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LNK562G Datasheet(PDF) 4 Page - Power Integrations, Inc. |
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LNK562G Datasheet(HTML) 4 Page - Power Integrations, Inc. |
4 / 16 page 4 LNK562-564 F 10/05 Applications Example The circuit shown in Figure 5 is a typical implementation of a 6 V, 330 mA, constant voltage, constant current (CV/CC) output power supply. AC input differential filtering is accomplished with the very low cost input filter stage formed by C1 and L1. The proprietary frequency jitter feature of the LNK564 eliminates the need for an input pi filter, so only a single bulk capacitor is required. Adding a sleeve may allow the input inductor L1 to be used as a fuse as well as a filter component. This very simple Filterfuse™ input stage further reduces system cost. Alternatively, a fusible resistor RF1 may be used to provide the fusing function. Input diode D2 may be removed from the neutral phase in applications where decreased EMI margins and/or decreased input surge withstand is allowed. In such applications, D1 will need to be an 800 V diode. The power supply utilizes simplified bias winding voltage feedback, enabled by LNK564 ON/OFF control. The resistor divider formed by R1 and R2 determine the output voltage across the transformer bias winding during the switch OFF time. In the V/I constant voltage region, the LNK564 device enables/disables switching cycles to maintain 1.69 V on the FB pin. Diode D3 and low cost ceramic capacitor C3 provide rectification and filtering of the primary feedback winding waveform.At increased loads, beyond the constant power threshold, the FB pin voltage begins to reduce as the power supply output voltage falls. The internal oscillator frequency is linearly reduced in this region until it reaches typically 50% of the starting frequency. When the FB pin voltage drops below the auto-restart threshold (typically 0.8 V on the FB pin, which is equivalent to 1 V to 1.5 V at the output of the power supply), the power supply will turn OFF for 800 ms and then turn back on for 100 ms. It will continue in this mode until the auto-restart threshold is exceeded. This function reduces the average output current during an output short circuit condition. No-load consumption can be further reduced by increasing C3 to 0.47 µF or higher. A Clampless primary circuit is achieved due to the very tight tolerance current limit trimming techniques used in manufacturing the LNK564, plus the transformer construction techniques used. Peak drain voltage is therefore limited to typically less than 550 V at 265 VAC, providing significant margin to the 700 V minimum drain voltage specification (BV DSS). Output rectification and filtering is achieved with output rectifier D4 and filter capacitor C5. Due to the auto-restart feature, the average short circuit output current is significantly less than 1A, allowing low cost rectifier D4 to be used. Output circuitry is designed to handle a continuous short circuit on the power supply output. Diode D4 is an ultra-fast type, selected for optimum V/I output characteristics. Optional resistor R3 provides a pre- load, limiting the output voltage level under no-load output conditions. Despite this pre-load, no-load consumption is within targets at approximately 140 mW at 265 VAC. The additional margin of no-load consumption requirement can be achieved by increasing the value of R4 to 2.2 k Ω or higher while still maintaining output voltage well below the 9 V maximum specification. Placement is left on the board for an optional Zener clamp (VR1) to limit maximum output voltage under open loop conditions, if required. Figure 5. 6 V, 330 mA CV/CC Linear Replacement Power Supply. D S FB BP J3-1 RTN 6 V, 0.33 A J3-2 L J-1 J-2 N D1 1N4937 RF1* 8.2 Ω 2.5 W C1 10 µF 400 V C2 0.1 µF 50 V L1 3300 µH D4 UF4002 D3 1N4005 C5 220 µF 25 V C3 330 nF 50 V C4* 100 pF 250 VAC *Optional components R3 2 k Ω VR1* 1N5240B 10 V R2 3 k Ω R1 37.4 k Ω T1 EE16 2 1 7 6 4 5 D2 1N4005 90-265 VAC LinkSwitch-LP PI-4106-101105 U1 LNK564P |
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