| 摘要 |
PURPOSE:To stably operate from DC to high frequencies, by providing the 3rd winding for a driving transformer and compulsively turning off an FET through a deenerigizing current flowed to this winding. CONSTITUTION:The ternary winding III is provided to a driving transformer T1. When a transistor Q1 turns on and a deenergizing current i1 flows to the primary windingI, a capacitor C3 is charged through a diode D6 with the charging current flowing to the winding III. On the other hand, a pulse width control circuit CONT2 applies an output VBE(Q4) between the base and emitter of the Q4 with a pulse width in response to the difference if an output voltage OUT exceeds a reference value. As a result, a transistor T4 turns on to discharge the charge in the capacitor C3. When this discharge current i2 flows, a Q2 is turned on and an energizing current i1 flows to the windingI. When the magnetic flux due to the current i2 is excessive, a voltage induced in the winding III extracts charges from the gate of an FETQ3 allowing to compulsively turn off the Q3. |
