Electronically Designed Fuse for Power Supply

Figure 1 

The circuit was designed to create an electronic fuse that would provide electronic stabilization in the power supply and avoid the existence of excess current.

• Fuse – a type of electrical and electronic device used for overcurrent protection wherein it blows to interrupt the excessive current so it would prevent further damage
• 2N1613 – an NPN medium power transistor in a TO-39 metal package used for high speed switching and amplification due to its low current with maximum 500 mA and low voltage with maximum 50 V
• 2N3055 – a complementary Silicon Epitaxial-Base planar NPN transistor mounted in Jedec TO-3 metal case for use as power transistor
• BC107 – an epitaxial NPN silicon planar transistor having the collector electrically connected to the TO 18 metal case

The presence of overcurrent, overvoltage, overtemperature, and abrupt application of a voltage are typical with all electronic devices that get connected to any power source. T It is usually caused by short circuits, incorrect connection, or damage of repaired appliance. This is the reason why the means for protecting a circuit from excessive voltage or current is a necessary component of any electrical power supply system. Using the circuit will provide an effective protection in the power supply that is giving an output voltage up to 45 Vdc to prevent more current to pass on to the external circuit connected.

Figure 2 

The values of the resistors depend on the amount of current passing through the transistors. The input for any circuit will come from the output of the power supply. The transistor Q2 will turn ON under normal working conditions and will function in the saturation region through R1 and Q1. The output of the transistor is approximately 2 V lower than the voltage of the power supply. The transistor Q3 will start to conduct if a voltage drop is detected at R2 that reaches 0.7 V. During the conduction period, the voltage present can be measured at 0.3 V. When the voltage between the base of Q1 and emitter of Q2 is at least 1.4 V, the transistors Q1-2 will function as a driver to the circuit.

In the event that the overcharging occurs, the voltage will be 1 V taken from the sum of 0.7 V & 0.3 V. This result would cause the circuit to be automatically regulated in the highest intensity with predetermined values. Alternatively, the transistors can be replaced with other models for as long as it will be suitable with the design.

The electronic fuse is mainly found in use to protect power supplies from short circuits or used to limit the current usage because of its adjustable feature. They are commonly used in monolithic integrated circuits, particularly in memory devices to define or alter the configuration or operation of the integrated circuits after fabrication. In the utility industry, the electronic fuse play an effective role in limiting the application due to fault current levels fuse speeds and relay-breaker speeds. Other uses of electronic fuses are in wall lamps, car chargers, or as thermal fuse, to replace the classic design of physical fuse.

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