slope compensation in smps
slope compensation in smps
(OP)
I am doing an offline flyback SMPS, and using UC3843 PWM controller
On page 8 (bottom) of the UC3843 datasheet...........
http://focus.ti.com/lit/ds/symlink/uc3843.pdf
..........it says we should use the clock ramp to provide a ramp for slope compensation.
However, on page 5 of "Six common reasons for power supply instability" by Dr Ray Ridley it says..............
"The solution to the current loop instability is well known—
add a compensating ramp. However, as shown above, it is
crucial that you don't try to use the clock ramp signal to generate
this."
Dr Ray Ridley's article can be found on .......
http://www.switchingpowermagazine.com
....in "Articles" in the "System design" section
(Dr Ridley's article is also here
http ://www.21d ianyuan.co m/bbs/atta chments/pd f/2008/07/ 16/1216185 133487d832 d335cc.pdf
)
So what do you think?
Do we use the clock to generate the ramp or not?
On page 8 (bottom) of the UC3843 datasheet...........
http://focus.ti.com/lit/ds/symlink/uc3843.pdf
..........it says we should use the clock ramp to provide a ramp for slope compensation.
However, on page 5 of "Six common reasons for power supply instability" by Dr Ray Ridley it says..............
"The solution to the current loop instability is well known—
add a compensating ramp. However, as shown above, it is
crucial that you don't try to use the clock ramp signal to generate
this."
Dr Ray Ridley's article can be found on .......
http://www.switchingpowermagazine.com
....in "Articles" in the "System design" section
(Dr Ridley's article is also here
http
)
So what do you think?
Do we use the clock to generate the ramp or not?





RE: slope compensation in smps
RE: slope compensation in smps
-Also, a fairly high turns ratio (Np/Ns) is required which increases leakage inductance.
RE: slope compensation in smps
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RE: slope compensation in smps
One solution to that is the half bridge diagonal topology.
That at least hard clamps your peak drain voltages to something sane, especially if your load unexpectedly falls off at max duty cycle.....
I would be limiting the duty cycle to less than 50%, run it in discontinuous mode, and let sleeping dogs lie.
RE: slope compensation in smps
For my power supplies I usually create a current-fed slope which gets discharged from the clock.