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DC barrel jack

The round power socket for wall adapters (5.5/2.1 mm). Usually centre positive; add reverse-polarity protection because adapters vary.

What it does#

The DC-005 jack takes the common 5.5 mm outer / 2.1 mm inner plug. Pins: 1 = centre pin, 2 = sleeve, 3 = switch (connected to the sleeve until a plug is inserted; useful to detect the plug or to switch a battery off). Most adapters are centre positive, marked ⊖–◯–⊕ on the label.

Example circuit: Centre (pin 1) is VIN_RAW; D1 (SS14) blocks a reversed adapter; C1 (1000 µF) buffers 12V. The switch pin is unused.
Centre (pin 1) is VIN_RAW; D1 (SS14) blocks a reversed adapter; C1 (1000 µF) buffers 12V. The switch pin is unused. Open the barrel_jack_input example from this page in PCB Canvas: “Insert into my schematic”.

Pitfalls#

  • Polarity is a convention, not a rule. Protect the input: a series Schottky (simple, ~0.4 V loss) or a P-MOSFET (almost no loss).
  • Voltage varies: a “12 V” unregulated adapter can measure 16 V without load. Size the regulator input (the AP63203 takes 32 V).
  • 2.1 vs 2.5 mm centre pins look alike; a 2.5 mm plug wobbles in a 2.1 mm jack.

Footprint#

Through-hole (C84007, extended), 3 A.