DC Electronic Circuit Breaker with Fast Trip

DC distribution is everywhere in student and prototype work — solar installations, battery banks, telecom supplies, EV auxiliary circuits — yet the protection most benches reach for is still the thermal-magnetic MCB, a device designed around AC mains behavior. In a DC circuit there is no natural current zero to quench an arc, and a thermal trip that takes seconds to react can let a shorted converter or a stalled motor destroy itself long before the contacts open. Fuses are faster but single-use and imprecise. An electronic DC breaker answers this with fully solid-state switching: power MOSFETs in the current path, a Hall-effect sensor watching current continuously, and a comparator stage that drops the gate drive the instant current exceeds a set threshold. The result is a resettable, adjustable protector that demonstrates genuine power-electronics concepts — gate driving, isolated current sensing, fault latching — in a compact 12–24 V prototype.

1. The DC source (12–24 V battery or bench supply) feeds the load through the MOSFET pass element, with the ACS712 sensor in series producing a voltage proportional to load current.
2. The sensor signal is filtered and fed to one input of the LM393 comparator; the other input carries the threshold reference set by the front-panel potentiometer.
3. Under normal load the sensor voltage stays below the reference, the comparator output keeps the TC4420 gate driver enabled, and the MOSFETs stay fully on with milliohm-level on-resistance.
4. When an overload or short drives current past the set threshold, the comparator flips and the gate driver pulls the MOSFET gates to ground — the pass element turns off and the load is isolated from the source.
5. The controller latches the trip state, lights the red fault LED and freezes the peak current reading on the OLED for the fault analysis in the report.
6. The output remains off until the user presses the front-panel reset button (or the configured auto-retry interval elapses), preventing repeated re-energization of a persistent fault.
7. During normal operation the controller continuously samples the sensor and updates the OLED with live current, threshold and status.

Tech stack:

• Arduino Nano (ATmega328P) for monitoring, display and reset logic
• IRF3205-class N-channel power MOSFETs as the series switching element
• ACS712-20A Hall-effect current sensor (isolated measurement)
• LM393 comparator for the fast hardware trip path
• TC4420 MOSFET gate driver
• 0.96-inch I2C OLED display for current and status readout
• KiCad for schematic and PCB layout; Arduino IDE for firmware
• 12–24 V DC source and test load (bench supply / battery, user side)

• [Solid-state MOSFET switching] N-channel power MOSFETs (IRF3205 class) form the series pass element. There are no moving contacts, no arcing and no contact wear, so the breaker can trip thousands of times where a relay-based cutoff would degrade.
• [Hall-effect current sensing] An ACS712-20A isolated sensor measures load current continuously without inserting a high-side shunt into the power path or disturbing the load ground. The controller sees true load current, including startup inrush.
• [Fast electronic trip] An LM393 comparator watches the sensor output against the threshold reference and pulls the MOSFET gate drive low on overcurrent. The design target is under 100 microseconds from fault to switch-off, derived from comparator and gate-driver propagation delays.
• [Adjustable trip threshold] The current limit is set with a front-panel potentiometer and read back on the display, so the same module demonstrates protection at 2 A for a small DC motor and 10 A for a battery bank.
• [Latch-off with manual reset] After a trip the output stays off until the reset button is pressed, so an intermittent short cannot repeatedly re-energize the load. An auto-retry mode is available as a configurable option.
• [Live current and status display] A 0.96-inch OLED shows measured current, the set threshold and trip/fault status, giving the examiner a visible, verifiable readout during the demonstration.
• [Inrush blanking for motor loads] A short configurable blanking window after switch-on ignores the normal startup surge of DC motors and capacitive loads, so the breaker trips on genuine faults rather than on turn-on transients.

• Assembled and wired DC electronic breaker prototype module
• Controller firmware (Arduino sketch) with threshold, inrush-blanking and reset logic
• Circuit schematic and wiring diagram (KiCad sources plus PDF)
• Bill of materials with part numbers and sourcing notes
• Project report PDF (background, design calculations, gate-drive and sensing design, buyer-run test procedure)
• PPT presentation for final review
• Viva Q&A preparation document (MOSFET switching, comparators, Hall-effect sensing, DC fault behavior)
• Setup and demo guide (wiring source and load, setting the threshold, demonstrating a trip safely)

• This is an academic prototype, not a certified protection device: it must not be used as the sole protection on mains-connected, high-energy or safety-critical installations.
• The sub-100 µs trip figure is a design target derived from comparator and gate-driver propagation delays, not a value measured on a calibrated high-speed rig; the report includes a buyer-run oscilloscope procedure to verify it.
• The continuous current rating depends on MOSFET heatsinking and ambient temperature; sustained operation near 10 A needs the specified heatsink and airflow, confirmed by the buyer's thermal check.
• The prototype covers low-voltage DC (12–24 V) only; it provides no AC mains protection and no galvanic isolation between source and load beyond the MOSFET off-state.
• Prototype wiring inductance and layout affect real switching behavior; the supplied PCB layout keeps the power loop tight, but a hand-wired build will trip slower than the design target.
• Single-pole low-side switching only: the load's positive rail stays connected to the source when tripped, which the report explains and the demo wiring accounts for.