Memorial University of Newfoundland Faculty of Engineering and Applied Science ENGR 3844 - Basic Electrical Components and Systems Part-II (Electronics)

EXP. 3844-1E

Voltage Divider and Wheatstone Bridge

PURPOSE To introduce students to various voltage divider and Wheatstone bridge circuits. INTRODUCTION 1.0 Voltage Divider Circuits The voltage divider circuit is used to reduce the supply voltage to the desired level at the load. A simple voltage divider circuit is shown in Figure 1 where a resistor is connected in series with the load. + E + VRS _ IL + VRS RS +

+

RS

E _

RL

VL

_

≡

_

+

RL

Load

VL

IL

Figure 1

KVL around the circuit gives, E - VRS - VL = 0 ⇒ VL = E - VRS = E - ILRS But, I L =

Ex RL E . Therefore, VL = RS + RL RS + RL

E 1.1

(1) (2)

However, this type of voltage divider has a serious disadvantage as the value of VL depends on the load current IL. If IL changes, the voltage drop across RS also changes and hence, the voltage drop across the load RL will also change. This change in voltage at the load is called voltage regulation. The load voltage will remain relatively constant if the load is maintained constant. In order to overcome the above limitation another type of voltage divider circuit is used which is shown in Figure 2. In this case a bleeder resistor is used in parallel with the load. + E + IT IL IT _ + VRS _ R S + + IL RS ≡ VL + VL E RL RB _ RB IB RL _ Load IB Figure 2

Using voltage divider rule, VL =

E (R B R L ) RS + RB RL

RB

RL =

(3)

RBRL RB + RL

If RB