FC9922

2012. 10. 31

6/8

Revision No : 0

Step 1. Calculating L1.

The output voltage V

(1) assuming a 30% peak-to-peak ripple.

L1 = (30V • 10.5µs) / (0.3 • 50mA) = 21mH

Select L1 22mH, I = 60mA. Typical SRF = 270KHz. Calculate

the coil capacitance.

C

1

=

1

22mH

≈ 15pF

Step 2. Selecting D1

Select D1 MUR160 with V

(V

Step 3. Calculating total parasitic capacitance using (3)

C

Step 4. Calculating the leading edge spike duration using

(4), (5)

T

135V • √2 • 33pF

+ 50ns

100mA

≈ 113ns < T

BLANK(MIN)

Step 5. Estimating power dissipation in FC9922 at 135VAC

using (8) and (10)

Switching power loss:

P

1

(135V • 33pF + 2 • 100mA• 20ns)(135V - 30V)

2 • 10.5µs

0.7

P

Minimum duty ratio:

D

Conduction power loss:

P

2

• 200Ω + 0.62 • 200µA • 135V

P

Total power dissipation in FC9922:

P

Step 6. Selecting input capacitor C

N

Output Power = 30V • 50mA = 1.5W

Select C

Figure 2. Universal 85-265VAC LED Lamp Driver

C

IN

AC Line

85-265V

C

DD

3

FC9922

D1

L1

LED

D2

U1

D3

D4

D5

C

IN2

L

IN

VRD1

F1

C

O

VDD

DRAIN

GND

1

2