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SSL2102T/DB/FLYB120V,598

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SSL2102 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Product data sheet Rev. 1.1 — 2 December 2011 7 of 22
NXP Semiconductors
SSL2102
Dimmable Greenchip driver for 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
.
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:
L
p
= primary self inductance
C
p
= parasitic capacitance on drain node
Fig 5. Bleeder circuit
014aaa571
WBLEED SBLEED
D2 D3
20 μA
LOW V DETECT
Q
RS
−0.1 V
−0.25 V
ISENSE GND
M2 M1
I1
Integrated
B1
OR
SSL2102 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Product data sheet Rev. 1.1 — 2 December 2011 8 of 22
NXP Semiconductors
SSL2102
Dimmable Greenchip driver for LED lighting
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.
Figure 6
shows the drain voltage together with the valley signal, the signal indicating the
secondary stroke and the RC voltage.
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 7 shows a typical curve for a reflected output voltage N at an output voltage of
80 V. This voltage is the output voltage transferred to the primary side of the transformer
with the factor N (determined by the turns ratio of the transformer). It 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 PWM system.
Fig 6. Signals for valley switching, flyback configuration
014aaa572
drain
valley
secondary
ringing
secondary
stroke
primary
stroke
secondary
stroke
RC
oscillator
regulation level
A
B
SSL2102 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Product data sheet Rev. 1.1 — 2 December 2011 9 of 22
NXP Semiconductors
SSL2102
Dimmable Greenchip driver for LED lighting
8.6 Demagnetization
The system operates in discontinuous conduction mode if the AUX pin is connected. As
long as the secondary stroke has not ended, the oscillator will not start a new primary
stroke. During the first t
sup(xfmr_ring)
seconds, demagnetization recognition is suppressed.
This suppression may be necessary in applications where the transformer has a large
leakage inductance and at low output voltages.
8.7 Overcurrent protection
The cycle-by-cycle peak drain current limit circuit uses the external source resistor
R
SENSE
1
to measure the current. The circuit is activated after the leading edge blanking
time t
leb
. The protection circuit limits the source voltage over the R
SENSE
resistor to
V
th(ocp)SOURCE
and thus limits the primary peak current.
8.8 Short-winding protection
The short-winding protection circuit is also activated after the leading edge blanking time.
If the source voltage exceeds the short-winding protection threshold voltage
V
th(swp)SOURCE
, the IC stops switching. Only a power-on reset will restart normal operation.
The short-winding protection also protects in case of a secondary diode short circuit.
8.9 Overtemperature protection
Accurate temperature protection is provided in the device. When the junction temperature
exceeds the thermal shut-down temperature, the IC stops switching. During thermal
protection, the IC current is lowered to the start-up current. The IC continues normal
operation as soon as the overtemperature situation has disappeared.
(1) At N V
o
=80V)
Fig 7. Typical phase of drain ringing at switch-on (at
0 200 400 800
f (kHz)
phase
(°)
40
20
−20
−40
0
014aaa573
600
1. R
SENSE
is the resistor between the SOURCE pin and GND
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SSL2102T/DB/FLYB120V,598

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Manufacturer:
NXP Semiconductors
Description:
LED Lighting Development Tools SSL Mains Dimmable LED Driver Demo
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