CCM offline flyback not that bad

[cupoftea]

Hi,
Whilst running 70W CCM flybacks on 240VAC, it was noted that when a BCM flyback (but in const frequency) has its secondary inductance increased so that it goes just into CCM, you dont suddenly see a sudden decrease in efficiency due to the reverse recovery. Even though it was using Ultra fast sec diode and not SiC.
I mean, we took it so that the primary turned on when sec was still conducting 200mA or so, and no appreciable difference in efficiency was seen.
I am wondering if there is some marketing going on, over-stating the benefit of BCM flyback chips?

Would like to do a 70W offline flyback in deep CCM for comparison, wonder what we would see efficiency wise?
Approx 10% worse effciency than BCM?.....1% worse efficiency?

 

[Velkarn]

I mean, we took it so that the primary turned on when sec was still conducting 200mA or so, and no appreciable difference in efficiency was seen.
I am wondering if there is some marketing going on, over-stating the benefit of BCM flyback chips?

i think its not only efficiency, moving to CCM lead to EMC issue

 

[Easy peasy]

unless you have a spec ann and can measure conducted RFI - your comments are not particularly insightful

 

[cupoftea]

Thanks, at various interviews, you are constantly asked, "what are the advantages of QR Flybacks".
I always say....

1...no reverse recovery of the output diode
2....Simple control as always DCM
3....Lower peak current as you never go into deep DCM
4...Many QR controllers available
5....less RFI probelms as the sec diode doesnt get "snapped off"

...there is then always a very. very long pregnant pause from the interviewers as if i have missed something.

...Presumably they are waiting for some info on efficiency comparison between BCM and deep CCM?

 

[Easy peasy]

better dynamic response than CCM. - easy to stabilise the loop - to enlarge on 2. as it is a bit broad

zero current or low current / low voltage turn on of the main switch - which is why it is EMC quiet