LNK353/354
of the diode for heatsinking. 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-HF
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
DS
does not exceed
675 V at the highest input voltage and peak (overload) output
power.
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
LIMIT(MIN)
at the
end of the t
LEB(MIN)
. Under all conditions, the maximum drain
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-HF,
transformer, output diode, and output
capacitors. Enough thermal margin should be allowed for
part-to-part variation of the R
DS(ON)
of
LinkSwitch-HF
as
specified in the data sheet. Under low line, maximum power,
a maximum
LinkSwitch-HF
SOURCE pin temperature of
100 °C is recommended to allow for these variations.
Design Tools
Up-to-date information on design tools can be found at the
Power Integrations website:
www.powerint.com.
TOP VIEW
Input Filter
Capacitor
Y1-
Capacitor
+
HV DC
Input
T
r
a
n
s
f
o
r
m
e
r
DC
Out
+
-
-
Output Filter
Capacitor
SEC
PRI
S
S
D
LinkSwitch-HF
Opto-
coupler
S
S
BP
FB
Maximize hatched copper
areas (
) for optimum
heatsinking
PI-3890-102704
C
BP
Figure 6. Recommended Printed Circuit Layout for LinkSwitch-HF in a Flyback Converter Configuration.
6
F
2/05
POWERINT [ POWER INTEGRATIONS, INC. ]
