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AN219

更新时间: 2024-11-20 03:18:47
品牌 Logo 应用领域
美国微芯 - MICROCHIP 电位器机械
页数 文件大小 规格书
6页 131K
描述
Comparing Digital Potentiometers to Mechanical Potentiometers

AN219 数据手册

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AN219  
Comparing Digital Potentiometers to Mechanical  
Potentiometers  
Earlier mechanical potentiometers were built by wrap-  
Author:  
Bonnie C. Baker,  
ping a resistive wire around a cylinder. With this con-  
struction, the wiper moves from one winding to the  
next. As the wiper is moved across the element, there  
are discrete steps in resistance. Following this style of  
fabrication, the mechanical potentiometer was built  
using a resistive thick film that was screened onto a  
ceramic substrate. With this construction, the change in  
resistance across the element is continuous.  
Microchip Technology Inc.  
INTRODUCTION  
Resistor potentiometers can be found in electronic cir-  
cuits across a wide spectrum of applications. Most typ-  
ically, they function in a voltage divider configuration in  
order to execute various types of tasks, such as offset  
or gain adjust. The two types of potentiometers com-  
pared in this application note are the mechanical poten-  
tiometer (also called a trimmer potentiometer) and the  
digital potentiometer. The physical descriptions and cir-  
cuit models of these two devices are shown in Figure 1.  
There are a variety of resistive materials that are used  
by mechanical potentiometer manufacturers. They  
include molded conductive plastic, conductive plastic  
film, screened conductive plastic, and cermet. Each  
resistive material has its own set of performance char-  
acteristics. In this application note the digital potentiom-  
eter will only be compared to the more popular cermet  
potentiometer. Cermet is a thick film resistive material  
that is a mixture of fine particles of ceramic or glass and  
precision metals such as silver, platinum, rhodium, or  
gold. The wiper of the mechanical potentiometer slides  
along the distance on the resistive material providing  
an analog resistive output that has an infinite number of  
positions across the span of the element.  
Basics of Mechanical Potentiometers  
The first type of potentiometer on the market was  
mechanical in nature. This type of potentiometer is still  
available and adjustments of the wiper are imple-  
mented by twisting a knob, moving a slider, or using a  
screw driver. Although this method seems awkward,  
given the advent of the digital potentiometer, mechani-  
cal potentiometers still find their way into various elec-  
tronic circuits.  
PA  
PW  
PB  
PA  
PW  
PB  
wiper  
resistance  
contact  
resistance  
MCP41010  
MCP42010  
An example of PCB  
mountableMechanical  
potentiometers  
Mechanical  
Potentiometer  
Model  
Digital  
Potentiometer  
Model  
Figure 1: The mechanical potentiometer is constructed so that the user can easily adjust the position of  
the wiper (PW) by hand or with a screw driver. The digital potentiometer is manufactured so that the  
position of the wiper is adjusted by means of a serial digital code. The circuit representation of the digital  
potentiometer and the mechanical potentiometer is fundamentally the same.  
2000 Microchip Technology Inc.  
Preliminary  
DS00219A-page 1  

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