Glass Fuses Mosfet Overcurrent Protection Circuit
Learn to build a glass-fused MOSFET overcurrent protection circuit to safeguard electronics. Step-by-step DIY guide, components, working, and FAQs included.
What Is a MOSFET Overcurrent Protection Circuit?
An electronic protection circuit, also known as a MOSFET overcurrent protection circuit, is an electrical circuit that operates MOSFETs as variable-controllable switches to short a load if the current that passes through the load is more than a specified limit. An electronic control is backed by the introduction of a glass fuse in the event of failure.
mosfet cutoff circuit for over current protection
A glass-fused MOSFET overcurrent protection circuit is an electronics safety project that is necessary to ensure that devices are protected against too much current that might destroy the parts. In this DIY project, a glass fuse is used as the primary protection device that blows when the current is greater than some predetermined point, and a MOSFET is used as a fast electronic switch turn off the current in the case of overcurrent.
The construction also provides dual protection to the circuit, with the large overcurrents being dealt with by the use of glass fuses, whilst short-term spikes or fault conditions can be responded to by the MOSFET. This kind of glass fuse combination of MOSFET overcurrent protection circuit is perfect in power supply, battery-powered applications, DC-DC converters, and at-home electronic applications where delicate devices demand high-quality protection. The construction of this circuit provides some useful experience in the field of electronics, such as how to sense current, switch with a MOSFET, and select a fuse to make the required choice.
Glass Fuse + MOSFET Overcurrent Protection Circuit
Dual-layer protection using a fast MOSFET cutoff combined with a replaceable glass fuse — ideal for DC systems, battery packs, and DIY power electronics.
Advantages of Using Glass Fuses with MOSFETs
- Dual Protection: MOSFET handles fast spikes; glass fuse provides large-current cutoff.
- Improved Safety: Reduces risk of overheating or component damage.
- Resettable/Replaceable: Fuse is replaceable; MOSFET resets after fault is cleared.
- Compact Design: Suitable for DC circuits and battery systems.
- Cost-Effective: Uses common components and simple design.
Components Required
| Component | Quantity | Purpose |
|---|---|---|
| Glass Fuse (0.5A–10A) | 1 | Primary overcurrent protection |
| N-Channel MOSFET (IRFZ44N / similar) | 1 | Electronic switching / cutoff |
| Shunt Resistor (0.01–0.1Ω) | 1 | Current sensing |
| Op-Amp / Comparator (LM358 / LM393) | 1 | Detects overcurrent and drives MOSFET gate |
| Pull-up / Bias Resistors | Various | Comparator reference & gate control |
| Capacitors | Various | Filtering and stability |
| LED Indicator | 1 | Trip / fault indication |
| Power Supply (DC 5–24V) | 1 | Circuit power |
| PCB / Perfboard | 1 | Assembly |
Working Principle
Input Stage: Power flows through a glass fuse to the MOSFET/drain — the fuse protects against sustained high currents.
Current Sensing: A low-value shunt resistor measures load current. Vshunt = I × Rshunt.
Decision Stage: Comparator/op-amp monitors the shunt voltage and compares it to a reference. On overcurrent, the comparator drives the MOSFET gate to cut off current.
Load Protection: MOSFET disconnects the load quickly. If the fault persists, the glass fuse may blow and must be replaced.
Indicators & Reset: LED shows trip state. MOSFET typically resets when the fault clears or power cycles; fuse replacement may be needed for sustained faults.
Circuit Diagram (Text)
Power Input → [Glass Fuse] → MOSFET (Drain) MOSFET (Source) → Shunt Resistor → Load → Ground Shunt Voltage → Comparator (+) Reference Voltage → Comparator (−) Comparator Output → MOSFET Gate (via gate resistor) Comparator Output → LED (with series resistor)
Step-by-Step Construction Guide
- Install the glass fuse in series with the power input (use proper fuse holder).
- Wire MOSFET: drain after fuse, source to shunt/load ground as per topology.
- Place shunt resistor in series with load (low-ohm, high-power rated).
- Build comparator circuit: feed shunt voltage to comparator + input and set threshold on − input.
- Drive MOSFET gate from comparator through a gate resistor; add pull-down to keep gate low when idle.
- Add LED indicator on comparator output with current-limiting resistor.
- Test with incremental loads; verify MOSFET cuts off at the desired trip current and the fuse only blows on sustained faults.
Applications
- DC power supplies and battery protection
- Solar power and charge controllers
- DC–DC converters and LED drivers
- Robotics and motor protection
- General DIY electronics safety
Troubleshooting Tips
| Problem | Fix |
|---|---|
| MOSFET not turning off | Check comparator reference, gate resistor, and gate pull-down; confirm comparator output swings correctly. |
| Fuse blowing too soon | Verify fuse rating and wiring; check for shorts or inrush currents that require slow-blow fuse. |
| LED not lighting on trip | Check LED polarity and series resistor; verify comparator output state during trip. |
| Load receives partial voltage | Check shunt placement and wiring; ensure MOSFET orientation is correct and not partially conducting. |
| Circuit oscillating/unstable | Add input filtering capacitors and small RC filter at comparator input; add hysteresis to comparator. |
Want a full schematic (SVG/PNG) or a PCB-ready layout for this circuit? I can generate it—tell me your preferred MOSFET and shunt values and I’ll create the schematic.
Frequently Asked Questions - Glass Fuses Mosfet Overcurrent Protection Circuit:
What is a MOSFET overcurrent protection circuit?
A circuit using MOSFETs to switch off load when current exceeds a limit, often combined with a glass fuse.
Why use glass fuses with MOSFETs?
Glass fuses provide backup protection for large currents, while MOSFETs respond quickly to spikes.
Which MOSFET is suitable?
N-channel MOSFETs like IRFZ44N or equivalent with appropriate voltage/current rating.
How is current sensed?
Using a low-value shunt resistor connected in series with the load.
Can this protect AC devices?
This circuit is mainly for DC applications; AC requires special design considerations.
How do I set the overcurrent threshold?
Adjust comparator reference voltage corresponding to desired current via shunt resistor.
Does the MOSFET reset automatically?
Yes, after overcurrent ends, MOSFET gate control can restore conduction; fuse must be replaced if blown.
What fuse rating should I use?
Select fuse slightly above maximum normal current of the load for protection.
Can I use this for battery systems?
Yes, suitable for Li-ion, lead-acid, or other DC battery circuits.
Is LED indicator necessary?
Optional, but it visually indicates when overcurrent occurs.
