I am trying to understand this circuit but as of yet I still have a number of gaps in my reasoning. So far I have deduced:
(assuming TR1 is ON and TR2 is OFF)
- left hand side capacitor charges towards 0.2-Vcc since Vc1 (voltage at collector of TR1) is tied to 0.2V due to transistor being ON (if
trigger input is at Vcc during steady state)
- right hand side capacitor charges to a small voltage (difference between Vcc and the voltage at Vc2 (voltage at collector of TR2)
which can be worked out using superposition is very small)
- upon negative edge trigger bases at TR1 and TR2 are pulled down since capacitors cannot handle sudden changes in voltage -> hence D1
is turned ON thus turning OFF TR1 –> Vc1 is no longer tied to 0.2V, goes to approx Vcc thus turning on TR2, Vc2 is now 0.2V.
These are my gaps in reasoning:
- What is the role of the 220K resistor?
- How the capacitors charge/discharge, to what voltages, when do they stop charging/discharging?
thank you for your help!