VOLTAGE DIVIDER WITH POSITIVE AND NEGATIVE VOLTAGE REQUIREMENTS
In many cases the load for a voltage divider requires both positive and negative voltages. Positive and negative voltages can be supplied from a single source voltage by connecting the ground (reference point) between two of the divider resistors. The exact point in the circuit at which the reference point is placed depends upon the voltages required by the loads.

For example, a voltage divider can be designed to provide the voltage and current to three loads from a given source voltage.

Given:


The circuit is drawn as shown in figure 3-66. Notice the placement of the ground reference point. The values for resistors R₁, R₃, and R₄ are computed exactly as was done in the last example. I_R1 is the bleeder current and can be calculated as follows:

Figure 3-66. - Voltage divider providing both positive and negative voltages.

Solution:


Calculate the value of R₁.

Solution:


Calculate the current through R₂ using Kirchhoff's current law.

At point A:


(or 195mA leaving point A)

Since E_R2 = E load 2, you can calculate the value of R₂.

Solution:


Calculate the current through R₃.


The voltage across R₃ (E_R3) equals the difference between the voltage requirements of loads 3 and 2.

Solution:


Calculate the value of R₃.

Solution:


Calculate the current through R₄.


The voltage across E_R4 equals the source voltage (E_s) minus the voltage requirement of load 3 and the voltage requirement of load 1. Remember Kirchhoff's voltage law which states that the sum of the voltage drops and emfs around any closed loop is equal to zero.

Solution:


Calculate the value of R₄.

Solution:


With the calculations just explained, the values of the resistors used in the voltage /divider are as follows:


From the information just calculated, any other circuit quantity, such as power, total current, or resistance of the load, could be calculated.