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'[EE] Suggest a transistor please?'
2012\03\13@141751 by Electron

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Hello,

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?

Possibly not a darlington.

If such a toy even exists. :P I can't find one.. a cheap one at least, but maybe
I'm missing some classic high voltage ~1.5A power transistor with high gain? I
need to use it as a switch, but I don't wanna use a MOSFET in this circuit, for
a lot of considerations (cost, ease of drive, number of components on the PCB..).

Thanks!
Mario

2012\03\13@160845 by M.L.

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On Tue, Mar 13, 2012 at 2:17 PM, Electron <spam_OUTelectron2k4TakeThisOuTspaminfinito.it> wrote:
>
> Hello,
>
> 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?
>
> Possibly not a darlington.
>
> If such a toy even exists. :P I can't find one.. a cheap one at least, but maybe
> I'm missing some classic high voltage ~1.5A power transistor with high gain? I
> need to use it as a switch, but I don't wanna use a MOSFET in this circuit, for
> a lot of considerations (cost, ease of drive, number of components on the PCB..).
>
> Thanks!
> Mario


Digikey doesn't list any with a gain that large. Have you considered a
hybrid? Use a small P MOSFET driving the NPN base.

FDV302 P-MOSFET is $.06 at large quantity. Rating says 120mA.
Use it to drive the base of a normal NPN which has a gain of 20 to 40 at 400V.

-- Martin K

2012\03\13@162438 by Spehro Pefhany

picon face
At 02:17 PM 13/03/2012, you wrote:

>Hello,
>
>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?
>
>Possibly not a darlington.
>
>If such a toy even exists. :P I can't find one.. a cheap one at
>least, but maybe
>I'm missing some classic high voltage ~1.5A power transistor with high gain? I
>need to use it as a switch, but I don't wanna use a MOSFET in this
>circuit, for
>a lot of considerations (cost, ease of drive, number of components
>on the PCB..).
>
>Thanks!
>Mario

It's unlikely you'll find a simple high voltage BJT with that much gain at high
current. A beta of around 10 is more like it. MJE13007 has a minimum gain of 8
at 2A, for example.

MOSFETs are cheap and plentiful, but the high voltage ones generally want 10V of
gate drive.

As M.L. suggests a buffer transistor driving a HV BJT is probably not a bad
way to go if you've got the 150mA or whatever to drive the base (from the
logic supply). You could use a low voltage MOSFET or small BJT such as a 2N4403
or 2N4401 (a couple of cents).

Best regards,


2012\03\13@190837 by RussellMc

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part 1 1699 bytes content-type:text/plain; charset="iso-8859-1" (decoded quoted-printable)

> >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 =
<www.daycounter.com/Calculators/Cascode/Cascode-Amp.gif>
>From page <http://www.daycounter.com/Calculators/Cascode/BJT-Cascode-Calculator.phtml>

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

Useful:
<http://www.qrp.pops.net/Cascode_BJT.asp>
<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=cascode&hl=en&safe=off&prmd=imvnsfd&source=lnms&tbm=isch&ei=V9FfT9_UNtCiiAfakN2GAg&sa=X&oi=mode_link&ct=mode&cd=2&ved=0CBcQ_AUoAQ&biw=1920&bih=1038>

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


part 2 4769 bytes content-type:image/gif; name="Cascode-Amp[1].gif" (decode)


part 3 181 bytes content-type:text/plain; name="ATT00001.txt"
(decoded base64)

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2012\03\13@192318 by Marcel Duchamp

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Cascode circuits work well for this application.


On 3/13/2012 4:07 PM, RussellMc wrote:
> 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
>
>
I've got an ARC5 in my garage.  They used to be a dime a dozen..

2012\03\13@201332 by cdb

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On Tue, 13 Mar 2012 19:17:38 +0100, Electron wrote:
:: 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?

Can't recall the gain off hand (think it is more like 50), but look at the BUJ302a from NXP - voltage CEo = 1500v and max current is 4A.  I use them as an alternative to TIP41's.

Colin
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