NUD4011

http://onsemi.com

5

APPLICATION INFORMATION (continued)

Design Guide for AC Applications

1. Define LED’s current:

sheet:

a. Per example in Figure 6,

totally different than for DC. This is because

current conduction only occurs during the time

peak current value and the conduction time.

a. Calculate

Sin

q

90 V = (120

2)

Sin

q

q = 32.027°

b. Calculate conduction time for

q = 32.027°. For

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)

2

= 5.37 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:

duty cycle;

If 8.33 ms is 100% duty cycle, then 5.37 ms is

64.46%, then:

Figure 6. 120 Vac Application

(Series LED’s array)

PWM

Current

Set Point

NUD4011

Boost

1

2

3

4

8

7

6

5

Full

Bridge

Rectifier

120 Vac

60 Hz

−

+

1

23

4

6. Calculate Power Dissipation on the NUD4011

device’s driver:

0.030 A

7. Establish Power Dissipation on the

NUD4011device’s control circuit per below

formula:

8. Calculate Total Power Dissipation on the device:

Figure 3), then select the most appropriate

recourse and repeat steps 1−8:

d. Use external resistors or parallel device’s

configuration

10. Calculate the junction temperature using the

thermal information on Page 8 and refer to

Figure 4 to check the output current drop due to

the calculated junction temperature. If desired,