LNK302/304-306
from AC input lines. It may be advantageous to place capacitors
C4 and C1 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.
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 ±00 °C or below.
This figure ensures adequate margin due to variations in
RDS(ON) from part to part. A battery powered thermocouple
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.
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:
±. 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 31 ns or better,
such as the BYV26C, is recommended.
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).
8
Rev. J 06/13
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