Integrated regulators for smart bias control

darkfenriz · 25th August 2004, 07:54 PM

Hallo
Just a weird idea to use LM317/LM337 regulator pair in a configuration like in the attachment
Is it worth considering or just rubbish???

(no values, simulation or whatever -just an idea)

johnnyx · 25th August 2004, 08:48 PM

How will the regulators pass the signal between VAS and output stage?

darkfenriz · 25th August 2004, 09:11 PM

Won't they??
hmm.. good question indeed..

maybe it was too bizzare to be possible
If I change the part like this will it solve:

Stocker · 25th August 2004, 09:57 PM

assuming it 'could' work,

what about temperature stability?

hughmon · 25th August 2004, 10:09 PM

In concept at least, it could work. One of the problems with three terminal regulators is that the output amp basically has 741 performance, only with a higher output current (read slow and noisy). The net result would be that you'd have to slow the amp down with a huge comp-cap, possibly to the point of where it wouldn't even do the top end of audio well. Temperature issues aside, why in the world would you want to use a clunk of a regulator like that in that kind of application??

Stocker · 26th August 2004, 01:37 AM

If you can't get the high-frequency response, it may make a novel sub amp.

darkfenriz · 26th August 2004, 08:46 PM

Quote:

Temperature issues aside, why in the world would you want to use a clunk of a regulator like that in that kind of application??

eeeeeeeeeh...
no reason, just a play, wanting to find new ways or maybe dead-ends
i was wondering if it is theortically possible
thanks and cheers

Nelson Pass · 26th August 2004, 09:24 PM

Why not try just one regulator and attach it's "ground"
to the Collector of the VAS current source?

GRollins · 26th August 2004, 09:40 PM

I used a 317 to bias a MOSFET output once. It worked, but I don't remember the details. I think I was using it to hold the output of two LF351s apart by the bias voltage.

Grey

johnnyx · 26th August 2004, 09:50 PM

A TL431 programmable Zenner type regulator might be better, to fix the voltage between the gates of the output MOSFETS. If these were lateral types, this could be set for the zero-temp-co point, about 70mA IIRC. VMOS fets need temperature compensation, so it wouldn't be appropriate for them. Lateral MOSFETS have a lower gate threshold voltage though, so the 2,5v min for the TL431 may be too high.

The LM317 type regulators have a very high input impedence; the input voltage can change a lot, but the current through it depends only on the load resistance and output voltage. They can be used as a current source (or sink). This is why I said they will not pass the signal. Bypass caps could transfer the signal though, and the regulators do need bypass caps...

You've got me thinking

25th August 2004, 09:57 PM	#4
Stocker diyAudio Member Join Date: Dec 2003 Location: Austin	assuming it 'could' work, what about temperature stability? __________________ Jesus loves you.

26th August 2004, 01:37 AM	#6
Stocker diyAudio Member Join Date: Dec 2003 Location: Austin	If you can't get the high-frequency response, it may make a novel sub amp. __________________ Jesus loves you.

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
Bias control problem with n-channel amplifier (Anthony E. Holton)	Hielke02	Solid State	4	1st May 2011 06:54 PM
Remote control for integrated tube amp	Driller99	Tubes / Valves	3	4th May 2008 06:15 AM
how do i add volume control on front of bias mosfet??	AudioGeek	Solid State	0	19th November 2005 10:12 PM
you guys are smart.. :D help :(	SkinnyBoy	Power Supplies	22	19th May 2005 09:36 AM

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

25th August 2004, 08:48 PM	#2
johnnyx diyAudio Member Join Date: Jan 2004 Location: manchester	How will the regulators pass the signal between VAS and output stage?

25th August 2004, 10:09 PM	#5
hughmon diyAudio Member Join Date: Jun 2004 Location: Los Angeles	In concept at least, it could work. One of the problems with three terminal regulators is that the output amp basically has 741 performance, only with a higher output current (read slow and noisy). The net result would be that you'd have to slow the amp down with a huge comp-cap, possibly to the point of where it wouldn't even do the top end of audio well. Temperature issues aside, why in the world would you want to use a clunk of a regulator like that in that kind of application??

26th August 2004, 09:24 PM	#8
Nelson Pass The one and only Join Date: Mar 2001	Why not try just one regulator and attach it's "ground" to the Collector of the VAS current source?

26th August 2004, 09:40 PM	#9
GRollins diyAudio Member Join Date: Feb 2001 Location: Columbia, SC	I used a 317 to bias a MOSFET output once. It worked, but I don't remember the details. I think I was using it to hold the output of two LF351s apart by the bias voltage. Grey

26th August 2004, 09:50 PM	#10
johnnyx diyAudio Member Join Date: Jan 2004 Location: manchester	A TL431 programmable Zenner type regulator might be better, to fix the voltage between the gates of the output MOSFETS. If these were lateral types, this could be set for the zero-temp-co point, about 70mA IIRC. VMOS fets need temperature compensation, so it wouldn't be appropriate for them. Lateral MOSFETS have a lower gate threshold voltage though, so the 2,5v min for the TL431 may be too high. The LM317 type regulators have a very high input impedence; the input voltage can change a lot, but the current through it depends only on the load resistance and output voltage. They can be used as a current source (or sink). This is why I said they will not pass the signal. Bypass caps could transfer the signal though, and the regulators do need bypass caps... You've got me thinking

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