UM10812 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
User manual Rev. 1.1 — 15 October 2014 8 of 24
NXP Semiconductors
UM10812
SSL5301DB1233 230 V 36 W LED driver demo board
UnderVoltage LockOut (UVLO) is reached when V
CC
<V
CC(stop)
(maximum 10 V).
6.4 Charge pump and filter damping
The charge pump capacitor C38 is connected to the drain of MOSFET Q1. When Q1
switches off, capacitor C37 is charged using D21. Capacitor C37 and resistor R56
determine the time constant. The values of R56 and C37 are selected, so a time constant
of 700 s is achieved. This time constant is required to latch a Leading-Edge (LE) triac
dimmer correctly. When Q1 switches on, the charge return through C38 is via D22.
The MOSFET Q4 conducts when the voltage on capacitor C37 exceeds the gate Q4
threshold voltage (10 V). The damping resistance is R55 = 4.7 in series with R
DSon
of
Q4 (0.5 ). This total resistance is small to maintain high efficiency.
When MOSFET Q4 is not conducting (e.g. during zero crossings of the mains or when an
LE triac dimmer switches on), resistors R53 and R54 determine the series damping
(totaling 150 ). This relatively high value of resistance is required to limit inrush current.
It is also required to dampen the ringing of the differential mode filter.
6.5 RC damper and bleeding circuit
To ensure that sufficient current is flowing through the LE triac dimmer when the dimmer
switches on, resistors R49 and R50 and capacitor C36 are required. After the LE triac
dimmer has latched and is conducting, the total of the bleeder current + the converter
current is sensed across resistors R66 and R68. R63 / (R63 + R64) attenuates the
voltage across R66 // R68 which is supplied to the BLS pin. This voltage is controlled to
the regulation voltage V
th(reg)BLS
. In this way, the total of the bleeder current and the
converter current is kept constant. To ensure its conduction throughout the dimming
range, this current is set greater than the hold current of the triac dimmer. Capacitor C39
ensures that the regulation loop is fast, especially at low dimming levels.
To achieve a similar power distribution across R51 + R52 and MOSFET Q3, the bleeder
resistors R51 and R52 are 330 .
6.6 Output capacitor and filtering
A provision for RC snubber across the secondary diode has been made on Printed-Circuit
Board (PCB).
The RC snubber is not mounted on the SSL5301DB1233 demo board, because it is not
required for this board. If necessary, it can improve the high-frequency EMI performance.
However, depending on the values chosen for resistors R42 and R48 and capacitor C35,
the overall system efficiency decreases.
To get I
ripple
< 30 %, output capacitors C10 and C11 (470 F) are chosen. When
capacitors C10 and C11 are 2 1000 F, the ripple can be decreased to < 15 %.
When the demo board is not operational, resistor R41 discharges capacitors C10 and
C11.
Extra differential and common-mode filtering at the LED output is realized using inductor
L3 and capacitors C12 and C13.
(12 paginas)
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