AN3372 datasheet(18/37 Pages) STMICROELECTRONICS

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PFC design rules

AN3372

18/37

Doc ID 018625 Rev 1

For this application boost inductance of 1 mH has been chosen.

6.3.4

Power MOSFET selection

For Power MOSFET selection the breakdown voltage and the RDS(on) must be considered.

The MOSFET used in this section is the STF11NM60ND.

Thermal measurements have confirmed this as the right choice for this device.

6.3.5

Boost diode selection

The PFC section is realized with a boost converter working in transition mode. The

STTHxL06 family, which is using ST Turbo2 600 V technology, is specially suited as the

boost diode in discontinuous or transition mode power factor corrections.

The selection criteria is based on breakdown voltage and current. A rough selection can be

performed adopting the following criterion:

●

The breakdown voltage must be higher than (Vout +

ΔVop) +margin

●

The diode current must be higher than 3 times the average current Iout.

In this case STTH1L06 has been chosen.

The average diode current is:

Equation 10

Use the following equation to evaluate the conduction losses:

Equation 11

Considering Tjmax = 150 °C and the maximum ambient temperature Tambmax = 50 °C, it is

possible to calculate the RTHJ-amb as follows:

Equation 12

The calculated Rth is higher than the STTH1L06 (diode RTj-a =70 °C/W) thermal resistance

junction-ambient, so no heatsink is needed.

In any case, thermal measurement confirms the real device temperature.

lamp

out

⋅

D10

out

D10

0.165

0.89

465

−

0.43

150

diode

a mbm ax

jmax

amb

TH J

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