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
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
Intrusion Detector
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