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Old 4th December 2011, 11:12 AM   #1
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Default Maximum power for Offline Flyback(90-265VAC)

Hello,

We are going to do an SMPS for a Class D audio guitar amplifier.

The Power level that we wish to choose, is that power level which is the maximum possible power level that can be done with a cheap flyback.

So do you know what that power level is?

The Class D amplifier will be of the half-bridge variety.
Vin = 90-265VAC.
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Old 5th December 2011, 03:09 PM   #2
gmarsh is offline gmarsh  Canada
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I've seen a NCP1651 based, single-stage PFC/flyback do 54V at 10A from a 85-264V input. Transformer was huge, output had horrible 120Hz ripple on it... but it was a battery charger so it didn't matter.

No reason you can't do the same, just make sure the class D section provides plenty of power supply rejection at 100/120Hz.
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Old 5th December 2011, 05:10 PM   #3
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The RMS currents in the power handling components of a flyback supply are significantly larger than for other topologies at the same output power level. Because of this, flyback supplies are not generally used above 100 watts or so.
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Old 5th December 2011, 06:08 PM   #4
gmarsh is offline gmarsh  Canada
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If you want cheap and higher power, you can't beat what's in a lot of LCD TVs nowadays.

Generic PFC stage, producing a "regulated" 400V, followed by an unregulated half-bridge forward converter running at maximum duty cycle. No output inductors, and the only feedback is overvoltage protection.
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Old 27th March 2012, 10:24 AM   #5
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sorry Sawyer, but ti.com disagree with you.heres a 150 Watt flyback.......


http://www.ti.com/lit/ml/slup078/slup078.pdf
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Old 28th March 2012, 01:14 PM   #6
gmarsh is offline gmarsh  Canada
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Quote:
Originally Posted by eem2am View Post
sorry Sawyer, but ti.com disagree with you.heres a 150 Watt flyback.......

http://www.ti.com/lit/ml/slup078/slup078.pdf
Why are you so insistent on proving people wrong? He said "not typically used above 100W or so" instead of "it's impossible", and besides it's been 3 months since anyone posted in the thread.

I'm pretty sure you could build a flyback capable of 100KW if you really wanted to. It'd be the most impractical power supply on the planet, completely pointless to build, but I wouldn't call it impossible.
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Old 28th March 2012, 06:07 PM   #7
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Quote:
Originally Posted by gmarsh View Post
I'm pretty sure you could build a flyback capable of 100KW if you really wanted to. It'd be the most impractical power supply on the planet...
Ja ja ja, a big mutually coupled inductor, a very big MOSFET array, a very big MOSFET driver, a ton of aluminium heat sink, and finally, a big PCB!!!
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Old 28th March 2012, 06:14 PM   #8
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100kw flyback would need a fan or liquid cooling etc.

I dont intend to proove anyone wrong , other than myself
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Old 29th March 2012, 01:42 AM   #9
Eva is offline Eva  Spain
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A 100W flyback with conventional magnetics and good coupling requires ETD29, otherwise it's ok (>=150W will require >=ETD39). The advantage over forward converter is lower part count.

PI TOPSWITCH ICs (and others) allow to make 100W-200W flybacks with low part count without compromises in protection or regulation, but be careful with pulse skip modes at low power because they can make poor class D circuits sing
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Old 1st April 2012, 11:35 AM   #10
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Thanks Eva,

do you mean that the low frequency of the burst repitions isnt filtered out by the class D output filter?
-thats good of you to say, i hadnt thought of that,
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