LNK500
Quick Design Checklist
3. Thermal check – At peak output power, minimum input
voltage and maximum ambient temperature, verify that the
temperature specifications are not exceeded for LinkSwitch,
transformer, output diode and output capacitors. Enough
thermal margin should be allowed for part-to-part variation
of the RDS(ON) of LinkSwitch as specified in the data sheet.
Under low line, peak power, a maximum LinkSwitch
SOURCE pin temperature of 100 °C is recommended to
allow for these variations.
Aswithanypowersupplydesign,allLinkSwitchdesignsshould
be verified on the bench to make sure that component
specifications are not exceeded under worst case conditions.
Note:Ina LinkSwitch circuit, theSOURCEisaswitchingnode.
This should be taken into consideration during testing.
Oscilloscope measurements should be made with probe
grounded to DC voltages such as primary return or DC rail but
not to SOURCE. Power supply input voltage should always be
suppliedusinganisolationtransformer. Thefollowingminimum
set of tests is strongly recommended:
4. Centered output characteristic – Using a transformer with
nominal primary inductance and at an input voltage midway
between low and high line, verify that the peak power point
occursatthedesirednominaloutputcurrent, withthecorrect
output voltage. If this does not occur then the design should
be refined to ensure the overall tolerance limits are met.
1. Maximum drain voltage – Verify that VDS does not exceed
675 V at highest input voltage and peak output power.
2. Maximumdraincurrent–Atmaximumambienttemperature,
maximum input voltage and peak output power, verify drain
current waveforms at start-up for any signs of transformer
saturation and excessive leading edge current spikes.
LinkSwitch has a minimum leading edge blanking time of
200 ns to prevent premature termination of the on-cycle.
Verify that the leading edge current spike event is below
current limit at the end of the 200 ns blanking period.
Design Tools
Up to date information on design tools can be found at the
Power Integrations Web site: www.powerint.com.
Input Filter
Capacitor
D
S
C
+
LinkSwitch
HV DC
Input
-
S
S
S
S
Transformer
Y1-
Capacitor
-
DC Out
+
Output
Capacitor
PI-2900-070202
Figure 11. Recommended Circuit Board Layout for LinkSwitch using P Package.
B
3/03
10
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