LNK500
3. Thermal check – At peak output power, minimum input
voltage and maximum ambient temperature, verify that the
temperaturespecifications are not exceededfor LinkSwitch,
transformer, output diode and output capacitors. Enough
thermalmarginshouldbeallowedforpart-to-partvariationof
theRDS(ON) ofLinkSwitchasspecifiedinthedatasheet. Under
lowline, peakpower, amaximumLinkSwitchSOURCEpin
temperature of 100 °C is recommended to allow for these
variations.
Quick Design Checklist
As with any power supply design, all LinkSwitch designs
should be verified on the bench to make sure that component
specifications are not exceeded under worst case conditions.
Note: In a LinkSwitch circuit, the SOURCE is a switching
node. This should be taken into consideration during testing.
Oscilloscopemeasurementsshouldbemadewithprobegrounded
to DC voltages such as primary return or DC rail but not to
SOURCE.Powersupplyinputvoltageshouldalwaysbesupplied
using an isolation transformer. The following minimum set of
tests is strongly recommended:
4. Centered output characteristic – Using a transformer with
nominalprimaryinductanceandataninputvoltagemidway
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,
maximuminputvoltageandpeakoutputpower, verifydrain
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 website: 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.
D
10 2/05
POWERINT [ Power Integrations ]
