Power supply equipped with multiple output voltages is a technique well developed now. With loads and electricity required gradually, output power by the power supply also has to be increased constantly. These days, many countries and energy organizations around the world have set up many energy policies, this makes improvement of power supply conversion efficiency an urgent issue. And reducing circuit loss of the power supply is also an important factor to address this issue. A conventional power supply, such as R.O.C. publication No. 200928707 entitled “Power supply equipped with a DC-DC converter modular structure” discloses a power supply (100) capable of supplying multiple voltage outputs (referring to its FIG. 1). It contains a conversion circuit on a circuit board (110). The circuit board (110) has a transformer (111) and other circuit elements located thereon to transform input power to multiple output powers at 12V, 5V and 3.3V. The output powers of varying voltages are linked to a module back panel (117) through a plurality of conducting wires (113A, 113B, 114A, 114B, 115A, 115B, 116A and 116B). The module back panel has a plurality of slots to couple with external conducting wires to connect to the power supply to get the multiple output powers. However, a new technique has been developed now that provides multiple windings on a transformer to supply multiple outputs of varying voltages at lower conversion efficiency. But such an approach has a drawback, namely when one set of output voltage is short circuit, other sets of output lines could be affected.
To improve the conversion efficiency of outputting multiple voltages, the aforesaid R.O.C. publication No. 200928707 discloses another type of circuit (as shown in its FIG. 2). It mainly includes a circuit board (210) to provide output power of 12V. The output power of 12V is sent to a DC-DC converter (213) to be converted to output power of 5V and 3.3V. Finally, the circuit board (210) and the DC-DC converter (213) output the aforesaid power through a module back panel (217). The second conventional circuit previously discussed provides improved conversion efficiency for conversion of 5V and 3.3V, and the output circuits of 12V and other output circuits of aforesaid lower voltages can independently execute short circuit or abnormal protection. However, connection of 12V output power to the module back panel (217) and DC-DC converter (213), and output power of 5V and 3.3V requires individual wire sets. Power loss on the wires is higher and more waste heat is generated.