[LectronFanModerator]

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 :

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 :

 

• This topic was modified 4 years, 7 months ago by Michael. Reason: Changed font and size styling for easier reading

[MichaelKeymaster]

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!

[GuentherParticipant]

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 4 years, 7 months ago by Michael. Reason: Changed font and size styling for easier reading

[LectronFanModerator]

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 4 years, 7 months ago by LectronFan.
• This reply was modified 4 years, 7 months ago by LectronFan.
• This reply was modified 4 years, 7 months ago by Michael. Reason: Changed font and size styling for easier reading

[MichaelKeymaster]

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

[GuentherParticipant]

Who needs more current and / or voltage – may be interested in this rather simple circuit with IC µA723 (about 50 years old, but still available for little money = UA723 / LM723 / MC1723 / …). The voltage can be controlled between 1.2 … 35 V, current can be  limited between 0.1 … 2 A) with 3 pots:

Since many years I am using this power supply – built in an earlier used metall case with meters – in my hobby corner:

with this parts:

for a version of max. 1A it might fit in an empty Lectron loudspeaker block – let’s see…

Here is the PCB ready for wiring:

Best,

G.

• This reply was modified 4 years, 6 months ago by Guenther.
• This reply was modified 4 years, 6 months ago by Michael. Reason: Changed font and size styling for easier reading

[LectronFanModerator]

Hello Guenther,

This is a neat project. Perfect for powering the Lectron in a controllable and safe way.

The Lectron power supply is also very good, but unfortunately only the voltage is controllable and not the current …

Good luck with the construction inside a Lectron cube !

Greetings

• This reply was modified 4 years, 6 months ago by Michael. Reason: Changed font and size styling for easier reading

[GuentherParticipant]

Hi all,

here is the ready-built unit, and is working very well. Easy handling and perfect function, controls are 2 LEDs beneath the grid: green for primary voltage, red for secondary voltage, intensity depending on Vout – I love it!

Best,

G.

• This reply was modified 4 years, 6 months ago by Michael. Reason: Changed font and size styling for easier reading

[LectronFanModerator]

Hello Guenther,

It fits ! It fits perfectly !

It is a very good and very practical Lectron block, I would love to build one too !

Has it been build around the circuit you proposed above ?

Many greetings

• This reply was modified 4 years, 6 months ago by Michael. Reason: Changed font and size styling for easier reading

[GuentherParticipant]

Hello Frank,

yes – it’s the same circuit inside except power transformer and instruments 🙂 .

The 2.2µF is connected directly to the emitter of 2N3055. I used the BD239C instead – don’t need more than 1 A for Lectron circuits – I hope…

Good luck,

G.

• This reply was modified 4 years, 6 months ago by Michael. Reason: Changed font and size styling for easier reading

[MichaelKeymaster]

Awesome engineering and creativity Günther!  Thank you.

[Author]

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