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DI-93

C

6/06

Power Integrations

5245 Hellyer Avenue

San Jose, California 95138

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APPLICATIONS HOTLINE

APPLICATIONS FAX

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please visit www.powerint.com

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,

Filterfuse, PI Expert and PI FACTS are trademarks of Power Integrations, Inc. Other trademarks are property of their respective

companies. ©Copyright 2006, Power Integrations, Inc.

For the latest updates, visit

www.powerint.com

Figure 3. Available Output Power at 1 W and 3 W Input Power.

Figure 2. Active-Mode Efficiency Performance.

Figure 4. Conducted EMI to EN55022 B Limit, at Full Load,

with 115 VAC, 60 Hz Input Voltage.

Ten components enable load overvoltage and over-current

protection:C13,C16,D10,Q1,Q2,R9,R10,R11,R14andVR3.

They work with the latching shutdown function as follows:

– If the supply output voltage goes above 36 V, VR3 conducts

and turns on Q2, which shorts the secondary winding of

T1. After 30 ms of U1 receiving no feedback, the supply

latches off.

20

10

0

10

5

0

15

20

25

30

35

Output Power (W)

40

30

70

80

90

60

50

115 VAC Input

230 VAC Input

.75

.50

.25

.00

140

100

120

80

160

180

200

220

240

260

280

AC Input Voltage

1.25

1.00

2.00

2.25

2.50

1.75

1.50

= 1 W Input Power

= 3 W Input Power

1.0

0.15

10.0

-100.0

-20

-10

0

10

20

30

40

50

60

80

70

MHz

– If the load pulls peak current for longer than the RC time

constant (≈ 60 ms) of C13 and R10, Q1 turns on, which turns

Q2 on and shorts the secondary winding of T1. Again, after

30 ms of U1 receiving no feedback, the supply latches off.

Capacitor C17 attenuates differential-mode conducted EMI.

Resistor R15 dampens high frequency ringing.

Key Design Points

• The value of C7 sets the reset time of the latched shutdown

function, once the AC input is removed. Verify that the

latch resets, within the time allowed, at the highest input

voltage.

• For thermal considerations, the PeakSwitch IC, the output

diode and their heatsinks, and the transformer core size

depend on the continuous-to-peak power ratio, and the

duration and frequency of the peak power pulses.

• Choose the values for R10 and C13 so that normal peak

loads will not turn Q1 on. However, do not set the RC

time constant so long that the supply does not latch off

within the 60 seconds specified by IEC 60950-1, section

2.5, Table 2B (Limited Power Sources requirements).