Design Idea DI-118 ® TinySwitch-III 4.5 W CV/CC Charger with <260 mW No-Load Consumption Application Device Power Output Input Voltage Output Voltage Topology Charger TNY276P 4.5 W 90-265 VAC 5.7 V, 800 mA Flyback Design Highlights • • • • • • • When the primary current reaches the MOSFET current limit, the controller turns it off, and the energy in T1 is transferred to the output. Schottky diode D6 and capacitor C5 rectify and filter the output. Inductor L3 and capacitor C7 attenuate the switching ripple on the output. Simple, low cost, low parts count CV/CC solution Low input power at no-load: <260 mW at 265 VAC Efficiency >65% at 90 VAC Meets CEC / ENERGY STAR requirements for active mode efficiency (66.8 % vs 62.6 % requirement) Compact design using small, low cost EE16 core size >15 dBµV margin to EN55022B conducted EMI limits No Y-capacitor: <10 µA line frequency leakage current The primary clamp (D5, R2, C4 and R1) limits the maximum peak drain voltage to less than the 700 V BVDSS rating of the internal MOSFET. Resistor R2 reduces high-frequency leakage inductance ringing and thereby EMI. The tightly controlled tolerances of U1 allow this configuration to still meet low no-load input power levels. Operation The CV/CC charger circuit shown in Figure 1 was designed as a Flyback converter, using TNY276P (U1). The device has its four SOURCE pins on one side of its 8-pin package, which simplifies the layout of the PCB copper for heatsinking. Additionally, the value of C3 selects the reduced current limit of U1. Both factors allow U1 to deliver full power from within a sealed enclosure, at an external ambient temperature of 40 °C. In less thermally challenging applications, a TNY275P operating at its standard current limit (C3 = 0.1 µF) could be used to reduce cost, without any other changes. The pi filter formed by C1, L1, L2 and C2 attenuates conducted EMI while C8 and R8 on the secondary side reduce high frequency ringing. The integrated frequency jitter feature of U1 along with E-ShieldTM techniques allow such simple EMI filtering to ensure compliance with EN55022B, even without a Y capacitor across the primary to secondary isolation barrier. The output is regulated using optocoupler feedback. During CV operation, reference IC U3 senses the output The internal MOSFET within U1 conducts current through the primary winding of T1 during each enabled switching cycle. L1 1 mH D1 1N4005 RF1 8.2 Ω 2.5 W D2 1N4005 90-265 VAC D3 1N4005 1 C4 1 nF 1 kV C1 4.7 µF 400 V C8 1 nF R8 50 V 10 Ω R1 200 kΩ NC NC 2 7 3,4 C2 4.7 µF 400 V 10 R3 1.2 Ω 2W L2 Ferrite Bead S RTN R4 100 Ω U2-B R7 13.7 kΩ 1% C6 100 nF 50 V EN/UV 5.7 V, 800 mA C7 100 µF 10 V T1 EE16 TinySwitch-III U1 TNY276P D L3 Ferrite Bead 3.5 × 7.6 mm D6 SB260 R2 100 Ω D5 1N4007GP D4 1N4005 C5 470 µF 10 V R5 1 kΩ BP/M S C3 1 µF 50 V Figure 1. 4.5 W, 5.7 V CV/CC Charger Using TNY276P. DI-118 U2-A PC817A U3 TL431 R6 10 kΩ 1% PI-4422-051006 September 2006 DI-89 DI-118 • For consistent EMI performance in production, manufacturing variations in transformer T1 must be minimized from unit to unit. This is especially important in designs that do not use a Y-capacitor. Place tape between the primary winding layers to reduce intra-winding capacitance. This will help reduce the no-load consumption. • Key Design Points 80 70 Winding Details Winding Order (pin numbers) Inductance AV 50 40 30 20 10 0 EE16, NC-2H material or equivalent, gap for ALG of 156 nH/T2 -10 5+5 pin horizontal -20 0.15 Shield: 28T, 2 × 33 AWG Primary: 120T, 33 AWG Shield: 8T, 2 × 27 AWG 5.7 V: 10T, 25 AWG T.I.W. Shield (3-NC), tape, primary (2-1), tape, shield (NC-3), tape, 5.7 V (10-7), tape Primary: 2.25 mH ±12% Leakage: 45 µH (max) Primary Resonant 850 kHz (min) Frequency Table 1. Transformer Design Parameters. T.I.W.: Triple Insulated Wire, NC: No Connection 1.0 10.0 100.0 MHz Figure 2. Worst-Case Conducted EMI (Output RTN Connected to Artificial Hand Input of LISN). Output Voltage (VDC) Bobbin QP 60 TRANSFORMER PARAMETERS Core Material EN55022B Limits 6.5 6 5.5 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 PI-4423-050906 • Verify that the maximum drain voltage is <650 V at high line and maximum overload condition. Adjust the values of R1 and C4 as necessary. However, avoid making the clamp circuit too large (ie. low value of R1 and high value of C4), as this will increase the no-load power consumption. Selecting a fast diode vs. an ultra-fast diode for D5 will improve efficiency by recovering leakage energy. If glass passivated (1N4007GP) is unavailable a FR107 may be used. dBµV • PI-4421-050906 voltage via R6 and R7 and drives the optocoupler. However, the control shifts to CC mode of operation when the voltage across R3 exceeds the forward drop of the photo-diode in U2. TinySwitch-III allows this simple CC sensing scheme to be used, while still meeting active mode efficiency requirements. 115 VDC 230 VDC Low Limit High Limit 0 100 200 300 400 500 600 700 800 900 Output Current (mA) Figure 3. Typical Output Characteristics. 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. 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 The PI logo, TOPSwitch, TinySwitch, LinkSwitch, DPA-Switch, PeakSwitch, EcoSmart, Clampless, E-Shield, Filterfuse, PI Expert and PI FACTS are trademarks of Power Integrations, Inc. Other trademarks are property of their respective companies. ©Copyright 2006, Power Integrations, Inc. For a complete listing of worldwide sales offices, please visit www.powerint.com Rev. A 09/06 www.powerint.com