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万能充电器电路图 Title Engineering Prototype Report for EP-16 - 2.75 W Charger/Adapter Using LNK501 (LinkSwitch) Specification 85 VAC to 265 VAC Input, 5.5 V, 500 mA Output Application Low Cost Charger/Adapter Author PI Applications Document Number EPR-1...

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Title Engineering Prototype Report for EP-16 - 2.75 W Charger/Adapter Using LNK501 (LinkSwitch) Specification 85 VAC to 265 VAC Input, 5.5 V, 500 mA Output Application Low Cost Charger/Adapter Author PI Applications Document Number EPR-16 Date 17-May-04 Revision 1.6 Features • Very low cost, low component count charger/adapter – replaces linear transformer based solutions • Extremely simple circuit configuration designed for high volume, low cost manufacturing – No surface mount components required • Small EE13 transformer allows compact size • Approximate constant voltage, constant current (CV/CC) primary sensed output characteristic – No optocoupler or sense resistors required • Efficiency greater than 71% • No-load power consumption <300 mW at 265 VAC • No Y1 safety capacitor required – Only transformer bridges primary-to-secondary safety barrier – Ultra low leakage design (<5 µA) 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. Power Integrations 5245 Hellyer Avenue, San Jose, CA 95138 USA. Applications Hotline: Tel: +1 408 414 9660 Fax: +1 408 414 9760 www.powerint.com EPR-16 - LinkSwitch 2.75 W Charger/Adapter 17-May-04 Table Of Contents 1 Introduction.................................................................................................................4 2 Power Supply Specification ........................................................................................5 3 Schematic...................................................................................................................7 4 Circuit Description ......................................................................................................8 4.1 Input Stage ..........................................................................................................8 4.2 LinkSwitch Operation ..........................................................................................9 4.3 Transformer.......................................................................................................10 4.4 Clamp and Feedback Components ...................................................................10 4.5 Output Stage .....................................................................................................11 5 PCB Layout ..............................................................................................................12 6 Bill Of Materials ........................................................................................................13 7 Transformer ..............................................................................................................14 7.1 Transformer Winding.........................................................................................14 7.2 Electrical Specifications.....................................................................................14 7.3 Materials............................................................................................................15 7.4 Transformer Build Diagram ...............................................................................15 7.5 Transformer Construction..................................................................................16 8 Performance Data ....................................................................................................17 8.1 Line and Load Regulation..................................................................................17 8.2 Efficiency ...........................................................................................................18 8.3 No-Load Input Power ........................................................................................18 9 Waveforms ...............................................................................................................19 9.1 Drain Voltage and Current Waveforms..............................................................19 9.1.1 90 VAC, Normal Operation.........................................................................19 9.1.2 265 VAC, Normal Operation.......................................................................19 9.2 Output Voltage Start-up Profile..........................................................................20 9.3 Load Transient Response (0.25 A to 0.5 A Load Step) .....................................20 9.4 Output Ripple Measurements............................................................................21 9.4.1 Ripple Measurement Technique ................................................................21 9.4.2 Output Voltage Ripple ................................................................................22 9.5 Thermal Measurements ....................................................................................23 9.6 Conducted EMI..................................................................................................24 9.6.1 Optional Components With Artificial Hand .................................................25 9.6.2 Optional Components Without Artificial Hand ............................................25 9.6.3 Optional Components Removed With Artificial Hand .................................26 10 Appendix A – EP-16 Enclosure Opening Procedures ..............................................27 10.1 Method 1 - Non-destructive ...............................................................................27 10.2 Method 2 - Destructive ......................................................................................27 11 Appendix B – LNK520P in the High-Side Configuration ..........................................28 11.1 Introduction........................................................................................................28 11.2 Comparison of LNK501 and LNK520 ................................................................28 11.3 Circuit Changes.................................................................................................29 11.4 Performance Data .............................................................................................30 11.4.1 Line and Load Regulation ..........................................................................30 11.4.2 Efficiency....................................................................................................31 Page 2 of 36 Power Integrations Tel: +1 408 414 9660 Fax: +1 408 414 9760 www.powerint.com 17-May-04 EPR-16 – LinkSwitch 2.75 W Charger/Adapter 11.4.3 No-Load Input Power..................................................................................32 11.5 EMI Performance...............................................................................................33 12 Revision History........................................................................................................34 Important Note: Although the EP-16 is designed to satisfy safety isolation requirements, this engineering prototype has not been agency approved. Therefore, all testing should be performed using an isolation transformer to provide the AC input to the prototype board. Page 3 of 36 Power IntegrationsTel: +1 408 414 9660 Fax: +1 408 414 9760 www.powerint.com EPR-16 - LinkSwitch 2.75 W Charger/Adapter 17-May-04 1 Introduction This document is an engineering report giving performance characteristics of a 5.5 V, 500 mA charger/adapter. The charger uses LinkSwitch – an integrated IC combining a 700 V high voltage MOSFET, PWM controller, start-up, thermal shut down and fault protection circuitry. The controller provides both duty cycle and current limit control to yield a constant voltage/constant current output characteristic without secondary-side sensing. This power supply is designed to provide a cost effective replacement for linear transformer based chargers and adapters while providing the additional benefits of universal input range and high energy efficiency. This document contains the power supply specification, schematic, bill of materials, transformer documentation, printed circuit board layout, and performance data. Figure 1 – EP-16 Populated Circuit Board. Figure 2 – EP-16 Assembled into Case with Cable (barrel −ve, tip +ve). Page 4 of 36 Power Integrations Tel: +1 408 414 9660 Fax: +1 408 414 9760 www.powerint.com 17-May-04 EPR-16 – LinkSwitch 2.75 W Charger/Adapter 2 Power Supply Specification Description Symbol Min Typ Max Units Comment Input Voltage VIN 85 265 VAC 2 Wire – no Protective Ground Frequency fLINE 47 50/60 64 Hz No-load Input Power (265 VAC) 0.3 W Output Output Voltage VOUT 5.0 5.5 6.0 V At peak output power point Output Ripple Voltage (res. load) VRIPPLE R 300 mV Resistive load, peak power Output Ripple Voltage (bat. load) VRIPPLE B 150 mV Battery load, peak power Output Current 1 IOUT 400 500 600 mA Total Output Power Continuous Output Power POUT 2 2.75 3.6 W Efficiency η 71 % Measured at output peak power point, 25 oC Environmental 1.2/50 Surge 2 kV 1.2/50 µs surge, IEC 1000-4-5, 12 Ω series impedance, differential and common mode 100 kHz Ring Wave Surge 2 kV 100 kHz ring wave, 500 A short circuit current, differential and common mode Ambient Temperature TAMB 0 40 oC Free convection, sea level Conducted EMI Meets CISPR22B / EN55022B & FCC B with artificial hand connected to output return Safety Designed to meet IEC950, UL1950 Class II Output VI Characteristic Specification 0 1 2 3 4 5 6 7 8 9 10 0 100 200 300 400 500 600 700 IOUT (mA) V O U T ( D C ) Figure 3 – EP-16 Output Characteristic Envelope. (Shading represents no-go areas.) Page 5 of 36 Power IntegrationsTel: +1 408 414 9660 Fax: +1 408 414 9760 www.powerint.com EPR-16 - LinkSwitch 2.75 W Charger/Adapter 17-May-04 Figure 4 – Battery Model Used for Testing. Note: EP-16 is designed for a battery load. If a resistive or electronic load is used the supply may fail to start up at full load. This is normal. To ensure startup into a resistive load, increase the value of C3 to 1 µF (see circuit description for more information). Page 6 of 36 Power Integrations Tel: +1 408 414 9660 Fax: +1 408 414 9760 www.powerint.com 17-May-04 EPR-16 – LinkSwitch 2.75 W Charger/Adapter 3 Schematic Figure 5 – EP-16 Low Cost, 2.75 W LinkSwitch Cell Phone Charger Schematic. Optional components L2, C6 and R4 may be fitted to the board to improve radiated EMI. The effect of these components is shown in the “Conducted EMI Results” section of this document. Optional component R3 may be fitted in place of L1 in applications where conducted EMI is filtered externally (e.g. in an embedded system). In this case a 0 Ω resistor or jumper should be used. In low power applications (less than approximately 1.5 W), a low value resistor may be used to provide sufficient conducted EMI filtering. A value in the range of 0 Ω to 10 Ω may be used. Page 7 of 36 Power IntegrationsTel: +1 408 414 9660 Fax: +1 408 414 9760 www.powerint.com EPR-16 - LinkSwitch 2.75 W Charger/Adapter 17-May-04 4 Circuit Description The schematic shown in Figure 5 provides a CV/CC (constant voltage/constant current) type output characteristic from a universal input voltage range of 85 VAC to 265 VAC. The nominal peak power point at the transition from CC to CV is 5.5 V at 500 mA. The precise output envelope specification is shown in Figure 3. 4.1 Input Stage The incoming AC is rectified and filtered by D1-4, C1 and C2. Resistor RF1 is a flameproof fusible type to protect against fault conditions and is a requirement to meet safety agency fault testing. This component should be a wire wound type to withstand input current surges while the input capacitors charge on application of power or during withstand line-transient testing. Metal film type resistors are not recommended, they do not have the transient dissipation capabilities required and may fail prematurely in the field. Lower values increase the resistor dissipation (V²/R power term) during transients, increasing resistor stress, while higher values increase steady state dissipation (I²R power term) and reduce efficiency. If a suitable flame proof resistor cannot be found (during failure flame proof resistors do not emit flames, smoke or incandescent material that may damage transformer insulation), then a standard fusible type may be used as long as a protective heat shrink sleeve is placed over the resistor. Please consult with a safety engineer or local safety agency. The value of C1 and C2 were selected to provide the smallest standard values to meet 3 µF/W, in this case two 4.7 µF, 400 V capacitors. Smaller values are possible (either 2.2 µF or 3.3 µF) however, the lower DC rail voltage will increase LinkSwitch dissipation, lowering efficiency and increasing line frequency output ripple. Differential mode EMI (<500 kHz) also typically increases. The input capacitance is split between C1 and C2 to allow an input π filter to be formed by L1. This filters noise associated with the supply to meet EN55022B / CISPR 22 B and FCC B conducted EMC limits, even when no Y safety capacitor is used. Ferrite bead L2 is optional, fitted to improve radiated EMI. Page 8 of 36 Power Integrations Tel: +1 408 414 9660 Fax: +1 408 414 9760 www.powerint.com 17-May-04 EPR-16 – LinkSwitch 2.75 W Charger/Adapter 4.2 LinkSwitch Operation When power is applied to the supply, high voltage DC appears at the DRAIN pin of LinkSwitch (U1). The CONTROL pin capacitor C3 is then charged through a switched high voltage current source connected internally between the DRAIN and CONTROL pins. When the CONTROL pin voltage reaches approximately 5.7 V relative to the SOURCE pin, the internal current source is turned off. The internal control circuitry is activated and the high voltage internal MOSFET starts to switch, using the energy in C3 to power the IC. As the current ramps in the primary of flyback transformer T1, energy is stored. This energy is delivered to the output when the MOSFET turns off each cycle. The secondary of the transformer is rectified and filtered by D6 and C5 to provide the DC output to the load. Control of the output characteristic is entirely sensed from the primary-side by monitoring the primary-side VOR (voltage output reflected). While the output diode is conducting, the voltage across the transformer primary is equal to the output voltage plus diode drop multiplied by the turns ratio of the transformer. Since the LinkSwitch is connected on the high side of the transformer, the VOR can be sensed directly. Diode D5 and capacitor C4 form the primary clamp network. The voltage held across C4 is essentially the VOR with an error due to the parasitic leakage inductance. The LinkSwitch has three operating modes determined by the current flowing into the CONTROL pin. During start-up, as the output voltage, and therefore the reflected voltage and voltage across C4 increases, the feedback current increases from 0 to approximately 2 mA through R1 into the CONTROL pin. The internal current limit is increased during this period until reaching 100%, providing an approximately constant output current. Once the output voltage reaches the regulated CV value, the output voltage is regulated through control of the duty cycle. As the current into the CONTROL pin exceeds approximately 2 mA, the duty cycle begins to reduce, reaching 30% at a CONTROL pin current of 2.3 mA. If the duty cycle reaches a 3% threshold, the switching frequency is reduced, which reduces energy consumption under light or no load conditions. As the output load increases beyond the peak power point (defined by ½·L·I²·f) and the output voltage and VOR falls, the reduced CONTROL pin current will lower the internal current providing an approximately constant current output characteristic. If the output load is further increased and the output voltage falls further to below a CONTROL pin current of 1 mA, the CONTROL pin capacitor C3 will discharge and the supply will enter auto-restart. Page 9 of 36 Power IntegrationsTel: +1 408 414 9660 Fax: +1 408 414 9760 www.powerint.com EPR-16 - LinkSwitch 2.75 W Charger/Adapter 17-May-04 4.3 Transformer The transformer is designed to always be discontinuous; all the energy is transferred to the load during the MOSFET off time. The energy stored in the transformer during discontinuous mode operation is ½·L·I²·f, where L is the primary inductance, I² is the peak primary current squared and f is the switching frequency. Since the value of LinkSwitch current limit and frequency directly determines the peak power or CV/CC transition point in the output characteristic, the parameter of current squared times frequency is defined in the datasheet. This parameter, together with the output power, is used to specify the transformer primary inductance. With a primary inductance tolerance of ±10%, the EP-16 is designed to provide the output current characteristic shown in Figure 3∗. As LinkSwitch is powered by the energy stored in the leakage inductance of the transformer, only a low cost two winding transformer is required. Leakage inductance should be kept low, ideally at less than 2% of the primary inductance. High leakage inductance will cause the CC characteristic to walk out as the output voltage decreases and increases the no-load consumption of the supply. With a figure of 50 µH for leakage, this design is able to meet a voltage tolerance of ±10% at the peak power point, including the effects of output cable drop. For tighter voltage tolerance across the whole load range, a secondary optocoupler can be added. For most battery charging applications, only the voltage at the peak power point is critical, thus ensuring sufficient voltage for charging. 4.4 Clamp and Feedback Components Diode D5 should either be a fast (trr <250 ns) or ultra-fast type to prevent the voltage across LinkSwitch from reversing and ringing below ground. A fast diode is preferred, being lower cost. Leakage inductance is filtered by R2, the optimum value providing the straightest CC characteristic. Capacitor C4 is typically fixed at 0.1 µF and should be rated above the VOR and be stable with both temperature and applied voltage. Low-cost, metalized plastic film capacitors are ideal; high value, low-cost ceramic capacitors are not recommended. Dielectrics used for these capacitors such as Z5U and Y5U are not stable and can cause output instability as their value changes with voltage and temperature. Stable dielectrics such as COG/NPO are acceptable but are costly when compared to a metalized plastic film capacitor. Page 10 of 36 Power Integrations Tel: +1 408 414 9660 Fax: +1 408 414 9760 www.powerint.com ∗ This includes LinkSwitch tolerance and line variation. 17-May-04 EPR-16 – LinkSwitch 2.75 W Charger/Adapter R1 was selected to program the peak power point to be 500 mA when a transformer with a nominal LP value was used. Initial values are selected using the expression (from Power Integrations Application note, AN-35): R1 ≅ (VFB - VC (IDCT)) / IDCT ≅ (54.1 – 5.75) / 2.3
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