| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem that a power supply circuit already turned on by a power switch and not operated for data-receiving, printing, or the like does not reduce power consumption to be smaller than that required for operating a control circuit. SOLUTION: The power supply circuit 1 includes: a constant voltage conversion circuit 2; a constant voltage conversion invalidation circuit 4 including a bipolar transistor Q40 for invalidating a function for output of a constant voltage by the constant voltage conversion circuit 2, and a field-effect transistor Q41; a timer circuit 5 including a field-effect transistor Q50, a bipolar transistor Q51, and a first delay circuit for setting first delay time until the field-effect transistor Q50 reaches a conductive state; and a load current detection circuit 3 for turning on the bipolar transistor Q51 at detection of a load current flowing in output terminals 6a, 6b and for turning off the bipolar transistor Q51 when no load currents are detected. COPYRIGHT: (C)2011,JPO&INPIT
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