| 摘要 |
PURPOSE:To allow a switching regulator to output a constant voltage even at the time of voltage dropping by inserting a circuit which is different between at the forward operating time and at the reverse operating time in a control circuit which prevents the ON period of a main switching element from becoming longer than the prescribed value. CONSTITUTION:When a non-stable DC voltage from a terminal 1 decreases, the ON periods of an exciting transistor 12 and a TR27 become short, the base voltage of a TR29 increases, and the collector voltage decreases. Accordingly, a diode 34 becomes ON, the base voltage of a TR32 decreases, is converted via impedance, and is applied to a Zener diode 18, and the emitter of a TR19. When the emitter voltage of the TR32 becomes lower than the Zener voltage 18, the collector currents of operational amplifiers TR19, TR20 increase, thereby increasing the voltage drop of a resistor 11 to increase the base voltage of the TR12. Thus, the ON period of a TR2 is limited, thereby preventing the vanishment of the output. In this manner, the abrupt voltage drop is remedied by small discharging time constant of a condenser 35, and the ordinary voltage drop is remedied by the large charging time constant of a condenser 35. |
