Design Idea DI-117 ® TinySwitch-III 15 W, 12 V Adapter with <100 mW No-Load Consumption Application Device Power Output Input Voltage Output Voltage Topology Adapters / General Purpose TNY279P 15 W 90-265 VAC 12 V Flyback Design Highlights • • • • • • • The internal MOSFET in U1 conducts current through the primary winding of T1 during each enabled switching cycle. 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 D7 and capacitor C8 rectify and filter the output. Inductors L3 and capacitor C9 attenuate the switching ripple on the output. Capacitor C3 selects the standard current limit of U1. For higher efficiency, the next larger (TNY280P) device may be used. In this case, the value of C3 would be changed to 1 µF, selecting the reduced current limit for the larger device, but no other circuit changes would be required. Simple, low cost, low parts count solution Low input power at no-load: <100 mW at 265 VAC High efficiency >81% at 90 VAC Meets CEC requirements for active mode efficiency (79 % vs. 73.5 % requirement) >10 dBµV margin to EN55022B conducted EMI limits Simple, primary-side output overvoltage latching shutdown protects load under fault conditions Low line frequency leakage current <10 µA Operation The primary clamp (D5, R1, C5, R5 and R6) limits the maximum peak drain voltage below the 700 V breakdown voltage of U1's internal MOSFET. Resistor R1 dampens the high-frequency ringing of the T1 leakage inductance. The TNY279 (U1) in the 8-pin DIP package selected for the flyback design in Figure 1 is ideal for adapter applications. The arrangement of the four SOURCE pins on one side of the package allows a small metal heatsink to be inserted. This allows the device to operate in a sealed adapter with an external ambient of 40 °C. C5 1 nF R5 R6 1 kV 240 kΩ 240 kΩ L4 1 mH D1 1N4005GP F1 3.15 A 90-265 VAC C6 68 pF 250 VAC D2 1N4005 3 C1 10 µF 400 V D4 1N4005 L3 Ferrite Bead 3.5 × 7.6 mm 10 D7 SB580 9 NC C2 22 µF 400 V R1 100 Ω C8 680 µF 25 V +12 V, 1.25 A C9 220 µF 25 V 5 RTN D6 1N4148 4 EF20 D5 FR107 D3 1N4005GP T1 1 C11 R7 1 nF 100 V 20 Ω R8 56 Ω C7 1 µF 50 V VR3 BZX79-B6V8 6.8 V L5 3.3 µH R4 47 Ω TinySwitch-III U1 TNY279P D R2 100 Ω S R9 1 kΩ R3 10 kΩ R11 39 kΩ 1% EN/UV C10 220 nF 50 V BP/M S C4 33 pF 1 kV U2-B C3 100 nF 50 V U2-A PC817A U3 LM431 R10 3 kΩ R12 10 kΩ 1% PI-4417-051106 Figure 1. 15 W, 12 V Output Supply Using TNY279P. DI-117 September 2006 DI-89 DI-117 The built-in frequency jitter and E-ShieldTM techniques allow simple EMI filtering to comply with EN55022B. Resistor R2 and C4 form an RC snubber to reduce high-frequency EMI. Output overvoltage protection (OVP) is provided on the primary side by sensing the voltage of the auxiliary transformer winding. Should the main feedback loop open due to failure of U2, then U1 will latch off once the current into the BP/M pin (via VR3) exceeds 6.5 mA. Diode D6 and capacitor C7 rectify and smooth the output of the auxiliary winding. The value of VR3 is selected to trigger the OVP latch when the main output, and hence the auxiliary output voltage, rises above the normal regulation range. Once triggered, cycling the AC power resets the OVP latch. To reduce no-load input power and thus increase light load efficiency, resistor R3 feeds the supply current for U1 from the auxiliary winding on the transformer. PI-4415-050806 35 30 Voltage (V) 25 20 Key Design Points • • • Verify maximum drain voltage is <650 V at high line, maximum overload. Adjust values of R5, R6 and C5 accordingly. However, avoid making the clamp too dissipative (low value of R5 and R6, and high value of C5) as this will increase no-load consumption. To prevent an increase in no-load consumption or false OVP triggering, VR3 should be selected to conduct only when the output voltage is outside the normal regulation range. Resistor R4 prevents excessive current from flowing into the BP/M pin. Fast recovery glass-passivated diodes were selected for D1 and D3 to reduce low frequency conducted EMI. Fast diodes such as FR107 are also suitable. TRANSFORMER PARAMETERS Core Material Bobbin 5 0 Winding Details Winding Order (Pin Numbers) 3 mm tape margin, shield (1-NC), tape, primary (3-1), tape, bias (5-4), tape, 12 V (10-9), tape Inductance -5 0 50 Time (ms) Figure 2. Worst-Case Open Loop Output Overvoltage (85 VAC, Full Load). 100 5+5 pin horizontal Shield: 24T, 28 AWG Primary: 62T, 31 AWG Bias: 5T, 4 × 28 AWG 12 V: 7T, 23 AWG T.I.W. 15 10 EF20, N67 or equivalent, gap for ALG of 203 nH/T2 Primary: 790 µH ±7% Leakage: 30 µH (max) Primary Resonant 650 kHz (min) Frequency Table 1. Transformer Design Parameters. T.I.W.: Triple Insulated Wire, NC: No Connection 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