SSL1623PH_1

© NXP B.V. 2008. All rights reserved.

Product data sheet

Rev. 01 — 15 September 2008

6 of 15

NXP Semiconductors

SSL1623PH

As soon as the oscillator voltage is high again and the secondary stroke has ended, the

circuit waits for a low drain voltage before starting a new primary stroke.

The primary stroke starts some time before the actual valley at low ringing frequencies,

and some time after the actual valley at high ringing frequencies. Figure 4 shows a typical

curve for a reflected voltage N

× V

Figure 5) transferred to the primary side of the transformer with the factor N (determined

by the turns ratio of the transformer). Figure 4 shows that the system switches exactly at

minimum drain voltage for ringing frequencies of 480 kHz, thus reducing the switch-on

losses to a minimum. At 200 kHz, the next primary stroke is started at 33

° before the

valley. The switch-on losses are still reduced significantly.

A: Start of new cycle with valley switching.

B: Start of new cycle in a classical system.

Fig 3.

Signals for valley switching

col007

drain

valley

secondary

ringing

secondary

stroke

primary

stroke

secondary

stroke

RC

oscillator

regulation level

A

B