| 摘要 |
PURPOSE:To protect an output transistor, by adding a comparator which performs a delaying action to a pulse controlling circuit of a separately excited switching regulator and suppressing temporarily the function of the pulse controlling circuit when an internal power supply is applied. CONSTITUTION:An operational amplifier 41 which uses the voltage V2 to its working power supply functions as a comparator when the voltage of comparison produced by resistances R42 and R43 is applied to a noninverse input terminal B. Then the voltage V2 affects a pulse increase controlling circuit 1 in the form of the control voltage through a rectifier D41 and in place of the voltage V1 regardless of the order of application of the internal power supplies V1 and V2. Then the voltage of a terminal C rises up gradually by the time constant of a capacitor C41 and the resistance 41 when the voltage V1 is applied. When the voltage of the teriminal C is coincident with the comparison voltage of a terminal B, the output voltage of the amplifier 41 is lowered. Thus the amplifier 41 loses the suppressed voltage. In this case, the circuit 3 has already started its function. The circuit 1 does not deliver a rectangular pulse having an unexpected maximum width of conduction. Thus the output transistors TR1 and TR2 can be protected. |
