how to make a passive switch with low input 100mV.

[Bilal_Ahm]

I want to make a circuit that should give output voltage 5v when input between 100 mV to 5v is applied and 0v as out put when input voltages are less than 100mV. i can not power my switch i need this switch to work passively.

i tried basic npn transistor, but it needs base voltages more than 0.7 Volts.

 

[KlausST]

Hi,

Use a comparator.

Klaus

 

[dick_freebird]

You might try a NPN pair, in a degenerated current-mirror
sort of form. One emitter is set to ~50mV. The other is
the input, needing some bias current pulled through it
to swing the load.

You won't get all the way to 0.000, more like Vce(sat).
You might do better with MOSFETs in this respect, but
you should expect matching issues worse than BJTs in
loose random discrete units.

 

[D.A.(Tony)Stewart]

Generating 5V out from 100mV in with a Passive Switch is not possible. Where does the 5V come from?

 

[Bilal_Ahm]

i have simulate the circuit in pspice.

one picture shows voltages and one is amperes. it shows that the right transistor is always in Saturation state. it draws current i can not afford that much current.
in the last i showed the picture of 0v at input side. again its taking 1mA.

 

[Bilal_Ahm]

i tried your solution,

but it draws current also in the off state. where there is no input current.

 

[crutschow]

I want to make a circuit that should give output voltage 5v when input between 100 mV to 5v is applied and 0v as out put when input voltages are less than 100mV. i can not power my switch i need this switch to work passively.
..........................

I don't understand. If you have 5V available, why can't you power a switch circuit? :-?

It will be difficult to get 100mV sensitivity with only a passive circuit. One possibility is a reed switch with a many turn winding to give a high sensitivity.

 

[Bilal_Ahm]

@ dick freebird
i tried your solution. trasistor on the right hand side draws current even in the OFF state.
i can not afford that much current. please any more suggestions to make it better.


@SunnySkyguy
12volts are always available as Vcc, but cant afford any leakage current in the OFF state.

 

[D.A.(Tony)Stewart]

@ dick freebird
i tried your solution. trasistor on the right hand side draws current even in the OFF state. View attachment 109922
i can not afford that much current. please any more suggestions to make it better.


@SunnySkyguy
12volts are always available as Vcc, but cant afford any leakage current in the OFF state.

What is the load?
Should there be hysteresis?
What is the source impedance?
Any filtering required for noise immunity?

Why not use a CMOS comparator?

 

[Bilal_Ahm]

@ SunnySkyGuy

the load is to drive a base of a NPN transistor.
no there should not be any hysteresis.
yes i have filter for noise immunity.


i can not use CMOS comparator because its usually from 1.28 to 11v and i have 12v BAT. for regulating 12 voltages to 5v i required a regulator which again have a lot of leakage current.

 

[D.A.(Tony)Stewart]

Why not use a CMOS comparator?

LP2901 draws 0.1mA operates up to 30V open drain out.

https://www.ti.com/lit/ds/symlink/lp2901.pdf

 

[schmitt trigger]

Bilal:
In the image that of the sensor you've posted, it clearly indicates a minimum input impedance of 1Meg, but it is preferred that it is 10Meg or higher.

That aspect, plus the very small output voltage, completely rules out a simple transistor solution.

Your best bet, as the previous poster mentions, is to use a LP2901 or similar CMOS comparator.