AN75

Issue 1 – January 2011

6

www.diodes.com

© Diodes Incorporated 2010

Free-wheel diode calculation

The free-wheel diode D

power loss. The maximum stress voltage rating of the free-wheel diode is the same as the MOSFET. It

is advisable to use ultra-low reverse recovery time T

switching ON loss. In the design example, 1A 600V rectifier, MUR160, is selected.

The worst case average current through the diode occurs at V

mA

202

V

373

V

42

1

mA

240

V

V

1

I

I

(max)

IN

(min)

LED

)

nom

(

LED

D(avg)

=

⎟

⎠

⎞

⎜

⎝

⎛ −

×

=

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

−

×

=

Assuming a constant forward voltage drop V

calculated,

mW

222

V

1

.

1

mA

202

V

I

P

F

)

avg

(

D

COND

_

D

=

×

=

×

=

Finally, the diode junction temperature without using the heat sink can be calculated from,

C

87

C

80

W

C

32

mW

222

T

θ

P

T

AMB

thJA

COND

_

D

j

o

o

o

=

+

×

=

+

×

=

The internal ambient temperature within the LED converter, T

W

C

is the thermal resistance for DO-201 package. For practical design, it is recommended to

keep the junction temperature below 110ºC to avoid temperature stress on the device.