SSL2101_4

© NXP B.V. 2009. All rights reserved.

Product data sheet

Rev. 04 — 28 August 2009

7 of 22

NXP Semiconductors

SSL2101

SMPS IC for dimmable LED lighting

8.4 Bleeder for dimming applications

The SSL2101 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 pin WBLEED and

(

−100 mV typically). The weak bleeder switch is switched off when the ISENSE voltage

switched off when the strong bleeder switch is switched on. See Figure 5.

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:

(2)

where:

Fig 5.

Bleeder circuit

014aaa571

WBLEED

SBLEED

D2

D3

20

µA

LOW V DETECT

Q

R

S

−0.1 V

−0.25 V

ISENSE

GND

M2

M1

I1

Integrated

B1

OR

1

2

π

×

L

p

C

p

×

()

×

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