Optocuploare

Amplificatoare-Izolatoare

Aplicaţii

Transformer Ground Isolation

Optocoupler Block Schematic

Tuning transmitter / receiver wavelengths

Texas Instruments first optocoupler

Analog optocouplers

Phototransistor / Photo-Darlington Optocouplers

Optocouplers using other photo-detectors in the output circuit :

a. a photo-FET, b. a Light-Activated SCR ( Silicon Controlled Rectifier) , and c. a Light-Activated -Triac

The Schottky Transistor

Typical digital optocoupler ( first manufactured by Hewlett-Packard )

Interfacing two logic circuits through optocouplers provides

ground isolation

Dual Analog Optocoupler

Free-space light barrier to detect obstacles

Confocal lens system increases detection resolution

Position transducer or /and tachometer using an optocoupler

Reflection Optocoupler

Checking the leaking current i.e. the isolation resistance

Path of the common mode in an optocoupler

Measuring the common mode rejection

Neutralizing parasitic capacitance

Neutralizing both common-mode capacitances in a dual link

Optocoupler’s CTR − Current Transfer Ratio

Measuring the D.C. CTR (statically )

Phototransistor turned into a controlled current generator to accurately determine CTR

Dark Current Measurement Circuit

Current vs. Voltage Characteristic of the Optocoupler Input LED

Determining the saturation voltage of the output phototransistor

Optocoupler Switching Mode Operation

Recommended circuit for measuring the optocoupler switching times

Optocoupler Transfer Characteristic in Frequency Domain

Optocoupler Pass-band Determination

Experimental result

Desensitivation of the Optocoupler Phototransistor

Faster Response

Using a cascode also speeds-up the circuit

Faster Turn-On

by Using the Classical Peaking Capacitor in the Base-Circuit of the LED Driver

The Effect of the Peaking Capacitor on the

Forward Current

Shortening the Switching Times by Prebiasing the LED

Practical Circuit for LED Pre-bias

Strong peaking

Typical Digital Optocoupler

Large Miller Capacitance of the Output Phototransistor Can Change the Output Characteristics

Replacing the Phototransistor

with a PD + Regular BJT Combination

Corrects the Previous Behavior

Open-Circuit

on behalf of the not-connected transistor hurts

( it is better to short its legs)

Like That !

Draining the charge out of the junction shortens optocoupler turn off

Coupling the discharge circuits is detrimental

Isolation Amplifiers

Ground Isolation Means Infinite Impedance Between the Meant Circuits

Isolation Amplifier Circuit Symbol

Controlled-Gain Amplifier Provides Optically-Isolated Control Circuit

Same function, different circuit

Basic Isolation Amplifier with Negative Feedback in the Receiver

Feedback Parallel-Series Topology Turns the Photodiode into a Current Generator

Feedback circuit loading effect

upon the basic amplifier

Equivalent Schematic of the Feedback Amplifier Showing the Loading Effects

Compensating for optocoupler non-linearity by using a matching-device in the feedback loop

Nonlinearity compensation through negative feedback in the transmitter

LEDs ‘True’ Control

Classical Compensated Isolation Amplifier

Differential Isolation Amplifier

Switch-Mode Amplifier

FM Modulation Used for Linear Signal Transfer Over a Light Barrier

PWM − Pulse-Width Modulation over Light Barrier

Principle of PWM

Manufacturer’s Recommended Circuit to Experimentally Obtain the Transfer Characteristic in the Frequency Domain

Isolation-Amplifier Transfer Characteristic

Different Configuration – Same Transfer Characteristic Envisaged

Isolation-Amplifier Gain vs. Frequency Characteristic, as Given in Data Sheet

Din capitolul Fotodioda,

urmatoarele două aplicaţii pot fi

considerate amplificatoare

izolatoare cu optocuploare

Densimeter

Intrusion Detector