> -----Original Message-----
> From: Roman Black [SMTP:fastvid@EZY.NET.AU]
> Sent: Tuesday, November 05, 2002 1:05 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: [EE]: Norp12
>
> Wrong again, it's an NPN transistor driving a
> relay with it's collector, therefore when the
> relay turns off the collector goes high (to
> about 1v higher to turn on the catch diode) and
> WHEN the collector goes high your suggestion of
> a cap to the base WILL turn the transistor back
> on, giving exactly the vibration he complained of.
> You may have forgot that the transistor is driven
> from a slowly changing analogue voltage, and when
> turning off the base will be JUST below 0.6v.
> Any + going voltage at the base will cause the
> vibration he complained of.
>
Surely the transistor will only just conduct enough to keep 0.6 volts on the
base, the transistor will not be able to be entirely switched off until the
cap is charged.  This would effectively cause the relay to switch off very
slowly.  I certainly don't see how this is going to cause an oscillation as
the cap is effectively providing NEGATIVE feedback at anything over DC.

Regards

Mike

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