High-Voltage 350-400V Complementary Transistors for VAS :needs info ?

[Workhorse]

Hi members,

Could someone help me by providing information on High voltage Transistors for VAS for my amp with Rails +-140V.

VCE~350-400V ,Ic~500mA To 5A, must be complementary and in production[no obsolete devices...]

MJE340/350 300V pair isnot working satisfactorily at such high rails....any good substitutes...


regards,
K a n w a r

[len_scanlan]

I've used these parts from On Semi. Nice fast driver transistors with a bit more power than MJE340/350...

MJE15034 / MJE15035

Vceo = 350V Ft = 30MHz.

[jacco vermeulen]

Sanyo's 2SA1786/2SC4646 and 2SA1773/2SC4616 are not chunky enough ?

"edit" : and 2SA1830/2SC47-something. Ic=2 amps, 4 amps peak.
(all in those horrible clip-spring package styles, a bit pricy overhere)

[Workhorse]

So It seems only Sanyo rules on High Voltage High Frequency Transistors domains.......

Thanks for the info!

K a n w a r

[rtarbell]

ONsemiconductor

==> They have two MONSTER output BJTs that they specify for audio use (they are also complementary).

MJL4281A (NPN)

and

MJL4302A (PNP)

Vceo breakdown is speced at 350V, max power is 230 watts

Also, the ONsemiconductor ThermalTrak transistors are speced at 350V breakdown (there are several kinds of ThermalTrak transistors, look for these):

NJL4281DG (NPN)

and

NJL4302DG (PNP)

These are 350V breakdown, 250 watts. You don't have to use the extra two leads for the diodes if you don't want; they just come with the built in diode if you want them to be biased with good thermal compensation.

All of the above are in TO-264 plastic cases, and they all have an ft of at least 30MHz (which is an AMAZING ft considering what I've seen from other power transistors in the 200W+ range).

[rtarbell]

Ohhh darn it; I just read your original post again and saw that you wanted VAS transistors, not output transistors, so forget my last post entirely...

The only high voltage VAS transistors that I know of are from ZETEX (www.zetex.com), they come in around :

Look for FTZ857 and FZT957 (surface mount), or

ZTX857 and ZTX957 (TO-92)

You can do a parametric search on their site for transistors in the 300Vceo+ range

[DIGORA]

http://perso.orange.fr/jm.plantefeve/2N3440.pdf

[jaycee]

Fairchild have KSC3503/KSA1381 which look just the job for a VAS... Vceo of 300V, low Cob and a high fT of 150MHz.

The only catch was, when I tried their models in a simulator, they didn't seem to recover well from clipping, instead sticking to the rail. This could of course be a fault with the models rather than the actual transistors.

edit: just spotted your high current requirement. In that case, I'd go with a driver transistor.

[rtarbell]

*Just a little inkling*

Stupid idea, and I'm not trying to be a wiseguy, but:

Have you thought about using a tube for your VAS? Tubes typically have more voltage handling capability than transistors, and I bet a few triodes can still handle about ~1 amp of current, maybe even more. You could use pentodes as well if you want for higher gain in the VAS.

The question here is, if you *do* use a tube, it would probably take the place of the NPN transistor ==> What could be done about the PNP transistor for the active load (if you are in fact using an active load)? I'm not to sure, but maybe a tube could solve half of your VAS challenge.

[Workhorse]

Originally posted by jaycee
Fairchild have KSC3503/KSA1381 which look just the job for a VAS... Vceo of 300V, low Cob and a high fT of 150MHz.

The only catch was, when I tried their models in a simulator, they didn't seem to recover well from clipping, instead sticking to the rail. This could of course be a fault with the models rather than the actual transistors.

edit: just spotted your high current requirement. In that case, I'd go with a driver transistor.

Thanks Jaycee,
The device you have mentioned is excellent and also available in our country[In our region these devices are from Sanyo], though its voltage is 300VCE[still has a safety margin of 20V assuming 280Vpk-pk , +-140VDC rails]
Since we are using Triple Deep Darlington Emitter Follower stage at output, hence Low current VAS couldn't be a problem..

As far as Clip sticking is concerned, that again depend upon circuit designs as well....

Ok, If I use this device [A1381/C3503] for VAS, could I also use it for PRE-DRIVER stage prior to drive the Drivers transistors as well which inturn drives the output devices......

regards,
K a n w a r