Digital isolator

[engr_joni_ee]

How we can convert 0 V and - 5V which is a status monitor signal having two voltage levels or states at 0 V and -5 V to 3.3 V and 0 V respectively to read by Microcontroller.

0 V => 3.3 V
-5 V => 0 V

Please suggest a suitable electronic device.

 

[crutschow]

What supply voltages do you have available?

 

[engr_joni_ee]

3.3 V and -5 V both are available. I guess I need a kind of voltage inverter but I have little knowledge on it.

 

[D.A.(Tony)Stewart]

0 V => 3.3 V
-5 V => 0 V
max-min out = gain =3.3/5 = + 0.66,
mav-min in

Solution : two inverting amplfiers on single supply R2R ... maybe or one Non-inverting bipolar supplies.

 

[FvM]

A npn transistor and two resistors.

 

[crutschow]

Here's the LTspice sim of a one-transistor circuit as FvM suggested:

 

[D.A.(Tony)Stewart]

Depending on your tolerances for gain and offset errors, here is another way

 

[engr_joni_ee]

Here's the LTspice sim of a one-transistor circuit as FvM suggested:

View attachment 198571

At 0 V input the transistor will not turn-on that result 3.3 V output, make sense.

At -5 V input the transistor will turn-on because the base is ground At 0 V and emitter at -5 V input that make the transistor turn-on, right ? but the 0V output is because of voltage divider using R1 and R2 ? the mid point of both resistors is output.

 

[D.A.(Tony)Stewart]

 

[KlausST]

Hi,

the headline talks about "isolator".
Thus my first question is: do both input signals refer to the same GND .. or are they galvanically isolated?

Next question: what microcontroller? Some microcontroller have built in comparators...

Klaus

 

[D.A.(Tony)Stewart]

Argh.


Why is the title Digital Isolator when all you ask is for a Level Shifter? Does it need isolation?
Why are you using a -5V sensor? What is it?

 

[crutschow]

At 0 V input the transistor will not turn-on that result 3.3 V output, make sense. At -5 V input the transistor will turn-on because the base is ground At 0 V and emitter at -5 V input that make the transistor turn-on, right ? but the 0V output is because of voltage divider using R1 and R2 ? the mid point of both resistors is output.

Correct for both input voltages.

But even if R2 were smaller, the lowest output voltage would be one base-emitter voltage-drop below ground due to the transistor.

 

[FvM]

Lowest output voltage is slightly negative, Vce,sat - Vbe. Resistors can be adjusted to get exactly 0, if necessary. crutschow did in post #6.

I just wanted to give an idea, there are many possible variations.