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How to get a 15V floating supply
How to get a 15V floating supply
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Old 13th February 2007, 03:36 PM   #1
rtarbell is offline rtarbell  United States
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Default How to get a 15V floating supply

Hello there,

I'm asking about how to make a cheap 15V floating supply from pre-existing +/- 80V supplies. The output current for the 15V supplies is not required to be much, maybe 100mA or so. I would need four of them.

Right now, the only solution I have is to use 15V DC wall adapters (wall warts), but that requires multiple outlet cords for one amp (I'm trying to use just one power cord for the whole amp, not five).

I've looked at charge pump IC's and the like, but I can't seem to find an IC/regulator/switching IC that provides a completely floating output voltage with minimal parts (I'm trying to avoid transformers and expensive magnetics).

==> Any ideas y'all could offer?
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Old 13th February 2007, 04:23 PM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
although you want to avoid extra transformers, that is the easy way to isolate a supply.
A dual secondary will give two independant isolated supplies.
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Old 13th February 2007, 04:57 PM   #3
audioPT is offline audioPT  Portugal
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Hi!

If you reduce a little the rail voltage from 80V to approx. 70v, by using pass transistors and zeners, you can use Texas Instruments' Power Modules PTB48510C or PT4711 depending on the needed power.
I'm using them within many of my projects / products with rails up to 55V with no problems.

The best of the PT4711 Module is the separate outputs. So I think 2 of these will satisfy your needs.

If you don't want to make a pre-regulation of your rails, you can use a 24V transformer and put it inside your case and use two of these PT4711 modules.

Also, you don´t need to use extra outlet cords, just get the power for this extra transformer at the input of the existing transformer (don't forget to use a fuse)
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Old 13th February 2007, 06:45 PM   #4
Minion is offline Minion  Canada
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When ever I need an Isolated extra supply in a curcuit Idea I use these very small Transformers that I have.....

These transformers have a 120v/240v Primary and a 24v,0v,24v secondary (or 12v,0v,12v when useing the 240v Tap with 120v ac power) and are only about an Inch square and output about 150mA of current...I use these with a adjustable regulator and a couple small filter caps to get the desired Voltage for whatever curcuit I need them for and they are so small that they are very easy to fit into existing enclosures and give me the Flexability to get a Variety of Voltages from as low as +/-9v up to +50v or +/-50v if I use 2 transformers......

I got these particular transformers on e-bay for $1 each and they have found use in several of my projects were I needed an extra supply voltage and didn"t have much space.....

Just a thought.....

Cheers
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Old 13th February 2007, 11:11 PM   #5
theAnonymous1 is offline theAnonymous1  United States
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Hello fellow Buffalonian.

I have two 18v 1.6VA dual secondary transformers that would work out well. You would need to regulate the outputs, but regulators are cheap. I will also throw in four 1A bridge rectifiers, one for each secondary. Then all you will need is some prototyping board from radioshack or ebay and a few capacitors.

Here is a link to some cheap 15v regulators on ebay. Shipping is cheap also.

http://cgi.ebay.com/L7815CV-15V-1Amp...QQcmdZViewItem

Here is a pic of your free gift.

Click the image to open in full size.
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Old 13th February 2007, 11:26 PM   #6
Ryssen is offline Ryssen  Sweden
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Cheap yes,but good no!
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Old 13th February 2007, 11:41 PM   #7
theAnonymous1 is offline theAnonymous1  United States
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Quote:
Originally posted by Ryssen
Cheap yes,but good no!
Thats a matter of opinion that would need to be based on their intended use. He could use adjustable regulators if fixed regs aren't good enough for whatever reason.
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Old 14th February 2007, 06:34 AM   #8
batee is offline batee  United States
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Here's what I came up with for a high voltage DC gate drive supply:

http://batee.com/projectsanddesigns/...ive_v_3.5.html

I use a $15 switching power supply to convert +165VDC to +12VDC required by the board shown.

I have built it and tested it from DC to 400KHz+. Works great.

Bryan A. Thompson
bryan@batee.com
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Old 14th February 2007, 02:01 PM   #9
rtarbell is offline rtarbell  United States
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Thank you ALL for your ideas, VERY helpful!!!


batee: I was surprised by your schematic in that each DC/DC converter is only rated for 66mA continuous output (according to the datasheet), but your circuit is able to switch large FETs (which can require transient gate currents up to 1A to switch "hard"). NOT that I doubt your results at all, I was just surprised! Let me ask you, how did you know that 66mA would be "enough" for the switch supply?

I guess my question is: if the power supply is rated at a continuous or RMS current of X amps, how many amps can it supply in a fast transient, such as to switch a FET on/off? If I have a "little current" available all the time, how large of a current can I draw from this in a transient burst?
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Old 14th February 2007, 02:36 PM   #10
AndrewT is offline AndrewT  Scotland
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Hi,
the FETs present a capacitive load not a resistive load related to output current.

The question should be;- what current is required to charge up the gate capacitance at the fastest switching speed that my circuit can generate?
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