NUD4011DR2G Просмотр технического описания (PDF) - ON Semiconductor

Номер в каталоге

Компоненты Описание

производитель

NUD4011DR2G

Low Current LED Driver

ON Semiconductor 

NUD4011

APPLICATION INFORMATION (continued)

Design Guide for AC Applications

1. Define LED’s current:

a. ILED = 30 mA

2. Define Vin:

a. Per example in Figure 5, Vin = 120 Vac

3. Define VLED @ ILED per LED supplier’s data

sheet:

a. Per example in Figure 6,

VLED = 3.0 V (30 LEDs in series)

VLEDs = 90 V

4. Calculate Resistor Value for Rext:

The calculation of the Rext for AC applications is

totally different than for DC. This is because

current conduction only occurs during the time

that the ac cycles’ amplitude is higher than VLEDs.

Therefore Rext calculation is now dependent on the

peak current value and the conduction time.

a. Calculate q for VLEDs = 90 V:

V = Vpeak Sin q

90 V = (120 Ǹ2) 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

c. Calculate the Ipeak needed for I(avg) = 30 mA

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:

I(avg) = Ipeak duty cycle;

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

64.46%, then:

Ipeak = I(avg) / duty cycle

Ipeak = 30 mA / 0.645 = 46 mA

d. Calculate Rext

Rext = 0.7 V / Ipeak

Rext = 15.21 W

5. Calculate Vdrop across the NUD4011 device:

a. Vdrop = Vin – Vsense – VLEDs

b. Vdrop = 120 V – 0.7 V – 90 V

c. Vdrop = 29.3 V

Full

Bridge

Rectifier 1

Vin

1

Boost

2

3

2

Rext

+

4

−

120 Vac

60 Hz

3

PWM

4

NUD4011

Current

Set Point

Iout

8

Iout

7

Iout

6

Iout

5

LED1

LED2

LED30

Figure 6. 120 Vac Application

(Series LED’s array)

6. Calculate Power Dissipation on the NUD4011

device’s driver:

a. PD_driver = Vdrop * I(avg)

b. PD_driver = 29.3 V 0.030 A

c. PD_driver = 0.879 W

7. Establish Power Dissipation on the

NUD4011device’s control circuit per below

formula:

a. PD_control = (Vin – 1.4 – VLEDs)@ / 20,000

b. PD_control = 0.040 W

8. Calculate Total Power Dissipation on the device:

a. PD_total = PD_driver + PD_control

b. PD_total = 0.879 W + 0.040 W = 0.919 W

9. If PD_total > 1.13 W (or derated value per

Figure 3), then select the most appropriate

recourse and repeat steps 1−8:

a. Reduce Vin

b. Reconfigure LED array to reduce Vdrop

c. Reduce Iout by increasing Rext

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,

compensate it by adjusting the value of Rext.

http://onsemi.com

5

Share Link: