At 01:54 PM 2/9/2006 +0200, you wrote:


>The switching time of the diode multiplied with the current flow
>through diode (which is not at all neglijible, in fact is a huge spike
>of current)

IT CANNOT >>>CANNOT<<<< EXCEED THE STEADY STATE COIL CURRENT!!!!

If you can switch it with a wimpy 2N3904 it's nothing to worry about.

>and multiplied with the voltage drop across diode (which
>is much greater than 0.6V because diode is not in direct conduction
>due the switching time, it's equal with the energy requested to be
>eaten by the suppressor device.

Hardly. First, the energy is not 'eaten by the suppressor device'
when you use a diode, MOST of it (95%) dissipates in the copper resistance
of the coil. After switching off a 12V relay, there is briefly (milliseconds)
a 12V + diode drop across the coil resistance internally (opposite polarity).
Secondly, the voltage at the collector of the BJT moves rather slowly. The BJT
switches off like molasses, and there is plenty of distributed
capacitance in the coil on top of that. There are NO terahertz or gigahertz
frequencies here where nanoseconds or picoseconds make a difference.
No magic, this is very straightforward low-frequency analog stuff.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff


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