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> >could anyone please suggest a cheap NPN transistor rated at least
> >400V and with a
> >current capability of at least 1.5A and a gain (at that current) of
> >at least 100?

Consider "cascode" connection.
The "o" is not a typo.
NPN low voltage driver has its collector  od drain connected to the
emitter or source of high voltage output transistor.
The output transistor has its base or gate connected to "Vref" (via a
resistor if it is a BJT) and the output transistor's collector od
drain drives th HC load.

The input transistor can be high gain but must carry the whole output
current. The output transistor can be low gain but must handle the
whole output current and voltage.

On saturation condition has Iout passing through both devices in series.
See attached diagram =3D
<http://www.daycounter.com/Calculators/Cascode/Cascode-Amp.gif>
>From page <http://www.daycounter.com/Calculators/Cascode/BJT-Cascode-Calcu=
lator.phtml>

Wikipedia covers it quite well
http://en.wikipedia.org/wiki/Cascode

Useful:
<http://www.qrp.pops.net/Cascode_BJT.asp>
<http://www.circuitstoday.com/fet-applications>
<http://www.qrp.pops.net/wwv-5-supplemental.asp>

A zillion images here:
<http://www.google.co.nz/search?q=3Dcascode&hl=3Den&safe=3Doff&prmd=3Dimvns=
fd&source=3Dlnms&tbm=3Disch&ei=3DV9FfT9_UNtCiiAfakN2GAg&sa=3DX&oi=3Dmode_li=
nk&ct=3Dmode&cd=3D2&ved=3D0CBcQ_AUoAQ&biw=3D1920&bih=3D1038>

I think I first tried this with an ECC83 in an ARC5 receiver front end :-)

Yee Ha!    http://bit.ly/ARC5_Receiver_Images





    Russell McMahon

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