mSMD110-33V - +5V Rail PTC Resettable Fuse
Auto-reset overcurrent protection for +5V power rail with 1.1A hold current.
- π View on JLCPCB: C70119
- π Datasheet: Contact manufacturer
Overviewβ
The mSMD110-33V is a PTC resettable fuse providing automatic overcurrent protection for the +5V power rail. It protects the L7805 linear regulator and downstream modules from overcurrent conditions while automatically resetting after cooling.
Part Informationβ
| Parameter | Value |
|---|---|
| JLCPCB Part Number | C70119 |
| Manufacturer Part Number | mSMD110-33V |
| Package | 1812 (4.5mm x 3.2mm) |
| Stock | 44,459 units (excellent availability) |
| Estimated Price | ~$0.10-0.15 |
| Type | Resettable Polymeric PTC |
Electrical Specificationsβ
Current Ratingsβ
| Parameter | Value | Unit | Conditions |
|---|---|---|---|
| Hold Current | 1.1 | A | Maximum safe continuous current |
| Trip Current | ~2.2 | A | Typical (2x hold current) |
| Voltage Rating | 33 | V | Maximum voltage |
Key Characteristicsβ
| Parameter | Value | Unit |
|---|---|---|
| Initial Resistance | <0.05Ξ© | (typical) |
| Trip Time @ 2x Hold | 1-5 | s |
| Reset Time | 30-60 | s |
| Operating Temp | -40 to +85 | Β°C |
Circuit Integrationβ
Protection Architectureβ
Layer 1: USB-PD Adapter β Overcurrent protection
Layer 2: LM2596S #2 (+7.5V) β Current limiting ~3-5A
Layer 3: LM7805 Linear Regulator β Current limiting ~1A, thermal shutdown
Layer 4: This PTC (1.1A hold / 2.2A trip) β Auto-reset protection
β
+5V Output to Modules
Circuit Placementβ
LM7805 Output βββ¬βββ PTC2 (1.1A) ββββ¬βββ TVS2 βββ +5V OUT
β mSMD110-33V β SD05
β β β
β ββββββGND
β
ββββ LED3 βββ R8 (1kΞ©) βββ GND
Blue status indicator
Protection Behaviorβ
Current vs Protection Stateβ
| Current | L7805 State | PTC State | Result |
|---|---|---|---|
| 0-1.0A | β Normal | β Normal | Normal operation |
| 1.0-1.5A | β οΈ Current limiting | β οΈ Warming | Both protections activating |
| >1.5A | π Hard limit (~1A max) | π Trips | Dual protection active |
Design Rationaleβ
Why 1.1A hold for 1.5A target?
Hold current: 1.1A
Design target: 1.5A (L7805ABD2T-TR max)
Note: PTC trips before reaching regulator max
Behavior:
β οΈ PTC will trip if load exceeds 1.1A sustained
β
Prevents false trips during power-on surge
β
Allows brief current spikes
β
Provides additional protection layer
β
L7805ABD2T-TR handles 1.5A but PTC limits to 1.1A
Note: The 1.1A PTC hold current is lower than the 1.5A regulator capacity. If 1.5A sustained current is needed, consider upgrading to a 1.5A PTC. For typical modular synth applications, 1.1A is usually sufficient.
Comparison to +12V Railβ
| Feature | +5V PTC (This) | +12V PTC |
|---|---|---|
| Hold current | 1.1A | 1.5A |
| Package | 1812 | SMD1210 |
| Regulator max | 1.5A | 1.5A |
| PTC limits to | 1.1A | 1.5A |
| Stock | 44,459 | 7,525 |
Note: The +5V PTC limits current to 1.1A, which is lower than the regulator's 1.5A capacity. For typical modular synth applications using the +5V rail (digital modules, some LEDs), 1.1A is usually sufficient.
Bill of Materialsβ
| Designator | Part | Package | JLCPCB Part # | Qty | Unit Price | Extended |
|---|---|---|---|---|---|---|
| PTC2 | mSMD110-33V | 1812 | C70119 | 1 | $0.10 | $0.10 |
Related Componentsβ
- Protected circuit: L7805ABD2T-TR (U7) - +5V Linear Regulator
- Upstream: LM2596S-ADJ #2 (U3) - +7.5V DC-DC Converter
- Overvoltage protection: SD05 (TVS2)
- Parallel rails: PTC +12V (C7529589), PTC -12V (C2830246)
Referencesβ
- Protection design:
/doc/docs/learning/protection-fuse-strategy.md - Circuit diagram: Diagram6 - +5V Linear Regulator
- JLCPCB Part Page: https://jlcpcb.com/partdetail/C70119