LM3445-120VFLBK/NOPB National Semiconductor, LM3445-120VFLBK/NOPB Datasheet - Page 11

• Manufacturer Part Number: LM3445-120VFLBK/NOPB
• Description: PROGRAMMERS, DEVELOPMENT SYSTEMS
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3445-120VFLBK/NOPB

• Current - Output / Channel: 365mA
• Outputs And Type: 1, Isolated
• Voltage - Output: 20V
• Features: Dimmable, TRIAC Dimmable
• Voltage - Input: 90 ~ 135VAC
• Utilized Ic / Part: LM3445
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Experimental Results
The LED driver is designed to accurately emulate an incan-
descent light bulb and therefore behave as an emulated
resistor. The resistor value is determined based on the LED
string configuration and the desired output power. The circuit
then operates in open-loop, with a fixed duty cycle based on
a constant on-time and constant off-time that is set by select-
ing appropriate circuit components. Like an incandescent
lamp, the driver is compatible with both forward and reverse
phase dimmers.
NON-DIMMING PERFORMANCE
In steady state, the LED string voltage is measured to be 20.1
V and the average LED current is measured as 365 mA. The
120 Hz current ripple flowing through the LED string was
Note 2: Original Circuit: R14 = 1.50Ω; Modification A: R14 = 1.20Ω; Modification B: R14 = 1.00Ω; Modification C: R14 = 0.75Ω
DIMMING PERFORMANCE
The LED driver is capable of matching or exceeding the dim-
ming performance of an incandescent lamp. Using a simple
rotary TRIAC dimmer, smooth and near logarithmic dimming
# of LEDs
LED CURRENT, OUTPUT POWER VERSUS NUMBER OF LEDS FOR VARIOUS CIRCUIT MODIFICATIONS ( V
V
IN
100.00
104.97
110.03
115.00
120.05
125.02
129.99
135.04
89.98
95.03
4
6
8
(V
RMS
V
)
IN
115.0
110.1
105.2
100.4
95.5
90.7
85.2
80.2
75.1
70.8
(V
I
RMS
Original Circuit
LED
I
IN
513
365
276
)
MEASURED EFFICIENCY AND LINE REGULATION (6 LEDS, NO TRIAC DIMMER)
(mA
MEASURED EFFICIENCY AND LINE REGULATION DATA (WITH TRIAC DIMMER)
(mA)
64
67
70
73
76
78
81
83
85
86
RMS
)
P
(Note
OUT
7.11
7.32
7.34
P
10.44
11.02
5.44
6.03
6.62
7.24
7.90
8.55
9.21
9.84
IN
(W)
(W)
2)
V
19.9
19.8
19.7
19.6
19.6
19.5
19.4
19.3
19.2
19.1
O
Modification A
I
LED
(V)
627
435
334
V
V
(mA)
OUT
19.24
19.40
19.55
19.69
19.83
19.95
20.06
20.14
20.22
20.29
AC
, no Triac Dimmer)
(V)
P
11
OUT
(Note
8.83
9.09
9.16
I
(W)
LED
measured to be 182 mA
ripple is a function of the value of energy storage capacitors
connected across the output port and the TRIAC firing angle.
The ripple current can be reduced by increasing the value of
energy storage capacitor or by increasing the LED string volt-
age. With TRIAC dimmers, the ripple magnitude is directly
proportional to the input power and therefore reduces at lower
LED current.
The LED driver switching frequency is measured to be close
to the specified 78.5 kHz. The circuit operates with a constant
duty cycle of 0.28 and consumes near 9.2 W of input power.
The driver steady state performance for an LED string con-
sisting of 6 series LEDs without using a triac dimmer is
summarized in the following table.
performance is achieved. By varying the firing angle of the
TRIAC dimmer and measuring the corresponding input and
output parameters, the dimming performance of the demon-
stration board driving 6 LEDs is summarized in the table
below.
2)
222
244
267
291
315
340
365
389
412
433
(mA)
Modification B
I
LED
I
O
683
481
367
351
323
295
269
258
248
222
199
176
159
(mA)
(mA)
P
OUT
4.27
4.73
5.22
5.73
6.25
6.78
7.32
7.83
8.33
8.79
(W)
P
OUT
(Note
10.03
10.22
10.16
pk-pk
(W)
at full load. The magnitude of the
Efficiency (%) Power Factor
2)
78.5
78.5
78.8
79.1
79.1
79.3
79.5
79.6
79.8
79.7
Modification C
I
LED
805
566
431
(mA)
P
OUT
7.0
6.4
5.8
5.3
5.0
4.8
4.3
3.8
3.4
3.0
(W)
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P
IN
94.7
94.8
94.9
95.0
95.0
95.1
95.1
95.0
94.9
94.8
OUT
(Note
11.91
12.23
12.12
= 120
(W)
2)