4 pin Mini-Molex (Berg plug) connector at the powersupply cable.
The PC floppy drive power connector is a 4-pin, 2.5 mm pitch connector from the AMP EI series (housing AMP 171822-4) used to deliver +5 V and +12 V to 3.5-inch floppy disk drives. It was defined in every major revision of the Intel ATX12V Power Supply Design Guide from v1.1 through to v2.2, and remains listed in the current ATX Version 3.0 specification, where it is explicitly marked “Do Not Include — For Historical Reference Only”. The smaller 2.5 mm pitch distinguishes it from the larger 5.08 mm Molex-style peripheral power connector used for hard disks and optical drives. Wire gauge is 20 AWG throughout, and wire colours follow the ATX standard: red for +5 V, black for ground, and yellow for +12 V.
| Pin | Name | Color | Description |
|---|---|---|---|
| 1 | +5V | red | +5 VDC |
| 2 | GND | black | +5 V Ground |
| 3 | GND | black | +12 V Ground (Same as +5 V Ground) |
| 4 | +12V | yellow | +12 VDC |
Signals
- +5V — +5 VDC supply rail (red wire, pin 1); powers the drive’s logic circuitry.
- GND — Ground return for the +5 V rail (black wire, pin 2).
- GND — Ground return for the +12 V rail (black wire, pin 3); the ATX specification connects both grounds to the same return path.
- +12V — +12 VDC supply rail (yellow wire, pin 4); powers the drive’s spindle and head-actuator motors.
Notes
- The connector housing is the AMP EI series part 171822-4 (TE Connectivity), with a 2.5 mm (0.098 in) contact pitch and four positions in a single row. Compatible crimp contacts are AMP 170262 / 170263 series.
- The housing is rated for an operating temperature of −20 °C to +95 °C and a voltage of 250 VAC. The TE Connectivity datasheet specifies a current rating of 2 A per circuit, consistent with 20 AWG wire at this pitch; some ATX power supply references cite up to 3 A per circuit, but the connector manufacturer’s own limit is 2 A.
- The connector is keyed by a polarising tab on the housing that prevents incorrect insertion.
- As of the ATX Version 3.0 Power Supply Design Guide (Intel, 2023), this connector is classified historical-reference only and is no longer required in new power supply designs.
Connector part numbers
- Socket housing: AMP 171822-4
- Socket: AMP 170262-1
- Maximum current per circuit: 2 A (per TE Connectivity datasheet); up to 3 A cited in some ATX PSU references
References
- ATX Version 3.0 Power Supply Design Guide v2.01 — Floppy Drive Connector (Historical Reference Only)
- ATX 12V Power Supply Design Guide v1.3 — full text via Internet Archive
- TE Connectivity / AMP 171822-4 — EI Series 4-position 2.5 mm connector housing (the 3.5-inch floppy “Berg” power connector).