5_V_UPS

Published:2009/6/26 5:22:00 Author:Jessie | From:SeekIC

A 9-V wall adapter supplies VIN. IC2 contains a low-battery detector circuit that senses VIN by means of R6 and R7. The detector output (pin 7) drives an inverter (Q1), which in tum drives the shut-down inputs IC of IC1 and SHDN of IC2. These inputs have opposite-polarity active levels. The common feedback resistors, R2 and R3 enable both regulators to sense the output voltage, VOUT. When IC2 shuts down, its output turns off. However, when IC1 shuts down, the whole chip assumes a low-power state and draws under 1 μA. L1, D2, C1, C2, R2, and R3 are part of the 250-mW switching regulator. Diodes D3 and D4 wire-OR the power connection to IC2, and C3 improves the linear regulator's load regulation.



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