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LR645 Datasheet(PDF) 3 Page - Supertex, Inc |
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LR645 Datasheet(HTML) 3 Page - Supertex, Inc |
3 / 9 page 3 LR645 LR645: SMPS Start-Up Circuit Symbol Parameter Min Typ Max Units Conditions I AUX Input current to V OUT - - 200 µA V AUX ≥ VOUT +1V applied to VOUT pin ΔV OUT/ ΔV IN Ripple rejection ratio1 50 60 - dB 120Hz, No Load e n Noise voltage1 - 25 - µV 0.01 to 100KHz I PEAK Output peak current2 - 30 - mA C OUT = 10µF, VIN = 400V V AUX External voltage applied to V OUT - - 13.2 V --- 8-lead, adjustable output voltage version only: Test conditions unless otherwise specified: T A = 25°C; VIN = 15 to 450V, COUT = 0.01µF V OUT Output regulation trim range1 8 - 12 V No load ΔV OUT Load regulation at 8V trim1 - 200 400 mV V IN = 15V, IOUT = 0 to 1.0mA Load regulation at 12V trim1 - 100 400 mV V IN = 50V, IOUT = 0 to 3.0mA Notes: 1. Guaranteed by design, not tested in production. 2. Pulse test duration < 1.0msec, Duty cycle < 2% One of the main applications for the LR645 is a start-up circuit for off-line switch-mode power supplies (SMPS), as shown in Figure1. A minimum output capacitance of 0.01µF is recommended for stability. The wide operating input volt- age range of the LR645 allows the SMPS to operate and start-up from rectified AC or a DC voltage of 15V to 450V without adjustment. During start-up, the LR645 powers the V CC line of the PWM IC with a nominal output voltage of 10V. The auxiliary voltage connected through a diode to the V OUT pin of the LR645 will start to increase. When the auxiliary voltage becomes larger than the output voltage the LR645 turns OFF its internal high voltage input line and output voltage, allowing the auxiliary voltage to power the V CC line of the PWM IC. The input cur- rent drawn by the LR645 from the high voltage line after start-up will therefore only be leakage current of the internal MOSFET switch, which is typically 0.1µA. The 3-terminal version shown in Figure 1 has load regula- tion guaranteed from 0 to 3.0mA at a fixed nominal output voltage of 10V. Applications requiring higher output current and/or a different output voltage can use the 8 pin adjustable version. Figure 1: SMPS Start-Up Circuit + 15V to 450V – + 5.0V – V AUX = 12V C OUT C IN V CC PWM IC LR6 GND V IN |
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Similar Description - LR645_07 |
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