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CV Power Adapter
Application Adapter Device LNK362P
Design Idea DI-89 (R) 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 ClamplessTM 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 PIs 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 PIs Clampless transformer techniques, which uses T1s 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 A) is received within a 40 ms period, U1 goes into autorestart 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 F 16 V D5 1N4934 VR1 BZX79B5V1 5.1 V, 2% R3 390 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 F 400 V
C2 3.3 F 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
DI-89 Key Design Points
* * * * * * The PI Xls spreadsheet calculates all of the parameters required to specify and build transformer T1. The power transformer must have a two layer primary winding to ensure that its intra-winding capacitance is sufficient for Clampless operation. The reflected output voltage (VOR) of this design was kept < 90 V (74 V) for Clampless operation. Since this supply has a Clampless drain node, it must be verified that the maximum drain voltage does not exceed 650 V when the flyback voltage spike occurs. The primary current ripple-to-peak ratio (KP) factor should be > 1 (ensures discontinuous conduction mode operation) to minimize conducted EMI. The maximum operating flux density (BM) was kept < 1500 Gauss to eliminate audible.
0.12 0.1
68 66
Efficiency (%)
64 62 60
58
85 VAC 115 VAC 230 VAC 265 VAC EPA Std
56 54
0
0.5
1
1.5
2
2.5
Output Power (W)
Figure 3. Harmonized (EPA, CEC) Active-Mode Efficiency vs. Output Power (25, 50, 75 & 100%).
PI-4235-110805
Input Power (W)
0.08
70 60
Amplitude (dBV)
0.06 0.04 0.02 0
50 40 30 20 -10 0 -10 -20 0.15 1 10 30
0
50
100
150
200
250
300
Input Voltage (VAC)
Figure 2. No-load Input Power Consumption vs. Input Voltage.
Frequency (MHz) Figure 4. Conducted EMI Scan to EN55022B Limits: Full-Load, 115 VAC, 60 Hz Input, with Artificial Hand.
For the latest updates, visit www.powerint.com Power Integrations reserves the right to make changes to its products at any time to improve reliability or manufacturability. Power Integrations does not assume any liability arising from the use of any device or circuit described herein. POWER INTEGRATIONS MAKES NO WARRANTY HEREIN AND SPECIFICALLY DISCLAIMS ALL WARRANTIES INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF THIRD PARTY RIGHTS. The products and applications illustrated herein (transformer construction and circuits external to the products) may be covered by one or more U.S. and foreign patents or potentially by pending U.S. and foreign patent applications assigned to Power Integrations. A complete list of Power Integrations' patents may be found at www.powerint.com. Power Integrations grants its customers a license under certain patent rights as set forth at http://www.powerint.com/ip.htm.
The PI logo, TOPSwitch, TinySwitch, LinkSwitch, DPA-Switch, EcoSmart, Clampless, E-Shield, Filterfuse, PI Expert and PI FACTS are trademarks of Power Integrations, Inc. Other trademarks are property of their respective companies. (c)Copyright 2005, Power Integrations, Inc.
Power Integrations
MAIN PHONE NUMBER +1 408-414-9200
A 11/05
5245 Hellyer Avenue
APPLICATIONS FAX +1 408-414-9760
San Jose, California 95138
For a complete listing of worldwide sales offices, please visit www.powerint.com
APPLICATIONS HOTLINE +1 408-414-9660
www.powerint.com
PI-4237-110805
80
PI-4236-110805

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