AN2794 datasheet(22/39 Pages) STMICROELECTRONICS

22 / 39 page

Design considerations

AN2794

22/39

Doc ID 14827 Rev 2

Figure 10.

Bottom layer

To obtain geometrical symmetry the HF transformer has been placed at the center of the

board, which has been developed using double-sided, 140

μm FR-4 substrate with

135 x 185 mm size. In addition, this placement of the transformer is the most suitable since

it is the bulkiest part of the board. Both the primary and secondary AC current loops are

placed very close to the transformer in order to reduce their area and consequently their

parasitic inductances. For this reason the MOSFET and rectifier diodes lie at the edges of

the PCB. Input loop PCB traces show identical shapes to guarantee the same values of

resistance and parasitic inductance. Also the IGBTs of the inverter stage lie at one edge of

the board. This gives the advantage of using a single heat sink for each group of power

components. The output filter is placed on the right side of the transformer, between the

bridge rectifier and the inverter stage.

The power supply section lies on the left side of the transformer, simplifying the routing of

the 15 V bus dedicated to supply all the control circuitry.

AM00631v1

AN2794 Datasheet(PDF) 22 Page - STMicroelectronics