Can you make 0-5V DC out of 2.5-0-2.5V AC - diyAudio
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Old 23rd September 2003, 02:31 PM   #1
Ralph is offline Ralph  Netherlands
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Default Can you make 0-5V DC out of 2.5-0-2.5V AC

Suppose not, but had to ask ...

edit: and make it good enough to use as 300B filament supply
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Old 23rd September 2003, 02:36 PM   #2
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Default Bas Horneman

Yes you can..

2,5v..................wire 1

0

2,5 ....................wire 2

gives you 5V AC across wire 1 and 2

Rectifier + caps gives you 5 * 1,6 for cap input PSU..is 8VDC.. (roughly)

7805 gives 5vdc regulated at 1A


or voltage dropping resistor (depending on current draw) to give 5vdc unregulated..

Cheers,
Bas
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Old 23rd September 2003, 02:41 PM   #3
dhaen is offline dhaen  Europe
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You have to take account of the drop across the rectifiers:
Schottky rectifier bridge, and a big resovoir cap.

Is it a heater supply?

Cheers,
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Old 23rd September 2003, 02:46 PM   #4
Ralph is offline Ralph  Netherlands
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Yes, it's a 300B filament supply. At this moment I'm using 0-14V AC to get 0-5VDC and that gives quiet some heat. And because the 2.5-0-2.5 was still available when I used AC I thought I might be possible ... but I'm afraid voltage will be too low to use a regulator. My 300B draws 1.41A @ 5V.
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Old 23rd September 2003, 02:46 PM   #5
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Quote:
and make it good enough to use as 300B filament supply
If that is the point of the exercise...you should use Schottkey IMO.
And go for a simple current regulated LM317 jobby..

Did you not buy the circuit boards from Doede?

Cheers,
Bas
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Old 23rd September 2003, 02:55 PM   #6
dhaen is offline dhaen  Europe
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Ralph,

Where is the 2.5-0-2.5 coming from?
If it's from an enclosed transformer, that you can't overwind, there are other solutions to "find some volts".
If you buy a small (15 or 30VA) toroid, you can hand wind some turns - perhaps 3 turns per volt, to put in series with the existing, to make the exact voltage required.

Sorry for the long rambling English. I'll clarify if you're interested.

Cheers,
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Old 23rd September 2003, 03:03 PM   #7
Ralph is offline Ralph  Netherlands
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Hi John,

Quote:
Sorry for the long rambling English
Clear enough for me The trafo is indeed closed and I think I'm just out of luck. Will proceed with my 0-14V solution and try to get rid of the heat.

Thanks, Ralph
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Old 23rd September 2003, 03:10 PM   #8
dhaen is offline dhaen  Europe
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Ralph,

If you are using a regulator, there is another way to reduce it's heat dissapation: You should reduce the value of the resovoir (smoothing) cap. This will increase the ripple to the regulator, and thus reduce the RMS voltage and the power. You must be careful not to reduce it too far. The voltage at the bottom of the ripple must still be enough for the regulator to operate correctly.

If you haven't got a scope, you can use a multimeter on AC range to check the output DC for ripple "break-through". Keep reducing the cap until the ripple breaks through, then go back one step.

Cheers,
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Old 23rd September 2003, 03:13 PM   #9
moamps is offline moamps  Croatia
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Quote:
Originally posted by Ralph

Will proceed with my 0-14V solution and try to get rid of the heat.

Hi,

If your secondary 5V is unused, connect them serial and out of phase with 14V secondary. You will get 14-5=9V AC on bridge. Strange idea but works.

regards
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Old 23rd September 2003, 03:16 PM   #10
dhaen is offline dhaen  Europe
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Good idea (again) moamps
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