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Simplest Blown Fuse Indicator Circuit

This Simplest Blown Fuse Indicator Circuit shows if fuse is good or bad without checking it by hand.

If fuse is okay then green LED turns ON.

If fuse blows then green LED goes OFF and red LED turns ON.

That means fuse is bad and needs to change.

Circuit Working:

Parts List:

ComponentDescriptionQuantity
Resistor
1k 1/4 watt1
Semiconductors
Diode 1N41481
LED Red 5mm, 20mA1
LED Green 5mm,20mA1
Fuse1

This circuit uses two LEDs red and green and one diode to show if fuse is blown.

How it works:

When fuse is good then current flows normally.

Very small voltage drop across the fuse.

Most voltage goes through diode 1N4148 around 0.7V.

Red LED stays OFF because not enough voltage turn it ON.

Green LED gets full voltage and lights up.

If fuse blows:

Circuit opens with no current flow.

Voltage now drops across the blown fuse.

Red LED gets enough voltage and turns ON and shows fuse is bad.

Green LED gets no power and turns OFF.

Formulas:

From the circuit with LED green and red lights up depends on voltage drop across the resistor and LED.

Choosing Resistor:

We need to pick right resistor for green LED.

This depends on:

Supply voltage Vsupply

LED forward voltage VfLED

Desired current ILED

Use ohms law:

R = (Vsupply – VfLED) / ILED

where:

Tips:

Check green LED datasheet for VfLED

Choose ILED within safe range usually from 10 to 20 mA

Try different resistor values or use online LED calculator

Check the LED lights are bright enough, but not with too much current.

How to Build:

To build a Simplest Blown Fuse Indicator Circuit we need to follow the below mentioned connections steps:

Power Supply:

Place LEDs and Resistor:

Connect Green LED:

Resistor Setup:

Red LED Cathode:

Place Diode 1N4148:

Connect Red LED Anode:

Find two ends of the fuse.

Testing ensure power is OFF first:

Safety Tips:

Conclusion:

This Simplest Blown Fuse Indicator Circuit shows fuse status like with green LED the fuse is OK and with red LED the fuse is blown.

This simple circuit shows fuse status using lights.

It helps in checking and fixing problems in electronics.

References:

DC blown fuse indicator circuit

Fuse blown indicator circuits compilation

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