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Old 28th June 2002, 06:44 PM   #11
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The design of the amp is such that the PSU is on a board right under the amplifier, really close to it. It looks like I should put an aluminum plate between the 2, I've been thinking about that for a while. Even at 60 Hz, we take measures to make sure noise doesn't get injected into the amp, at 50kHz...
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Old 28th June 2002, 07:12 PM   #12
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Quote:
Originally posted by Kilowatt


P.S. When I tried your link, it said "You are not authorized to view this page"
Try to remove the dot after com. There's a dot at the end by mistake.

http://www.mag-inc.com/
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Old 28th June 2002, 07:23 PM   #13
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Thank you.
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Old 5th February 2004, 09:00 PM   #14
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Here are some numbers on a toroid I just wrapped I wanted to see it's effectiveness running at other frequencies then it's design frequency.

It's was wrapped for 22khz.

6 turns on the primary of 6 28-gauge paralleled wires, 20 turns on the secondary of 6 28-gauge wires paralleled. All numbers were with a 220ohm load across the secondary coils. Wave generator gain is flat. Toroid is roughly 1"o.d. .6" i.d. hieght .25".

Curious thing is lines 8 and 9 say more power out then in which is impossible, or it is currently, and I'm wondering if my setup or test instruments are flawed some how. Or is there some kind of magnetic phenomena I don't know about that would create this incorrect read?

I'm using a standard pc based sine wave generator, Nch, out through an Sb-live sound card into a simple amplifier I built. Primary current read was done by breaking in between the transformer and one lead wire, secondary current read was done by putting the dmm in between on side of the 220ohm resistor and transformer. The current read is direct wire inside the dmm so there were not any losses there.

The voltage was read across the input and output points on the transformer with the 220 ohm connected for both primary and secondary reads.

I did the tests multiple times with 2 different dmm's with very close results.

Any thoughts.
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Old 6th February 2004, 02:09 AM   #15
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The numbers look right. The core probably doesn't handle the low 15kHz too well because it will force it into the non-linear or saturation region on the B-H curve. Those frequencies above the red numbers are due to losses. The core losses increase exponentially with frequency and copper losses will also increase due to the skin effect. If you are going to run a transformer at a higher frequency it is designed to run at a lower flux which also increases losses exponentially. Many transformers are designed to run at a Bmax of only 200 to 700G to minimize core losses. To do this more turns are required. There is a tradeoff that must be weighed because the copper losses will also increase. The skin effect can be minimized by making a single winding from several smaller wires in parallel but with the same total of copper area.

Another interesting thing that is sometimes overlooked is: Don't forget that when current is switched through the windings a voltage drop is lost across them due to series impedances of the wire. This voltage must be subtracted because it is not applied to the core. The same on the secondary side. What is the point? This could effect your turns ratio. If, with is voltage drop, makes the turns ration close to what you want the step-up or step-down voltage to be, the switching circuitry will operate at too high of a duty cycle. You don't want that.

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Old 6th February 2004, 05:47 PM   #16
lucpes is offline lucpes  Europe
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Quote:
Originally posted by Easyamp
Here are some numbers on a toroid I just wrapped I wanted to see it's effectiveness running at other frequencies then it's design frequency.

It's was wrapped for 22khz.

6 turns on the primary of 6 28-gauge paralleled wires, 20 turns on the secondary of 6 28-gauge wires paralleled. All numbers were with a 220ohm load across the secondary coils. Wave generator gain is flat. Toroid is roughly 1"o.d. .6" i.d. hieght .25".

Curious thing is lines 8 and 9 say more power out then in which is impossible, or it is currently, and I'm wondering if my setup or test instruments are flawed some how. Or is there some kind of magnetic phenomena I don't know about that would create this incorrect read?

I'm using a standard pc based sine wave generator, Nch, out through an Sb-live sound card into a simple amplifier I built. Primary current read was done by breaking in between the transformer and one lead wire, secondary current read was done by putting the dmm in between on side of the 220ohm resistor and transformer. The current read is direct wire inside the dmm so there were not any losses there.

The voltage was read across the input and output points on the transformer with the 220 ohm connected for both primary and secondary reads.

I did the tests multiple times with 2 different dmm's with very close results.

Any thoughts.
The SB Live garbles any frequency output above 15kHz, so your measurements are not valid. Better use a decent sound card or a tone generator.
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Old 7th February 2004, 04:56 AM   #17
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After reading your reponse I opened up my case only guessing that it was my sb-live but after seeing which card I was plugged into I realized my mistake.

You are right about the high frequency response of the sblive, I switch it in and attached my frequency counter and the sb-live actually doesn't go any higher then about 22khz although the cheaper and crappier (is that a word) Ess card goes all the way 60khz or maybe more, I haven't tested higher.

But the test's were done with my counter attached and the frequencies listed are all correct as for the other values thet must be close with respect to primary to secondary transfer efficiency.

There is something wrong with the test though, it maybe noise or lack of an equal up down wave, or the test setuo in genral, I don't know, but you can't have something for nothing. I'll look for a good wave generator or build one I guess.
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Old 7th February 2004, 06:35 AM   #18
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For a car amp you say... What about building a boost converter? Unless I'm missing something here, the secondary windings with a fixed turns ratio ratio seem like unnecessary complications. Do the secondary windings have to be isolated for your application?

Boost converters have several advantages: simplicity, efficiency, and flexibility. Assuming a suitable amplifier design, you could make it work with 2-ohm loads, 4-ohms, or 8-ohms or more with similar power output at each load by varying the output voltage. The green rectangle in the picture represents a boost regulator i.c., feedback resistors, and probably a couple of other small components to keep it happy.

Also, about what was said earlier: toroidal cores aren't the only type of core with low emissions, low-profile E-cores from Ferroxcube are also good (for high-current applications you can stack several of them alongside each other).

CM
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Old 7th February 2004, 09:01 AM   #19
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Easyamp,

what are you trying to do??

What is the ferrite material you are using or do you have any data on Al, Ae and max suggested B?

Be carefull berfore your soundcard is broken.
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Old 7th February 2004, 01:22 PM   #20
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Quote:
For a car amp you say... What about building a boost converter?
I have thought about using other topologies like charge pumps or inductor boost converters, but wouldn't you need to build two seperate pumps for positive and negative? This being my thought it seems easier to build a oscillator with some type of regulation for control, current amplifier, and a center tapped secondary step up coil.

Quote:
what are you trying to do??
I'm just learning, and trying to figure out the smps's. But I guess once I 'm able to properly build my own I will use it as a psu in a car audio system, when I get a car.

Quote:
What is the ferrite material you are using or do you have any data on Al, Ae and max suggested B?
It's just one I found on an old APC UPS board I salvaged so I don't know much about it. I do know it's important when calculating frequency and load as well as other stuff, to know what core your using, but I'm just experimenting.
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