a special power circuit

Although this circuit has a simple structure, it can generate three sets of DC voltages from two identical secondary windings, which are +5V, -5V and +12V required by some microprocessors. The characteristic of the circuit is the connection method of diodes D2 and D3. They are connected across the two sets of AC power supplies E2 and E3 and play a full-wave rectification role. In the positive half cycle, E2 charges C2 through D2, and the current path is b→C2(+)→C2(-)→D2→a; in the negative half cycle, E3 charges C3 through D3, and the current path is d→D3→C2 (+)→C2(-)→C. Diodes D1 and D4 form a general half-wave rectifier. The input voltages of the two three-terminal regulators 7805 are provided by C2 and C3 respectively, while the input voltages of the 7812 are provided by the positive addition of the voltages on C1 and C2.