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6/06

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Power Integrations

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Power Integrations reserves the right to make changes to its products at any time to improve reliability or manufacturability. Power Integrations does

not assume any liability arising from the use of any device or circuit described herein. POWER INTEGRATIONS MAKES NO WARRANTY HEREIN AND

SPECIFICALLY DISCLAIMS ALL WARRANTIES INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A

PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF THIRD PARTY RIGHTS. The products and applications illustrated herein (transformer

construction and circuits external to the products) may be covered by one or more U.S. and foreign patents or potentially by pending

U.S. and foreign patent applications assigned to Power Integrations. A complete list of Power Integrations' patents may be found at

www.powerint.com. Power Integrations grants its customers a license under certain patent rights as set forth at http://www.powerint.com/ip.htm.

The PI logo, TOPSwitch, TinySwitch, LinkSwitch, DPA-Switch, PeakSwitch, EcoSmart, Clampless, E-Shield,

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companies. ©Copyright 2006, Power Integrations, Inc.

For the latest updates, visit

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Figure 2. Conducted EMI Plot of the Schematic Shown in

Figure 1 for 3 Strings of 4 LED's (10 V, 66.6 mA).

Figure 3. VI Characteristic of the Schematic Shown in

Figure 1.

Key Design Points

• The output is not safety isolated from the input.

• The circuit shown in Figure 1 has a total output current

tolerance of ±12% (including ∆t of 50 °C).

• To prevent noise coupling and to decrease EMI, place the

input filter components physically away from the source

node of the LinkSwitch-TN and L1 inductor. The DC input

filter capacitors C1 and C2 can be placed, as a barrier,

between the AC input and U1/L1.

adequatefilteringofthecurrentsensevoltage.Valuesabove

linearity.

• Select C5 based on the acceptable peak current through

the LEDs. Larger values of capacitance reduce peak LED

current. Typical values are 100 nF to 100 µF, low ESR.

With no capacitor the peak output current is equal to the

internal current limit of U1.

• With the values of R1 and R2 shown, the value of R3 is

calculated by R3 = 2 V / I

• The supply's total required output current is determined

by the number of LED strings in the load, and is limited

by the value of L1 and the current limit of U1. For this

circuit, the load should be ≤100 mA and ≤1.25 W total.

1.0

0.15

10.0

100.0

-20

-10

0

10

20

30

40

50

60

80

70

MHz

QP

AV

Average

Quasi-Peak

0

40

20

60

80

100

120

Output Current (mA)

10

15

5

0

20

25

AC Input = 85 V

AC Input = 265 V