-----Urspr=FCngliche Nachricht----- =

Von: "Wouter van Ooijen" <wouter@voti.nl>
An: "'Microcontroller discussion list - Public.'" <piclist@mit.edu>
Gesendet: Montag, 06. Februar 2006 23:04
Betreff: RE: [EE] Transient Suppression - was Re: [ee] 3904 base resistor


> > I don't think that the problem is speed or current - the =

> > problem is the voltage. A 1N4148 is rated with 100 Volts and =

> > this could be less if you switch off a relay. =

> =

> How can you even approach 100V when switching a low-voltage relais? When
> the relais is energised there is just the power supply voltage (5, 12,
> 24V), when the transistor switches of the diode will conduct so the
> voltage is just 0.6V.
> =

Because it is dynamic, not static. Due to the capacity is charging in the p=
n-zone. And when the transistor shuts off the current through the relay a t=
ransient spike will be the result. During this time the voltage across the =
diode will go much higher than the supply voltage.

Regards

Enrico

-- =

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