TRANSOFRMER COUPLED DC SECONDARY POWER SUPPLY

摘要

PURPOSE:To prevent overvoltage in an astable power supply system by forming a control circuit such that the control object is switched from first to second switching element on the condition that a power detecting circuit detects overpower. CONSTITUTION:Number of turns of primary winding L11 in a transformer 20 is increased over that of a winding NP11 required for normal control and an intermediate tap Tm is provided in the way. A switching element 12 is connected with the intermediate tap Tm and a second switching element 15 is connected with a terminal tap Te. A power detecting circuit 45 detects a load power from a stabilized power system 32 in a secondary power supply circuit 30 exceeding over a set level, and a primary control circuit 50 switches the control object from the switching element 12 to the second switching element 15 on condition that the secondary power detecting circuit 45 detects overpower. This constitution prevents overvoltage even in such case as the stabilized power supply system 32 is loaded heavily and an astable power supply system 31 is loaded lightly.