LNK403-409/413-419
7 W High Power Factor Non-Dimmable LED Driver
Design Example with Enhanced Line Regulation
pin provides excellent line regulation over the entire 90 VAC to
265 VAC input range.
The circuit schematic in Figure 7 shows a high power-factor
LED driver based on a LNK413EG from the LinkSwitch-PH
family of devices. It was optimized to drive an LED string at a
voltage of 21 V with a constant current of 0.33 A, ideal for
PAR20/PAR30 lamp retro-fit applications. The design operates
over the universal input voltage range of 90 VAC to 265 VAC
and is a non-dimming application. A non-dimming application
has tighter output current variation with changes in the line
voltage than a dimming application. It’s key to note that, although
not specified for dimming, no circuit damage will result if the
end user does operate the design with a phase controlled
dimmer.
The VOLTAGE MONITOR pin current is also used by the device
to set the line input overvoltage and undervoltage protection
thresholds.
Diode D1 and VR1 clamp the drain voltage to a safe level due to
the effects of leakage inductance. A Zener clamp was selected
for lowest component count and highest efficiency. Diode D5 is
necessary to prevent reverse current from flowing through U1
during the period when the AC input voltage is lower than the
reflected output voltage (VOR). A space efficient RM6 core was
selected for this design. The RM core geometry helps
minimizes audible noise but requires the use of flying leads to
meet safety spacing requirements.
Circuit Description
Diode D3, C6, R5, R9 and R18 create the primary bias supply
from an auxiliary winding on the transformer. Resistor R5
provides filtering of leakage inductance generated voltage
spikes to improve tracking of the bias and output voltages. It
also forms a pole with C6 at ~100 Hz. Resistors R9 and R18
act as a small load to ensure that the bias voltage collapses
during output short-circuit when U1 enters auto-restart
operation to protect the supply.
Input Stage
Fuse F1 provides protection from component failures while RV1
provides a clamp during differential line surges, keeping the
peak drain voltage of U1 below the 725 V rating of the internal
power FET. Bridge rectifier BR1 rectifies the AC line voltage.
EMI filtering is provided by L1-L3, C2 together with the safety
rated Y class capacitor (C7) that bridges the safety isolation
barrier between primary and secondary. Resistor R2 and R3
act to damp any resonances formed between L1, L2, C2 and
the AC line impedance. A small bulk capacitor (C3) is required
to provide a low impedance source for the primary switching
current. The maximum value of C2 and C3 is limited in order to
maintain a power factor of greater than 0.9.
Output overvoltage and load disconnection protection is
provided by D8, C14, R24, VR3, C15, R23 and Q2. Should the
output LED load become disconnected the output voltage will
rise causing an associated rise in the bias winding voltage
across C14. Once this exceeds the voltage rating of VR3, Q2
turns on pulling down the FEEDBACK pin of U1 and initiating
auto-restart operation. Once in auto-restart the low duty cycle
of operation (~3%) together with the small pre-load on the
output prevents the output voltage rising to a high level. Once
the output load is reconnected normal operation resumes.
LinkSwitch-PH Primary
To provide peak line voltage information to U1 the incoming
rectified AC peak charges C8 via D6. This is then fed into the
VOLTAGE MONITOR pin of U1 as a current via R4, R7 and R8.
The VOLTAGE MONITOR pin current and the FEEDBACK pin
current are used internally to control the average output LED
current. The combined value of R4, R7 and R8 (3.909 MW)
and R11, R12 (1.402 MW) connected to the VOLTAGE MONITOR
Capacitor C12 provides local decoupling for the BYPASS pin of
U1 which is the supply pin for the internal controller. During
C5
C4
R6
20 kΩ
150 µF 150 µF
21 V, 330 mA
35 V
35 V
FL1
1
FL2
L3
1000 µH
D2
MBRS4201T3G
D6
DL4007
VR1
P6KE200A
FL3
6
RTN
D1
UF4007
R5
75 Ω
C6
D3
DL4936
22 µF
R4
50 V
2 MΩ
BR1
DF06S-E3/45
600 V
2
R2
1%
1 kΩ
R18
R9
T1
RM6
R7
1 MΩ
1%
F1
3.15 A
10 kΩ 10 kΩ
L
D5
L1
R8
909 kΩ
1%
C3
100 nF
400 V
C8
1 µF
400 V
ES1D
1000 µH
C2
90 - 265
VAC
22 nF
D4
RV1
275 VAC
1N4148
275 VAC
L2
1000 µH
R10
3 kΩ
D
S
V
R15
150 kΩ
D8
R11
1.0 MΩ
1%
N
CONTROL
BAV21WS-7-F
LinkSwitch-PH
U1
LNK413EG
BP
R3
1 kΩ
VR3
ZMM5259B-7
39 V
Q2
MMBT3904
R
FB
R12
402 kΩ
1%
R19
24.9 kΩ
1%
C14
1 µF
50 V
C15
100 nF
50 V
C12
R24
10 kΩ
R23
1 kΩ
10 µF
10 V
C7
2.2 nF
250 VAC
PI-5991-101210
Figure 8. Schematic of an Isolated, Non-Dimmable, High Power Factor, Universal Input, 7 W LED Driver.
7
www.powerint.com
Rev. D 08/11
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