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Design Idea DI-60 (R) LinkSwitch Low Cost 2.5 W
Regulated Charger/Adapter
Application Charger/Adapter Device LNK501 Power Output 2.5 W Input Voltage 85-265 VAC Output Voltage 5.5 V Topology Flyback
Design Highlights
* Replaces a linear transformer based power supply at the same or lower cost, with better output regulation * No-load input power consumption < 300 mW, at 230 VAC input: meets worldwide energy conservation guidelines * Extremely simple circuit - requires only 29 components! * Output voltage (CV) tolerance: 10% at peak power point * Output current (CC) tolerance: 25% when L 10% * Features short-circuit, open loop and thermal protection * Typically about 70% efficient! * Meets EN550022 B EMI without a Y-1 Safety capacitor * Ultra-low leakage current: < 5 A at 265 VAC input
The bias/feedback winding (T1, pins 3-4) provides U1 with CONTROL pin current. In CV mode, that current is controlled by the U2-phototransistor. At start-up and in CC mode, when U2 is OFF, R5 provides the current path. Diode D6 is in the return leg of the winding, making it shield the core from the primary winding. The bias winding and the primary-tosecondary shield winding (T1, pin 1) both reduce EMI. Resistor R3 and C4 reduce EMI. CONTROL pin capacitor C6 stores energy and supplies it back to U1 at start-up, determines the "restart attempt rate" in the auto-restart mode, shunts high frequency switching noise around U1 and provides U1 with the instantaneous MOSFET gate-drive current it requires. The combined voltages of VR1, R7 and the U2-LED determine the output voltage. Resistor R8 provides bias current to VR1. The output voltage can be fine-tuned by adjusting the values of R7 and R8. LinkSwitch solutions must only operate in discontinuous conduction mode. PO ~ 0.5 L I2f, where PO = Output Power, L = transformer primary inductance, I = LinkSwitch peak current, f = Switching frequency and = Efficiency. I2f is accurately controlled for LinkSwitch; therefore, PO is proportional to L.
Operation
Fusible resistor RF1 gives short-circuit fault protection and limits start-up inrush current. Inductors L1 and L2 and capacitors C1 and C2 form a low-cost pi () filter that attenuates conducted EMI. Transformer (T1) winding phasing and D7 orientation let no secondary winding current flow when the U1-MOSFET is ON, so the primary winding current stores its energy in the core of T1. When the U1-MOSFET turns OFF, the energy stored in T1 drives current out of the secondary winding, forward biasing D7, charging C7 and developing/maintaining the output voltage across C7. The RCD network of C3, D5, R1 and R2 clamps the flyback voltage across the primary winding, as the U1-MOSFET turns OFF.
D1-D4 1N4005 x 4 L1 1.0 mH C3 1 nF 500 V
T1 EE13 Lp = 2.36 mH 8
D7 11DQ06
5.5 V, 0.45 A
12T 26 AWG TIW 1 1 114T 34 AWG 2 D5 1N4007G PC817A N
D C
5 4 3
RTN
L
85 - 265 VAC
C4 100 pF 500 V PC817A U2
U2 LinkSwitch U1 LNK501
L2 Ferrite Bead
S
C6 220 nF
D6 BAV20
VR1 5.1 V 2%
PI-3695-103103
Figure 1. 2.5 W LinkSwitch Based Charger/Adapter.
DI-60
www.powerint.com
December 2004
DI-60
Typical applications are chargers for cell phones, PDAs, portable audio devices and shavers or power sources embedded within home appliances and consumer electronics, such as TV standby and bias supplies.
300 250
Input Power (mW)
Key Design Points
* Set VOR within 36 V to 60 V (50 V being optimum) * Transformer primary inductance tolerance must be 10%, to maintain CC limit tolerances (25/20%) * To allow more time for reaching regulation at startup (or into a fully resistive load), increase C6 to 1 F * If battery voltage is less than 2 V, then the LinkSwitch will not come out of its auto-restart mode * To lower the ripple voltage into non-battery loads, an LC filter or LDO must be added onto the output
200 150 100 50 0 60 90 120 150 180 210 240 270
Input Voltage (VAC)
Figure 3. No Load Input Power Consumption.
6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 50
PI-3696-091003
TRANSFORMER PARAMETERS
Core Material Bobbin TDK PC40 EE13, AL = 182 nH/T2 EE13 Horizontal 8 pin Bias: 39T, 34 AWG Primary: 114T, 34 AWG Shield: 13.5T, 2 x 31 AWG Secondary: 12T, 26 AWG (TIW) Bias (4-3), tape, Primary (2-1), tape, Shield (1-open), tape, Secondary (6-5), tape 2.36 mH 10% 300 kHz (minimum)
Output Voltage (V)
115 VAC 230 VAC Low Limit High Limit
Winding Details
Winding Order (pin numbers)
150
250
350
450
550
Primary Inductance Primary Resonant Frequency
Output Current (A)
Figure 2. Load Regulation-CV/CC Characteristics.
Table 1. Transformer Construction Information.
For the latest updates, visit www.powerint.com 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 LIMITATION, 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
Power Integrations
MAIN PHONE NUMBER +1 408-414-9200
B 12/04
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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-3697-091003

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