Fixed 24V rail for analog and bias supplies
The L78L24ACUTR is a positive fixed linear regulator delivering 24 V output at up to 100 mA from a SOT-89-3 package. It accepts a maximum input of 40 V, giving roughly 16 V of headroom above the regulated rail — enough to ride through ripple on a loosely regulated 28 V or 36 V bus without dropping out. The 37 dB PSRR at 120 Hz means the output attenuates full-wave-rectified ripple by about 70× — relevant when the supply comes from a mains-frequency transformer and bridge rectifier, where 120 Hz is the dominant noise component.
What the ratings mean for the BOM line
With a 6 mA quiescent current (Iq), the regulator's own draw is a fixed overhead on the input rail regardless of load — at light loads like a 10 mA sensor bias, the Iq represents 37% of the total input current, so the efficiency is low, but that is typical for a linear regulator in this class. Built-in protection against over-current, over-temperature, and short-circuit means the regulator folds back or shuts down before damaging itself — useful when the downstream load is a capacitor bank that draws inrush at power-up.
The 0°C lower operating limit means no special cold-start handling, but the tab's solder joint should be inspected for voiding if the regulator runs near its 100 mA limit continuously.
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