As illustrated, 555 and R1, R2, C1 composition controlled multivibrator, its oscillation frequency in addition to the RC time constant related to, but also by the control termi
nal of the DC level is adjusted. While the DC level from the reference frequency f. 555 output and the oscillation frequency fo Nfn common locking square wave output of RS flip-flop, after the low-pass filtered to produce. CD4001 two NOR gates as RS flip-flop, RS flip-flop in the locked case, the duty cycle of the output unchanged, thus filtered DC level unchanged. If the oscillation frequency f0 of 555 to a high drift (or fn fall), the duty increase, DC control level will be a corresponding increase in frequency will decline; and vice versa.