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Electronics Forum / Components / July 2009400-500V TO-92 etc npn / pnp BJT ?
It's a bit more than the usual voltage. The MPSA44 / 94 JUST makes it but the datasheet doesn't give hFE @ low Vce and the '94 seems to be rare. Any other candidates ? Cascoding could be problematical in this application due to volt drop ( I need a current source of about 6mA capable of handling a high voltage but with a low 'drop-out' voltage ). Other packages could be OK but I may need TO-92 at least for dissipation reasons. Graham >It's a bit more than the usual voltage. The MPSA44 / 94 JUST makes it >but the datasheet doesn't give hFE @ low Vce and the '94 seems to be [quoted text clipped - 8 lines] > >Graham NPN:- ST STX-616 Fairchild KSP44TA C1573 PNP:- Zetex ZTX560 Best regards, Spehro Pefhany  Signature"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 > >It's a bit more than the usual voltage. The MPSA44 / 94 JUST makes it > >but the datasheet doesn't give hFE @ low Vce and the '94 seems to be [quoted text clipped - 17 lines] > PNP:- > Zetex ZTX560 Thanks. The current gain of the Zetex part is nicely high and of course saturates well too. It has an npn near direct complement the ZTX458 too. Graham > > >It's a bit more than the usual voltage. The MPSA44 / 94 JUST makes it > > >but the datasheet doesn't give hFE @ low Vce and the '94 seems to be [quoted text clipped - 18 lines] > Thanks. The current gain of the Zetex part is nicely high and of course > saturates well too. It has an npn near direct complement the ZTX458 too. Follow-up. Zetex kindly sent me 10 samples of each by courier despite the fact that Farnell stock them too. All credit to Zetex. Graham due to the hugely increased level of spam please make the obvious adjustment to my email address > It's a bit more than the usual voltage. The MPSA44 / 94 JUST makes it > but the datasheet doesn't give hFE @ low Vce and the '94 seems to be [quoted text clipped - 8 lines] > > Graham Apex PA94 op amp with 450 volt power supplies wired as a current source. Bob > > It's a bit more than the usual voltage. The MPSA44 / 94 JUST makes it > > but the datasheet doesn't give hFE @ low Vce and the '94 seems to be [quoted text clipped - 8 lines] > > Apex PA94 op amp with 450 volt power supplies wired as a current source. Does it also work at 4V ? It sound expensive too. Graham >> > It's a bit more than the usual voltage. The MPSA44 / 94 JUST makes it >> > but the datasheet doesn't give hFE @ low Vce and the '94 seems to be [quoted text clipped - 13 lines] > > Graham 4volts for output or supplies? From negative to positive swing of the opamp. Bob > "Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message > >> [quoted text clipped - 14 lines] > > 4volts for output or supplies? From negative to positive swing of the opamp. I think you misunderstood the question. I can do discrete design. I just modelled what I wanted with Spehro's advice and My God it's good. Little change in current ( as far as it matters ) from 2V to 400V. Graham >> "Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message >> >> [quoted text clipped - 25 lines] > > Graham build it with a negative supply for the low side of your current source then you can go down to zero volts or negative. Bob > "Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message > >> "Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message [quoted text clipped - 26 lines] > build it with a negative supply for the low side of your current source then > you can go down to zero volts or negative. No need in this application and no negative supply. It also has to be cheap. Graham |
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