7

NR021506

HV9925

Step 1. Calculating L1.

The output voltage V

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

Select L1 68mH, I=30mA. Typical SRF = 170KHz. Calculate

the coil capacitance.

Step 2. Selecting D1

Usually, the reverse recovery characteristics of ultra-

fast rectifiers at I

manufacturer’s data books. The designer may want to

experiment with different diodes to achieve the best result.

Select D1 MUR160 with V

= 100mA) and C

Step 3. Calculating total parasitic capacitance using:

(3)

Step 4. Calculating the leading edge spike duration using:

(4), (5)

Step 5. Estimating power dissipation in HV9925 at 264VAC

using (8) and (10)

Let us assume that the overall efficiency η = 0.7.

Switching power loss:

Switching power loss:

Minimum duty ratio:

Minimum duty ratio:

Conduction power loss:

Conduction power loss:

Total power dissipation at V

Total power dissipation at V

AC(max)

AC(max)

Total power dissipation at V

Total power dissipation at V

Total power dissipation at V

Total power dissipation at V

:

Step 6. Selecting input capacitor C

IN

Select C

Metalized Polyester Film).

Design Example 2

Let us now design a PWM-dimmable LED lamp driver using

the HV9925:

Input:

Universal AC, 85-135VAC

Output Current: 50mA

Load:

®

®

OSRAM, V

The schematic diagram of the LED driver is shown in Fig.3.

We will use an aluminum electrolytic capacitor for C

to prevent interruptions of the LED current at zero crossings

of the input voltage. As a“rule of thumb”, 2~3μF per each

watt of the input power is required for C

Step 1. Calculating L1.

The output voltage V

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

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

the coil capacitance.

Step 2. Selecting D1

Select D1 ES1G with V

Step 3. Calculating total parasitic capacitance using: (3)

Step 4. Calculating the leading edge spike duration using

(4), (5)

Step 5. Estimating power dissipation in HV9925 at 135VAC

using (6), (7) and (9)

Switching power loss:

Switching power loss:

L

V

s

mA

mH

1

41 10

0 3 20

68

=

⋅

⋅

=

µ

.

C

L

SRF

mH

KHz

pF

⋅

⋅

=

⋅

⋅

≈

1

1 2

1

68

2 170

13

2

2

(

)

(

)

π

π

C

pF

pF

pF

pF

pF

+

+

+

=

5

5

13

8

31

T

V

pF

mA

ns

ns T

SPIKE

BLANK MIN

=

⋅

⋅

+

≈

<

264

2 31

100

20

136

(

)

P

mW

P

s

V

pF

mA

ns

V

V

⋅

⋅

+ ⋅

⋅

(

)

−









1

2 10

264

31

2 100

20

264

41

0 7

µ

.

D

V

V

⋅

⋅

≈

0 71 41

0 7 264

0 16

.

/( .

)

.

P

mA

A

V

mW

⋅

(

+

⋅

⋅

≈

0 25 20

210

0 63 200

264

55

2

.

.

Ω

µ

P

mW

mW

mW

+

=

125

55

180

Output Power

=

⋅

=

41 20

820

V

mA

mW

L

V

s

mA

mH

1

30

10 5

0 3 50

21

=

⋅

⋅

=

.

.

µ

C

L

SRF

mH

KHz

pF

⋅

⋅

=

⋅

⋅

≈

1

1 2

1

22

2 270

15

2

2

(

)

(

)

π

π

T

V

pF

mA

ns

ns T

SPIKE

BLANK MIN

=

⋅

⋅

+

≈

<

135

2 35

100

35

100

(

)

C

pF

pF

pF

pF

pF

+

+

+

=

5

5

13

8

31

F

V

V

V

s

kHz

⋅

−

⋅

⋅

=

135

2 30

0 7

135

2 10

78

/ .

µ