• Dhanush kumar S

# Voltage divider

Updated: Dec 1, 2020

In all the appliances and #electrical machinery, resistors are present to control the flow of electric #current in the circuit. Those resistors may be connected in series or parallel combinations according to the requirement. #Voltage division is the concept of distributing the input voltage among the resistive components involved in that circuit. Apart from just dividing the voltage across the #circuit, the voltage divider is also used in reducing the magnitude of voltage, creating reference voltage, helps the microcontroller to measure the voltage of a sensor. In this article, we are going to discuss in detail the various mechanisms involved in voltage dividing and applications of it.

### Voltage divider:

A potential divider or voltage divider can be defined as a passive linear circuit that produces an output voltage which is a fraction of the applied input voltage. The voltage divider can be differentiated into 4 models depending upon the components involved in its design. A resistive voltage divider, capacitive, inductive, and lowpass resistive-capacitive divider. Circuit diagram of voltage divider

In the general case, let us consider two impedances(Z1 and Z2) connected in series combination. Those impedances can be resistive, capacitive, or inductive. The input voltage is applied across the series combination and the output voltage is measured at Z2. Using ohm's law,

Vout = (Z2/Z1+Z2) * Vin

where Vin=I*(Z1+Z2)

The transfer function(H) which is a rational function of frequency is nothing but the ratio of the output voltage to the input voltage. H can be obtained using the above-mentioned equations.

### Resistive voltage divider:

In this case, both the impedances Z1 and Z2 are resistors. So the equation for obtaining the output voltage becomes,

Vout=(R2/R1+R2)*Vin

If the resistance value of both resistors is assumed to be equal, then Vout= 1/2*Vin. At this condition voltage dropped across each resistor will be exactly half the supply voltage for the two resistors. According to Kirchoff's voltage law, the voltage across the series combination is given by the sum of individual voltages across resistors R1 and R2. Circuit diagram of resistive voltage divider

By using ohm's law, the voltage across series [V]=I*(R1+R2). By employing the above 2 equations, the voltage across the two resistors can be derived as,

The Voltage across resistor R1= V*(R1/R1+R2)

The voltage across resistor R2= V*(R2/R1+R2)

### Inductive voltage divider:

These inductive voltage dividers measure the voltage drop across inductors connected in a series combination to a common AC supply. When the inductors are applied with a DC supply of low frequency, it may result in a short circuit. Because the reactance of those inductors allow any DC current to pass through them easily. Inductive reactance helps us to find the inductive voltage division between the series-connected inductors. Circuit diagram of inductive voltage divider

Inductive reactance(XL)=2πfL

where XL is the inductive reactance in ohms, f is the frequency in hertz, L is the inductance in henries. The output voltage is calculated with the help of individual inductance(L1 and L2) of the inductors, and the applied input voltage.

Vout=(L2/L1+L2)* Vin

The voltage across each inductor can be calculated after finding the inductive reactance XL1 and XL2 using the inductance values L1 and L2.

VL1= V*(XL1/XLT)

VL2=V*(XL2/XLT)

where XLT =XL1+XL2 and V is the applied input voltage.

### Capacitive voltage divider:

Same as that of inductors, the capacitors also won't permit DC input voltage to pass-through them. High-frequency capacitive voltage dividers are employed in display devices and touch-screen #technologies. They are mostly used to step-down high voltage to produce low voltage output signals. Capacitive reactance plays a major role in capacitive voltage dividing which is inversely proportional to both frequency and capacitance. Circuit diagram of capacitive voltage divider

Capacitive reactance(XC)=1/2πfC

where XC is the capacitive reactance in ohms, f is the frequency in hertz, C is the capacitance in Farads. The output voltage is calculated with the help of individual capacitance(C1 and C2) of the capacitors, and the applied input voltage.

Vout=(C1/C1+C2)* Vin

The voltage across each capacitor can be calculated after finding the capacitive reactance XC1 and XC2 using the capacitance values C1 and C2.

VC1= V*(XC1/XCT)

VC2=V*(XC2/XCT)

where XCT =XC1+XC2 and V is the applied input voltage.

### Applications of voltage divider:

• The potentiometer acts as a variable voltage divider which is used for controlling the speed of ceiling fan and also in controlling the volume of radios.

• Devices such as multimeter, Wheatstone bridge, and voltmeter are constructed based on the concept of voltage dividing.

• High voltage resistor dividers are used to measure voltages up to 100kV.

• They are also employed in the process of logic level shifting.

• For example, Interfacing a 5V logic output to a 3.3V input can cause damage to the 3.3V circuit. The voltage divider with an output ratio of 3.3/5 can solve this issue.