AN2530

Transformer and resonant components

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3

Transformer and resonant components

In order to avoid the majority of the most difficult problems related to resonant converters,

great care must be taken in the design of those components whose primary task is to

transfer the energy from the rectified line to the load. These components are the

transformer, external inductor, capacitor divider network and the power switches.

Several "methods" and approaches have been taken into account in order to calculate the

power transformer and the external inductor (refer to Section 7: References at the end of

this application note). AN1660 forms the basis for this application note and provides

calculations for this objective.

The objective of this application note is to take a closer look at the power stage, so that just

the final results for the transformer and the external inductor are shown. However, it is

important to notice that the transformer's type (material, size and shape) plays one of the

main roles in any converter. For resonants, the coil type is important also.

Table 2 gives transformer and coil data. Litz wires have been used.

3.1

Transformer

●

Brand: Epcos

●

Type: ETD34

●

Material: N67

4

Converter's protection schemes, overcurrent,

overvoltage

Overcurrent and overvoltage protection features can be added easily thanks to the pins of

the L6598 controller. In this section we show how to calculate these values according to the

operational parameters chosen.

Again, refer to AN1660 (ZVS resonant converter for consumer application using L6598 IC)

or use your own "method" to calculate the peak current. You should expect to be at the

maximum at L1 (as well as transformer's primary) and take a safety margin (10% more for

example). In this case, the maximum current should be 1.8 A, so we set the maximum

current to 2 A.

Table 2.

Tr1 Transformer’s windings details

Turns

Wires

Wire's diameter [mm]

Primary

50

14

0.2

Secondary

14

38

0.2

Aux.

3

1

0.2