PURPOSE: To prevent the malfunction during the make of the power supply with a simple constitution, by connecting the two diodes to each other at the cathode side and then isolating the charging current of the capacitor from the current flowing to the differentiating circuit.

CONSTITUTION: Switch S is turned on at time t0; the negative trigger is supplied at time t1; the output pulse is terminated at time t2; the steady state is obtained at time t3; and switch S is turned off at time t4. Thus potential v" at point x" is reduced down to nearly OV since the flowing of the current is blocked by diode D-1 and although the residual charge of capacitor C-1 may reduce potential vx' at point x'. Then voltage V applied to the whole of monostable multivibrator circuit B is applied immediately to point x" through capacitor C-2 and diode D-2 when switch S is turned on again at time t5. And voltage vx" which is not reduced much becomes immediately higher than the forward voltage between the base and the emitter of transistor T-2 never to cut off T-2. In such way, the malfunction during the make of the power supply can be prevented.