Abstract: A battery back-up system providing a short term hold-up for a converter type switched power supply. The back-up system includes a regulated charger circuit for maintaining the battery in a charged condition and a direct current fan which cools the power supply in both the normal and battery back-up modes. Over-voltage protection for the system is provided during the battery back-up mode, and protection for the battery is provided against excessive battery charging voltages. The fan and regulator are automatically turned off when the battery reaches a deep discharge condition to protect the battery.

Abstract: A switched power supply of the self-balancing push-pull square-wave converter type which includes a pair of switching transistors connected to the primary of a transformer and which are driven by a square-wave oscillator, and which also includes a pre-regulator chopper connected to the transistors. A ripple voltage appears on the output of the pre-regulator which is a function of the current flow through the individual transistors, and this voltage is coupled through a capacitor and a series resistor to the square-wave oscillator to terminate the drive current through each transistor for each cycle in which the current flow through the transistor exceeds a predetermined maximum.