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LNK353P Datasheet(PDF) 4 Page - Power Integrations, Inc. |
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LNK353P Datasheet(HTML) 4 Page - Power Integrations, Inc. |
4 / 16 page LNK353/354 F 2/05 4 Applications Example A 2.4 W CC/CV Charger Adapter The circuit shown in Figure 5 is a typical implementation of a 5.7 V, 400 mA, constant voltage, constant current (CV/CC) battery charger. The input bridge formed by diodes D1-D4, rectifies the AC input voltage. The rectified AC is then filtered by the bulk storage capacitors C1 and C2. Resistor RF1 is a flameproof, fusible, wire wound type and functions as a fuse, inrush current limiter and, together with the π filter formed by C1, C2 and L1, differential mode noise attenuator. This simple EMI filtering, together with the frequency jittering of LinkSwitch-HF (U1), a small value Y1 capacitor (CY1), and shield windings within T1, and a secondary-side RC snubber (R5, C5), allows the design to meet both conducted and radiated EMI limits. The low value of CY1 is important to meet the requirement of low line frequency leakage current, in this case <10 µA. 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, C3, R1 and R3 form the primary clamp network. This limits the peak drain voltage due to leakage inductance. Resistor R3 allows the use of a slow, low cost rectifier diode by limiting the reverse current through D5 when U1 turns on. The selection of a slow diode improves efficiency and conducted EMI. Output rectification is provided by Schottky diode D6. The low forward voltage provides high efficiency across the operating range and the low ESR capacitor C6 minimizes output voltage ripple. In constant voltage (CV) mode, the output voltage is set by the Zener diodeVR1 and the emitter-base voltage of PNPtransistor Q1. The V BE of Q1 divided by the value of R7 sets the bias current through VR1 (~2.7 mA). When the output voltage exceeds the threshold voltage determined by Q1 and VR1, Q1 is turned on and current flows through the LED of U2. As the LED current increases, the current fed into the FEEDBACK pin increases, disabling further switching cycles of U1. At very light loads, almost all switching cycles will be disabled, giving a low effective switching frequency and providing low no-load consumption. Duringloadtransients,R6andR8ensurethattheratingsofQ1are not exceeded while R4 prevents C4 from being discharged. Resistors R9 and R10 form the constant current (CC) sense circuit. Above approximately 400 mA, the voltage across the senseresistorexceedstheoptocouplerdiodeforwardconduction voltage of approximately 1 V. The current through the LED is therefore determined by the output current and CC control dominatesovertheCVfeedbackloop.CCcontrolismaintained even under output short circuit conditions. D S FB BP RF1 8.2 Ω 2.5 W 85-265 VAC 5.7 V, 400 mA J3-2 RTN J3-1 J1 J2 R3 200 Ω R5 68 Ω R1 100 k Ω R4 5.1 k Ω R6 6.8 Ω R9 200 Ω R10 2.4 Ω 1 W R8 390 Ω U2A PC817D VR1 BZX79B5V1 5.1 V, 2% R7 220 Ω U2B PC817D D1 1N4005 D2 1N4005 D5 1N4007GP D3 1N4005 D4 1N4005 D6 SS14 C6 330 µF 16 V Q1 MMST 3906 L1 1 mH CY1 100 pF C1 4.7 µF 400 V C3 2.2 nF 400 V 5 3 4 5 9 8 T1 EE16 NC NC U1 LNK354P C2 4.7 µF 400 V C4 100 nF C5 2.2 nF LinkSwitch-HF PI-3891-070204 Figure 5. Universal Input, 5.7 V, 400 mA, Constant Voltage, Constant Current Battery Charger Using LinkSwitch-HF. |
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