Building my first AC/DC 700w SMPS

A

Adonix

New member
Hello everyone,

I'm new to this forum and high voltage SMPS, therefore, i'll need your help with my 700W SMPS +-35V. I have read some of the threads and i really liked the proposed projects.

For my project, I have found a website that can help with designing the SMPS (poweresim) and for my specs, they recommend a flyback AC/DC smps using the following design:
Untitled.jpg

According to their charts, this is the best SMPS configuration since power dissipation is around 70W with an efficiency of 84%. I have attached the poweresim file that can be uploaded to their website to view the design and the charts.
View attachment Flyback AC-DC_UC3842_ETD49.zip

Can you guys tell me if really this design is good before i start building it? I'm somehow skeptical about flyback SMPS since i have read on nxp's site (http://www.nxp.com/documents/application_note/APPCHP2.pdf) that these power supplies are suited for 200W low input voltage circuits.

Thanks for your help :)
adonix
 
A

Adonix

New member
Thanks Cobra for your reply.

I've still not decided about my SMPS projet regarding wich topology to use and the amount of needed power.
I guess that i didn't correctly compute the SMPS's needed power and i'll need some confirmation.
if my amp has 6 channels, 50 Wrms per channel and operating at +-35 V, i'll need a PSU that can deliver a peak current of Ipeak = Sqrt(2*Po/RL) = Sqrt(2*50/8) = 3.6 A (per channel) which means that each supply rail must deliver 6*3.6 = 21 A !!
In this case, my SMPS must have an output power of (35*21) + (35*21) = 1480 W!!

Now this is huge!
Should i design the SMPS using the RMS current which is equal to Irms = Sqrt(Po/RL) = Sqrt(50/8) = 2.5 A (per channel) which means a total of 6 * 2.5 A = 15 A.
In this case, the SMPS power must be 1050 W.

I'm confused here. I guess that i'm doing something wrong with my calculation. 1050 W to deliver 300 Wrms is too much :(

Can someone help?
 
Corvett

Corvett

New member
I think you will need 1KW SMPS, specially if you are using Class-AB Amplifier.

Also, building 1000W SMPS to drive 300W amplifier is better, it will never put stress at the power supply, even if you over drive the amplifiers!
 
A

Adonix

New member
Corvett said:
I think you will need 1KW SMPS, specially if you are using Class-AB Amplifier.

Also, building 1000W SMPS to drive 300W amplifier is better, it will never put stress at the power supply, even if you over drive the amplifiers!
Click to expand...

Yep, this is true.

However, as i know, SMPS consume large energy at low load since they have the lowest efficiency at low currents. Therefore, if my amp will draw most of the time 100W, my amp won't be energy efficient :(
 
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