DFS06M datasheet(34/42 Pages) STMICROELECTRONICS

34 / 42 page

AN1262 APPLICATION NOTE

34/42

Bridge rectifier selection.

An integrated bridge (DF06M, 4x1A/600V, GI) has been selected.

Input Bulk Capacitor.

From table 5, in order for the valley voltage on the input cap to be around 90 V, a minimum capacitance of about

27 µF should be used. A standard 22 µF/400V electrolytic capacitor will be chosen. After few iterations, the (1)

cycle converges at Vinmin = 84.9V, Tc = 2.11 ms. From eqn. 2, VDCmin = 103.2 V.

Table 23b) shows the results of a second step of calculations, aimed at checking that no limit of the device is

violated. The result is OK.

Operating conditions @ Vin = VDCmin and thermal check.

The results are listed in table 23c). With these data the power dissipated by the L6590 is calculated and the

result is shown in table 23d).

From eqn. 3, the maximum junction-to-ambient thermal resistance needed for reaching thermal balance at Tj =

125 °C is 51.2 °C/W. From the diagrams of fig. 21 it is possible to see that this can be obtained with about 1 cm

copper area on the PCB.

Figure 21. L6590 Family Packages Junction-to-Ambient Thermal Resistance

Pre-design Choices

120 V

Reflected voltage

ηT

0,9

Transformer efficiency

Vspike

80 V

Leakage inductance overvoltage

VCC

12 V

L6590 supply voltage

0.6 V

Secondary diode forward drop

VBF

3 V

Bridge Rectifier + EMI filter voltage drop

SO16W

Rthja vs. PCB copper area

Pdiss = 1.4 W

0.511.5

22.533.5

4.5

[cm^2]

[°C/W]

1 Oz 2 Oz

MINIDIP

Rthja vs. PCB copper area

Pdiss = 1.4 W

0.511.522.5

33.544.5

[cm^2]

[°C/W]

1 Oz 2 Oz

Table 22. (continued)

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