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UCC28070A PFC controller in DCM?

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Advanced Member level 5
Jun 13, 2021
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How does the UCC28070A manage in DCM?
If you have a 60kHz 1kW PFC over 100-265VAC (390Vout), then a sendust inductor which spans 250uH to 212uH sounds reasonable. However, at say 250W load and 240VAC input, the inductor current will be in DCM. How does the UCC28070A manage this when it does its inductor downslope reconstruction? Does it result in more THD than say using a L4981A or a UC3854 controller?


Attached is LTspice of it at 100VAC


  • LT1248 Boost PFC 1000W
    3.7 KB · Views: 71

Also, if you are doing a UCC28070A Boost PFC with...
Vout = 390V
Pout = 1000W
N (CT) = 50:1
VAC minimum input = 200VAC
Fsw = 60kHz

.....then if you go to a loading of just 250W, and with 265VAC input, then the multiplier output current peak is just 12uA. !!...This is the current which controls the Boost PFC inductor current....won't such a small control current be deluged by the noise?

At lower input powers, the control current would be even less than that!

In post 388168 , #4 of this forum we previously agreed that 12uA was too low and would be deluged by noise.

To add to the problem list if i may.
Doing 1kW Boost with UCC28070A. (230VAC, 60kHz, 0.9 Max duty)
I have set it for 250W load...but have only loaded it with 40k resistance. (7W)
At startup, the FET blows up.
The Cout=270uF gets charged up to 390V, and then the fet blows D-S short, Gate 37 ohm to D and S.
I only have 2A fuse for now.
I suspect my Current sense transformer is saturating at startup.
Its an E20/10/6 50:1.
Reset is by zener diode series cct...zener is 56v.
I suspect staircasing of inductor current.
Current limit is set for 5.2A so i am surprised this is happening.

I am going to limit the max duty cycle to 0.5 and try and get a look at the burden resistor voltage with the diff probe.
Any other ideas?

Blown FET was 950V, 9A STW6NK95....

Thats the third blown fet now.
It will start up no probs into cout=22uF and 7w load.

I also have the burden near the sense transformer, and then the signal has to go back ~13cm to the control board.....i may move the burden to the control board and take the whole CST output back to the control board.

I dont have isolation transformer so any signal i probe is full of common mode noise due to diff probe Micsig DP0007
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