optocuploare amplificatoare-izolatoare aplicaţii
TRANSCRIPT
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Optocuploare
Amplificatoare-Izolatoare
Aplicaţii
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Transformer Ground Isolation
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Optocoupler Block Schematic
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Tuning transmitter / receiver wavelengths
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Texas Instruments first optocoupler
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Analog optocouplers
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Phototransistor / Photo-Darlington Optocouplers
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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
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The Schottky Transistor
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Typical digital optocoupler ( first manufactured by Hewlett-Packard )
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Interfacing two logic circuits through optocouplers provides
ground isolation
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Dual Analog Optocoupler
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Free-space light barrier to detect obstacles
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Confocal lens system increases detection resolution
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Position transducer or /and tachometer using an optocoupler
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Reflection Optocoupler
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Checking the leaking current i.e. the isolation resistance
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Path of the common mode in an optocoupler
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Measuring the common mode rejection
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Neutralizing parasitic capacitance
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Neutralizing both common-mode capacitances in a dual link
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Optocoupler’s CTR − Current Transfer Ratio
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Measuring the D.C. CTR (statically )
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Phototransistor turned into a controlled current generator to accurately determine CTR
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Dark Current Measurement Circuit
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Current vs. Voltage Characteristic of the Optocoupler Input LED
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Determining the saturation voltage of the output phototransistor
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Optocoupler Switching Mode Operation
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Recommended circuit for measuring the optocoupler switching times
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Optocoupler Transfer Characteristic in Frequency Domain
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Optocoupler Pass-band Determination
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Experimental result
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Desensitivation of the Optocoupler Phototransistor
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Faster Response
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Using a cascode also speeds-up the circuit
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Faster Turn-On
by Using the Classical Peaking Capacitor in the Base-Circuit of the LED Driver
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The Effect of the Peaking Capacitor on the
Forward Current
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Shortening the Switching Times by Prebiasing the LED
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Practical Circuit for LED Pre-bias
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Strong peaking
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Typical Digital Optocoupler
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Large Miller Capacitance of the Output Phototransistor Can Change the Output Characteristics
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Replacing the Phototransistor
with a PD + Regular BJT Combination
Corrects the Previous Behavior
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Open-Circuit
on behalf of the not-connected transistor hurts
( it is better to short its legs)
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Like That !
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Draining the charge out of the junction shortens optocoupler turn off
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Coupling the discharge circuits is detrimental
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Isolation Amplifiers
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Ground Isolation Means Infinite Impedance Between the Meant Circuits
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Isolation Amplifier Circuit Symbol
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Controlled-Gain Amplifier Provides Optically-Isolated Control Circuit
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Same function, different circuit
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Basic Isolation Amplifier with Negative Feedback in the Receiver
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Feedback Parallel-Series Topology Turns the Photodiode into a Current Generator
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Feedback circuit loading effect
upon the basic amplifier
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Equivalent Schematic of the Feedback Amplifier Showing the Loading Effects
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Compensating for optocoupler non-linearity by using a matching-device in the feedback loop
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Nonlinearity compensation through negative feedback in the transmitter
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LEDs ‘True’ Control
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Classical Compensated Isolation Amplifier
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Differential Isolation Amplifier
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Switch-Mode Amplifier
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FM Modulation Used for Linear Signal Transfer Over a Light Barrier
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PWM − Pulse-Width Modulation over Light Barrier
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Principle of PWM
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Manufacturer’s Recommended Circuit to Experimentally Obtain the Transfer Characteristic in the Frequency Domain
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Isolation-Amplifier Transfer Characteristic
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Different Configuration – Same Transfer Characteristic Envisaged
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Isolation-Amplifier Gain vs. Frequency Characteristic, as Given in Data Sheet
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Din capitolul Fotodioda,
urmatoarele două aplicaţii pot fi
considerate amplificatoare
izolatoare cu optocuploare
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Densimeter
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Intrusion Detector