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TNY274-280 Datasheet(PDF) 8 Page - Power Integrations, Inc. |
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TNY274-280 Datasheet(HTML) 8 Page - Power Integrations, Inc. |
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8 / 24 page  Rev. N 12/21 8 TNY274-280 www.power.com 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 undervoltage lockout, primary sensed output overvoltage latching shutdown protection, high efficiency (>80%), and very low no-load consumption (<50 mW at 265 VAC). Output regulation is accomplished using 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 ms. The output voltage is regulated by the Zener diode VR3. When the output voltage exceeds the sum of the Zener and opto- coupler 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 falls below the feedback threshold, a conduction cycle is allowed 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 frequency and scaling switching losses with load. This provides 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 of VR2 and the BYPASS/MULTIFUNCTION (BP/M) pin voltage (28 V+5.85 V), current begins to flow into the BP/M pin. When this current exceeds I SD the internal latching shutdown circuit in TinySwitch-III is activated. This condition is reset when the BP/M pin voltage drops below 4.9 V after removal of the AC input. In the example shown, on opening the loop, the OVP trips at an output of 17 V. For lower no-load input power consumption, the bias winding may also be used to supply the TinySwitch-III device. Resistor R8 feeds current into the BP/M pin, inhibiting the internal high-voltage current source that normally maintains the BP/M pin capacitor voltage (C7) during the internal MOSFET off time. This reduces the no-load consumption of this design from 140 mW to 40 mW at 265 VAC. Figure 14. TNY278P, 12 V, 1 A Universal Input Power Supply. 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 C7 100 nF 50 V U1 TNY278PN 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 used 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-4244-111708 † † TinySwitch-III |
Similar Part No. - TNY274-280 |
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Similar Description - TNY274-280 |
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