9. SMD Fuse for Motor Controller Input
1. Component Purpose & Calculation
The 12V motor draws up to 3A during normal running. But during startup, a DC motor can briefly draw several times its running current as inrush. A fast-blow fuse would trip on every motor start.
A slow-blow (time-delay) fuse tolerates brief inrush spikes but still opens if the overcurrent is sustained — protecting the PCB traces and components from a real fault.
Fuse Rating Selection:
Normal load = 3A. With margin for startup and derating, a 4A slow-blow fuse is selected. This holds during brief inrush but blows on sustained overcurrent above 4A.
Required: Board Mount · 4A · ≥32VDC · Slow Blow · 1206 · SMD · Littelfuse · RoHS
2. How to Find It on DigiKey
Go to DigiKey.com → Circuit Protection → Fuses
Apply these filters:
- Fuse Type → Board Mount (exclude Cartridge Style)
- Current Rating (Amps) → 4A
- Voltage Rating - DC → 32V or higher
- Response Time → Slow Blow
- Package / Case → 1206 (3216 Metric)
- Mounting Type → Surface Mount
- Manufacturer → Littelfuse Inc.
- Part Status → Active
Important: Do not select a fast-blow fuse for motor circuits. Motors draw high inrush current during startup — a fast-blow fuse will nuisance-trip on every power-on.
3. Key Specifications & What They Mean
| Specification | Required | Why |
|---|---|---|
| Fuse Type | Board Mount | Soldered on PCB; no external holder. |
| Current Rating | 4A | 3A load + margin for motor startup. |
| Voltage Rating | ≥32VDC | Adequate margin over 12V supply. |
| Response Time | Slow Blow | Tolerates motor inrush without tripping. |
| Package | 1206 | Compact SMD for PCB mounting. |
| Manufacturer | Littelfuse | Company AVL requirement. |
| RoHS | Yes | Compliance required. |
4. Selecting a Safe, Production-Ready Part
The filtered list will show matching parts. Before you pick one, check: Is it Active? Is stock available? Is a datasheet available?
Full checklist: How to Select a Safe, Production-Ready Component — EWskills Guide