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Old 19th April 2010, 04:49 AM   #1
c12mech is offline c12mech  United States
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Question 48v power supply design questions

I am working on a hybrid amp that requires a 48v 350ma power supply. I have a 24v 1.5a transformer that I would like to use. I'm just having trouble getting from 24v to 48v. Power supply designs are my week point. I'm learning as I go. Thanks for any help.

Bryant
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Old 19th April 2010, 02:24 PM   #2
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Use one end of the secondary as common. On the other end of the winding connect two diodes, one positive out, one negative out. Two suitable capacitors. There you go.
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Old 19th April 2010, 03:44 PM   #3
AndrewT is offline AndrewT  Scotland
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that voltage doubler circuit he's suggested is not a good idea for a high current supply. They work well at low currents but not at 350mA.

The 24Vac with a voltage doubler will give almost 70Vdc on very light load and as the load increases the ripple becomes enormous causing the average voltage to fall.
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Old 20th April 2010, 12:53 AM   #4
c12mech is offline c12mech  United States
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Most of the designs that I have seen are the voltage doubler type and as you say the ripple makes it almost useless at that point. I found a 48v 3a transformer but am unsure how to get the amps down to the level I need. I know it's just a matter of adding resistors and capacitors but in what order and where. Right now all of those formulas I had memorized are just gone.
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Old 20th April 2010, 01:25 AM   #5
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I did not suggest a voltage doubler but a Delon (bridge) circuit.
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Old 20th April 2010, 12:06 PM   #6
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by mickeymoose View Post
I did not suggest a voltage doubler but a Delon (bridge) circuit.
Hi,
it is the same as a voltage doubler, using diodes and capacitors to double the voltage.
If the correct name for the circuit is "Delon" then that is something else I will try to remember.
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Old 20th April 2010, 12:09 PM   #7
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by c12mech View Post
...... I found a 48v 3a transformer but am unsure how to get the amps down to the level I need.
the circuit/load will draw as much current as it needs. Do not try to reduce the current, simply satisfy the demand.

A 48Vac 3Aac will give you 65 to 75Vdc and continuous output of 750mA and stay cool.

If you want 48Vdc you need a 33Vac to 35Vac transformer.
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Old 20th April 2010, 02:11 PM   #8
star882 is offline star882  United States
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Use a boost PFC converter.
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"Fully on MOSFET = closed switch, Fully off MOSFET = open switch, Half on MOSFET = poor imitation of Tiffany Yep." - also applies to IGBTs!
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Old 20th April 2010, 04:21 PM   #9
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Quote:
Originally Posted by c12mech View Post
I am working on a hybrid amp that requires a 48v 350ma power supply. I have a 24v 1.5a transformer that I would like to use. I'm just having trouble getting from 24v to 48v. Power supply designs are my week point. I'm learning as I go. Thanks for any help.

Bryant
So go to AnTek and buy the right transformer for $11 or $13.

G
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Old 20th April 2010, 07:39 PM   #10
paulb is offline paulb  Canada
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I think Andrew's replies have been the only useful ones so far.
I'm all about trying to use parts on hand. You could use your 48VAC transformer and a simple transistor regulator to drop the ~70VDC unregulated to 48VDC. You'll need a fair heatsink on the transistor, it would be dissipating about (70-48)V * 350 mA = 7.7W.
Here's an example:
zener regulated power supply
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