Hello, I have questions about this version of an Astable Multivibrator: +v |______________ | | R1 1M e | ________b Q2 PNP | | c | | | | | | | c | |___b Q1 NPN | | e | | | | | GND | | | C1 10uF | | | |______________|___ | R2 100 Ohm | GND
*Spice Netlist Q2 3 4 6 Q2N3905 Q1 4 5 0 Q2N3904 C1 3 5 10uF V1 6 0 DC 4.5 R2 3 0 100 R1 5 6 1000000Looking at Multisim Oscilloscope simulations, I can see how when the circuit is first activated, the capacitor slowly charges up to .6 volt and turns the NPN transistor on. This in turn turns on the PNP transistor, charges the cap to -V and causes a voltage spike across R2. The cap then slowly discharges and the cycle repeats. What I _dont_ understand is how if you increase the resistance of R2 (to somewhere around 700 - 1000 ohms), a threshold is reached where the circuit breaks down. Shouldnt a discharged cap been "seen" as a short and, once Q2 turns on and clears a path to the voltage source, be immediately charged no matter what the value of R2 is? Obviously not, but why? If this could be explained in the most noobish (ie minimal math :) ) terms possible I would greatly appreciate it.