18650ma Battery charger Voltage Protector Circuit
Build a 18650 battery charger with voltage protection using TL431. Ensures safe charging, prevents overcharge, and extends battery life.
TL431 voltage protector for 18650
The battery charger will have a 18650 battery with TL431 voltage protection to ensure safe charging that will terminate at 4.2 V and prevent overcharging to prolong the battery life.
simple overcurrent protection circuit
A short-circuit overcurrent protection circuit is an important safety measure in electronics and electrical systems to ensure the safety of the equipment in case of overcurrent flow. This circuit detects the overcurrent when a short circuit or momentary explosion happens and cuts the power to the load to prevent failure of components, fire hazards, or damage to power sources.
Fuses, circuit breakers, or electronic components MOSFETs and current sensors, may be used as the overcurrent protection circuit. Current-sensing resistors, comparators, and relays or transistors are commonly used in modern DIY circuits and are used to reduce instantaneous load in the circuit when the current rises beyond a safe operational value. This guide will discuss the constituents, working principle, circuit diagramstep-by-stepep construction, as well as trip advice to construct a highly reliable short-circuit overcurrent protection system to be used in AC and DC applications.
Importance of Overcurrent Protection in Circuits
- Protects Devices: Prevents damage to sensitive electronics and appliances.
- Prevents Fire Hazards: Avoids overheating of wires and components.
- Improves Reliability: Ensures stable operation of power systems.
- Enhances Safety: Protects users from electrical risks.
- Supports Longevity: Extends circuit and power source lifespan.
Components Required for DIY Circuit
| Component | Quantity | Purpose |
|---|---|---|
| Fuse or Circuit Breaker | 1 | Initial protection for high current |
| Current Sensing Resistor (Shunt) | 1 | Detects overcurrent |
| Operational Amplifier / Comparator | 1 | Compares sensed current with reference |
| MOSFET or Relay | 1 | Switches load ON/OFF |
| Resistors | 2–5 | Biasing and voltage division |
| Capacitor | 1 | Filtering and stability |
| Power Supply | 1 | Powers the circuit |
| LED Indicator | 1 | Shows overcurrent status |
| PCB / Breadboard | 1 | Assembly platform |
Working Principle of Overcurrent Protection
1. Current Sensing
The shunt resistor measures load current through the voltage drop across it.
2. Comparison Stage
A comparator compares the sensed voltage with a reference representing the maximum safe current.
3. Load Disconnect
If the current exceeds the threshold, the comparator triggers a MOSFET or relay to disconnect the load.
4. Indicator LED
The LED turns on to indicate a fault/overcurrent condition.
5. Reset & Recovery
After clearing the fault, the system can reset automatically or manually.
Circuit Diagram Explanation
- Shunt Resistor: Placed in series with the load for current sensing.
- Comparator Input: One input receives shunt voltage; the other receives reference voltage.
- Comparator Output: Drives MOSFET gate or relay coil to disconnect the load.
- LED Indicator: Shows fault conditions through comparator output.
- Power Supply: Powers comparator and switching device.
Step-by-Step Construction Guide
- Place a shunt resistor in series with the load and connect its voltage drop to the comparator.
- Set reference voltage according to the desired maximum safe current.
- Connect the MOSFET or relay so that the comparator output controls the load.
- Add an LED with a resistor to show fault indication.
- Test circuit with normal and overcurrent conditions and adjust threshold if needed.
Applications of Overcurrent Protection Circuits
- Power supplies (AC/DC)
- Battery chargers and inverters
- Motors and industrial loads
- Home appliances
- DIY electronics projects
Troubleshooting Tips
- Load not disconnecting → Check comparator reference voltage and wiring.
- MOSFET/relay not switching → Ensure proper gate/base drive voltage.
- False triggering → Add a filtering capacitor to comparator input.
- LED not lighting → Verify resistor value and polarity.
- Circuit not powering → Check supply voltage and connection polarity.
