Question about voltage input output

Thread Starter

Jim Pap

Joined Nov 27, 2020
6
So i have this simple circuit.While my voltage input is 5V why is my output 3.3V? Can someone explain this to me.Thanks in advance!



Screenshot_25.png
 

bertus

Joined Apr 5, 2008
21,524
Hello,

There is no series resistor for the led.
Put a 470 Ohms resistor in series with the led.
Depending on the type of led, the voltage will be clamped at the forward voltage of the led.

Bertus
 

Thread Starter

Jim Pap

Joined Nov 27, 2020
6
That was the given circuit.Dont mind the led it can be a lamp like here.I just dont understand where 1.7 volts have gone since i have input 5V and i get 3.3.You get me now?
Hello,

There is no series resistor for the led.
Put a 470 Ohms resistor in series with the led.
Depending on the type of led, the voltage will be clamped at the forward voltage of the led.

Bertus
hi Jim,
What would you say the LED current level is.??
LED type and operating voltage.?
E

Screenshot_26.png
 

ericgibbs

Joined Jan 29, 2010
13,585
hi,
If you check the data sheet for a typical OR Gate it will give you an idea how much output current can be output from the Gate.
The Gate has an internal resistance
E
ESP_ 117.png
 
Last edited:

bertus

Joined Apr 5, 2008
21,524
Hello,

I mean the supply voltage of U1 in the simulator, not the input voltages.
How are the supply settings?

Bertus
 

crutschow

Joined Mar 14, 2008
27,697
I just dont understand where 1.7 volts have gone since i have input 5V and i get 3.3.
As bertus said, without a series resistor, the output is clamped at the forward voltage of the LED which is about 3.3V in the simulator.
The 1.7V is dropped in the gate output resistance.

An LED is a diode (Light Emitting Diode) so has a very low resistance once you reach it's characteristic forward voltage.
It does not act as a resistor the way an incandescent bulb does.
 
Top