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Shelton said:Hi All
Can someone tell me what is the purpose of the 10n cap in parallel with the 1k resistor which is on the base of the transistor in this circuit ?
Thanks in advance.
**broken link removed**
Shelton.
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.ericgibbs said:hi,
When the npn is hard ON, the top of the cap/base charges to a +V potential wrt 0V.
As the npn is switched OFF the charge/voltage across the cap is reversed wrt to the pnp base so the pnp switches OFF faster.
It does speed up the ON transition (or at least enhances the positive feedback), but it does nothing for the OFF transition, as I explained above.The cap speeds up the switch ON/OFF of the pnp.
hi,Shelton said: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 ?