SSL2102 Datasheet, PDF (7/21 Pages) NXP Semiconductors – Mains LED driver IC for dimmable LED lighting

NXP Semiconductors
SSL2102
SMPS IC for dimmable LED lighting
8.4 Bleeder for dimming applications
The SSL2102 IC contains some circuitry intended for mains dimmer compatibility. This
circuit contains two current sinks that are called bleeders. A strong bleeder is used for
zero-cross reset of the dimmer and TRIAC latching. A weak bleeder is added to maintain
the hold current through the dimmer.
The strong bleeder switch is switched on when the maximum voltage on the WBLEED pin
and the SBLEED pin is below the V_th(SBLEED) level (52 V typically). The weak bleeder
switch is switched on as soon as the voltage on pin ISENSE exceeds the V_{th(high)(ISENSE)}
level (−100 mV typically). The weak bleeder switch is switched off when the ISENSE
voltage drops below the V_{th(low)(ISENSE)} level (−250 mV typically). The weak bleeder switch
is also switched off when the strong bleeder switch is switched on. See Figure 5.
WBLEED
M2
SBLEED
D2
Q
SR
I1
20 µA
B1
LOW V DETECT
D3
Integrated
M1
−0.1 V
OR
−0.25 V
ISENSE
Fig 5. Bleeder circuit
GND
014aaa571
8.5 Valley switching
A new cycle is started when the primary switch is switched on (see Figure 6). After a time
determined by the oscillator voltage, RC and the internal regulation level, the switch is
turned off and the secondary stroke starts. The internal regulation level is determined by
the voltage on pin PWMLIMIT.
After the secondary stroke, the drain voltage shows an oscillation with a frequency of
approximately:
-----------------------¹-----------------------
(2)
2 × π × (L_p × C_p)
where:
L_p = primary self inductance
C_p = parasitic capacitance on drain node
SSL2102_1
Product data sheet
Rev. 01 — 29 June 2009
© NXP B.V. 2009. All rights reserved.
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