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| Design Idea DI-123 TinySwitch-III Application Device (R) 9.65 W, Dual Output Power Supply for Residential Heating Control Power Output Input Voltage 9.65 W 185-265 VAC Output Voltage 5V / 0.25 A, 24 V / 0.35 A Topology Flyback Residential Heating Control TNY275P Design Highlights * * * * * Simple, low cost design only requires 38 parts <150 mW no-load consumption at 230 VAC input Meets CEC / ENERGY STAR active-mode efficiency and no-load input power requirements Both outputs exhibit good cross regulation Meets CISPR-22 Class B/EN55022 B without input X or Y capacitors or an input common mode choke MOSFET is turned off. Then the energy stored in T1 transfers to the secondary where it is rectified and filtered by D1 and C2 and D4 and C5. The primary side RCD clamp (D8, C4 R1 and R8) limits the peak DRAIN voltage spike caused by transformer leakage inductance. Power Integrations E-ShieldTM transformer construction techniques, the RCD clamp, a snubber (R11 and C14), a simple filter (C7, C8, L1 and L5) and the frequency jitter function of the TinySwitch-III family, provide good EMI margin, even with the output return connected to safety earth ground (see Figure 3). Operation The flyback converter shown in Figure 1 uses a TNY275 (U1) to provide two output voltages: 5 V at 250 mA and 24 V at 350 mA. Typical applications are residential heating controllers (furnace) or any application where 2 outputs are required. The 9.65 W of output power is delivered by using the increased current limit of U1, which is selected by the value of C11. 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 L2 330 H R8 75 k Key Design Points * * The turns ratio of the two secondary winding was optimized for output voltage centering. The use of a fast instead of an ultrafast diode for D8 improves efficiency by recovering some leakage inductance energy. R10 10 C13 1/2 W 470 pF L4 FB C4 1 nF 1 kV 1 T1 10 24 V, 350 mA C12 47 F 35 V C6 100 F 16 V 5 V, 250 mA D1 UF4003 6 D4 1N5819 C2 220 F 35 V L3 FB D2 1N4937 L F1 1A D3 1N4007 3 R1 100 185-265 VAC C7 10 F 400 V C8 10 F 400 V D D8 FR106 8, 9 EF20 C5 330 F 10 V RTN R2 47 EN/UV BP/M TinySwitch-III U1 TNY275P N R11 100 S R3 15 k 1% R9 261 k 1% D5 1N4937 D7 1N4007 R12 30 U2 PC817A R4 1 k C10 R5 100 nF 3.3 k C14 33 pF 1 kV L5 FB C15 0.1 F 50 V C11 10 F 50 V L3, L4 and L5 are 3.5 mm x 10 mm Ferrite beads. U3 LM431 2% R6 10 k 1% PI-4495-090706 Figure 1. TinySwitch-III 9.65 W Residential Heating Controller Power Supply. DI-123 September 2006 DI-89 DI-123 70 60 50 40 EN55022B Limits QP AV QP PI-4496-090706 * * * * Maximize the value of R8 and minimize the value of C4 for the lowest no-load consumption. However, verify that the peak drain voltage is <650 V at high line, under maximum overload conditions. Select transformer wire gauge sizes so that each winding layer occupies the full bobbin width. This lowers leakage inductance and improves output cross regulation. Use option to add E-Shield windings in PI Transformer Designer software to reduce conducted EMI noise generation. To lower the no-load power consumption even further, use an optional bias supply circuit to feed the rated data sheet current (through a series resistor) to the BP/M pin of U1. Load Range (mA) 50-250 88-350 Regulation (%) -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 80 dBV 30 20 10 0 -10 -20 0.15 1.0 AV 10.0 100.0 MHz Output (V) 5 24 Figure 3. Worst Case Conducted EMI at 230 VAC, Full Load Output Return Grounded. TRANSFORMER PARAMETERS Core Material Bobbin PI-4497-090506 Table 1. Worst Case Output Cross Regulation at 185 VAC Output Loads Varied as Shown and Maximum Deviation Recorded. 80 79 EF20 TDK PC40, or equivalent ALG of 323 nH/T2 EF20, 10 pin (5+5), horizontal Pin Shine P-2015 or equivalent Shield: 15T, 2 x 31 AWG Primary: 36T + 35T, 33 AWG Shield: 4T, 5 x 29 AWG 5 V: 3T, 4 x 26 AWG T.I.W. 24 V: 11T, 26 AWG T.I.W. (4 x 26 AWG = quadfilar 26 AWG) Apply 2 mm tape margin to both sides of bobbin Shield (1-NC), tape, Primary (3-1), Shield (NC-1), 5 V (6-8), 24 V (10-6) Primary: 1.62 mH 5% Leakage: 50 H maximum 800 kHz (minimum) Efficiency (%) Winding Details 78 77 76 75 Winding Order (Pin Numbers) 185 205 225 245 265 AC Input Voltage (V) Inductance Primary Resonant Frequency Figure 2. Full Load Efficiency vs Input Voltage. Table 2. Transformer Construction Information. For the latest updates, visit www.powerint.com TIW = Triple Insulated Wire, NC = No Connect 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 Expert and PI FACTS are trademarks of Power Integrations, Inc. Other trademarks are property of their respective companies. (c)Copyright 2006, Power Integrations, Inc. Rev. A 09/06 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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