Eric, this isn't true, because there is no pullup on the collector of the NPN. The cap simply discharges through the 1k resistor when the NPN turns off. It does nothing to aid in the turn off of the PNP.
Ok - so it is used basically to speed up the on signal for the PNP?
What is the difference when one connects a cap and a resistor in series compared to when one connects a cap and resistor in parallel - I know they are used in timed circuits, but is there any difference? I not talking about the circuit posted above, but in general terms ?
Ok - so it is used basically to speed up the on signal for the PNP?
What is the difference when one connects a cap and a resistor in series compared to when one connects a cap and resistor in parallel - I know they are used in timed circuits, but is there any difference? I not talking about the circuit posted above, but in general terms ?
hi,
In general terms:
When a cap/res are in parallel the 'dc' component of the signal is not blocked.
With a res/cap in series any 'dc' component of the signal is blocked, so the following circuit does not 'see' the 'dc' signal, only the 'ac' signal.
Commonly used in audio amplifiers.
This simple explanation does not cover cases where the res/cap parallel or series network is used as a frequency filter.
For such a simple combination of res/caps in parallel or series, the analysis of circuit can be complex, depending upon many factors, such as frequency, source and load impedances.
Put simply, at high frequencies the capacitor will act like a short circuit so it will behave like a piece of wire; at DC the capacitor will not conduct so it will behave like a resistor and at intermediate frequencies the resistor and capacitor both come in to play but calculating the impedance is too complex for the average nube.