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Old 26th November 2006, 05:48 PM   #1
john65b is online now john65b  United States
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Default Re-Rectify DC?

Hey all, got a confusing (for me) one...on 41hz.com, in the AMP3X writeup, halfway down the window it clearly shows the AMP32-PS top and bottom describing the Voltage input.

Keep in mind this is the AMP32-PS - with a power supply onboard. You can see the Full Wave Bridge Rectifiers and the Smoothing Caps. The question is it says it can take a AC or DC power connection to this on board power supply.

What happens when you send DC into a Bridge Rectifier/Smoothing Caps arrangement? Do you get a square wave AC or is it still rectified DC?

I saw this and couldn't leave it alone...maybe one of you EE wizbangs out ther can confirm this is possible or is a mistake?

If it is possible, I have tons of 20VDC 3.5 Amp laptop power supplies I would love to be able to use on a few Gainclone and Tripath amps...
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Old 26th November 2006, 06:29 PM   #2
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I'm no expert, but I believe when you send DC through a bridge rectifier you just end up with the same DC minus the voltage drop of the diodes.
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Old 26th November 2006, 06:38 PM   #3
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thats what happens.

the reason to use a full bridge rectifier with DC sources are:
1.) potential to use supply with DC or AC source.
2.) prevents current flow from load to supply.
3.) connects the DC supply to the load in the correct polarity.

the downside for the DC case is the extra losses in the diodes.
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Old 26th November 2006, 07:32 PM   #4
BWRX is offline BWRX  United States
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Alternatively, you don't have to use the rectifier at all. Just jumper in your DC power and ground to the appropriate through holes where the rectifier would go.
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Old 26th November 2006, 08:37 PM   #5
john65b is online now john65b  United States
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So I can use two Laptop Power supplies - one to the rectifier for the positive rail, and one to the rectifier for the negative rail, and connect the grounds of both power supplies for the centertap...

As I said, I have many of these that I was just going to throw up on ebay for $5...now I can use them for a +/- 19V 120VA power supply...perfect for a low power gainclone or parallal a few more (four for around 400VA?) to use for my Amp5 I have yet to build...
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Old 26th November 2006, 08:39 PM   #6
john65b is online now john65b  United States
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BWRX - yes, I see what you are saying, but I would have to connect the DC upstream of the Reservoir caps, as I doubt these laptop power supplies have any...
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Old 26th November 2006, 11:00 PM   #7
BWRX is offline BWRX  United States
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I'm not sure what you mean by "upstream" but the large electrolytic caps will be connected to the supply rail and ground no matter what, so it technically doesn't matter where you jumper in DC on the board. I would remove the rectifier and use those through holes because that's the best place to do it.
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Old 26th November 2006, 11:39 PM   #8
v-bro is offline v-bro  Netherlands
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Default Re: Re-Rectify DC?

Quote:
Originally posted by john65b
If it is possible, I have tons of 20VDC 3.5 Amp laptop power supplies I would love to be able to use on a few Gainclone and Tripath amps...
AMP9.....

41hz.com....

Works fine on lower voltage...don't know about the 3.5A issue though..
Is this peak or nominal?
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Old 28th November 2006, 02:43 AM   #9
Gorilla is offline Gorilla  United Kingdom
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Quote:
Originally posted by john65b
So I can use two Laptop Power supplies - one to the rectifier for the positive rail, and one to the rectifier for the negative rail, and connect the grounds of both power supplies for the centertap...

As I said, I have many of these that I was just going to throw up on ebay for $5...now I can use them for a +/- 19V 120VA power supply...perfect for a low power gainclone or parallal a few more (four for around 400VA?) to use for my Amp5 I have yet to build...
Very unlikely. Both supplies will be referenced to ground so connecting the positive of one to the ground of the other will be a short circuit.

Quote:
Originally posted by BWRX
I'm not sure what you mean by "upstream" but the large electrolytic caps will be connected to the supply rail and ground no matter what, so it technically doesn't matter where you jumper in DC on the board. I would remove the rectifier and use those through holes because that's the best place to do it.
Technically you are right, but it would be bad in practice to not have your filter capacitors connected 'upstream', between your supply and load. Else, the ripple current that your capacitors are meant to be filtering will cause voltage ripple on your amps supply. Most significant for long leads or high frequencies.
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Old 28th November 2006, 11:11 AM   #10
BWRX is offline BWRX  United States
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Quote:
Originally posted by Gorilla
Technically you are right, but it would be bad in practice to not have your filter capacitors connected 'upstream', between your supply and load.
The large cap is connected directly to the rectifier, so if you jumper in DC at the rectifier location the large supply cap will be between the external supply and the chip which, as you said Gorilla, is the best place for it.
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