Power Rails & Supplies#

Supply verification, ripple, regulation, current draw, sequencing, energy storage behavior. Power is the first thing to check and the last thing people suspect — and it causes more mysterious failures than almost anything else.

• Is voltage present? — First check at power-up. Confirm the rail exists before looking at anything downstream.
• Is voltage correct under load? — Static regulation and load-dependent droop. What the rail looks like when the circuit is actually drawing current.
• How much ripple / noise on the rail? — AC on top of DC. Switching converter ripple, LDO noise, and knowing what’s acceptable vs. problematic.
• Is current draw expected? — Total supply current, per-rail current, and spotting overcurrent or undercurrent conditions.
• Are rails sequencing correctly? — Multi-rail systems where order matters. FPGA supplies, mixed-signal boards, and anything with enable chains.
• How is the bulk capacitance / battery behaving? — Energy storage health. Bulk cap ESR, battery voltage under load, and holdup time.