High voltage output amp(with NPN transistors) - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 13th March 2004, 02:00 PM   #1
Gunders is offline Gunders  Norway
diyAudio Member
 
Join Date: Nov 2002
Location: Norway
Default High voltage output amp(with NPN transistors)

As mentioned in an older thread I have a final project at school where my group have to make a 3-phase generatorsimulator.
My part is to make an amplifier which have to give out +-800V.

I have now done some design with the amplifier, but I still have some problems and I hope somebody here can help me.

So far I have tried Marshall Leach's double barrelled amplifier, and added an extra cascode stage to protect the outputtransistors.
Even though I have added an extra cascode stage it isn't enough to protect the PNP transistors.
The max voltage the transistors see now is about 530V. For the NPN transistors this is okay as NPN types are easy available with voltages up to 1200-1500V.
For the PNP types it's an another story, here the maximum voltage for available transistors seems to be about 400-500V. If I could find 600V PNP types it would help a lot, but it's still a bit on the risky side so 700V PNP types would be great.

What I try to do now is to design an amplifier with NPN types only, but I haven't yet found the right way to do it.
It's here I hoped somebody could help me with an proper outputstage with NPN transistor only.


Here is the schematic for the amp so far. This design is only used to verify that this kind of design works properly and the voltage over the transistors is shared equally. The final design will of course use other transistors than those used in this schematic.
Attached Images
File Type: jpg amp.jpg (62.3 KB, 649 views)
  Reply With Quote
Old 13th March 2004, 02:05 PM   #2
diyAudio Member
 
Frank Berry's Avatar
 
Join Date: Sep 2003
Location: Midland, Michigan
How much output power?
Could you use an output transformer to step up the voltage?
__________________
Frank
  Reply With Quote
Old 13th March 2004, 02:28 PM   #3
Gunders is offline Gunders  Norway
diyAudio Member
 
Join Date: Nov 2002
Location: Norway
Quote:
Originally posted by Frank Berry
How much output power?
Could you use an output transformer to step up the voltage?
Not very/extremely much output power, absolutely max outputcurrent is 100mA but 10-20mA is more realistic under normal conditions.

An output transformer have been considered, but the company I work for would like to see an amp without transformers.
They have a solution today which uses outputtransformers, but they would like to make it smaller and lighter.
  Reply With Quote
Old 13th March 2004, 02:39 PM   #4
diyAudio Member
 
Join Date: Sep 2002
Location: Sweden
I haven't tried to figure out how or if it would work with cascoding
for high-voltages, but have you considered something like a
quasi-complementary output? You will still need PNPs, of course,
but not for the output stage.

Another alternative, could a bridged amp be acceptable?
  Reply With Quote
Old 13th March 2004, 02:53 PM   #5
Gunders is offline Gunders  Norway
diyAudio Member
 
Join Date: Nov 2002
Location: Norway
Quote:
Originally posted by Christer
I haven't tried to figure out how or if it would work with cascoding
for high-voltages, but have you considered something like a
quasi-complementary output? You will still need PNPs, of course,
but not for the output stage.

Another alternative, could a bridged amp be acceptable?
I don't know how to implement a brigded amp to a 3-phase system where you have the phases L1-L2-L3 and GND as a referance for the 3 phases. Suggestions are welcome.

I just took a look at the quasi-complementary output stage, if the PNP transistor in the outputdriver stage could be removed it would be great.
Wouldn't it be possible to drive a outputstage of this kind in a push-pull manner?
If I could use a lower voltage for the driverstage a quasi-complementary output may be a alternative, but I can't see how I can use a lower voltage in the driverstage.
  Reply With Quote
Old 13th March 2004, 05:45 PM   #6
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
cascading doesn't have to be symetrical, just add a few more stages to the pnp side

while you're at it you might want to look more closely into the divider chain ac load division and include device input Z in the calc


on a system level i would start with a nonisolated ac rect bridge dc supply and work with 400/600 V devices, then the 3 phase ouput transformer provides isolation and step up with a low system cost - control inputs may be isolated with signal xfmrs or opto isolators - or use wireless digital tech (irda for really cheap)
  Reply With Quote
Old 15th March 2004, 07:52 AM   #7
Gunders is offline Gunders  Norway
diyAudio Member
 
Join Date: Nov 2002
Location: Norway
well, here's my only working NPN outputstage so far.
The output waveform is pretty symetrical and with low distortion.
Even if it's a working design i don't know if I have biased it properly so it would be nice if smoebody could help me a bit.
The problem is the frequencyresponse, it looks rather awful.
The amp seems to have some zero's in the transferfunction.
Attached Images
File Type: jpg npn.jpg (65.5 KB, 379 views)
  Reply With Quote
Old 15th March 2004, 07:54 AM   #8
Gunders is offline Gunders  Norway
diyAudio Member
 
Join Date: Nov 2002
Location: Norway
Here's the AC analysis.
Attached Images
File Type: jpg ac.jpg (92.1 KB, 418 views)
  Reply With Quote
Old 15th March 2004, 08:06 AM   #9
Gunders is offline Gunders  Norway
diyAudio Member
 
Join Date: Nov 2002
Location: Norway
It is something wrong with the first schematic, here's a correct one.
Attached Images
File Type: jpg npn.jpg (73.9 KB, 408 views)
  Reply With Quote
Old 17th March 2004, 12:19 PM   #10
diyAudio Member
 
Workhorse's Avatar
 
Join Date: Dec 2004
Arrow Commentable Thoughts

Hey Man why are u stick around those Bipolars , Why dont u use IGBT s with rating upto 2KV . U can implement total n-type design with them very well.

With High Voltage Upto 100000000000000KV Regards
AAAAAAAAMMMMMMPPPMAAAAN
  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 for VAS stage rtarbell Parts 4 15th November 2005 12:13 AM
high voltage transistors bocka Solid State 2 21st October 2005 07:29 AM
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 12:01 PM.


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