Question about voltage divider

[mannokhkhkhk2207]

I am seeking for help regarding to question about voltage divider.

Someone in the Internet said that if I want to get 1.5V from a 9V source I can connect the 9V source to 2 resistors (500ohms and 100ohms) in series just like this picture.

By KVL, I know that Vout takes same voltage of Z2. However, my problem is why Vout will take 1.5V in this case. In my view, Vout may connected to some loads and finally connected to the GND, we can view it as a resistor too! In this situation, we should know the resistance of Vout and Z2 in order to calculate the total resistance of them as in series and compare with Z1 to find out the voltage consuming ratio.

So my question is why we can know Vout without knowing the resistance beyond Vout?

 

[betwixt]

We can't see your picture but from the description you give it sounds like a simple two-resistor potential divider. You are both right, the ratio of the resistors will determine the voltage at their junction but as you correctly assume, the effect of the load across the lower resistor has to be taken into account.

You are seeing the reason why we normally use active voltage regulator circuits to maintain a constant voltage when the load is unknown or variable. If you know the load and it will remain constant, you can use a single resistor to drop the voltage, just use the formula (Vin - Vout)/I to calculate it's value. If the load is going to change, you need a regulator circuit.

Brian.

 

[chuckey]

As a rule of thumb if the divider takes 10 times the expected output current you will have a good working setup.
Frank

 

[tarun0xe]

I am seeking for help regarding to question about voltage divider.

Someone in the Internet said that if I want to get 1.5V from a 9V source I can connect the 9V source to 2 resistors (500ohms and 100ohms) in series just like this picture.

By KVL, I know that Vout takes same voltage of Z2. However, my problem is why Vout will take 1.5V in this case. In my view, Vout may connected to some loads and finally connected to the GND, we can view it as a resistor too! In this situation, we should know the resistance of Vout and Z2 in order to calculate the total resistance of them as in series and compare with Z1 to find out the voltage consuming ratio.

So my question is why we can know Vout without knowing the resistance beyond Vout?

The Vout is just voltage across Z2 i.e node voltage. This will only remain at 1.5V till the load resistance we are connecting has reasonably high value in comparison to Z2(so that parallel combination of Z2 and that load resistance remains near to that of Z2) in this way only a limited amount of current will pass through that load. If that load has resistance near to that of Z2, off course their parallel combination will decide the actual voltage across load.