| 摘要 |
PROBLEM TO BE SOLVED: To provide a highly efficient switching power circuit for printer devices capable of coping with load fluctuation over a wide range. SOLUTION: The power circuit is provided with a transformer 1 for voltage conversion, a transistor 2 for large power as a main switching element that controls the primary-side current of the transformer 1 for voltage conversion, a transistor 3 for small power as a sub switching element parallel-connected with the transistor 2 for large power, a drive circuit 4a set so as to optimally drive the transistor 3 for small power under light load, and a drive circuit 5a set so as to optimally drive the transistor 2 for large power when maximum output is produced. Currents passed through the transistor 2 for large power and the transistor 3 for small power, respectively, are detected through a switch control circuit 8a, and current paths are switched according to the current values of the transistor 2 for large power and the transistor 3 for small power. High efficiency is thereby obtained.
|
