Low Noise Power Supply for Audio Circuits

This low noise audio power supply circuit can reduces noise and ripple voltage by 40dB over the 100Hz to 20kHz audio range. In portable application such as cellular phones and multimedia notebook computers, a clean source of 5V power for driving audio circuits can be provided by this circuit. Noise up to 1000Hz or so is rejected by most linear regulators and the bulk of a low-frequency passive filter is not compatible in portable applications. Noisy Vcc in the range 4.5V to 6V is accepted by this circuit. Here’s the circuit diagram:

This circuit also produces quiet Vcc at a DC level 7% lower. For example, the circuit produces 4.65V at 1A from a nominal 5V source, with only 200µA of quiescent current. The physical layout is very small: one SOT23 transistor, one µMAX (shrink SO-8) op amp, and a few passive components. 10µF is the largest capacitor, and the resistors can be 0.1W or surface-mount 0805 size. [Source: maxim-ic.com]