Opto Couplers – Types & Applications

Opto Couplers – Types &
Applications

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Introduction
 Opto-isolators or Opto-couplers, are made up of a light emitting device, and a
light sensitive device.
 The light emitter is nearly always an LED.
 The light sensitive device may be a photodiode, phototransistor, or more
esoteric devices such as thyristors, TRIACs etc.
 Nowadays a lot of electronic equipment is using opt coupler in the circuit.
 An opt coupler or sometimes refer to as opt isolator allows two circuits to
exchange signals yet remain electrically isolated.
 This is usually accomplished by using light to relay the signal.

Description
 The standard opt coupler circuits design uses a LED shining on a phototransistor-
usually it is a npn transistor and not pnp.
 The signal is applied to the LED, which then shines on the transistor in the IC.
 The light is proportional to the signal, so the signal is thus transferred to the
photo-transistor.
 Most commonly used is an opto-coupler MOC3021 an LED diac type
combination.
 The opto coupler usually found in switch mode power supply circuit in many
electronic equipment.
 It is connected in between the primary and secondary section of power
supplies.

Application or Function in the Circuit
 Monitor high voltage.
 Output voltage sampling for regulation.
 System control micro for power ON/OFF.
 Ground isolation.

4 Different Opto Couplers
There are four different types of Opto Couplers.
1. MOC3020
2. MOC3021
3. MCT2E
4. MOC363

1.Working Principle of MOC3020
 The MOC3020 are designed for interfacing between electronic controls and
power triac to control resistive and inductive loads for Vac operations.
 The principle used in opto-coupler is, MOC’s are promptly available in integrated
circuit form and don’t require very complex circuitry to make them work.
 Simply give a small pulse at the right time to the LED in the package.
 The light produced by the LED activates the light sensitive properties of the diac
and the power is switched on.
 The isolation between the low power and high power circuits in these optically
connected devices is typically few thousand volts.

Features of MOC3020
 400 V Photo-TRIAC Driver Output.
 Gallium-Arsenide-Diode infrared source and optically-coupled silicon triac driver.
 High isolation – 500 Vpeak.
 Output driver designed for 220 Vac.
 Standard 6-terminal plastic DIP.
 Directly interchangeable with Motorola MOC3020, MOC3021 and MOC3022

Typical applications of MOC3020
 Solenoid/valve controls
 Lamp ballasts
 Interfacing microprocessors to 115/240 Vac peripherals
 Motor controls
 Incandescent lamp dimmers

Application of MOC3020
 One LED can be connected in series with MOC3021.
 When high is given from micro controller such that we can know that current is
flowing in internal LED of the opto-coupler.
 The idea is to use a power lamp whose activation requires mains AC as
opposed to a DC voltage.
 A TRIAC, lamp load and a supply voltage are connected in series.
 In negative half cycle the same thing repeats.
 Thus the lamp glows in both the cycles in a controlled manner depending upon
the triggering pulses at the opto isolator.

Block Diagram

2. MOC3021
 MOC3021 is an opto-coupler designed for triggering TRIACS.
 By using this we can trigger anywhere in the cycle, so can call them as non-
zero opto-coupler.
 MOC3021 are very widely used and can be quite easily obtained from many
sources.

Pin Description
 Pin 1: Anode
 Pin 2: Cathode
 Pin 3: No connection (NC)
 Pin 4: Main terminal
 Pin 5: No connection (NC)
 Pin 6: Main terminal

Features
 400 V Photo-triac driver output
 Gallium-Arsenide-Diode Infrared Source and Optically-Coupled Silicon triac driver
 High Isolation 7500 V Peak
 Output Driver Designed for 220 Vac
 Standard 6-terminal plastic DIP

Application of MOC3021
 The most commonly used is an opto-coupler MOC3021 with an LED diac type
combination.
 Additionally while using this with microcontroller and one LED can be connected
in series with MOC3021.
 LED to indicate when high is given from micro controller such that we can know
that current is flowing in internal LED of the opto-coupler.
 When logic high is given then the current flows through the LED from pin 1 to 2.
 So in this process LED light falls on DIAC causing 6 and 4 to close.
 During each half cycle current flows through gate, series resistor and through
opto-diac for the main thyristor / triac to trigger for the load to operate.

3. MCT2E
 The MCT2E series of opto-coupler devices each consist of gallium arsenide
infrared LED and a silicon NPN phototransistor.
 They are packaged in a 6-pin DIP package and available in wide-lead
spacing.

Pin Description
 Pin 1: Anode.
 Pin 2: Cathode.
 Pin 3: No connection.
 Pin 4: Emitter.
 Pin 5: Collector.
 Pin 6: Base.

Features
 Isolation test voltage 5000 VRMS.
 Interfaces with common logic families.
 Input-output coupling capacitance < 0.5 PF.
 Industry standard dual-in-line 6 pin package.
 Compliant to ROHS directive 2002/95/EC.

Application of MCT2E
 It is a combination of 1 LED and a transistor.
 Pin 6 of transistor is not generally used and when light falls on the base-
emitter junction then it switches and pin5 goes to zero.
 When logic zero is given as input then the light doesn’t fall on transistor so
it doesn’t conduct which gives logic one as output.
 When logic 1 is given as input then light falls on transistor so that it
conducts.
 This makes transistor switched ON and it forms short circuit this makes the
output is logic zero as collector of transistor is connected to ground.

4. MOC363
 The MOC3063 devices consist of gallium arsenide infrared emitting diodes
optically coupled to monolithic silicon detectors performing the functions of
zero voltage crossing bilateral triac drivers.

Features
 Simplies logic control of 115/240 Vac power.
 Zero crossing voltage.
 dv/dt of 1500 V/µs typical, 600 V/µs guaranteed.
 VDE recognized.
 Underwriters Laboratories (UL) recognized.

Applications
 Solenoid/valve controls
 Static power switches
 Temperature controls
 AC motor starters and drivers
 Lighting controls
 E.M. contactors
 Solid state relay

Working of MOC3063
 An opto-coupler MOC3063 with an LED SCR type combination.
 Additionally while using this opto-coupler with microcontroller and one LED
can be connected in series with MOC3063
 LED to indicate when high is given from micro controller such that we can
know that current is flowing in internal LED of the opto-coupler.
 When logic high is given then the current flows through LED from pin 1 to 2.
 The LED light falls on SCR causing 6 and 4 to close only at the zero cross of
the supply voltage.

Opto Couplers – Types & Applications

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Opto Couplers – Types & Applications