Question about voltage input output

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!

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

ericgibbs

Joined Jan 29, 2010
13,585
hi Jim,
What would you say the LED current level is.??
LED type and operating voltage.?
E

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

bertus

Joined Apr 5, 2008
21,524
Hello,

What is the supply voltage of the chip in the simulator?

Bertus

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

Last edited:

Jim Pap

Joined Nov 27, 2020
6
Hello,

What is the supply voltage of the chip in the simulator?

Bertus
Its 5V for logical "1" and 0 for logical "0"

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.

BobaMosfet

Joined Jul 1, 2009
1,848
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!

View attachment 235322
Title: Understanding Basic Electronics, 1st Ed.
Publisher: The American Radio Relay League
ISBN: 0-87259-398-3

MrChips

Joined Oct 2, 2009
24,143
Remove the LED and measure the voltage at the output of the gate.

Audioguru again

Joined Oct 21, 2019
3,505
The OR gate has no part number then we do not know if it is RTL, DTL, TTL or Cmos logic family. They all have different output high voltages.