Constant Power Fusing Arrangement for 110/220 Volt Power Supplies
Original Publication Date: 1988-Nov-01
Included in the Prior Art Database: 2005-Feb-15
A constant overload protection is provided for a power supply operated on 110 or 220 volts AC. Because the time-current characteristics of UL/CSA fuses for 110 volts AC and SEMKO fuses for 200 volts AC are incompatible by definition, a fuse of each type is required for product safety approval when a power supply is operated on 110 or 220 volts AC. If the two fuses are conventionally connected in series, there is the possibility of an overload at 220 volts AC being twice that at 110 volts AC. This is avoided through arranging the circuit so that only the UL/CSA fuse is in the circuit when 110 volts AC is applied. An AC voltage, which may be either 110 volts AC or 220 volts AC, is applied between lines 1 and 2. When the voltage supplied between the lines 1 and 2 is 110 volts AC, switch 3 is closed.