Maximum power for Offline Flyback(90-265VAC)

eem2am · 4th December 2011, 10:12 AM

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.

gmarsh · 5th December 2011, 02:09 PM

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.

sawreyrw · 5th December 2011, 04:10 PM

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.

gmarsh · 5th December 2011, 05:08 PM

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.

eem2am · 27th March 2012, 09:24 AM

sorry Sawyer, but ti.com disagree with you.heres a 150 Watt flyback.......

http://www.ti.com/lit/ml/slup078/slup078.pdf

gmarsh · 28th March 2012, 12:14 PM

Quote:

Originally Posted by eem2am

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.

Osvaldo de Banfield · 28th March 2012, 05:07 PM

Quote:

Originally Posted by gmarsh

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!!!

eem2am · 28th March 2012, 05:14 PM

100kw flyback would need a fan or liquid cooling etc.

I dont intend to proove anyone wrong , other than myself

Eva · 29th March 2012, 12:42 AM

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

eem2am · 1st April 2012, 10:35 AM

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,

4th December 2011, 10:12 AM	#1
eem2am diyAudio Member Join Date: Jun 2011	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.

29th March 2012, 12:42 AM	#9
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	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 __________________ I use to feel like the small child in The Emperor's New Clothes tale

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5th December 2011, 02:09 PM	#2
gmarsh diyAudio Member Join Date: Apr 2004 Location: Halifax, NS, Canada	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.

5th December 2011, 04:10 PM	#3
sawreyrw diyAudio Member Join Date: Apr 2006 Location: Minnesota	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.

5th December 2011, 05:08 PM	#4
gmarsh diyAudio Member Join Date: Apr 2004 Location: Halifax, NS, Canada	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.

27th March 2012, 09:24 AM	#5
eem2am diyAudio Member Join Date: Jun 2011	sorry Sawyer, but ti.com disagree with you.heres a 150 Watt flyback....... http://www.ti.com/lit/ml/slup078/slup078.pdf

28th March 2012, 05:14 PM	#8
eem2am diyAudio Member Join Date: Jun 2011	100kw flyback would need a fan or liquid cooling etc. I dont intend to proove anyone wrong , other than myself

1st April 2012, 10:35 AM	#10
eem2am diyAudio Member Join Date: Jun 2011	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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