DI-91 Design Idea TinySwitch-III (R) 12 W Universal Input CV Adapter Application Device Power Output Input Voltage Output Voltage Topology General Purpose TNY278PN 12 W 85 - 265 VAC 12 V Flyback Design Highlights * No-load consumption <50 mW at 265 VAC (R8 fitted) * Active mode efficiency >75% (CEC 2008, 72.4%) * BP/M pin capacitor value selects MOSFET current limit (ILIMIT-1, ILIMIT, or ILIMIT+1): for design flexibility * Output OVP function senses overvoltage on the output through the primary bias winding * Accurate (5%), auto-recovering, hysteretic thermal shutdown function maintains safe PCB temperatures * Auto-restart function protects against output short circuits and open feedback loops * >3.2 mm package pin creepage: reliable operation in high humidity and high pollution environments Operation This universal input, 12 V, 1 A, flyback converter was designed around a member of the TinySwitch-III IC family, the TNY278PN. Because of the many features integrated into the device family, the supply only requires 31 through-hole components (no SMT), which enables a simple, single-sided PCB layout to be used. The use of an E-shieldTM in the transformer, a low-noise drainnode clamp (R2, C4 and D5), a single Y capacitor (C5) and the device's switching frequency jitter function enable a low-cost pi filter (C1, L1 and C2) to attenuate conducted EMI enough to provide more than 10 dB of margin to EN550022 requirements (see Figure 4). The clamp circuit Zener (VR1) only conducts briefly during startup and at worst-case overload, just before the autorestart function is activated. Although TinySwitch-III family members do not need a bias winding to operate, one was used in this design to take advantage of the IC's output OVP detection function. If an open loop fault causes an overvoltage on the output, VR2 will conduct. When the current into the BP/M pin exceeds 5.5 mA, an internal latch triggers and disables MOSFET switching (see Figure 3), until AC power is removed and reapplied (to reset the latch). Resistor R3 limits the current through VR2, while R3 and R7 attenuate the portion of the leakage inductance spike that appears in the bias winding. C5 2.2 nF 250 VAC VR1 P6KE150A D1 1N4007 J1 85-265 VAC D2 1N4007 F1 3.15 A R2 100 C1 6.8 F 400 V C4 10 nF 1 kV R1 1 k C2 22 F 400 V RV1 275 VAC D4 1N4007 8 C10 1000 F 25 V 6 3 R7 4 20 +12 V, 1 A J3 C11 100 F J4 25 V RTN 2 D6 UF4003 5 VR2 1N5255B 28 V L1 1 mH C6 1 F 60 V R3 47 1/8 W *R5 and R8 are optional components L2 Ferrite Bead 3.5 x 7.6 mm D7 BYV28-200 1 D5 1N4007GP R5* 3.6 M J2 D3 1N4007 NC T1 C7 is configurable to adjust U1 current limit, see circuit description D S R8* 21 k 1% EN/UV R6 390 1/8 W U2 PC817A BP/M S TinySwitch-III U1 TNY278PN VR3 BZX79-C11 11 V C7 100 nF 50 V R4 2 k 1/8 W PI-4244-122007 Figure 1. www.powerint.com TinySwitch-III 12 W, Universal Input, CV Adapter. February 2007 86 84 Efficiency (%) The output voltage is determined by the series sum of the voltages across VR3, R6, and the LED in U2. The values of R4 and R6 can be adjusted to fine tune the output voltage of the supply, and a TL431 can be used in place of VR3, for tighter output voltage regulation. PI-4274-013106 88 When R8 (optional) is installed, it supplies current to the BP/M pin, which reduces the no-load consumption of the supply. When R5 (also optional) is installed, the current it feeds into the EN/UV pin of the IC enables the input undervoltage lockout function (UVLO), and sets the start-up threshold at 65 VAC. 82 80 TNY279 (with ILIMIT-1) TNY278 (with std ILIMIT) TNY277 (with ILIMIT+1) CEC/ENERGY STAR Minimum TNY278 (with ILIMIT+1) 78 76 74 72 70 68 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 Output Current (A) Operating Efficiency vs ILIMIT+, ILIMIT- and Device Size. PI-4288-012506 Figure 2. 15 0 0 250 500 Time (ms) Figure 3. BP/M Pin OVP Function Shuts Down Power Supply. 80 PI-4289-012506 *Note: This supply was not thermally designed to continuously deliver the extended power range that could be obtained by operating a TNY278 with its MOSFET current limit set at that of a TNY279. 0 Voltage (V) Key Design Points * In the TinySwitch-III family of devices, the MOSFET current limit can be selected from 3 levels by the value of capacitance on the BP/M pin. This gives the designer a number of options, which are shown in Figure 2. First, a TNY279 could be used, with the current limit of a TNY278, to obtain higher efficiency. Second, a TNY277 could be used, with the current limit of a TNY278, to deliver the same power at a lower efficiency. Lastly, a TNY278 could be used, with the current limit of a TNY279, to extend the power capability of the supply*. * The UVLO function integrated into U1 only enables MOSFET switching to occur once the current flowing into the EN/UV pin exceeds 25 A. Changing the UVLO threshold voltage requires changing the value of R5 so that 25 A flows through it at the desired threshold voltage. * If output OVP is not required and no-load power consumption of 150 mW (max, at 265 VAC input) is acceptable, then R7, D6, C6, R3 and VR2 can be eliminated and the bias winding removed from T1, for an even lower parts count. 70 Amplitude (dBV) 60 50 40 30 20 -10 0 -10 -20 0.15 1 10 30 Frequency (MHz) Figure 4. Conducted EMI Scan (Line): 113 VAC, Full Load. Power Integrations 5245 Hellyer Avenue San Jose, CA 95138, USA. Main: +1 408-414-9200 Customer Service Phone: +1-408-414-9665 Fax: +1-408-414-9765 Email: usasales@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. On the Web www.powerint.com 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)2006, Power Integrations, Inc. C 02/08 DI-91