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| Design Idea DI-122 TinySwitch-III Application Device (R) 13 W (17.2 W Peak) Non-Isolated Power Supply for White Goods: <150 mW No-load Power Consumption Power Output Input Voltage 85-265 VAC Output Voltage -5 V, 2.0 A / -12 V, 0.25 A / 0.6 A Pk Topology Flyback White Goods TNY279P 13 W / 17.2 W Pk Design Highlights * Lowcost,lowcomponentcountsolution * ImpedancefreepathfromNeutraltooutputRTN,ideal forapplicationsdrivingtriacs * <150mWno-loadconsumptionat230VACinput * Bothoutputsexhibitgoodcrossregulation * Maximumambienttemperatureofupto70C * MeetsCISPR-22ClassB/EN55022BEMIlimits withoutaninputcommonmodechoke Feedback is taken directly from the -5 V output. Once the output exceeds the voltage defined by the VBE of Q1 and ratingofVR1,Q1isbiasedon.Thispullscurrentoutofthe EN/UV pin of U1 and disables the next switching cycle. By adjusting the number of enabled to disabled cycles, output regulationismaintained. ThevalueofR7setsthebiascurrentthroughVR1,operating the Zener closer to its specified test current. Resistor R6 limits the base current of Q1, R5 and C8 roll-off of high frequency gain and R3 limits the current out of the EN/UV pin. Diode D3 ensures the EN/UV pin is clamped to >-0.3Vwith respect to the SOURCE pin of U1. Power Integrations E-ShieldTM transformer construction techniques, the RCD clamp, a simple filter (C4, C5 and L1), small X-type (C1) and Y-type (C2) capacitors and the frequency jitter function of the TinySwitch-III family, provide good EMI margin (see Figure 3). Using a one square inch metal shield, located underneath U1 and T1 (connected to the SOURCE pin of U1) can further reduce EMI noise generation. 1 T1 EF20 10 D4 SB530 C11 2200 F 10 V C9 470 F 25 V L3 3.3 H C10 47 F 25 V C12 47 F 16 V RTN Operation The non-isolated flyback converter shown in Figure 1 uses a TNY279toprovidetwooutputvoltages:-5Vat2Aand-12V at250mAcontinuousand600mApeak. The MOSFET integrated within U1 switches the primary of transformer T1. Each time it turns on, the primary current ramps until it reaches an internal current limit and the MOSFET is turned off. During the off time, the energy stored in T1 transfers to the secondary where it is rectified and filtered by D4 and C11 and D5 and C9. The primary side RCD clamp (D2,C6,R1andR2)limitsthepeakDRAINvoltagespike caused by transformer leakage inductance. Line F1 3.15 A D1 1N4007 L1 1000 H C6 1 nF 1 kV R1 200 k 0.5 W 8 C2 1 nF 250 VAC Safety Earth Ground C1 47 nF 275 VAC * R2 200 D2 1N4007GP ** C4 33 F 400 V ** C5 33 F 400 V 7 3 -5 V, 2 A D5 SB3100 -12 V, 250 mA (600 mA pk) D TinySwitch-III U1 TNY279P EN/UV BP/M R3 4.7 k Q1 PN2222A R6 5.1 k R5 1 k C8 100 nF 50 V R4 47 S VR1 BZX79-B4V7 4.7 V, 2% R7 620 C7 100 nF 50 V Neutral D3 1N5817 *One square inch metal shield (connected to the S pin of U1) under U1 and T1 eliminates the need for C2. **For high-line only operation (180 VAC input, minimum), 10 F (400 V) capacitors can be used for C4 and C5. PI-4498-112906 Figure 1. TinySwitch-III 13/17.2 W White Good Power Supply. DI-122 January 2007 DI-89 DI-122 Key Design Points * The secondary side bias current, set by R7, should be kept lowtominimizelightloadandno-loadpowerconsumption. * The output voltage that is reflected across the transformer (VOR)shouldbekeptlowtominimizethelossesinthe primary side RCD clamp. *Optimizetheturnsratioofthetwooutputsforvoltage centering. * For good output cross regulation, design for continuous conductionmode(minimizethevalueofKPinthe PI Xlsspreadsheet). * Use a Schottky diode for D3 to limit EN/UV pin >-0.3V. * AstheforwarddropofD3isafunctionoftemperature,diode type and current, use a schottky diode. Do not reduce the value of R3, and verify EN/UV pin absolute maximum ratingsareobservedatlowtemperatures(~<-10C). -5 V 20% on -5 V, 100% on -12 V 100% on -5 V, 20% on -12 V 100% on -5 V, 5% on -12 V 82 80 * ThevalueofR4canbeusedtomakesmalloutput voltageadjustments. * Theregulationpointisthesumofthevoltageratingof VR1,VBE(Q1)andthevoltageacrossR4((VBE(Q1)/R7)xR4). * BiasingtheZenerbelowitstestcurrentlowersits voltagedrop,inthiscaseto~4.3V. *Selecttransformerwiregaugesizessothateachwinding layer occupies the entire bobbin width (lowers leakage inductanceandimprovesoutputcrossregulation). * Use option to add E-ShieldwindingsinPI Transformer Designer softwaretoreduceconductedEMInoise generation. * No-load power consumption can be lowered by adding a bias winding to feed the supply current of U1 into the BP pin. 70 60 50 40 EN55022B Limits QP AV PI-4500-090706 80 -12 V dBV -5.05 V -5.03 V -5.02 V -11.49 V -12.95 V -13.90 V 30 20 10 0 -10 QP AV Table 1. Worst Case Cross Regulation at 85 VAC. PI-4499-090606 -20 0.15 1.0 10.0 70.0 MHz Figure 3. Conducted EMI at 230 VAC, Full Load. Efficiency (%) 78 76 74 72 70 Nominal Load TRANSFORMER PARAMETERS EF20 TDK PC40, or equivalent Core Material ALG of 142 nH/T2 Bobbin Winding Details 85 115 145 175 205 235 265 EF20, 10 pin (5 + 5) Shield: 23T, Primary: 95T Shield: 9T (trifilar), -5 V: 5T, -12 V: 7T 1.28 mH 10% AC Input Voltage (V) Primary Inductance Figure 2. Full Load Efficiency vs. Input Voltage. For the latest updates, visit www.powerint.com Table 2. Transformer Construction Information. 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,PeakSwitch,EcoSmart, Clampless,E-Shield,Filterfuse,StackFET, PI ExpertandPI FACTS are trademarks of Power Integrations, Inc. Other trademarks are property of their respective companies. (c)Copyright 2007, Power Integrations, Rev. A 1/07 Power Integrations 5245 Hellyer Avenue San Jose, CA 95138 Phone: 1-408-414-9200 Apps: 1-408-414-9660 Apps Fax: 1-408-414-9760 For a complete listing of worldwide sales offices, please visit www.powerint.com |
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