CV Power Adapter
Application
Adapter
Device
LNK362P
Design Idea DI-89
®
LinkSwitch-XT
Low Cost 2 W
Power Output
2W
Input Voltage
85-265 VAC
Output Voltage
6.2 V
Topology
Flyback
Design Highlights
•
•
•
•
•
•
•
Low-cost, low parts-count CV solution: 20 components
Proprietary IC design and winding techniques enable a
Clampless™
drain-node
± 5% over-temperature threshold – with hysteretic
recovery – keeps PCB temperatures below safety limits
Auto-restart: output short circuit and open loop protection
IC creepage > 3.2 mm: no arcing in humid environments
Easily meets all EPS energy efficiency standards
Meets CISPR-22 Class B EMI with sufficient margin
the ringing of the filter. Switching frequency jitter and
PIʼs
E-Shield
transformer construction technology enable
this design to meet EN55022 Class-B conducted EMI with
good margin (see Figure 4). Y capacitor C4 (optional) can
improve the unit-to-unit repeatability of EMI scans.
This supply also takes advantage of PIʼs
Clampless
transformer
techniques, which uses T1ʼs primary winding capacitance to
clamp the voltage spike that its leakage inductance causes,
each time the MOSFET in U1 turns off. Therefore, this
converter has no primary clamp components connected to
the drain-node.
From no-load until maximum output power (2 W) is delivered,
the LNK362P (U1) regulates the output voltage by skipping
switching cycles, based on the current delivered into the
feedback (FB) pin. If the output is over loaded and no feedback
(< 49
µA)
is received within a 40 ms period, U1 goes into auto-
restart mode. In auto-restart, MOSFET switching is enabled
for about 40 ms approximately every 800 ms if no feedback
is received within the 40 ms window of enabled switching.
C4*
100 pF
250 VAC
T1
EE16 9
C5
330
µF
16 V
D5
1N4934
VR1
BZX79-
B5V1
5.1 V, 2%
R3
390
Ω
1/8 W
R2
1k
1/8 W
6.2 V,
322 mA
J3-1
Operation
This
LinkSwitch-XT
based flyback converter (Figure 1) provides
2 W of tightly regulated constant voltage (CV) output power,
while meeting the active-mode efficiency and no-load power
consumption requirements of all harmonized energy efficiency
(EPA, CEC) standards (see Figure 2 and Figure 3).
Diodes D1– D4 rectify the AC input. The resulting DC is filtered
by bulk storage capacitors C1 and C2. Components L1, L2, C1
and C2 form a conducted EMI noise filter. Resistor R1 dampens
L1
1 mH
4
5
3
8
NC NC
J1
RF1
8.2 k
2.5 W
D1
1N4005
D2
1N4005
R1
3.9 k
1/8 W
J3-2
85-265
VRMS
C1
3.3
µF
400 V
C2
3.3
µF
400 V
U2
PC817A
J2
LinkSwitch-XT
U1
LNK362P
D3
1N4005
D4
1N4005
L2
1 mH
D
FB
BP
S
C3
100 nF
50 V
PI-4205-110805
*Optional component
Figure 1. LNK362 Based 6.2 V, 322 mA, 2 W, Low-cost, Flyback CV Output Power Adapter.
DI-89
www.powerint.com
November 2005
POWERINT [ POWER INTEGRATIONS, INC. ]
