- Joined Jun 30, 2018
I have a CD4060 oscillator circuit that I need to give a 40 Minute time period from the 14th stage. Historically, I have trimmed the capacitor with smaller caps to get the desired 40 minutes.... typically 1.5 Uf some odd . I then tried trimming the capacitor with a large value resistor ( 300K Ohm ) with the assumption that the resistor would cause a slightly greater discharge rate and thus increase the frequency, which would reduce the resultant time span. In practice, I observe that the OPPOSITE occurs! The frequency is LOWER! I have exploited the anomaly by using a smaller capacitor ( 1 Mf ) and trimming the frequency DOWN to stretch out the time to my wanted 40 minutes. Can anyone explain how a "leaky" capacitor will DECREASE an RC oscillator frequency?