Hi,
Would you agree, the App Note sluu312b (below) contains a sub-circuit that is wrong?....it concerns the bit on page 3 which imposes a compensatory ramp onto the current sense signal. This sub circuit would clearly not provide a ramp, since the burden resistor acts as such a low value “bottom divider” resistor that the ramp would be too insignificant. The attached LTspice sim proves this (see circuit number 2, which demo’s the incorrectness)
(BTW, the ramp is needed because the Current transformer magnetising current subtracts too much from the “ideal signal” at low load and at the mains zero crossings)
(There is also a DC level added, and this is needed to overcome other effects at light load/zero_x.)
Also, why on page 3 do they try to use the UCC27324 Gate drive chip output to produce the ramp?…..surely they should use the gate drive output on the UCC28070A chip itself?….it would allow far less noisy layout.
Do you agree that in the PDF and LTspice sim attached, the method of circuit number 4 is the best way to achieve what the App Note is trying to actually do?
(Unfortunately, we cannot go to the ti.com forum, since you need a company email address, and we are merely hobbyists)
App Note sluu312b
https://www.ti.com/lit/ug/sluu312b/sluu312b.pdf?ts=1653521265498&ref_url=https%3A%2F%2Fwww.google.com%2F
UCC28070A PFC controller (see pages 35 , 36 for relevant pages to this post)
https://www.ti.com/lit/ds/symlink/ucc28070a.pdf?ts=1653493319157&ref_url=https%3A%2F%2Fwww.ti.com%2Fproduct%2FUCC28070A
Would you agree, the App Note sluu312b (below) contains a sub-circuit that is wrong?....it concerns the bit on page 3 which imposes a compensatory ramp onto the current sense signal. This sub circuit would clearly not provide a ramp, since the burden resistor acts as such a low value “bottom divider” resistor that the ramp would be too insignificant. The attached LTspice sim proves this (see circuit number 2, which demo’s the incorrectness)
(BTW, the ramp is needed because the Current transformer magnetising current subtracts too much from the “ideal signal” at low load and at the mains zero crossings)
(There is also a DC level added, and this is needed to overcome other effects at light load/zero_x.)
Also, why on page 3 do they try to use the UCC27324 Gate drive chip output to produce the ramp?…..surely they should use the gate drive output on the UCC28070A chip itself?….it would allow far less noisy layout.
Do you agree that in the PDF and LTspice sim attached, the method of circuit number 4 is the best way to achieve what the App Note is trying to actually do?
(Unfortunately, we cannot go to the ti.com forum, since you need a company email address, and we are merely hobbyists)
App Note sluu312b
https://www.ti.com/lit/ug/sluu312b/sluu312b.pdf?ts=1653521265498&ref_url=https%3A%2F%2Fwww.google.com%2F
UCC28070A PFC controller (see pages 35 , 36 for relevant pages to this post)
https://www.ti.com/lit/ds/symlink/ucc28070a.pdf?ts=1653493319157&ref_url=https%3A%2F%2Fwww.ti.com%2Fproduct%2FUCC28070A
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