Application report SLUA604

Magnus Pihl67

Where does the formula in chapter 4.4.2.2 come from, and why is the output power times two in the formula?
Thanks in advance.

Application report SLUA604:
www.ti.com/.../slua604.pdf

over 7 years ago

0 John Stevens over 7 years ago

TI__Expert 7395 points

Magnus,

Thanks for your interest in TI here.

That comes from the energy / power equation for DCM flybacks : Pout = 1/2 L(Ipeak^2) f solved for the L magnetizing inductance. See this paper for details:

Regards

John

0 Magnus Pihl67 over 7 years ago

Intellectual 260 points

Thanks. That makes sense. Now, the skin depth in equation in 4.4.2.3 does not end up correctly. It reads: 7,5/sqrt(100k) = 0,24mm. But when I calculate it, it turns out to be 0,024mm.

0 Mike O' over 7 years ago in reply to Magnus Pihl67

TI__Guru* 85556 points

Hello Magnus,

I went through the calcuation of skin depth from the application as you did and came up with the same number that you did.

I have used the following equation to calculate skin depth for copper and the units work out. I calculate the skin depth of a copper wire at 100 kHz to be roughly 0.206mm

Regards,

Mike

0 Mike O' over 7 years ago in reply to Mike O'

TI__Guru* 85556 points

Sorry the equation did not post. I have attached it for your reference.

Power management

Power management forum

Application report SLUA604