Module 2.6 Voltage Divider Circuits PDF

Preview

Summary

Detailed course notes that includes formulas and tutorial work related to the topic....

Description

VOLTAGE DIVIDER CIRCUITS The purpose of this circuit is to reduce the supply voltage to the level required by the load. The simplest method is the use of a series dropping resistor

When load current flows, the series dropping resistor causes a voltage drop (Vs) which subtracts from the supply voltage (E) giving the required voltage across the load (VL). From Kirchhoff's voltage law: VL = E - Vs VL = E - ILRs

Example

Design a voltage divider circuit to provide 6V at a current of .5 amps to a motor, from a 9V battery

This simple circuit has a serious disadvantage since the value of Rs is based on a particular value of load current and any change in load current will change the voltage dropped by the series resistor and consequently VL will change also. This change in voltage with load is referred to as regulation. The circuit will only work well if the load current remains relatively constant.

The following graph indicates how the voltage will vary from its designed value when the load current changes.

The addition of a bleeder resistor in parallel with the load will make the circuit less sensitive to changes in load current.

IT = IL + IB If the bleeder current is large compared to the load current, then IT will remain more constant with changes in IL and the load voltage will have better regulation.

Example

An amplifier operates at 15V and draws a current of 20mA. Design a series voltage divider circuit to operate it from a 25V supply. If the current falls to 10mA, calculate the new load voltage.

If IL changes to 10mA

Example

Redesign the previous circuit with the addition of a bleeder resistor drawing a current of 100mA. If the current falls to 10mA, calculate the new load voltage. (assume bleeder current remains constant)

If load current falls to 10 mA

A Potentiometer is a variable voltage divider.

VL can be varied from 0 to E volts.

Multiple Voltage Divider Circuit This circuit is used to provide more than one different voltage from a single source. A number of series resistors can be used to accomplish this.

Example

Design a voltage divider circuit to provide the following loads from a 500V supply. 1. 400V @100mA 2. 300V @50mA 3. 100V @10mA Design for a bleeder current of 20mA....