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Motore di ricerca datesheet componenti elettronici |
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Motore di ricerca datesheet componenti elettronici |
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LT1737 Scheda tecnica(PDF) 21 Page - Linear Technology |
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LT1737 Scheda tecnica(HTML) 21 Page - Linear Technology |
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21 / 28 page  21 LT1737 1737f TYPICAL APPLICATIO S BASIC APPLICATION WITH 3-WINDING TRANSFORMER Figure 8 shows a compact, low power application of the LT1737. Transformer T1 is an off-the-shelf VERSA-PAC TM, #VP1-0190, produced by Coiltronics. As manufactured, it consists of six ideally identical independent windings. In this application, two windings are stacked in series on the primary side and three are placed in parallel on the secondary side. This arrangement provides a 2:1 primary- to-secondary turns ratio while maximizing overall effi- ciency. The remaining primary side winding provides a ground-referred version of the flyback voltage waveform for the purpose of feedback. The design accepts an input voltage in the range of 8V to 25V and outputs an isolated 5V. To prevent overvoltage on the LT1737 and the gate of MOSFET M1, an LT1121 low dropout linear regulator is employed (U2). Resistor di- vider R11/R12 sets the output of U2 at nominally 8.25V. (A few hundred millivolts of dropout will therefore be seen at the very bottom of the input supply range.) The positive going drive potential at the LT1737 GATE pin is typically 2V or so below its VCC supply pin, so a logic level MOSFET has been specified for M1. Capacitor C6 sets the switching frequency at approxi- mately 200kHz. Optimal load compensation for the transformer and secondary circuit components is set by resistor R8. Resistor R10 provides a guaranteed mini- mum load of about 20mA to maintain rough output voltage regulation. The soft-start and UVLO features are unused as shown. PGND ISENSE GATE VC FB R1 0.2 Ω 0.5W IRC TYPE LR 2010 M1 IRLL014 R2 5.1 Ω 5% 1 10 7 3 T1 COILTRONICS VP1-0190 6 4 2 5 R13 51 Ω 5% VCC UVLO 3VOUT SGND 1737 F08 RCMPC ROCMP MINENAB LT1737 R7 51k 5% R6 51k 5% C6 47pF 50V NPO 6 8 7 3 910 15 16 2 1 2 8 3 14 13 12 4 5 11 1 ENDLY SFST OSCAP tON C5 1nF 25V X7R R8 4.3k 5% R9 68 Ω 5% D2 1N5250 D3 MBR0540 R5 51k 5% R11 24k 5% C1: SANYO ALUMINUM ELECTROLYTIC (35CV331GX) C2: SANYO POSCAP (10TPC68M) C8: SANYO POSCAP (10TPA33M) D1: MOTOROLA 30V, 3A SCHOTTKY RECTIFIER D2: 20V, 500mW ZENER DIODE D3: MOTOROLA 40V, 0.5A SCHOTTKY RECTIFIER R12 20k 5% R4 3.92k 1% R3 12.7k 1% C3 1 µF 25V Z5U C1 330 µF 35V VIN C7 0.1 µF 25V Z5U C9 1nF 25V X7R C4 470pF 50V X7R OUT U2 LT1121 ADJ INP GND • • • • 11 8 • 12 D1 MBRD330 9 • + C2 68 µF 10V + C8 33 µF 10V L1 1 µH OPTIONAL OUTPUT FILTER + R10 240 Ω 5% VOUT 5V 500mA VOUT 5V 500mA L1: COILCRAFT DO1608C-102 1 µH, 0.05Ω INDUCTOR M1: INT’L RECTIFIER IRLL014 60V, 0.2 Ω LOGIC LEVEL N-CH MOSFET U2: LINEAR TECHNOLOGY MICROPOWER LDO REGULATOR Figure 8. 8V-25V to Isolated 5V Converter VERSA-PAC is a trademark of Coiltronics, Inc. |
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