Basic Theory of Nonstop DC Power Supply

The Nipron nonstop DC power supply is a power supply unit with built-in UPS (Uninterruptible Power Supply) capability. The nonstop power supply has a DC input (from a battery) in addition to conventional AC input. The power supply unit can be operated from both AC and DC inputs simultaneously and also either of the dual inputs. With this unique architecture, the Nipron nonstop power supply can continue to feed the DC output power without being interrupted by a power outage or power line failure. When a long-term power outage occurred, the DC (battery) input mode of operation sustains the DC output power for a while to allow the computer system to shut down securely.

The nonstop power supply consists of a switch-mode power supply plus additional battery, DC to AC converter, and battery charger as shown in the block diagram (see figure below).  The input circuit block (primary side) has two input gates (DC and AC inputs), which are isolated each from the other. The AC and DC inputs separately go into the switch-mode converters (engines), whose square-wave outputs are transferred to a common power transformer. When normal AC input is coming in, the AC input engine drives the transformer and causes the rectifier/smoothing circuit (secondary side) to output a DC power. The battery charger, which is paralleled with the DC input converter, keeps the battery being charged. When the AC input is interrupted (by a power outage or power line failure), the battery and DC input engine feed the primary power of power supply in place of the AC input engine. Thus, the power supply can continue to output the DC power. 
It is also possible to drive the power supply with both AC and DC input engines simultaneously (when the AC input voltage is low). The power supply can shift smoothly from AC to DC input or DC to AC input operating mode without causing undesired output transience.