• This topic has 4 replies, 3 voices, and was last updated 1 week, 5 days ago by mwpeters75.
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    • #8229
      LectronFan
      Moderator

      Hi all,

      Have you also encountered the thrill building your own Lectron circuit and connecting the battery or power supply ?

      Did I made a mistake somewhere ? Will the circuit smoke or not ? Is it safe ?

      Well, today I present you an automatic fuse !

      With the components chosen, the power supply will disconnect at 200mA.

      After building the circuit, check the meter reading.

      When you press S1, the power output will be grounded via a 47 Ohm resistor.

      Now check the meter reading, what do you notice ?

      Here’s the circuit :

      Electronic fuse

      A short circuit description :

      In normal condition (no current overload), T1 & T2 form a Darlington pair (ain’t it lovely ?). The base of T1 is connected via R1 to the positive power rail and will conduct and so is T2.

      9V will flow through the lamp and will be present at the output and the meter circuit.

      Now, when we press S1, a higher current (of about 200mA) will flow through the lamp. The voltage across the lamp will turn T3 on. When T3 is conducting, the base of T1 will be more negative causing T2 to shut off and blocking the battery voltage.

      When S1 is released, the situation is back to normal.

      A question for the Lectroneers, How can we modify the circuit so power turns off at lower currents ( for instance 100 mA) ?

      Note down your ideas here !

      Many greetings,

      Frank

      And here a picture of the setup :

      Electronic Fuse setup

       

      • This topic was modified 2 weeks, 4 days ago by mwpeters75. Reason: Changed font and size styling for easier reading
    • #8235
      mwpeters75
      Keymaster

      Hi Frank,

      Great lesson instruction, thank you.  I will hazard a guess and say change the value of R1.  To what value, a bit beyond me.  Thank you for this fun electronic fuse!

    • #8254
      Guenni75
      Moderator

      Hi Frank,

      the circuit is very useful and effective – so I built a special block to meet my needs. The light bulb can bee changed to have different limits, from 2…20 Ω resistance (cold) of the filament, depending of the actual experiment(s). This is – by the way – the answer of your question above 🙂

      Here I use a 5.3V 0.3A light bulb to have a limitation at about 125mA (the light bulb to the right is a 0.1A type!):

      Thanks again, Frank!

      G.

      • This reply was modified 1 week, 5 days ago by mwpeters75. Reason: Changed font and size styling for easier reading
    • #8255
      LectronFan
      Moderator

      Hi Guenther,

      This makes Lectron so exiting ! Building circuits in a easy and fast way and creating new blocks with these circuits.

      Also thank you for great looking modules and designs !

      And also many thanks to Michael for giving us the forum platform to substitute ideas.

      Indeed, by changing the light bulb to other types, we can alter the cutoff current.

      For a permanent design, we can use a BC517 (Darlington transistor) which is able to deliver 0,4 A Collector current (the Silicon 2N3704 transistors used in the Lectron sets have 0,5 A).

      The light bulb is also interesting compared to a normal resistor since it also acts as a VDR (Voltage Depending Resistor) as the filament heats up and thus increasing the resistance.

      Many greetings

      • This reply was modified 1 week, 6 days ago by LectronFan.
      • This reply was modified 1 week, 6 days ago by LectronFan.
      • This reply was modified 1 week, 5 days ago by mwpeters75. Reason: Changed font and size styling for easier reading
    • #8265
      mwpeters75
      Keymaster

      You two gentlemen are amazing!  Thanks so much for this high degree of innovation.  Mr. Greger would be so proud to see this sort of development work.  

      Best,
      Michael

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