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TNY278PN Datasheet(PDF) 8 Page - Power Integrations, Inc. |
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TNY278PN Datasheet(HTML) 8 Page - Power Integrations, Inc. |
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8 / 24 page  8 E2/06 TNY274-280 Applications Example The circuit shown in Figure 14 is a low cost, high efficiency, flyback power supply designed for 12 V, 1 A output from universal input using the TNY278. The supply features under-voltage lockout, primary sensed output overvoltage latching shutdown protection, high efficiency (>80%), and very low no-load consumption (<50mWat265VAC). Outputregulationisaccomplishedusing a simple zener reference and optocoupler feedback. The rectified and filtered input voltage is applied to the primary winding of T1. The other side of the transformer primary is driven by the integrated MOSFET in U1. Diode D5, C2, R1, R2, and VR1 comprise the clamp circuit, limiting the leakage inductance turn-off voltage spike on the DRAIN pin to a safe value. The use of a combination a Zener clamp and parallel RC optimizes both EMI and energy efficiency. Resistor R2 allows the use of a slow recovery, low cost, rectifier diode by limiting the reverse current through D5. The selection of a slow diode also improves efficiency and conducted EMI but should be a glass passivated type, with a specified recovery time of ≤2 µs. The output voltage is regulated by the Zener diode VR3. When theoutputvoltageexceedsthesumoftheZenerandoptocoupler LED forward drop, current will flow in the optocoupler LED. This will cause the transistor of the optocoupler to sink current. When this current exceeds the ENABLE pin threshold current the next switching cycle is inhibited. When the output voltage fallsbelowthefeedbackthreshold,aconductioncycleisallowed to occur and, by adjusting the number of enabled cycles, output regulation is maintained. As the load reduces, the number of enabled cycles decreases, lowering the effective switching frequencyandscalingswitchinglosseswithload. Thisprovides almost constant efficiency down to very light loads, ideal for meeting energy efficiency requirements. As the TinySwitch-III devices are completely self-powered, there is no requirement for an auxiliary or bias winding on the transformer. However by adding a bias winding, the output overvoltage protection feature can be configured, protecting the load against open feedback loop faults. When an overvoltage condition occurs, such that bias voltage exceeds the sum ofVR2 and the BYPASS/MULTIFUNCTION (BP/M) pinvoltage(28V+5.85V),currentbeginstoflowintothe BP/Mpin. Whenthiscurrentexceeds5mAtheinternallatching shutdown circuit in TinySwitch-III is activated. This condition is reset when the BP/M pin voltage drops below 2.6 V after removal of the AC input. In the example shown, on opening the loop, the OVP trips at an output of 17 V. D S S BP/M EN/UV L1 1 mH D1 1N4007 RV1 275 VAC F1 3.15 A D2 1N4007 C1 6.8 µF 400 V C6 1 µF 60 V C2 22 µF 400 V C10 1000 µF 25 V C5 2.2 nF 250 VAC C11 100 µF 25 V +12 V, 1 A 85-265 VAC RTN J4 J3 J1 J2 C7 100 nF 50 V U1 TNY278P C4 10 nF 1 kV VR1 P6KE150A NC 8 6 4 T1 2 5 1 3 D5 1N4007GP D6 UF4003 D7 BYV28-200 U2 PC817A VR2 1N5255B 28 V VR3 BZX79-C11 11 V C7 is configurable to adjust U1 current limit, see circuit description *R5 and R8 are optional components R5* 3.6 M Ω R3 47 Ω 1/8 W R4 2 k Ω 1/8 W R6 390 Ω 1/8 W R7 20 Ω R8* 21 k Ω 1% R1 1 k Ω R2 100 Ω D3 1N4007 D4 1N4007 L2 Ferrite Bead 3.5 × 7.6 mm PI-4244-021406 † † TinySwitch-III Figure 14. TNY278P, 12 V, 1 A Universal Input Power Supply. |
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Similar Description - TNY278PN |
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