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c12mech 19th April 2010 03:49 AM

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

mickeymoose 19th April 2010 01:24 PM

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.

AndrewT 19th April 2010 02:44 PM

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.

c12mech 19th April 2010 11:53 PM

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.

mickeymoose 20th April 2010 12:25 AM

I did not suggest a voltage doubler but a Delon (bridge) circuit.

AndrewT 20th April 2010 11:06 AM

Quote:

Originally Posted by mickeymoose (Post 2159639)
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.

AndrewT 20th April 2010 11:09 AM

Quote:

Originally Posted by c12mech (Post 2159604)
...... 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.

star882 20th April 2010 01:11 PM

Use a boost PFC converter.

stratus46 20th April 2010 03:21 PM

Quote:

Originally Posted by c12mech (Post 2158629)
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

paulb 20th April 2010 06:39 PM

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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