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LNK562D Datasheet(PDF) 5 Page - Power Integrations, Inc. |
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LNK562D Datasheet(HTML) 5 Page - Power Integrations, Inc. |
5 / 16 page LNK562-564 5 Rev. H 11/08 Key Application 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 Schottky 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 suitably sized core to allow a practical transformer design (see Table 2). 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-LP design will be discontinuous, which also has the benefit of allowing lower-cost fast (vs. 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. Clampless designs should only be used for P O ≤ 2.5 W using a V OR of ≤ 90 V 2. For designs with P O ≤ 2 W, a two-layer primary must be used to ensure adequate primary intra-winding capacitance in the range of 25 pF to 50 pF. 3. For designs with 2 < P O ≤ 2.5 W, a bias winding must be added to the transformer using a standard recovery rectifier diode (1N4003– 1N4007) 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. FordesignswithP 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. V OR (Reflected Output Voltage), 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-LP 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 is not recommended, as it does not provide any better reduction of audible noise than dip varnishing. And although vacuum impregnation has the benefit of increased transformer capacitance (which helps in Clampless designs), it can also upset the mechanical design of the transformer, especially if shield windings are used. Higher flux densities are possible, increasing the power capability of the transformers above what is shown in Table 2. 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. Bias Winding Feedback To give the best output regulation in bias winding designs, a slow diode such as the 1N400x series should be used as the rectifier. This effectively filters the leakage inductance spike and reduces the error that this would give when using fast recovery time diodes. The use of a slow diode is a requirement in Clampless designs. LinkSwitch-LP Device Core Size LNK562 LNK563 LNK564 EE13 1.1 W 1.4 W 1.7 W EE16 1.3 W 1.7 W 2 W EE19 1.9 W 2.5 W 3 W Table 2. Estimate of Transformer Power Capability vs. LinkSwitch-LP Device and Core Size at a Flux Density of 1500 Gauss (150 mT). |
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