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LNK364DN-TL Datasheet(PDF) 5 Page - Power Integrations, Inc. |
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LNK364DN-TL Datasheet(HTML) 5 Page - Power Integrations, Inc. |
5 / 16 page LNK362-364 2-5 5 Rev. E 11/08 The LinkSwitch-XT is completely self-powered from the DRAIN pin, requiring only a small ceramic capacitor C3 connected to the BYPASS pin. No auxiliary winding on the transformer is required. Key Application Considerations LinkSwitch-XT Design Considerations Output Power Table The data sheet maximum output power table (Table 1) represents the maximum practical continuous output power level that can be obtained under the following assumed conditions: 1. The minimum DC input voltage is 90 V or higher for 85 VAC input, or 240 V or higher for 230 VAC input or 115 VAC with a voltage doubler. The value of the input capacitance should be large enough to meet these criteria for AC input designs. 2. Secondary output of 6 V with a fast PN rectifier diode. 3. Assumed efficiency of 70%. 4. Voltage only output (no secondary-side constant current circuit). 5. Discontinuous mode operation (K P >1). 6. A primary clamp (RCD or Zener) is used. 7. The part is board mounted with SOURCE pins soldered to a sufficient area of copper to keep the SOURCE pin temperature at or below 100 °C. 8. Ambient temperature of 50 °C for open frame designs and an internal enclosure temperature of 60 °C for adapter designs. Below a value of 1, K P is the ratio of ripple to peak primary current. Above a value of 1, K P is the ratio of primary MOSFET OFF time to the secondary diode conduction time. Due to the flux density requirements described below, typically a LinkSwitch-XT design will be discontinuous, which also has the benefits of allowing lower cost fast (instead of ultra-fast) output diodes and reducing EMI. Clampless Designs Clampless designs rely solely on the drain node capacitance to limit the leakage inductance induced peak drain-to-source voltage. Therefore, the maximum AC input line voltage, the value of V OR, the leakage inductance energy, a function of leakage inductance and peak primary current, and the primary winding capacitance determine the peak drain voltage. With no significant dissipative element present, as is the case with an external clamp, the longer duration of the leakage inductance ringing can increase EMI. The following requirements are recommended for a universal input or 230 VAC only Clampless design: 1. A Clampless design should only be used for P O ≤ 2.5 W, using the LNK362† and a V OR** ≤ 90 V. 2. For designs where P O ≤ 2 W, a two-layer primary should be used to ensure adequate primary intra-winding capacitance in the range of 25 pF to 50 pF. 3. For designs where 2 < P O ≤ 2.5 W, a bias winding should be added to the transformer using a standard recovery rectifier diode to act as a clamp. This bias winding may also be used to externally power the device by connecting a resistor from the bias-winding capacitor to the BYPASS pin. This inhibits the internal high-voltage current source, reducing device dissipation and no-load consumption. 4. For designs where P O > 2.5 W Clampless designs are not practical and an external RCD or Zener clamp should be used. 5. Ensure that worst-case high line, peak drain voltage is below the BV DSS specification of the internal MOSFET and ideally ≤ 650 V to allow margin for design variation. †For 110 VAC only input designs it may be possible to extend the power range of Clampless designs to include the LNK363. However, the increased leakage ringing may degrade EMI performance. **V OR is the secondary output plus output diode forward voltage drop that is reflected to the primary via the turns ratio of the transformer during the diode conduction time. The V OR adds to the DC bus voltage and the leakage spike to determine the peak drain voltage. Audible Noise The cycle skipping mode of operation used in LinkSwitch-XT can generate audio frequency components in the transformer. To limit this audible noise generation, the transformer should be designed such that the peak core flux density is below 1500 Gauss (150 mT). Following this guideline and using the standard transformer production technique of dip varnishing practically eliminates audible noise. Vacuum impregnation of the transformer should not be used due to the high primary capacitance and increased losses that result. Higher flux densities are possible, however careful evaluation of the audible noise performance should be made using production transformer samples before approving the design. Ceramic capacitors that use dielectrics, such as Z5U, when used in clamp circuits may also generate audio noise. If this is the case, try replacing them with a capacitor having a different dielectric or construction, for example a film type. LinkSwitch-XT Layout Considerations See Figure 6 for a recommended circuit board layout for LinkSwitch-XT (P & G package). Single Point Grounding Useasinglepointgroundconnectionfromtheinputfiltercapacitor to the area of copper connected to the SOURCE pins. |
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