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 7 of 24
NXP Semiconductors
UM10812
SSL5301DB1233 230 V 36 W LED driver demo board
6. Functional description
6.1 Input filtering
Common-mode and differential mode filters are implemented to reduce common-mode or
differential mode noise (see Figure 7
). This noise originates from the HF switching
currents/voltages in the primary side of the converter. Filters prevent that it returns to the
mains. The common-mode filter is L5 (or L2), C14 and C34. The differential mode filter is
L1 (including leakage of L5), C2, C3, C8, and C9. The noise is also kept to a minimum by:
• Small primary current loop from C2 to pin 1 of T1, pin 3 of T1 to the drain of external
MOSFET Q1. Ground return from sense resistors R1, R2 back to ground of C2.
• Snubber components D3, R6, R46 and C1 closely parallel to pins 1 and 3 of T1
• To reduce capacitance to surroundings, the track length from pin 3 of T1 to the drain
of the external MOSFET must be small.
• Small secondary current loop from pin 10 of T1 to D19 and C10 and returning to pin 9
of T1
For the 36 W application, the value of capacitor C2 must be high enough to act as a buffer
for the HF currents flowing in the primary side through L
p
of T1. It must be low enough to
maintain a high PF. A value of 470 nF gives good results.
6.2 R
mains
detection (RMAINS pin)
The SSL5301T uses a detection level of 20 A to detect mains zero crossing. The input
current from the mains is derived from the mains input voltage via resistors R13, R14,
R15, R44 and R45.
For 230 V mains detection at maximum input mains, the resistor values are:
• R13, R14, and R15: 330 k
• R44 and R45: 0
The resulting mains zero crossing detection is: .
To remove unwanted noise at low input voltage levels, extra external filtering on the
RMAINS pin is realized with C7 = 220 pF.
To prevent non-detection of the zero crossing, an additional circuit on the mains input is
included. However, this circuit is only required if measurements are carried out on the
demo board using oscilloscope probes. The circuit is comprised of diodes D7 and D8,
resistors R16, R17, R18 and R69, capacitor C6, and transistor Q2. It is operational if 5 V
to 10 V is supplied externally to header S2 (with pins 2 and 3 of S3 shorted). It is also
operational when pins 1 and 2 of S3 are shorted.
6.3 Supply voltage
The SSL5301T supply voltage (V
CC
) is generated using an auxiliary winding, diode D5,
resistor R7, a 24 V Zener diode (D27), and transistor Q6.
OverVoltage Protection (OVP) is a latched protection. It is reached at a minimum supply
voltage of 28 V at the V
CC
pin, which corresponds to a 52 V LED voltage.
330 k 330 k
330 k+20 A
(12 pagine)
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