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Voltage Divider

Posted on : Sun , 01 2014 by : virusi

Theory of operation :


One of the most widespread circuit fragments are voltage dividers. So what is a voltage divider? Voltage dividers are often used in circuits to generate a particular voltage from a larger input voltage. Fig.1 is showing a simple voltage divider.

VoltageDivider
Fig.1 Voltage divider
Let’s apply Ohm’s Law for the
R_{2}
:
\large R_{2} = \frac{V_{out}}{I}
(1)
Now calculate the voltage for
R_{2}
according to (1) equation :
\large V_{out} = I*R_{2}
(2)

In equation (2) we don’t know the current (I) of the circuit but you can see that resisters are connected in series so we can apply Ohm’s for those resistors that are connected series :

\large I = \frac{V_{in}}{R_{1}+R_{2}}
(3)

Setting equation (2) and (3) we have :

\large V_{out} = \frac{R_{2}}{R_{1}+R_{2}}*V_{in}
(4)

Note that the output voltage is always less (or equal) than the input voltage. You could amplify the out voltage if one of the resistances is negative this can be achieved with negative incremental resistances (e.g. the tunnel diodes) or even true negative resistances (e.g. negative-impedance converter).

Often you will want to generate different output voltages this can be achieved by replacing resistor
R_{2}
with a potentiometer with only two connection wire or you can replace
R_{1}
and
R_{2}
with a 3 wire potentiometer. Below you can check all 3 schematic in action.

Practical Example :


If you don’t see the example below than you should follow this steps:

– In your browser allow Java SE 7.

– Lower you java security settings (Go to Control Panel >> Java >> Security and set the security level to medium) .

– Edit Site List (Go to Control Panel >> Java >> Security and click on Edit Site List… and add eagerlearning.org in the list).

Sorry, you need a Java-enabled browser to see the simulation.
This is a simple circuit with 2 resistors and 1 voltage source. The diagram is showing the current and voltage that is flowing between the 2 resistors (
 V_{out}
). If you want to change the value of a component just double click on it and insert the desired value.
Last updated on Mon , 03 2014
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