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gjpollitt

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  1. thanks for the reply so the time constant for one side would be r*c = 470*10uf = 4.7 ms ? The components affecting the current would be the led, capacitor and resistor? if this was flowing through c1 and q2 was turned on then would that be the case as if q1 was off then would you need to consider that in the path? r1 is connected to the pos side of c1 and current would flow and charge c1, what affect would r3 have on the neg side c1? would this affect the time constant/current flowing through c1? and how do you determine the saturation current for a transistor eg bc108? is it the case that across an led that is not on there is a voltage drop of approx .7v then when it is turned on approx 1.4v drop, for a standard led? how would you solve for the impedance of this circuit or would that not apply to this? would this be classed as an ac circuit with the current changing direction? so many questions I know but once I get my head around how this works properly then I dont think I will have many probs understanding similar circuits. many thanks graham
  2. I am playing with this exact same circuit. May I ask if somebody could be kind enough to give me a brief explanation of what is happening the moment the circuit is turned on? I have a brief idea of whats going on but im not sure if its correct. Is R1 used for current limiting and also as part of the RC time circuit with C1? Is the path to ground for charging C1 through the base of Q2? I thought the transistor would not turn on until approx .7 volt is at the base. Will there still be a slight leakage of current to emitter when the base is below the .7v? Also what happens to the voltage stored in the caps when they have stopped charging, does the voltage pass through the collector to emitter? Thanks Graham
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