nud4011 ON Semiconductor, nud4011 Datasheet - Page 5

• Manufacturer Part Number: nud4011
• Description: Low Current Led Driver
• Manufacturer: ON Semiconductor

Design Guide for AC Applications
1. Define LED’s current:
2. Define V
3. Define V
4. Calculate Resistor Value for R
5. Calculate V
sheet:
The calculation of the R
totally different than for DC. This is because
current conduction only occurs during the time
that the ac cycles’ amplitude is higher than V
Therefore R
peak current value and the conduction time.
a. I
a. Per example in Figure 5, V
a. Per example in Figure 6,
a. Calculate q for V
b. Calculate conduction time for q = 32.027°. For
c. Calculate the I
d. Calculate R
a. V
b. V
c. V
a sinuousoidal waveform Vpeak happens at
q = 90°. This translates to 4.165 ms in time for
a 60 Hz frequency, therefore 32.027° is 1.48 ms
and finally:
Conduction time = (4.165 ms – 1.48 ms)
Since a full bridge rectifier is being used (per
Figure 6), the frequency of the voltage signal
applied to the NUD4011 device is now 120 Hz.
To simplify the calculation, it is assumed that
the 120 Hz waveform is square shaped so that
the following formula can be used:
If 8.33 ms is 100% duty cycle, then 5.37 ms is
64.46%, then:
LED
drop
drop
drop
V
V
V = V
90 V = (120
q = 32.027°
I
I
I
R
R
(avg)
peak
peak
ext
ext
LED
LEDs
= 30 mA
in
= V
LED
= 120 V – 0.7 V – 90 V
= 29.3 V
:
= 0.7 V / I
= 15.21 W
= I
= 30 mA / 0.645 = 46 mA
= I
drop
ext
peak
= 3.0 V (30 LEDs in series)
in
= 90 V
@ I
(avg)
peak
ext
– V
calculation is now dependent on the
across the NUD4011 device:
LED
peak
sense
/ duty cycle
Sin q
LEDs
= 5.37 ms
peak
per LED supplier’s data
needed for I
duty cycle;
2 )
– V
ext
= 90 V:
for AC applications is
LEDs
Sin q
APPLICATION INFORMATION (continued)
in
ext
= 120 Vac
:
(avg)
= 30 mA
http://onsemi.com
LEDs
2
.
5
+
−
120 Vac
60 Hz
10. Calculate the junction temperature using the
Rectifier
6. Calculate Power Dissipation on the NUD4011
7. Establish Power Dissipation on the
8. Calculate Total Power Dissipation on the device:
9. If P
Bridge
2
device’s driver:
NUD4011device’s control circuit per below
formula:
Figure 3), then select the most appropriate
recourse and repeat steps 1−8:
thermal information on Page 8 and refer to
Figure 4 to check the output current drop due to
the calculated junction temperature. If desired,
compensate it by adjusting the value of R
Full
a. P
b. P
c. P
a. P
b. P
a. P
b. P
a. Reduce V
b. Reconfigure LED array to reduce V
c. Reduce I
d. Use external resistors or parallel device’s
configuration
D_total
D_driver
D_driver
D_driver
D_control
D_control
D_total
D_total
1
4
Figure 6. 120 Vac Application
> 1.13 W (or derated value per
3
(Series LED’s array)
= P
= 0.879 W + 0.040 W = 0.919 W
out
= V
= 29.3 V
= 0.879 W
in
= (V
= 0.040 W
D_driver
by increasing R
PWM
Boost
drop
R
in
V
ext
1
2
3
4
in
– 1.4 – V
* I
+ P
(avg)
0.030 A
Set Point
D_control
NUD4011
Current
LEDs
ext
)@ / 20,000
L
L
L
drop
ED30
I
I
I
I
ED1
ED2
out
out
out
out
8
7
6
5
ext
.