SSL1623PH Datasheet, PDF (6/15 Pages) NXP Semiconductors – SMPS ICs for mains LED drivers

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_o of 80 V. This voltage is the output voltage V_o (see
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.
primary
stroke
secondary
stroke
secondary
ringing
drain
valley
secondary
stroke
RC
oscillator
regulation level
Fig 3.
A: Start of new cycle with valley switching.
B: Start of new cycle in a classical system.
Signals for valley switching
A
B
col007
SSL1623PH_1
Product data sheet
Rev. 01 — 15 September 2008
© NXP B.V. 2008. All rights reserved.
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