AN3027 datasheet(18/41 Pages) STMICROELECTRONICS

18 / 41 page

Designing a TM PFC

AN3027

18/41

Doc ID 16134 Rev 4

From

(12) and Equation 35 the maximum thermal resistance to keep the junction

temperature below 125 °C is:

Equation 36

Because the calculated Rth is lower than the STTH2L06 thermal resistance junction-

ambient, a heatsink is not needed to properly dissipate the heat.

3.4

L6563S biasing circuitry

In this section we describe the dimensioning of the power components as well as the biasing

circuitry for the L6563S. For reference, the internal schematic of the L6563S is represented

below in

Figure 8. For more details on the internal functions please refer to the datasheet.

Figure 8.

L6563S internal schematic

Pin 1 (INV): This pin is connected both to the inverting input of the E/A and to the OVP

circuitry. A resistive divider has to be connected between the boost regulated output voltage

and this pin. The internal reference on the E/A non-inverting input is 2.5 V (typ.). The PFC

output voltage (Vout) is set at its nominal value by the resistor ratio of the feedback output

divider. RoutH and RoutL are then selected considering the nominal output voltage (4) and

diode

ambx

125

−

284

125

−

AN3027 Datasheet(PDF) 18 Page - STMicroelectronics