Demonstration board description

UM0727

6/18

Doc ID 15906 Rev 1

Regulation of the output voltage is performed by secondary feedback on the 24 V output.

The feedback network consists of a programmable voltage reference, TSM1011, driving an

optocoupler which ensures the required insulation between the primary and secondary

sections. The optotransistor drives the feedback pin (RFMIN) which controls the operation of

the IC.

The resonant transformer is based on a two-slot coil former and an EER39-PC40 ferrite

core, manufactured by TDK. The transformer ensures safety insulation in accordance with

EN60950.

In Table 2 the main features of the transformer are listed and in Figure 3 and 4 the pinout

and the geometrical characteristics are shown respectively.

Figure 3.

Resonant transformer: pinout

Table 2.

Resonant transformer specifications

Parameter

Value

Core

EER39 – PC40

Coil former

2 slot

Primary inductance, Lp

450 µH ± 10%

Leakage inductance, Llk

150 µH ± 10%

Primary turns, Np

32 (0.15x20) – 220 m

Secondary turns, Ns

2x7 (0.2x30) (bifilar) – 40 m

Auxiliary turns, Naux

8 (on primary winding)