AN3286 datasheet(11/42 Pages) STMICROELECTRONICS

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AN3286

Testing the board

Doc ID 17998 Rev 1

11/42

Testing the board

2.1

Typical board waveforms

The VIPer25 is operated in quasi-resonant mode. The ZCD (zero current detect) pin is able

to sense the transformer demagnetization and switch on the MOSFET on the valley of the

drain voltage ringing that follows the transformer demagnetization.

The converter has been designed so that in full load condition the MOSFET is always

switched on, on the first valley of the transformer demagnetization, within the entire input

voltage range. This operation mode is referred to as “quasi-resonant”, or “boundary”

between discontinuous conduction mode (DCM) and continuous conduction mode (CCM).

Figure 5 and 6 show drain current and voltage waveforms at nominal input voltages

(115 VAC and 230 VAC) and maximum load (2 A). Figure 7 and 8 show the same waveforms

in the same load condition, but at minimum and maximum input voltage respectively.

Figure 5.

Drain current and voltage at max.

load 115 VAC

Figure 6.

Drain current and voltage at max.

load 230 VAC

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