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Design Idea DI-78 (R) LinkSwitch-HF Low Cost 1.6 W
CV/CC Charger/Adapter
Application Charger/Adapter Device LNK353 Power Output 1.6 W Input Voltage 85-265 VAC Output Voltage 5.2 V Topology Flyback
Design Highlights
* * * * * * * Low cost, low component count solution No-load power consumption <300 mW - meets worldwide energy efficiency requirements Low leakage current design, <10 A Universal AC input range - single design worldwide Secondary-side feedback gives accurate voltage and constant current output Small size and weight Meets EN55022 B EMI limits
through the use of transformer shield windings, a snubber (R4 and C9) across the output diode, and by the internal switching frequency jitter of LinkSwitch-HF. LinkSwitch-HF uses ON/OFF control to regulate the output. Current >49 A fed from the BYPASS pin capacitor C5 into the FEEDBACK pin disables the MOSFET for that switching cycle. To maximize efficiency, a Schottky diode (D7) is used to rectify the secondary. Filtering is provided by a low ESR capacitor C6 and for most battery chargers, no additional filtering is required. During CV operation the output voltage is determined by the sum of the Q1 VBE voltage and VR1. As the voltage increases above this level, Q1 is biased on and current is fed through the optocoupler LED, thus inhibiting switching cycles to maintain regulation. The transition to CC operation occurs when the voltage developed across R9 and R8 exceeds the LED forward voltage of U2 (~1 V). Resistors R7 and R8 limit the optocoupler current during transients. Resistor R5 limits the base current of Q1 and R6 provides a bias current through VR1 (~0.5 mA).
C10 100 pF Y1 C9 R4 680 pF 62 100 V L2 Bead R5 5.1 R6 1.2 k 5.2 V, 320 mA J3 C7 100 F 10 V Q1 2N3906 VR1 BZX79B5V1 5.1 V, 2%
Operation
The AC input is rectified and filtered and applied to one side of the primary winding. The other end of the primary is connected to the DRAIN pin of U1. During the on-time of U1, energy is stored in the transformer and delivered to the load when U1 switches off. A simple RCD clamp (D5, R2, C3 and R3) limits the peak drain voltage. A simple pi () filter formed by C1, L1 and C2 together with RF1 are sufficient to attenuate differential conducted EMI. Common mode and radiated EMI generation is minimized
C3 R3 2.2 nF 200 k 400 V BR1 MD5S 0.5 A, 600 V
1
C1 2.2 F 400 V R1 200 k
7
D7 10BQ060
RF1 J1 8.2 85-265 VAC J2
R2 200
4
6 NC NC T1 EP10 Lp = 900 H C6 470 F 10 V
C2 2.2 F 400 V
D5 1N4007G
D
R7 390 R8 100 1%
FB BP
L1 Bead
LinkSwitch-HF U1 LNK353
S
U2B PC817D C5 0.1 F 50 V
U2A PC817D R9 3 1/2 W
J4 RTN
PI-3899-072204
Figure 1. Schematic of a 1.6 W, 5.2 V Constant Voltage, 320 mA Constant Current Charger Using LNK353P.
DI-78
www.powerint.com
November 2004
DI-78 Key Design Points
* * Diode D5 should be a glass passivated type to guarantee a specified recovery time and should be used with R2 fitted to limit reverse pull-out current. Select the value of C1 and C2 to meet differential line surge withstand requirements.
PI-3900-070104
* * * *
Select the initial value of R9 using: R9 = VF(U2)/IO. Small adjustments may be made by changing the value of R8. Use an optocoupler with a high CTR (300% to 600%) to improve CC linearity and variability. For VR1 select a Zener series with a low test current. Inductor L2 and C7 are typically not required for battery loads.
225 200 175 150 125 100 75 50 25 0 0 50 100 150 200 250 300
PI-3902-070104
80 70 60 50 40
QP AV
250
dBV
30 20 10 0 -10 -20 0.15 1.0
Quasi Peak
Average
No-Load Input Power (mW)
10.0
70.0
Input Voltage (VAC) Figure 4. No-Load Input Power vs. Line Voltage.
MHz
Figure 2. Conducted EMI Plot, 230 VAC Input, Maximum Load and Output Return Connected to Artificial Hand Input of LISN.
PI-3901-070604
TRANSFORMER PARAMETERS
Core Material Bobbin Winding Details Primary Inductance EP10 (TDK PC40), gapped for AL of 54.1 nH/T2 EP10 Horizontal, 8-pin Shield 1: 23T, 38 AWG x 2, tape, Primary: 129T, 38 AWG, tape, Shield 2: 10T, 31 AWG x 2, tape, Secondary: 11T, 32 AWG triple insulated, tape 900 H 5%
6 5 4 3 2 1 0
Low Limit High Limit 85 VAC 265 VAC
Output Voltage (VDC)
0
80
160
240
320
400
Primary Resonant 900 kHz (minimum) Frequency Leakage Inductance 70 H (maximum)
Output Current (mA) Figure 3. V-I Output Characteristic.
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Table 1. Transformer Design Parameters.
Power Integrations may make changes to its products at any time. Power Integrations has no liability arising from your use of any information, device or circuit described herein nor does it convey any license under its patent rights or the rights of others. POWER INTEGRATIONS MAKES NO WARRANTIES HEREIN AND SPECIFICALLY DISCLAIMS ALL WARRANTIES INCLUDING, WITHOUT LIMITATIONS, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF THIRD PARTY RIGHTS. The products and applications illustrated herein (including circuits external to the products and transformer construction) 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. The PI logo, TOPSwitch, TinySwitch, LinkSwitch, DPA-Switch and EcoSmart are registered trademarks of Power Integrations. PI Expert and PI FACTS are trademarks of Power Integrations. Copyright 2004, Power Integrations
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