PPTC vs One-Time Fuse: Overcurrent Protection

1. Two ways to stop overcurrent

A PPTC (polymeric positive temperature coefficient) device is a resettable fuse: when current exceeds its trip point the polymer heats, expands and its resistance jumps by orders of magnitude, cutting the current. Remove the fault and it cools back to a low resistance.

A one-time fuse melts a metal element and stays open until replaced. It is precise, fast and unambiguous — but single-use.

2. The ratings that matter

Rating	PPTC	One-time fuse
Key spec	Ihold / Itrip	Irated, I²t
Trip ratio	Itrip ≈ 2 × Ihold	sharp at rated current
Reset	automatic	no (replace)
Trip time	seconds (thermal)	milliseconds
Leakage after trip	small residual current	zero
Best for	repeat faults, USB / IO ports	safety-critical, battery packs

PPTC hold current must be derated for ambient temperature: at 60–70°C a part may hold only 70–80% of its 25°C rating. Always check the derating curve.

3. When a PPTC is the right choice

• Ports that see repeated faults (USB, HDMI, sensor connectors)
• Boards where a service call to replace a fuse is expensive
• Low-voltage DC rails where a few seconds of trip delay is acceptable
• Keep I_hold at ≥ 1.5× your normal load current

4. When a one-time fuse is the right choice

• Safety / compliance requires a non-resettable break
• Battery packs and high-energy rails where a PPTC may not interrupt
• Fast, predictable clearing (I²t) is needed
• Select voltage rating ≥ system voltage and interrupt rating ≥ available fault current

5. How to choose

• Repeated, benign faults → PPTC
• One-shot safety break or high fault energy → fuse
• Check ambient temperature derating and trip time at your fault current
• Pair with a TVS for surge and ESD, since neither fuse stops a fast transient

Related products

• Resettable Fuse Series
• SMD Fuse Series
• TVS/ESD Protection
• Power Inductor Series