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Old 1st July 2006, 09:52 PM   #1
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Default Question on efficiency if PWM amps and PS

I'm a little confused about efficiency with switched output stages and PS.

Do you get all the efficiency advantage if you use the Hypex modules with a standard PS?

If so, then what's the big deal about switching PS? Smaller size?

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Old 2nd July 2006, 12:19 AM   #2
DcibeL is offline DcibeL  Canada
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The efficiency of the amplifier does not depend on the type of power supply used. Switch mode power suppies are more efficient than linear supplies, and in many cases cost less. Class D amps are fairly happy with switch mode supplied because noise from the power supply will not affect the signal as much as with say a class AB amp, generally speaking.

Switch mode power supplies are also smaller and weigh less than their linear counterpart if that is a concern in your design.
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Old 2nd July 2006, 12:25 AM   #3
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OK then, roughly what is the efficiency of a conventional PS at 0, 50% and 100% of rail voltage, and where is the power dissipated?

One reason I'm asking is because my Crown K2, while efficient at high power, dissipates a minimum of 80 W and gets hot.
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Old 2nd July 2006, 03:12 AM   #4
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Noah,

Many switching PSU's use a linear supply for a front end... so it is entirely possible for a linear supply to be more efficient than a switcher. Switcher's claim to fame is reduced size and weight. In the case of a large supply, this translates into cost as well.

Yes, you will realize PWM efficiency regardless of PSU type.

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Old 2nd July 2006, 03:37 AM   #5
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"Many switching PSU's use a linear supply for a front end..."

Do you mean many switching amps?

If not, what's a front end to a PS, and what's after it?

"Yes, you will realize PWM efficiency regardless of PSU type."

That's good to know in any case

I can't think of anything (xformer, rectifier, caps) in a regular PS that should be very dissipative.

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Old 2nd July 2006, 04:12 AM   #6
poobah is offline poobah  United States
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The general desire in a switcher is to run directly off line... this eliminates the mains transformer altogether. Because the input to a switcher PSU can be made very tolerant of ripple voltage, the size of the filter caps cam be dramatically reduced as well. All this creates a raw voltage (front end) for switcher circuitry (DC to DC converotr) to convert and regulate up, down, whatever.

As far as switching PSU's are concerned; they exhibit efficiency worse than a linear at low power output levels... Why? the lights are on, the AC is on, the computers etc... but everyone is at lunch.



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Old 2nd July 2006, 04:32 AM   #7
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That sounds great; are such PS available to the DIYer?

"As far as switching PSU's are concerned; they exhibit efficiency worse than a linear at low power output levels... "

Are you joking? Or are you serious, but the amount of idle power is very low?

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Old 2nd July 2006, 04:55 AM   #8
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I use four standard switching supplies in series for my amp setup and the idle power consumption with no load attached is around 50w.
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Old 2nd July 2006, 05:00 AM   #9
poobah is offline poobah  United States
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Sure Noah,

Google Kepco, Condor, Power One

No, not joking... switchers can consume alot of power at idle.
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Old 2nd July 2006, 05:50 AM   #10
Duo is offline Duo  Canada
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Well, to put it in retrospect; a switcher has all this stuff to run when it's idle.

For example, the first section of the power supply must draw current to run the PWM IC(s) and then the driver and output transistors which in turn energize the transformer. After the transformer, you have rectifiers, output caps, filters, etc and a feedback loop. Many switching supplies also have fans...


All of these things draw little bits of current, and in some cases, a fair bit depending on the power supply.
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