L6986ITR datasheet(11/60 Pages) STMICROELECTRONICS

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4.4

Iso-buck operation principle

The picture below describes the operation principle of the iso-buck converter.

When the high side MOSFET is turned on, the current flows through the primary winding of the transformer

and charges the primary output capacitor. Considering the dot convention of the transformer, the voltage at the

anode of the Schottky diode is negative, hence the diode is reverse biased and no current flows in the secondary

winding. The load connected to the secondary output is supplied by Cout2.

When the low side MOSFET is turned on, the voltage applied at the transformer windings inverts its polarity.

As consequence, the Schottky diode is now forward biased and allows the current to flow from the secondary

winding to Cout and the load. Under this condition the energy transfer from primary to secondary side occurs.

Figure 7. Iso-buck basic operating principle

The waveforms in the figure below reproduce the trend of the current in the two windings in according to the

switch node transitions.

L6986I

Iso-buck operation principle

DS13647 - Rev 1

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