The use of a maintenance-free alarm-type backup battery is essential for ensuring longevity and reliability. These batteries are designed to withstand long periods of use while maintaining a high terminal voltage, thereby providing adequate power during outages.

Overall, this circuit design emphasizes efficiency, safety, and reliability, making it suitable for various applications beyond just burglar alarms. The ability to accommodate different battery capacities offers flexibility for users, allowing for customization based on specific power requirements.Although this Power Supply was designed for the Modular Burglar Alarm - it has other applications. It provides an output of 12-volts - at a current of up to 1-amp. In the event of a mains failure - the back-up battery takes over immediately. And when mains power is restored - the battery recharges automatically. The 7805 needs the larger heatsink because it has to dissipate a lot of energy - especially when called upon to recharge a flat battery. Its 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 standing upright.

The links are bare copper wire on the component side of the board. 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. Use a genuine alarm type back-up battery. They are maintenance-free. Their terminals can be held at 13v8 for many years - with no apparent ill effects. They have a life expectancy of about five years. However, they tend not to recover from a very deep discharge. If you wish - you can use a smaller or larger capacity battery. 🔗 External reference