Re: Circuit & Component Check

From: Dominic-Luc Webb (dlwebb_at_canit.se)
Date: 01/10/05 

Date: Mon, 10 Jan 2005 11:58:29 +0100

> > Dominic-Luc Webb wrote:
> >
> > >>I tried yesterday with some odd components lying around, but only had an
> > >>NPN transistor, no MOSFET, which resulted in my motor going fast and
> > >>slow, instead of fast and off!!
> > >
> > > Danny, it will be great to see how this progresses. I am interested in
> > > the reason why the effect on speed is occurring. It sounds like a
> > > problem I am encountering with the 2N3055 NPN power transistor. I do
> > > not find conditions under which it actually shuts off and I do not
> > > understand why.
> >
> > I still don't fully understand the differences between all these
> > different types of transistors/FETs... Since all works fine with the
> > MOSFET (ZVN4206A), I assumed the transistor was just "amplifying" or
> > something. A low from my chip seems to vary between 0V and -0.04 or so,
> > so maybe this is by design - dunno! The resistor I was using was an BC108A.
>
> Study the data sheets and come back with anything you see that doesn't
> make sense to you.
>
> --
> John Popelish

One thing that does not make sense is that Danny gets a varying low. I
would think low should be right at ground potential for this circuit.

I think BC108 is not a resistor, but a small signal NPN, about 0.1 Ic
and 300 Mhz with a large Hfe.

Dominic

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