Abstract: In a DC power supply or a battery charger, plural output filter capacitors remain highly charged after the load is removed and the converter is turned off. A transistor connected across the capacitors is non-conductive during normal power supply operation and a bleed resistor connecting the transistor to the output capacitors is not in the circuit during normal power supply operation. When the power supply is turned off and the load is removed, the transistor is automatically rendered conductive with the removal of the pulsed output of the power supply's power transformer to the transistor, with the energy stored in the capacitors safely and quickly discharged to the output return via the bleed resistor which is placed in circuit by the conducting transistor.

Abstract: A live circuit battery tester allows for determining the condition of batteries under load without disconnecting the batteries and a battery charger from the load or in any way disrupting system operation during the test. Battery testing is prevented when the batteries are being used in an emergency or if they are recharging from a recent discharge. The battery tester is under microcomputer control and incorporates automatic-self diagnostics and provides a visual indication if the batteries are good or if a specific problem is detected such as if the batteries are missing, have open cells, are sulfated or are in imminent danger of failure. The battery tester determines if the charger is operating properly and tests for an open cell, bad battery connection, sulfated battery, and a weak battery and provides a visual indication of any of these problems as well as an indication of a properly operating battery.

Abstract: A zero-voltage-switched, full-bridge, phase-shifted DC-DC converter for use in a DC power supply or battery charger includes a power transformer, four switching transistors connected to form a full bridge, and a decoupling capacitor and resonant inductor connected in series to the primary winding of the power transformer. At high loads, i.e., high output voltages, the resonant inductor charges the stray and internal capacitance of the switching transistors. Under light loads or in a no-load condition, with the current through the resonant inductor insufficient to allow the inductor to recharge these capacitances, the combination of a second inductor connected at one end to the central tap of the power transformer's primary winding and at its second opposed end to the middle point of a capacitive voltage divider, permits the second inductor to store enough energy to effectively recharge the stray and internal capacitance of the switching transistors for improved operating efficiency.