STCMB1 datasheet(19/59 Pages) STMICROELECTRONICS

19 / 59 page

DocID028958 Rev 4

19/59

STCMB1

Application information

Figure 7. Conventional COT controlled PFC

Since the slope of the inductor current during the on-time is proportional to the input voltage,

there is a perfect linear relation between the instantaneous AC voltage and the current

drawn by the circuit, which would ideally provide a perfect unity power factor and no

distortion when the on-time is kept constant along a line cycle.

Unfortunately, parasitic elements (essentially, the parasitic capacitance of the drain node,

Cdrain) cause a negative offset in the inductor current shape as can be seen in Figure 8. In

particular, the negative peak current ILvy can be calculated as follows:

Equation 1

Approximating the inductor current with a triangular waveshape, the commanded peak

current is:

Equation 2

and its average value in a switching cycle is:

Equation 3

(x)

The last term “(x)” in Equation 3 is non-sinusoidal (constant) and causes distortion in the

input current.



sin

drain

out

Lvy







Lvy

Lpk

sin









sin

drain

out

drain

Lpk

Lvy















STCMB1 Datasheet(PDF) 19 Page - STMicroelectronics

STCMB1 Datasheet(HTML) 19 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59

Datasheet Download

Link URL