15. PPTC Fuse for Speaker Output Protection
1. Component Purpose & Calculation
If the speaker output is shorted or the amplifier clips at full power for a sustained period, the current can exceed safe levels for the speaker voice coil and amplifier output stage.
A PTC fuse in the speaker line trips on sustained overload, protecting both the speaker and amplifier. It resets automatically when the fault clears.
Current Calculation:
P = 10W, R = 4Ω. I = √(P/R) = √(10/4) = √2.5 ≈ 1.58A RMS
With 25–55% margin for thermal derating and dynamic peaks: Ih = 2.0A to 2.5A
Required: Polymeric · Ih 2.0–2.5A · ≥16V · Imax ≥10A · Through Hole · Littelfuse
2. How to Find It on DigiKey
Same category and similar filters as Task 2:
- Current - Hold (Ih) → 2.0A to 2.5A
- Voltage - Max → 16V or higher
- Mounting Type → Through Hole
- Manufacturer → Littelfuse Inc.
Tip: Audio amplifiers may have brief transient peaks well above the RMS current. The PTC’s thermal mass prevents it from tripping on short music peaks — it only trips on sustained overload lasting several seconds.
3. Key Specifications & What They Mean
| Specification | Required | Why |
|---|---|---|
| Type | Polymeric | Standard resettable PTC. |
| Hold Current | 2.0–2.5A | Normal ~1.6A + derating/peak margin. |
| Voltage Max | ≥16V | Exceeds 12V amplifier supply. |
| Current Max | ≥10A | Survives short-circuit on speaker output. |
| Mounting | Through Hole | Robust for audio output path. |
| 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 the manufacturer reputable? Is a datasheet available?
Full checklist: How to Select a Safe, Production-Ready Component — EWskills Guide