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Transient response: BCM PFC vs Average Current Mode PFC?

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cupoftea

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Hi,
Would you agree, BCM PFC can more readily be done with faster transient response for 300W PFC over 100-265VAC.
I mean, say you wanted to have lower voltage rise following full-to-no-load transient...then you would pick BCM, would you agree?
The AvCM has an error amp on the current aswell as the voltage...so its going to be slower.
Also, as is known, AvCM PFC needs a V^2 term to be put in the multiplier, otherwise at low line, the transient response is very slow....BCM does not suffer this.

So BCM is for when you want to limit that upper rise on vout, following full-to-no-load transient...would you concur?

Besides, its a general rule that when you have a bigger swing in inductor current, you can more easily get a faster transient response......may you nod in agreement?
 

The voltage loop on any PFC has to be in the 1Hz - 7Hz BW range in order not to affect the sine wave current trying to be drawn from the mains - if too fast the volt loop will try to suppress the current peak and lift current near zero xings - albeit delayed ....
--- Updated ---

BCM will allow a slightly faster current loop which will allow more accurate tracking of the current demand, giving - hopefully - lower THD
 
Thanks, and also, i believe that BCM PFC doesnt suffer the reduction in bandwidth that Av Currnt Mode PFC does when at 100VAC input when 100-265VAC operation is required?
Though BCM PFC looks like it could be tricky with a small sendust torroid?

So....Doing 300W PFC for 100-265VAC, 390Vout.
Will use 135uF on output (3x47u), and am wondering about having a switchable feedback loop so that if vout goes above 415Vdc then it can quickly get back down again, due to a faster loop when above 415Vdc. (so we would switch the feedback loop at about 415Vdc and rising).....we dont want vout going up above 420Vdc.

I dont think this would give us a standards fail?, ...as they only test for THD on smooth constant load, so the vout would never touch 415Vdc during standards test.

As you know, with 135uF on vout, The Vpkpk on vout would be 18V....so normally it'd be 381V to 399Vdc.
 
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