Differential amplifier comparator troubleshooting

Thread Starter

idrbur

Joined Jan 11, 2018
22
I have build a differential amplifier comparator and it works fine except that instead of switching voltage between zero and 5v, it toggles it between 3.5v and 5v.
So, I would like to know if there's a way to make it switch between 0-5v.
The schematic is as followsScreenshot_2021-11-26-09-41-26-620_com.everycircuit.free.jpg
 

crutschow

Joined Mar 14, 2008
28,538
I would like to know if there's a way to make it switch between 0-5v.
Add a PNP transistor with the emitter connect to +5V, the base connected to the top of the 12kΩ resistor (disconnect the resistor from +5V), and the collector connected to a resistor (e.g. 1kΩ) to ground.
You should get a voltage swing of 0 to 5V (minus the collector-emitter saturation voltage) at the transistor collector.
 

Thread Starter

idrbur

Joined Jan 11, 2018
22
Add a PNP transistor with the emitter connect to +5V, the base connected to the top of the 12kΩ resistor (disconnect the resistor from +5V), and the collector connected to a resistor (e.g. 1kΩ) to ground.
You should get a voltage swing of 0 to 5V (minus the collector-emitter saturation voltage) at the transistor collector.
I don't quite understand the way you are telling me to do the connection can you post a schematic.
Also I don't have PNP transistors right now ..is it possible to achieve 0 to 5v swing with NPN transistor
 

Ian0

Joined Aug 7, 2020
4,119
I have build a differential amplifier comparator and it works fine except that instead of switching voltage between zero and 5v, it toggles it between 3.5v and 5v.
So, I would like to know if there's a way to make it switch between 0-5v.
The schematic is as followsView attachment 253580
Replace the right-hand-side transistor with a PNP type, emitter to the positive supply.
The two resistors connected to that transistor are unnecessary.
That makes a conventional differential amplifier.
[Edit] The way you have connected the bottom of V to ground is particularly confusing.
 
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