Auxiliary power supply idea

JohnG · 28th April 2002, 07:26 PM

This idea may be old hat, but I didn't find it in the archives.

I am building (slowly) a Tripath-based amp using a EB-0104A eval board, Jensen input transformers, etc. I am using a 1kVA, 55V toroidal transformer from Avel-Lindberg as the main pwoer transformer. I found some scrap rack-mount cases at work. Since the case is a little tight, and I didn't want to give up power supply capacitance (36000uF for each of the positive and negative supply rails), I had real trouble figuring where to put another transformer (even a small one) for the 5V supply.

Then it hit me! I could wind extra turns on the main toroid. With 120V RMS in, I get 0.69V RMS/turn. Ten turns gives me a nominal 8.6VDC with diode losses, and if I allow for a 25% output drop due to low line or heavy load, this gives me about 6.4VDC or so on the output. I plan to regulate this with an LT1763 low noise, low dropout regulator.

Also, I was thinking about winding the auxiliary winding with coaxial cable. That way I can tie the outer conductor to ground and have an electrostatic shield.

I hope to finish my amp sometime this summer (kids and work keep me quite busy).

Hope this helps someone.

John

GRollins · 28th April 2002, 10:20 PM

It will work. I can only see two possible downsides:
1) If you start placing a serious load on the secondaries (total of all secondaries), you could cook the primary.
2) If you wind a lot of turns on the outside of the transformer for a high voltage secondary, you could interfere with the heat dissipation.
In your case, only wanting 5V, as long as you don't ask too much current, you should be in good shape. I'd recommend spacing the turns equally around the core so as to distribute the load (electrical and thermal) evenly.
Go for it.

Grey

JohnG · 29th April 2002, 02:09 AM

Thanks for the input. My load current should be less than 100mA, and I had planned on distributing the turns around the circumference of the transformer.

I figured the extra windings were better than dropping voltage from the positive rail, where I'd be looking at about 6-8W dissipation. Now I should see less than a watt.

John

GRollins · 29th April 2002, 03:16 AM

Piece of cake.

Grey

Peter Daniel · 29th April 2002, 04:18 AM

I did the same when I was using Zen amp and Bride of Zen preamp together in one chassis as an integrated amp. I wound the wire for preamp supply on 300W Zen toroid. It worked without a problem.

28th April 2002, 07:26 PM	#1
JohnG diyAudio Member Join Date: Mar 2002 Location: Upstate NY	Auxiliary power supply idea This idea may be old hat, but I didn't find it in the archives. I am building (slowly) a Tripath-based amp using a EB-0104A eval board, Jensen input transformers, etc. I am using a 1kVA, 55V toroidal transformer from Avel-Lindberg as the main pwoer transformer. I found some scrap rack-mount cases at work. Since the case is a little tight, and I didn't want to give up power supply capacitance (36000uF for each of the positive and negative supply rails), I had real trouble figuring where to put another transformer (even a small one) for the 5V supply. Then it hit me! I could wind extra turns on the main toroid. With 120V RMS in, I get 0.69V RMS/turn. Ten turns gives me a nominal 8.6VDC with diode losses, and if I allow for a 25% output drop due to low line or heavy load, this gives me about 6.4VDC or so on the output. I plan to regulate this with an LT1763 low noise, low dropout regulator. Also, I was thinking about winding the auxiliary winding with coaxial cable. That way I can tie the outer conductor to ground and have an electrostatic shield. I hope to finish my amp sometime this summer (kids and work keep me quite busy). Hope this helps someone. John

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
Making your own winding for auxiliary supply	rtarbell	Parts	2	4th March 2008 07:36 AM
A new DHT power supply idea	astouffer	Tubes / Valves	11	28th October 2007 02:22 AM
new kid has a power supply idea	lyons5959	Power Supplies	21	21st November 2006 03:56 AM
Power supply idea	KBK	Pass Labs	33	20th November 2006 05:38 PM
Power Supply Idea	PaulHilgeman	Solid State	10	24th April 2003 04:56 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

28th April 2002, 10:20 PM	#2
GRollins diyAudio Member Join Date: Feb 2001 Location: Columbia, SC	It will work. I can only see two possible downsides: 1) If you start placing a serious load on the secondaries (total of all secondaries), you could cook the primary. 2) If you wind a lot of turns on the outside of the transformer for a high voltage secondary, you could interfere with the heat dissipation. In your case, only wanting 5V, as long as you don't ask too much current, you should be in good shape. I'd recommend spacing the turns equally around the core so as to distribute the load (electrical and thermal) evenly. Go for it. Grey

29th April 2002, 02:09 AM	#3
JohnG diyAudio Member Join Date: Mar 2002 Location: Upstate NY	Thanks for the input. My load current should be less than 100mA, and I had planned on distributing the turns around the circumference of the transformer. I figured the extra windings were better than dropping voltage from the positive rail, where I'd be looking at about 6-8W dissipation. Now I should see less than a watt. John

29th April 2002, 03:16 AM	#4
GRollins diyAudio Member Join Date: Feb 2001 Location: Columbia, SC	Piece of cake. Grey

29th April 2002, 04:18 AM	#5
Peter Daniel diyAudio Member Join Date: Jul 2002 Location: Toronto, Canada	I did the same when I was using Zen amp and Bride of Zen preamp together in one chassis as an integrated amp. I wound the wire for preamp supply on 300W Zen toroid. It worked without a problem.