It has a permanent magnet rotor which issurrounded by a stator. Such motors are called as four-phaseor unipolar stepper motor. Construction of Stepper Motor Commonly used stepper motors have four statorwindings that are paired with a center tappedcommon. Stepper motors commonly have a permanentmagnet rotor (shaft) surrounded by a stator 18. Introduction to Stepper Motor17 Stepper motor is a widely used device thattranslates electrical pulses into mechanicalmovement Stepper motor is used in applications suchas disk drives dot matrix printer robotics etc.
#OPTICAL ISOLATOR 120V PWM DRIVERS#
Interfacing an optoisolator The optoisolator comes in a small ICpackage with four or more pins When placing an optoisolator between twocircuits, we must use two separate voltagesources, one for each side Unlike relays, no drivers need to be placedbetween the microcontroller/digital outputand the optoisolators15 16. Optoisolator Optoisolator (also called optocoupler) areused to isolate two parts of a system An optoisolator has an LED (light-emittingdiode) transmitter and a photosensorreceiver, separated from each other by a gap When current flows through the diode, ittransmits a signal light across the gap andthe receiver produces the same signal withthe same phase but a different current and13 amplitude 14. Reed switch When the reed switch is placed in a magneticfield, the contact is closed When the magnetic field is removed, thecontact is forced open by its spring The reed switch is ideal for moist and marineenvironments where it can be submerged infuel or water They are also widely used in dirty and dustyatmospheres since they are tightly sealed11 12. Wear and tear on the contact points cancause the relay to malfunction after a while Solid-state relays have no such limitations Extremely low input current and smallpackaging make solid-state relays ideal formicroprocessor and logic control switching They are widely used in controlling pumps,solenoids, alarms, and other powerapplications9Solid-state relay 10. Solid-state relay In this relay, there is no coil, spring, ormechanical contact switch The entire relay is made out of semiconductormaterials These relays have switching response timemuch faster than that of electromechanicalrelays The life cycle for the electromechanical relaycan vary from a few hundred thousands to fewmillion operations8 9.
#OPTICAL ISOLATOR 120V PWM DRIVER#
Driving a relay Digital systems and microcontroller pins lacksufficient current to drive the relay While the relays coil needs around 10 mA tobe energized, the microcontrollers pin canprovide a maximum of 1-2 mA current For this reason, a driver is placed, such asthe ULN2803, or a power transistor betweenthe microcontroller and the relay6 7. For example, wecan have SPST (single pole,single throw), SPDT(single pole, double throw), and DPDT (double pole,double throw) relays The voltage and current needed to energize the coil The maximum DC/AC voltage and current that canbe handled by the contacts5 6.
Criteria for Choosing a Relay The contacts can be normally open (NO) or normallyclosed (NC). One such relay is called an electromechanical(or electromagnetic) relay The EMRs have three components: the coil,spring, and contacts When current flows through the coil, a magneticfield is created around the coil (the coil isenergized), which causes the armature to beattracted to the coil3RELAYS AND OPTOISOLATORS 4. RELAYS AND OPTOISOLATORS A relay is an electrically controllable switchwidely used in industrial controls,automobiles, and appliances It allows the isolation of two separatesections of a system with two differentvoltage sources For example, a +5V system can be isolatedfrom a 120V system by placing a relaybetween them2 3.
1The 8051 Microcontroller andEmbedded SystemsCHAPTER 16Motor Control: Relay,PWM, DC and StepperMotorsĢ.
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