Rev. J 06/13

8

LNK302/304-306

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from AC input lines. It may be advantageous to place capacitors

C4 and C5 in-between LinkSwitch-TN and the AC input. The

second rectifier diode D4 is optional, but may be included for

better EMI performance and higher line surge withstand

capability.

Quick Design Checklist

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

should be verified for proper functionality on the bench. The

following minimum tests are recommended:

1. Adequate DC rail voltage – check that the minimum DC input

voltage does not fall below 70 VDC at maximum load,

minimum input voltage.

2. Correct Diode Selection – UF400x series diodes are recom-

mended only for designs that operate in MDCM at an

ambient of 70

°C or below. For designs operating in

continuous conduction mode (CCM) and/or higher ambients,

then a diode with a reverse recovery time of 35 ns or better,

such as the BYV26C, is recommended.

3. Maximum drain current – verify that the peak drain current is

below the data sheet peak drain specification under worst-

case conditions of highest line voltage, maximum overload

(just prior to auto-restart) and highest ambient temperature.

4. Thermal check – at maximum output power, minimum input

voltage and maximum ambient temperature, verify that the

LinkSwitch-TN SOURCE pin temperature is 100

°C or below.

This figure ensures adequate margin due to variations in

R

meter is recommended to make measurements when the

SOURCE pins are a switching node. Alternatively, the

ambient temperature may be raised to indicate margin to

thermal shutdown.

In a LinkSwitch-TN design using a buck or buck-boost converter

topology, the SOURCE pin is a switching node. Oscilloscope

measurements should therefore be made with probe grounded

to a DC voltage, such as primary return or DC input rail, and not

to the SOURCE pins. The power supply input must always be

supplied from an isolated source (e.g. via an isolation transformer).