Ups 5Volt Circuit
A 9-V wall adapter supplies Vm. IC2 contains a low-battery detector circuit that senses l7IN by means of R6 and R7. The detector output Cpin 7) drives an inverter (Ql), which in turn drives the shut-down inputs Ic of 1C1 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, V0VT. 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 . LI, D2, Gl, C2, R2, and R3 are part of the 250-mW switching regulator. Diodes D3 and D4 wire-OR the power connection to IC2, and 03 improves the linear regulator`s load regulation.