This exponential waveform generator circuit provides you with a waveform which sinks exponentially from a specific voltage to near-zero, after which quickly resets to reactivate the sequence.
How it Works
In the beginning C1 is charged to +12V, and O1, O2 are each off.
The timing capacitor at this time there discharges gently by means of R1, the exponentially sinking voltage occurring at low impedance at the output of unity-gain buffer RC2. R
2 puts a stop to the leakage current from O1 impacting the discharge as D1 is reverse-biased.
Any time the voltage on C1 extends to a merit beyond zero that may be fixed by R3, R4, the open collector O/P of IC1 turns out low, switching on O1 and quickly recharging C1.
IC1 of course reverts to its initial condition virtually instantly, however the recharge state is extended for a few milliseconds through the positive feedback loop by way of R5, C2 and O2, to guarantee C1 charges completely.
After that time period C2 is additionally completely charged, and O2 goes off, switching off Q1, and enabling the gradual discharge of C1 to commence yet again.
Using the part values proven for this exponential waveform generator circuit every phase continues roughly ten seconds.