LNK362-364

C

12/05

7

Optocoupler

Place the optocoupler physically close to the LinkSwitch-XT to

minimize the primary-side trace lengths. Keep the high current,

high voltage drain and clamp traces away from the optocoupler

to prevent noise pick up.

Output Diode

For best performance, the area of the loop connecting the

secondary winding, the output diode and the output filter

capacitor should be minimized. In addition, sufficient copper

area should be provided at the anode and cathode terminals

of the diode for heat sinking. A larger area is preferred at the

quiet cathode terminal. A large anode area can increase high

frequency radiated EMI.

Quick Design Checklist

As with any power supply design, all LinkSwitch-XT designs

should be verified on the bench to make sure that component

specifications are not exceeded under worst-case conditions.The

following minimum set of tests is strongly recommended:

1. Maximum drain voltage – Verify that V

650 V at the highest input voltage and peak (overload) output

power. The 50 V margin to the 700 V BV

gives margin for design variation, especially in Clampless

designs.

2. Maximum drain current –At maximum ambient temperature,

maximum input voltage and peak output (overload) power,

verify drain current waveforms for any signs of transformer

saturation and excessive leading-edge current spikes at

startup. Repeat under steady state conditions and verify that

the leading-edge current spike event is below I

end of the t

current should be below the specified absolute maximum

ratings.

3. Thermal Check – At specified maximum output power,

minimum input voltage and maximum ambient temperature,

verify that the temperature specifications are not exceeded

for LinkSwitch-XT, transformer, output diode and output

capacitors. Enough thermal margin should be allowed for

part-to-part variation of the R

specified in the data sheet. Under low line, maximum power,

a maximum LinkSwitch-XT SOURCE pin temperature of

105 °C is recommended to allow for these variations.

Design Tools

Up-to-date information on design tools can be found at the

Power Integrations web site: www.powerint.com.