AC Neon Lamp filament or Semiconductor blown fuse Indicator

AC Neon Lamp filament or Semiconductor blown fuse Indicator circuit

AC Neon lamp filament or semiconductor blown fuse indicator circuit

This simple circuit tells you have a blown fuse without removing the fuse from its holder or semiconductor fuse status. This neon lamp fuse indicator circuit makes neon lamp flash up if a fuse blows or open.

The fault finding point of view  there is a disadvantage of the semiconductor type fuses. It is they haven’t filaments to indicate fuse state. because we need a this type fuse indicator.

AC Neon Lamp filament Semiconductor blown fuse Indicator light circuit


R1 560kΩ
R2 100kΩ
C1 0.1µF 400V
D1 1N4001


As lone as the fuse is good, the fuse is conductive, so there is no voltage appear between the fuse connection. However if the fuse is open or blown the full supply voltage appears between fuse connections. At this time the neon lamp will start to flash on and off.

C1, R1, R2 and neon lamp act as very low frequency neon oscillator. neon flash rate can be altered by changing the value of C1, R1 and R2.

This blown fuse indicator will work with a wide range of AC supply voltages from 90V to 300V. The neon flash rate also depends on the supply voltage. So you need to change C1, R1 and R2 valves to get desired flash rate.

Above circuit can be used with few milliampere to many ampere fuse.

AC Neon Lamp blown fuse Indicator blown fuse Indicator light fuse failure state circuit

Please send your ideas, which are very important for our success…

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8 comments on “AC Neon Lamp filament or Semiconductor blown fuse Indicator
  1. H.Perera says:

    Very useful. Thank you very much

  2. mk says:

    very nice lllmeess u
    long time

  3. Jan Durand says:

    Unfortunately D1 is placed directly across the AC supply with nothing limiting the current., hence it will fail spectacularly with all the flames and smoke it can muster.
    Please fix this!

  4. Interestingly, the cool !!! Bi Volt! it works from 90V to 300V.. Nice!.

  5. Mohammad says:


  6. emmanuel says:

    I love this circuit

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