# What is the current of this voltage divider?

#### Zane Finner

Joined Jan 29, 2018
30
I need to know the current of the output of the current divider. I know V = I(R) and I = V/I but idk if I add the resistances or what.
I couldn't find an answer online I want the bottom output to be alone, and the top to go to ground. Sorry, forgot to include that! #### bertus

Joined Apr 5, 2008
20,878
Hello,

As the resistors are equal, the output voltage will be 1/2 the input voltage with no load.
As the resistors are quite large the voltage will drop when a load is connected.

Bertus

#### Zane Finner

Joined Jan 29, 2018
30
Hello,

As the resistors are equal, the output voltage will be 1/2 the input voltage with no load.
As the resistors are quite large the voltage will drop when a load is connected.

Bertus
I meant to say current XD.
Thanks for the fast response though!

#### dl324

Joined Mar 30, 2015
11,883
I know V = I(R) and I = V/I
I want the bottom output to be alone, and the top to go to ground. Sorry, forgot to include that!
This doesn't make sense. Please attach a schematic.

#### Zane Finner

Joined Jan 29, 2018
30
Oh, I think I figured it out! Since it divides the voltage (duh) its 2.5/10k!
is this correct? It seems correct haha

#### bertus

Joined Apr 5, 2008
20,878
Hello,

Wich current do you want to know?

Bertus

#### Zane Finner

Joined Jan 29, 2018
30
Hello,

Wich current do you want to know?

Bertus
Just the top alone. I want the bottom connected to ground. Sorry, its been such a long day.

#### bertus

Joined Apr 5, 2008
20,878
Hello,

What will be the load, as that will influence the output voltage and the total current.

Bertus

#### Zane Finner

Joined Jan 29, 2018
30
Hello,

What will be the load, as that will influence the output voltage and the total current.

Bertus
Well, I know that whatever it is before load, I can use the series equation, but if it was connected alone to ground, what would it be?

#### bertus

Joined Apr 5, 2008
20,878
Hello,

Do you mean the short circuit current?
When the output is shorted, there will be no voltage accross the bottom 10K resistor.
The current will be 30 Volts / 10K Ohms = 3 mAmps.

Bertus

#### Zane Finner

Joined Jan 29, 2018
30
Hello,

Do you mean the short circuit current?
When the output is shorted, there will be no voltage accross the bottom 10K resistor.
The current will be 30 Volts / 10K Ohms = 3 mAmps.

Bertus
I mean the middle one while both are connected to ground. Sorry, I gotta be honest. I'm really bad at this. I'm studying over the summer but in my textbook, I just guess I'm stuck. Here, I will redraw a schematic and attach it
oof, I meant to put 30v haha

#### LesJones

Joined Jan 8, 2017
2,726
As the connection between the junction of the two resistors and ground is the ONLY connection to ground in your schematic the current to ground is zero. Your text description was not clear enough to translate it into the schematic in post #11 which is why you did not get an answer before post #11.

Les

#### BR-549

Joined Sep 22, 2013
4,938
Zane.....The current there is zero......but you just gave the ground a bipolar voltage.

#### Zane Finner

Joined Jan 29, 2018
30
Okay, I figured it all out guys. I got a bit confused with what bertus said, than I found this: (see attachment)

I'm not confused anymore. I see that the second resistor and the load resistor get combined with the parralel equation to find all the voltage going out in the normal voltage dividing formula

#### ArakelTheDragon

Joined Nov 18, 2016
1,350
Ohm's law is something that you must learn first and then deal with electronics.

#### dl324

Joined Mar 30, 2015
11,883
Ohm's law is something that you must learn first and then deal with electronics.
His problem was with algebra, not Ohm's Law.
I know V = I(R) and I = V/I

#### shortbus

Joined Sep 30, 2009
8,044
OK you guys, help out an old dummy, me. Which resistor sets the output current in a voltage divider? Top or bottom? Not to do with this or any particular schematic just in general. I have always just copied what they show in a data sheet type or book circuit schematic, because I don't design stuff for myself.

#### dl324

Joined Mar 30, 2015
11,883
OK you guys, help out an old dummy, me. Which resistor sets the output current in a voltage divider? Top or bottom?
In the circuit in the first picture; both.

The follow up question was what load would be placed across the bottom resistor. The rule of thumb for resistive divider is that the current in the divider should be 10X the load current. In the original question, the divider current was 1.5mA, so the load would be limited to 0.15mA.

• shortbus

#### ArakelTheDragon

Joined Nov 18, 2016
1,350
His problem was with not knowing Omh's law, and that does not mean the formula, but understand it! If you do not know which resistor sets the current in a voltage divider, all you did was copy the formula from somewhere and than ask because you did not try to understand anything by yourself.

I did not say you are dummy, but you should try to understand without help and not want someone else to solve your problem.

#### AnalogKid

Joined Aug 1, 2013
8,687
OK you guys, Which resistor sets the output current in a voltage divider? Top or bottom?
Both. Current from the center node of a voltage divider into an external load of some kind is determined by the load - in parallel with the bottom resistor and in series with the top resistor. To see how the two resistors combine to affect the output, see this:

https://en.wikipedia.org/wiki/Thévenin's_theorem

The Thevenin equivalent of the circuit in post #1 is a 15 V battery with a 5K resistor in series. Starting with that, you can use Ohm's Law to calculate the voltage across a load resistor. Also, make the two resistors non-equal to see the effects of having the upper resistor higher and lower than the lower resistor.

ak

• Zane Finner and shortbus