spacecat wrote:
>> All circuits obey the laws of physics.  However this one will still
>> have a problem without a diode from the collector to the +5V supply.
>
> If you just fit a diode it will stop the TX resetting and cause it to
> saturate. you either need to put a snubber across the the Transistor  or
> zenner + diode

Huh?  The diode won't cause the transformer to saturate.  It provides a
path for the current thru the primary when the transistor shuts off and is
therefore no longer a path for the current.  The forward drop accross the
diode will cause the current to decrease over time until it reaches zero.

The only bad effect is if the transistor gets turned on again while the
diode is still conducting (still current in the primary).  This will cause
a short across the supply during the diode's reverse recovery time.  It
will also maintain an minimum DC current in the primary.  This is bad
because of wasted I**2 * R losses and because it allows less AC headroom
before hitting transformer core saturation.


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