MOSFET or NPN for class A output stage

AudioGeek · 12th July 2005, 10:57 PM

Looking to build a SE Class A amp...

either a MOSFET or NPN output..

what are adv vs disadv?

Can I use a choke to load either of these?

Thanks!

darkfenriz · 12th July 2005, 11:34 PM

NPN driving NMOSFET
cheers

kilowattski · 12th July 2005, 11:38 PM

Quote:

Originally posted by AudioGeek
Looking to build a SE Class A amp...

either a MOSFET or NPN output..

what are adv vs disadv?

Can I use a choke to load either of these?

Thanks!

Go to the Pass Labs forum. You will be able to find everything you want and more. Also check out http://www.passdiy.com if you haven't already.

PMA · 13th July 2005, 06:10 AM

Quote:

Originally posted by darkfenriz
NPN driving NMOSFET
cheers

Or NMOS driving PNP power BJT.

bocka · 13th July 2005, 07:23 AM

There are a lot of pro's and con's for each device. It's impossible to say which is better, because no device is ideal.

MOSFET advantages:

Very high input resistance
No second breakdown

MOSFET disadvantages:

low gm
high and nonlinear input capacitance (HEXFET & co)
sensitive to parasitic oscillations

BJT advantages:

high gm

BJT disadvantages:

low input impedance
second breakdown effects
base currents

amplifierguru · 13th July 2005, 07:35 AM

Not to mention that the Pd losses in a MOSFET output stage are considerably greater than a BJT stage - at least for emitter followers! Even greater waste of energy.

AudioGeek · 13th July 2005, 11:39 PM

Ok... well back to basics:

how do I design an emitter follower class A SE output stage with BJT using a choke as a load?

Workhorse · 14th July 2005, 09:43 AM

Quote:

Originally posted by amplifierguru
Not to mention that the Pd losses in a MOSFET output stage are considerably greater than a BJT stage - at least for emitter followers! Even greater waste of energy.

If the output swing is Rail to Rail and the output mosfets are only N-channel Vertical ones than NO BJT ON THIS PLANET DARES TO TOUCH THE EFFICIENCY CRITERIA OF N_CHANNEL VERTICAL MOSFETS...IN CLASS-AB AMPS

Greg,
I donot ..not at all agree with you......at this time.....

K a n w a r

darkfenriz · 14th July 2005, 10:04 AM

Kanwar
Greg considered emitter (source) follower. Do you know any NCHMOS P-P amp with follower output (low open loop impedance)?

Workhorse · 14th July 2005, 10:14 AM

Quote:

Originally posted by darkfenriz
Kanwar
Greg considered emitter (source) follower. Do you know any NCHMOS P-P amp with follower output (low open loop impedance)?

In N-Mos PP upper rail mos act as source follower amplifier and lower rail mos act as common source amplifier but it can be made to achieve Av=1 using "current gain cell" which qsc uses....

12th July 2005, 10:57 PM	#1
AudioGeek diyAudio Member Join Date: Jan 2004 Location: Minnesota	MOSFET or NPN for class A output stage Looking to build a SE Class A amp... either a MOSFET or NPN output.. what are adv vs disadv? Can I use a choke to load either of these? Thanks! __________________ It is not you... you are it.

13th July 2005, 11:39 PM	#7
AudioGeek diyAudio Member Join Date: Jan 2004 Location: Minnesota	so for a BJT output stage... Ok... well back to basics: how do I design an emitter follower class A SE output stage with BJT using a choke as a load? __________________ It is not you... you are it.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Bipolar/MOSFET CFP output stage	ashok	Solid State	25	28th November 2010 09:31 AM
AMP with inverting output stage mosfet	fab	Solid State	112	28th January 2007 04:32 AM
single mosfet output stage ?	AudioGeek	Solid State	1	1st January 2007 02:31 AM
Mosfet output stage help (please)	bob123	Class D	5	3rd January 2006 11:48 PM
MOSFET output stage on Gainclone	soundNERD	Chip Amps	3	2nd November 2004 11:21 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	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

12th July 2005, 11:34 PM	#2
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	NPN driving NMOSFET cheers

13th July 2005, 07:23 AM	#5
bocka diyAudio Member Join Date: Jul 2003 Location: Hannover	There are a lot of pro's and con's for each device. It's impossible to say which is better, because no device is ideal. MOSFET advantages: Very high input resistance No second breakdown MOSFET disadvantages: low gm high and nonlinear input capacitance (HEXFET & co) sensitive to parasitic oscillations BJT advantages: high gm BJT disadvantages: low input impedance second breakdown effects base currents

13th July 2005, 07:35 AM	#6
amplifierguru Account Disabled Join Date: Aug 2004 Location: Earth	Not to mention that the Pd losses in a MOSFET output stage are considerably greater than a BJT stage - at least for emitter followers! Even greater waste of energy.

14th July 2005, 10:04 AM	#9
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	Kanwar Greg considered emitter (source) follower. Do you know any NCHMOS P-P amp with follower output (low open loop impedance)?

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)