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AN1317 - APPLICATION NOTE

because the input voltage is too low to insure a proper operation of the converter, which is about to shut

down.

2.2 VIPer20 In Inverter Topology

The inverter schematic is derived from the Buck one of fig. 1 by just swapping the inductor L1 and the

free wheeling diode D3. The resulting schematic is given fig. 5. There is a major difference with the Buck

from a functional point of view : when the on chip Power MOSFET is turned on, the inductor L1 does not

charge anymore through the load but between the mains lines. The output load now gets all its energy

during the MOSFET off state, through the inductor L1 and the free wheeling diode D3.

As a consequence, the zener diode DZ1 is no more necessary because of two reasons:

• The charge of the tank capacitor C2, now independent from the load, is always possible.

always under control.

Compared to the Buck, the current flowing through the load is in the opposite direction so that the output

voltage becomes now negative. As a consequence, the output capacitor C5 polarity must be swapped

and the anode of the diode D2, supplying the VIPer20, must now be connected to the ground lead GND

Vd