Q Factor for offline CCM Voltage mode flyback

[Faringdon]

Hi,
In AN57, Power integrations say we must take Q = "0.15 to 0.3", when calculating the power stage transfer function.
(as part of feedback loop analysis)
However, TN-203 by Microsemi.com, on page 8, points out that the Q factor is by w0/Q = R/LE

where
LE = the effective inductance.

The microsemi one takes into account that  its the load that is damping the Output LC....so it must be correct.
Where are Power integrations getting "0.15 to 0.3 from?

[mtwieg]

Hi,
In AN57, Power integrations say we must take Q = "0.15 to 0.3", when calculating the power stage transfer function.
(as part of feedback loop analysis)
However, TN-203 by Microsemi.com, on page 8, points out that the Q factor is by w0/Q = R/LE

I can't find a coherent definition of Q in either document. And I wouldn't assume both would define it the same way, and therefore wouldn't expect them to suggest similar values...

The microsemi one takes into account that  its the load that is damping the Output LC....

I don't see this, do you expect everyone to read these things top to bottom for you? And relying on the load for damping is very poor practice IMO.

Where are Power integrations getting "0.15 to 0.3 from?

Impossible to say without a coherent definition of Q. That app note shows an additional LC filter on the output of the flyback, so assigning a single Q value to the entire thing doesn't seem reasonable.