switches, relays, and

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Switches, Relays, andPower-Control Semiconductors

ISMAIL, S ST.,MT

Ps.LISTRIK

2010



OBJECTIVES Understand mechanical switch types,

configurations, and terms. Describe the types and operation of

electromechanical relays. Understand the characteristics of solid-state

relays and the advantages anddisadvantages of solid-state relayscompared with electromechanical relays.

Comprehend the operation of powertransistors and power amplifiers, calculatetransistor circuit currents, and select areplacement power transistor



INTRODUCTION

An important ability of almost allcontrol systems is to regulate the

flow of electrical power becauseelectricity is usually the link betweenthe controller and the actuator



Three classifications of components :

Electromechanical devices such as

switches and relays, Power transistors and field effect

transistors

A group of semiconductor devices called

thyristors



SWITCHES A mechanical switch is a device that

can open or close, thereby allowing a

current to flow or not



Toggle Switches

Probably the most common switchtype is the toggle switch.



Athree-position switch: on±off±on



A slide switch



Push-B

utton Switches

Push-button switches are almostalways the momentary type pressuremust be maintained to keep the switchactivated



Push-button switches and Limit

switches



Other Switch Types

A limit switch is a push-buttonswitch mounted in such a position

that it is activated by physical contactwith some movable object

An example is a car door switch, whichsenses whether or not the door is closed



A DIP switch is a set of small SPSTswitches built into a unit shaped like

an integrated circuit (IC) (DIP standsfor dual in-line package).



Rotary switch operation

The rotary switch is constructed of switch wafers mounted along a

single shaft



A thumbwheel switch (ten-decimalposition)



A membrane switch



RELAY

S

Electromechanical Relays

The electromechanical relay (EMR)

is a device that uses anelectromagnet to provide the force toclose (or open) switch contacts, inother words, an electrically powered

switch



An electromagnetic relay



A selection of relays



A reed relay The reed relay is unique because the small

reed like contacts are encapsulated in a smallsealed glass tube that is evacuated or filledwith an inert gas like dry nitrogen



Solid-State Relays A solid-state relay (SSR) is a purely solid-

state device that has replaced the EMR in manyapplications, particularly for turning on and off

AC loads such as motors



SSR circu

it A block diagram of the interior of an

SSR

switches, relays, and

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