opto couplers – types & applications
TRANSCRIPT
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.
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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.
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Application or Function in the Circuit
Monitor high voltage.
Output voltage sampling for regulation.
System control micro for power ON/OFF.
Ground isolation.
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4 Different Opto Couplers
There are four different types of Opto Couplers.
1. MOC3020
2. MOC3021
3. MCT2E
4. MOC363
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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.
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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
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Typical applications of MOC3020
Solenoid/valve controls
Lamp ballasts
Interfacing microprocessors to 115/240 Vac peripherals
Motor controls
Incandescent lamp dimmers
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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.
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Block Diagram
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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.
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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
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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
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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.
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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.
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Pin Description
Pin 1: Anode.
Pin 2: Cathode.
Pin 3: No connection.
Pin 4: Emitter.
Pin 5: Collector.
Pin 6: Base.
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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.
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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.
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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.
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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
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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.
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Applications
Solenoid/valve controls
Static power switches
Temperature controls
AC motor starters and drivers
Lighting controls
E.M. contactors
Solid state relay
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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.
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Block Diagram
