An MCU based uninterruptible power supply using an MC68F333

Inverting power supplies and high voltage/current switches form the basis for many uninterruptible power supply (UPS) designs. In a very basic sense, a 60 Hz square wave with minimal filtering may suffice in many applications. Not only is power quality a factor but so is the speed at which a UPS can be brought online. As the need for quality power increases and response times to switch in the UPS decrease, more sophisticated controllers for UPSs must be used. Microcontrollers, such as the MC68F333, provide an excellent vehicle to implement intelligent UPS systems. The MCU can provide the intelligence and the peripheral modules to measure and monitor external voltage levels and frequency. From this information intelligent decisions can be made on whether to enable a power conditioning circuit or to completely switch over to a UPS until the main source of power has been restored. Microcontrollers, because of the inherent ability to generate complex, high speed timing signals that can be phase and frequency locked together, makes these devices a natural choice when designing modern UPSs. These MCU-based designs allow for higher PWM switching speeds, better monitoring of the external line voltage and enhanced ability to determine what type of malfunction is occurring when trouble happens. From this information MCU based UPSs can be built to economically provide back-up power when warranted by external conditions.