Topswitch: Error Amplifier & Modulator transfer function....mixing log and non-log numbers
Hello,
Please assist with the expression for the transfer function of the modulator and error amplifier of this TL431 based feedback loop for a TOPswitch Flyback from Power integrations. (its in a well known book)
It looks like they are mixing in decibel numbers and “normal” numbers in the same expression?
The modulator and error amplifier circuit is shown as attached on page 466. Page 467 (Equn 8.35) shows the transfer function. However, Equn 8.35 on page 467 shows the parameter “G0”.
“G0” is shown in Equn 8.36 on page 467.
“G0” comprises the “Gpwm” parameter which is shown on page 455 (also attached)
The question is, “Gpwm” is a decibel number…… Why are they putting a decibel number into equation 8.35 on pg 467?
…..Equn 8.35 (pg 467) is an expression that needs to be calculated, (working through the complex numbers), and then that should have a log taken of its magnitude to express it in decibels…..so why is “Gpwm” in there as a decibel number already?
(by the way the pages are from a single SMPS book)
评论
I believe so, i am trying to find time to read the full book. The Power Int AN57 gives the expression, but uses "KTL431" (open loop gain of TL431) , but the book doesnt use this, which seems odd.
I believe so, i am trying to find time to read the full book. The Power Int AN57 gives the expression, but uses "KTL431" (open loop gain of TL431) , but the book doesnt use this, which seems odd.
I don't quite get the conceptual leap the author is making on page 455. To get from %duty/ma to V/A presupposes also an input voltage and a transformer ratio, not mentioned or supplied. Is the author tying this data into a previously mentioned simulation circuit?