High voltage transistors for VAS stage - diyAudio
Go Back   Home > Forums > Design & Build > Parts

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 12th November 2005, 12:57 AM   #1
diyAudio Member
 
Join Date: Sep 2005
Default High voltage transistors for VAS stage

Okay, I've looked EVERYWHERE but have had no luck in finding the following:

I need to find a transistor model (BJT preferred, but MOSFET would do as well) with a breakdown voltage of at least 300V, power dissipation of 5w or more, current handling of at least .5 amps, and either NPN or PNP.

They will be used as both a common emitter and a cascode common base pair. I know most power transistors have these specs, but they are usually not good for common emitter or common base configuration. Currently, I'm using ZETEX FZT857 and FZT957 for my stage (3.5W per transistor), but they're getting over-powered in simulation for worst case.

Thank you! Your help is much appreciated!
  Reply With Quote
Old 12th November 2005, 03:31 AM   #2
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
you could consider paralleling, if your'e using emitter degeneration it is easy

another option is cascaded/totem pole like the super leach

maybe somewhere in earlier discussions you could find 1 or 2 transistor solutions?

http://www.diyaudio.com/forums/showt...042#post747042
  Reply With Quote
Old 12th November 2005, 08:31 AM   #3
AndrewT is online now AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
are you designing an audio power amp?
Is 500mA necessary for a VAS stage?
Often a 50mA to 140mA device will do here.
A low current device will usually have a lower Cob which is often a prerequisite for this location.
Can an EF be used to help the loading on the VAS?
If you are really in trouble then I second the staggered cascode as a solution. But what are the drawbacks?
__________________
regards Andrew T.
  Reply With Quote
Old 12th November 2005, 12:30 PM   #4
diyAudio Member
 
Join Date: Sep 2005
I was considering paralleling the devices for double the power hanlding, and I could do it for the common emitter stage (with emitter degenerator resistors), but how would I do that with the common base stage afterwards? Ideas?
  Reply With Quote
Old 15th November 2005, 12:13 AM   #5
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
current happily adds in parallel, just connect b-b, c-c and 2 degenerated ce, one for each emitter
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
High voltage Opamp with power transistors sivan_and Solid State 13 1st January 2009 10:42 AM
high voltage transistors bocka Solid State 2 21st October 2005 07:29 AM
High voltage output amp(with NPN transistors) Gunders Solid State 9 17th March 2004 12:19 PM
TO-3 transistors and high voltage DC ih Solid State 7 16th January 2002 11:36 AM


New To Site? Need Help?

All times are GMT. The time now is 09:42 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2