Opto-isolator

Last updated
Schematic diagram of an opto-isolator showing source of light (LED) on the left, dielectric barrier in the center, and sensor (phototransistor) on the right Optoisolator Pinout.svg
Schematic diagram of an opto-isolator showing source of light (LED) on the left, dielectric barrier in the center, and sensor (phototransistor) on the right

An opto-isolator (also called an optocoupler, photocoupler, or optical isolator) is an electronic component that transfers electrical signals between two isolated circuits by using light. [1] Opto-isolators prevent high voltages from affecting the system receiving the signal. [2] Commercially available opto-isolators withstand input-to-output voltages up to 10  kV [3] and voltage transients with speeds up to 25 kV/μs. [4]

Contents

A common type of opto-isolator consists of an LED and a phototransistor in the same opaque package. Other types of source-sensor combinations include LED-photodiode, LED-LASCR, and lamp-photoresistor pairs. Usually opto-isolators transfer digital (on-off) signals and can act as an electronic switch, but some techniques allow them to be used with analog signals.

History

The value of optically coupling a solid state light emitter to a semiconductor detector for the purpose of electrical isolation was recognized in 1963 by Akmenkalns, et al. (US patent 3,417,249). Photoresistor-based opto-isolators were introduced in 1968. They are the slowest, but also the most linear isolators and still retain a niche market in the audio and music industries. Commercialization of LED technology in 1968–1970 caused a boom in optoelectronics, and by the end of the 1970s the industry developed all principal types of opto-isolators. The majority of opto-isolators on the market use bipolar silicon phototransistor sensors. [5] They attain medium data transfer speed, sufficient for applications like electroencephalography. [6] The fastest opto-isolators use PIN diodes in photoconductive mode.

Operation

An opto-isolator contains a source (emitter) of light, almost always a near infrared light-emitting diode (LED), that converts electrical input signal into light, a closed optical channel (also called dielectrical channel [7] ), and a photosensor, which detects incoming light and either generates electric energy directly, or modulates electric current flowing from an external power supply. The sensor can be a photoresistor, a photodiode, a phototransistor, a silicon-controlled rectifier (SCR) or a triac. Since LEDs can sense light in addition to emitting it, construction of symmetrical, bidirectional opto-isolators is possible. An optocoupled solid-state relay contains a photodiode opto-isolator which drives a power switch, usually a complementary pair of MOSFETs. A slotted optical switch contains a source of light and a sensor, but its optical channel is open, allowing modulation of light by external objects obstructing the path of light or reflecting light into the sensor.

Electric isolation

Planar (top) and silicone dome (bottom) layouts - cross-section through a standard dual in-line package. Relative sizes of LED (red) and sensor (green) are exaggerated. Optoisolator topologies both.svg
Planar (top) and silicone dome (bottom) layouts –cross-section through a standard dual in-line package. Relative sizes of LED (red) and sensor (green) are exaggerated.
Optocoupler on a circuit board. Note the pair of class Y1 safety capacitors. Optocoupler with class Y1 caps.jpg
Optocoupler on a circuit board. Note the pair of class Y1 safety capacitors.

Electronic equipment and signal and power transmission lines can be subjected to voltage surges induced by lightning, electrostatic discharge, radio frequency transmissions, switching pulses (spikes) and perturbations in power supply. [8] Remote lightning strikes can induce surges up to 10  kV, one thousand times more than the voltage limits of many electronic components. [9] A circuit can also incorporate high voltages by design, in which case it needs safe, reliable means of interfacing its high-voltage components with low-voltage ones. [10]

The main function of an opto-isolator is to block such high voltages and voltage transients, so that a surge in one part of the system will not disrupt or destroy the other parts. [2] [11] Historically, this function was delegated to isolation transformers, which use inductive coupling between galvanically isolated input and output sides. Transformers and opto-isolators are the only two classes of electronic devices that offer reinforced protection — they protect both the equipment and the human user operating this equipment. [12] They contain a single physical isolation barrier, but provide protection equivalent to double isolation. [12] Safety, testing and approval of opto-couplers are regulated by national and international standards: IEC 60747-5-2, EN (CENELEC) 60747-5-2, UL 1577, CSA Component Acceptance Notice #5, etc. [13] Opto-isolator specifications published by manufacturers always follow at least one of these regulatory frameworks.

An opto-isolator connects input and output sides with a beam of light modulated by input current. It transforms useful input signal into light, sends it across the dielectric channel, captures light on the output side and transforms it back into electric signal. Unlike transformers, which pass energy in both directions [note 3] with very low losses, opto-isolators are unidirectional (see exceptions) and they cannot transmit power . [14] Typical opto-isolators can only modulate the flow of energy already present on the output side. [14] Unlike transformers, opto-isolators can pass DC or slow-moving signals and do not require matching impedances between input and output sides. [note 4] Both transformers and opto-isolators are effective in breaking ground loops, common in industrial and stage equipment, caused by high or noisy return currents in ground wires. [15]

The physical layout of an opto-isolator depends primarily on the desired isolation voltage. Devices rated for less than a few kV have planar (or sandwich) construction. [16] The sensor die is mounted directly on the lead frame of its package (usually, a six-pin or a four-pin dual in-line package). [7] The sensor is covered with a sheet of glass or clear plastic, which is topped with the LED die. [7] The LED beam fires downward. To minimize losses of light, the useful absorption spectrum of the sensor must match the output spectrum of the LED, which almost invariably lies in the near infrared. [17] The optical channel is made as thin as possible for a desired breakdown voltage. [16] For example, to be rated for short-term voltages of 3.75 kV and transients of 1 kV/μs, the clear polyimide sheet in the Avago ASSR-300 series is only 0.08 mm thick. [18] Breakdown voltages of planar assemblies depend on the thickness of the transparent sheet [16] and the configuration of bonding wires that connect the dies with external pins. [7] Real in-circuit isolation voltage is further reduced by creepage over the PCB and the surface of the package. Safe design rules require a minimal clearance of 25 mm/kV for bare metal conductors or 8.3 mm/kV for coated conductors. [19]

Opto-isolators rated for 2.5 to 6 kV employ a different layout called silicone dome. [20] Here, the LED and sensor dies are placed on the opposite sides of the package; the LED fires into the sensor horizontally. [20] The LED, the sensor and the gap between them are encapsulated in a blob, or dome, of transparent silicone. The dome acts as a reflector, retaining all stray light and reflecting it onto the surface of the sensor, minimizing losses in a relatively long optical channel. [20] In double mold designs the space between the silicone blob ("inner mold") and the outer shell ("outer mold") is filled with dark dielectric compound with a matched coefficient of thermal expansion. [21]

Types of opto-isolators

Device type [note 5] Source of light [7] Sensor type [7] SpeedCurrent transfer ratio
Resistive opto-isolator
(Vactrol)		 Incandescent light bulb CdS or CdSe photoresistor (LDR)Very low<100% [note 6]
Neon lamp Low
GaAs infrared LED Low
Diode opto-isolatorGaAs infrared LEDSilicon photodiode Highest0.1–0.2% [22]
Transistor opto-isolatorGaAs infrared LEDBipolar silicon phototransistor Medium2–120% [22]
Darlington phototransistorMedium100–600% [22]
Opto-isolated SCRGaAs infrared LED Silicon-controlled rectifier Low to medium>100% [23]
Opto-isolated triacGaAs infrared LED TRIAC Low to mediumVery high
Solid-state relay Stack of GaAs infrared LEDsStack of photodiodes driving
a pair of MOSFETs or an IGBT 		Low to high [note 7] Practically unlimited

Resistive opto-isolators

The earliest opto-isolators, originally marketed as light cells, emerged in the 1960s. They employed miniature incandescent light bulbs as sources of light, and cadmium sulfide (CdS) or cadmium selenide (CdSe) photoresistors (also called light-dependent resistors, LDRs) as receivers. In applications where control linearity was not important, or where available current was too low for driving an incandescent bulb (as was the case in vacuum tube amplifiers), it was replaced with a neon lamp. These devices (or just their LDR component) were commonly named Vactrols, after a trademark of Vactec, Inc. The trademark has since been genericized, [note 8] but the original Vactrols are still being manufactured by PerkinElmer. [24] [note 9]

The turn-on and turn-off lag of an incandescent bulb lies in hundreds of milliseconds range, which makes the bulb an effective low-pass filter and rectifier but limits the practical modulation frequency range to a few Hertz. With the introduction of light-emitting diodes (LEDs) in 1968–1970, [25] the manufacturers replaced incandescent and neon lamps with LEDs and achieved response times of 5 milliseconds and modulation frequencies up to 250 Hz. [26] The name Vactrol was carried over on LED-based devices which are, as of 2010, still produced in small quantities. [27]

Photoresistors used in opto-isolators rely on bulk effects in a uniform film of semiconductor; there are no p-n junctions. [28] Uniquely among photosensors, photoresistors are non-polar devices suited for either AC or DC circuits. [28] Their resistance drops in reverse proportion to the intensity of incoming light, from virtually infinity to a residual floor that may be as low as less than a hundred Ohms. [28] These properties made the original Vactrol a convenient and cheap automatic gain control and compressor for telephone networks. The photoresistors easily withstood voltages up to 400 volts, [28] which made them ideal for driving vacuum fluorescent displays. Other industrial applications included photocopiers, industrial automation, professional light measurement instruments and auto-exposure meters. [28] Most of these applications are now obsolete, but resistive opto-isolators retained a niche in audio, in particular guitar amplifier, markets.

American guitar and organ manufacturers of the 1960s embraced the resistive opto-isolator as a convenient and cheap tremolo modulator. Fender's early tremolo effects used two vacuum tubes; after 1964 one of these tubes was replaced by an optocoupler made of a LDR and a neon lamp. [29] To date, Vactrols activated by pressing the stompbox pedal are ubiquitous in the music industry. [30] Shortages of genuine PerkinElmer Vactrols forced the DIY guitar community to "roll their own" resistive opto-isolators. [31] Guitarists to date prefer opto-isolated effects because their superior separation of audio and control grounds results in "inherently high quality of the sound". [31] However, the distortion introduced by a photoresistor at line level signal is higher than that of a professional electrically-coupled voltage-controlled amplifier. [32] Performance is further compromised by slow fluctuations of resistance owing to light history, a memory effect inherent in cadmium compounds. Such fluctuations take hours to settle and can be only partially offset with feedback in the control circuit. [33]

Photodiode opto-isolators

A fast photodiode opto-isolator with an output-side amplifier circuit Optically isolated.jpg
A fast photodiode opto-isolator with an output-side amplifier circuit

Diode opto-isolators employ LEDs as sources of light and silicon photodiodes as sensors. When the photodiode is reverse-biased with an external voltage source, incoming light increases the reverse current flowing through the diode. The diode itself does not generate energy; it modulates the flow of energy from an external source. This mode of operation is called photoconductive mode. Alternatively, in the absence of external bias the diode converts the energy of light into electric energy by charging its terminals to a voltage of up to 0.7 V. The rate of charge is proportional to the intensity of incoming light. The energy is harvested by draining the charge through an external high-impedance path; the ratio of current transfer can reach 0.2%. [22] This mode of operation is called photovoltaic mode.

The fastest opto-isolators employ PIN diodes in photoconductive mode. The response times of PIN diodes lie in the subnanosecond range; overall system speed is limited by delays in LED output and in biasing circuitry. To minimize these delays, fast digital opto-isolators contain their own LED drivers and output amplifiers optimized for speed. These devices are called full logic opto-isolators: their LEDs and sensors are fully encapsulated within a digital logic circuit. [34] The Hewlett-Packard 6N137/HPCL2601 family of devices equipped with internal output amplifiers was introduced in the late 1970s and attained 10  MBd data transfer speeds. [35] It remained an industry standard until the introduction of the 50 MBd Agilent Technologies [note 10] 7723/0723 family in 2002. [36] The 7723/0723 series opto-isolators contain CMOS LED drivers and a CMOS buffered amplifiers, which require two independent external power supplies of 5 V each. [37]

Photodiode opto-isolators can be used for interfacing analog signals, although their non-linearity invariably distorts the signal. A special class of analog opto-isolators introduced by Burr-Brown uses two photodiodes and an input-side operational amplifier to compensate for diode non-linearity. One of two identical diodes is wired into the feedback loop of the amplifier, which maintains overall current transfer ratio at a constant level regardless of the non-linearity in the second (output) diode. [38]

A novel idea of a particular optical analog signal isolator was submitted on 3, June 2011. The proposed configuration consist of two different parts. One of them transfers the signal, and the other establishes a negative feedback to ensure that the output signal has the same features as the input signal. This proposed analog isolator is linear over a wide range of input voltage and frequency. [39] However linear opto couplers using this principle have been available for many years, for example the IL300. [40]

Solid-state relays built around MOSFET switches usually employ a photodiode opto-isolator to drive the switch. The gate of a MOSFET requires relatively small total charge to turn on and its leakage current in steady state is very low. A photodiode in photovoltaic mode can generate turn-on charge in a reasonably short time but its output voltage is many times less than the MOSFET's threshold voltage. To reach the required threshold, solid-state relays contain stacks of up to thirty photodiodes wired in series. [21]

Phototransistor opto-isolators

Phototransistors are inherently slower than photodiodes. [41] The earliest and the slowest but still common 4N35 opto-isolator, for example, has rise and fall times of 5 μs into a 100 Ohm load [42] and its bandwidth is limited at around 10 kilohertz - sufficient for applications like electroencephalography [6] or pulse-width motor control. [43] Devices like PC-900 or 6N138 recommended in the original 1983 Musical Instrument Digital Interface specification [44] allow digital data transfer speeds of tens of kiloBauds. [45] Phototransistors must be properly biased and loaded to achieve their maximum speeds, for example, the 4N28 operates at up to 50 kHz with optimum bias and less than 4 kHz without it. [46]

Design with transistor opto-isolators requires generous allowances for wide fluctuations of parameters found in commercially available devices. [46] Such fluctuations may be destructive, for example, when an opto-isolator in the feedback loop of a DC-to-DC converter changes its transfer function and causes spurious oscillations, [20] or when unexpected delays in opto-isolators cause a short circuit through one side of an H-bridge. [47] Manufacturers' datasheets typically list only worst-case values for critical parameters; actual devices surpass these worst-case estimates in an unpredictable fashion. [46] Bob Pease observed that current transfer ratio in a batch of 4N28's can vary from 15% to more than 100%; the datasheet specified only a minimum of 10%. Transistor beta in the same batch can vary from 300 to 3000, resulting in 10:1 variance in bandwidth. [46]

Opto-isolators using field-effect transistors (FETs) as sensors are rare and, like vactrols, can be used as remote-controlled analog potentiometers provided that the voltage across the FET's output terminal does not exceed a few hundred mV. [38] Opto-FETs turn on without injecting switching charge in the output circuit, which is particularly useful in sample and hold circuits. [11]

Bidirectional opto-isolators

All opto-isolators described so far are uni-directional. Optical channel always works one way, from the source (LED) to the sensor. The sensors, be they photoresistors, photodiodes or phototransistors, cannot emit light. [note 11] But LEDs, like all semiconductor diodes, [note 12] are capable of detecting incoming light, which makes possible construction of a two-way opto-isolator from a pair of LEDs. The simplest bidirectional opto-isolator is merely a pair of LEDs placed face to face and held together with heat-shrink tubing. If necessary, the gap between two LEDs can be extended with a glass fiber insert. [48]

Visible spectrum LEDs have relatively poor transfer efficiency, thus near infrared spectrum GaAs, GaAs:Si and AlGaAs:Si LEDs are the preferred choice for bidirectional devices. Bidirectional opto-isolators built around pairs of GaAs:Si LEDs have current transfer ratio of around 0.06% in either photovoltaic or photoconductive mode — less than photodiode-based isolators, [49] but sufficiently practical for real-world applications. [48]

Types of configurations

A reflective pair (left) and two slotted couplers with the light paths in purple Gabelkopp.jpg
A reflective pair (left) and two slotted couplers with the light paths in purple

Usually, optocouplers have a closed pair configuration. This configuration refers to optocouplers enclosed in a dark container wherein the source and sensor are facing each other.

Some optocouplers have a slotted coupler/interrupter configuration. This configuration refers to optocouplers with an open slot between the source and sensor that has the ability to influence incoming signals. The slotted coupler/interrupter configuration is suitable for object detection, vibration detection, and bounce-free switching.

Some optocouplers have a reflective pair configuration. This configuration refers to optocouplers that contain a source that emits light and a sensor that only detects light when it has reflected off an object. The reflective pair configuration is suitable for the development of tachometers, movement detectors and reflectance monitors.

The later two configurations are frequently referred to as optosensors or photoelectric sensors .

See also

Notes

  1. ↑ Real-world schematic diagrams omit the barrier symbol, and use a single set of directional arrows.
  2. ↑ Based on conceptual drawings published by Basso and by Mims, p. 100. Real-world LEDs and sensors are much smaller; see the photograph in Avago, p. 3 for an example.
  3. ↑ A transformer can have as many coils as necessary. Each coil can act as a primary, pumping energy into a common magnetic core, or as a secondary – picking up energy stored in the core.
  4. ↑ The input side circuitry and the LED must be matched, the output side and the sensor must be matched, but there is, usually, no need to match input and output sides.
  5. ↑ See Horowitz and Hill, p. 597, for an expanded list of opto-isolator types with their schematic symbols and typical specifications.
  6. ↑ Current through the photoresistor (output current) is proportional to the voltage applied across it. In theory it can exceed 100% of input current, but in practice dissipation of heat according to Joule's law limits current transfer ratio at below 100%.
  7. ↑ Low-cost solid-state relays have switching times of tens of milliseconds. Modern high-speed solid-state relays like Avago ASSR-300 series (see datasheet) attain switching times of less than 70 nanoseconds.
  8. ↑ According to the United States Patent and Trademark Office, trademark registered in 1969 for "photocell combined with a light source" is now dead (USPTO database record serial number 72318344. Retrieved November 5, 2010). The same trademark, registered in 1993 for "medico-surgical tubing connector sold as a component of suction catheters" is now live and owned by Mallinckrodt Inc. (USPTO database record serial number 74381130. Retrieved November 5, 2010).
  9. ↑ Vactec was purchased by EG&G (Edgerton, Germeshausen, and Grier, Inc.), a defense contractor, in 1983. In 1999 EG&G purchased formerly independent PerkinElmer, and changed own name PerkinElmer (see reverse takeover). An unrelated company, Silonex (a division of Carlyle Group) brands its photoresistive opto-isolators Audiohm Optocouplers.
  10. ↑ The former semiconductor division of Agilent Technologies operates as an independent company, Avago Technologies, since 2005.
  11. ↑ Exception: Ternary and quaternary GaAsP photodiodes can generate light. - Mims, p. 102.
  12. ↑ "Even the garden variety signal diodes you use in circuits have a small photovoltaic effect. There are amusing stories of bizarre circuit behavior finally traced to this." - Horowitz and Hill McCoulny, p. 184.

Related Research Articles

<span class="mw-page-title-main">Diode</span> Two-terminal electronic component

A diode is a two-terminal electronic component that conducts current primarily in one direction. It has low resistance in one direction and high resistance in the other.

<span class="mw-page-title-main">Photodiode</span> Converts light into current

A photodiode is a semiconductor diode sensitive to photon radiation, such as visible light, infrared or ultraviolet radiation, X-rays and gamma rays. Photodiode is a PN semiconductor material that produces current or voltage Photovoltaics when it absorbs photons Semiconductor Optoelectronics . The physics of electron excitation for photodiodes are similar to Photoconductivity typically implemented as a Photoresistor or as switches in Thyristor#Photothyristors. Photodiodes can be used for detection and measurement applications, or optimized for the generation of electrical power in solar cells. Photodiodes are used in a wide range of applications throughout the electromagnetic spectrum from IR, visible light, UV photocells to gamma ray spectrometers.

<span class="mw-page-title-main">Optoelectronics</span> Branch of electronics involving optics

Optoelectronics is the study and application of electronic devices and systems that find, detect and control light, usually considered a sub-field of photonics. In this context, light often includes invisible forms of radiation such as gamma rays, X-rays, ultraviolet and infrared, in addition to visible light. Optoelectronic devices are electrical-to-optical or optical-to-electrical transducers, or instruments that use such devices in their operation.

A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and control systems, where electrical signals are converted to and from other physical quantities. The process of converting one form of energy to another is known as transduction.

<span class="mw-page-title-main">Preamplifier</span> Electronic amplifier that converts weak signal into strong signal

A preamplifier, also known as a preamp, is an electronic amplifier that converts a weak electrical signal into an output signal strong enough to be noise-tolerant and strong enough for further processing, or for sending to a power amplifier and a loudspeaker. Without this, the final signal would be noisy or distorted. They are typically used to amplify signals from analog sensors such as microphones and pickups. Because of this, the preamplifier is often placed close to the sensor to reduce the effects of noise and interference.

<span class="mw-page-title-main">Schmitt trigger</span> Electronic comparator circuit with hysteresis

In electronics, a Schmitt trigger is a comparator circuit with hysteresis implemented by applying positive feedback to the noninverting input of a comparator or differential amplifier. It is an active circuit which converts an analog input signal to a digital output signal. The circuit is named a trigger because the output retains its value until the input changes sufficiently to trigger a change. In the non-inverting configuration, when the input is higher than a chosen threshold, the output is high. When the input is below a different (lower) chosen threshold the output is low, and when the input is between the two levels the output retains its value. This dual threshold action is called hysteresis and implies that the Schmitt trigger possesses memory and can act as a bistable multivibrator. There is a close relation between the two kinds of circuits: a Schmitt trigger can be converted into a latch and a latch can be converted into a Schmitt trigger.

<span class="mw-page-title-main">Single-photon avalanche diode</span> Solid-state photodetector

A single-photon avalanche diode (SPAD), also called Geiger-mode avalanche photodiode is a solid-state photodetector within the same family as photodiodes and avalanche photodiodes (APDs), while also being fundamentally linked with basic diode behaviours. As with photodiodes and APDs, a SPAD is based around a semi-conductor p-n junction that can be illuminated with ionizing radiation such as gamma, x-rays, beta and alpha particles along with a wide portion of the electromagnetic spectrum from ultraviolet (UV) through the visible wavelengths and into the infrared (IR).

<span class="mw-page-title-main">Photodetector</span> Sensors of light or other electromagnetic energy

Photodetectors, also called photosensors, are sensors of light or other electromagnetic radiation. There are a wide variety of photodetectors which may be classified by mechanism of detection, such as photoelectric or photochemical effects, or by various performance metrics, such as spectral response. Semiconductor-based photodetectors typically use a p–n junction that converts photons into charge. The absorbed photons make electron–hole pairs in the depletion region. Photodiodes and photo transistors are a few examples of photo detectors. Solar cells convert some of the light energy absorbed into electrical energy.

A general-purpose input/output (GPIO) is an uncommitted digital signal pin on an integrated circuit or electronic circuit board which may be used as an input or output, or both, and is controllable by software.

<span class="mw-page-title-main">Electronic component</span> Discrete device in an electronic system

An electronic component is any basic discrete electronic device or physical entity part of an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singular form and are not to be confused with electrical elements, which are conceptual abstractions representing idealized electronic components and elements. A datasheet for an electronic component is a technical document that provides detailed information about the component's specifications, characteristics, and performance.

<span class="mw-page-title-main">Electronic symbol</span> Pictogram used to represent various electrical and electronic devices or functions

An electronic symbol is a pictogram used to represent various electrical and electronic devices or functions, such as wires, batteries, resistors, and transistors, in a schematic diagram of an electrical or electronic circuit. These symbols are largely standardized internationally today, but may vary from country to country, or engineering discipline, based on traditional conventions.

<span class="mw-page-title-main">Image sensor</span> Device that converts images into electronic signals

An image sensor or imager is a sensor that detects and conveys information used to form an image. It does so by converting the variable attenuation of light waves into signals, small bursts of current that convey the information. The waves can be light or other electromagnetic radiation. Image sensors are used in electronic imaging devices of both analog and digital types, which include digital cameras, camera modules, camera phones, optical mouse devices, medical imaging equipment, night vision equipment such as thermal imaging devices, radar, sonar, and others. As technology changes, electronic and digital imaging tends to replace chemical and analog imaging.

<span class="mw-page-title-main">Galvanic isolation</span> Isolating sections of electrical systems

Galvanic isolation is a principle of isolating functional sections of electrical systems to prevent current flow; no direct conduction path is permitted.

<span class="mw-page-title-main">Solid-state relay</span> High-power solid-state electronic switching device responding to an external control signal

A solid state relay (SSR) is an electronic switching device that switches on or off when an external voltage is applied across its control terminals. They serve the same function as an electromechanical relay, but solid-state electronics contain no moving parts and have a longer operational lifetime. Solid state relays were invented in 1971 by the Crydom Controls division of International Rectifiers.

In electronics, an electronic switch is a switch controlled by an active electronic component or device. Without using moving parts, they are called solid state switches, which distinguishes them from mechanical switches.

Electro-optical sensors are electronic detectors that convert light, or a change in light, into an electronic signal. These sensors are able to detect electromagnetic radiation from the infrared up to the ultraviolet wavelengths. They are used in many industrial and consumer applications, for example:

<span class="mw-page-title-main">Resistive opto-isolator</span>

Resistive opto-isolator (RO), also called photoresistive opto-isolator, vactrol, analog opto-isolator or lamp-coupled photocell, is an optoelectronic device consisting of a source and detector of light, which are optically coupled and electrically isolated from each other. The light source is usually a light-emitting diode (LED), a miniature incandescent lamp, or sometimes a neon lamp, whereas the detector is a semiconductor-based photoresistor made of cadmium selenide (CdSe) or cadmium sulfide (CdS). The source and detector are coupled through a transparent glue or through the air.

<span class="mw-page-title-main">James R. Biard</span> American electrical engineer and inventor (1931–2022)

James Robert Biard was an American electrical engineer and inventor who held 73 U.S. patents. Some of his more significant patents include the first infrared light-emitting diode (LED), the optical isolator, Schottky clamped logic circuits, silicon Metal Oxide Semiconductor Read Only Memory, a low bulk leakage current avalanche photodetector, and fiber-optic data links. In 1980, Biard became a member of the staff of Texas A&M University as an Adjunct Professor of Electrical Engineering. In 1991, he was elected as a member into the National Academy of Engineering for contributions to semiconductor light-emitting diodes and lasers, Schotky-clamped logic, and read-only memories.

High voltage interface relays, a.k.a., interface relays: or coupling relays or insulating interfaces is a special class of electrical relays designed to provide informational and electrical compatibility between functional components isolated from each other and not allowing for a direct connection due to a high difference of potentials. A common design principle of these devices is a special galvanic isolation module between the input (control) and the output (switching) circuits of the relay. Interface relays are widely used in control and protection systems of high voltage electronic and electrophysical equipment and in high power installations.

<span class="mw-page-title-main">Diamond buffer</span>

The diamond buffer or diamond follower is a four-transistor, two-stage, push-pull, translinear emitter follower, or less commonly source follower, in which the input transistors are folded, or placed upside-down with respect to the output transistors. Like any unity buffer, the diamond buffer does not alter the phase and magnitude of input voltage signal; its primary purpose is to interface a high-impedance voltage source with a low-impedance, high-current load. Unlike the more common compound emitter follower, where each input transistor drives the output transistor of the same polarity, each input transistor of a diamond buffer drives the output transistor of the opposite polarity. When the transistors operate in close thermal contact, the input transistors stabilize the idle current of the output pair, eliminating the need for a bias spreader.

References

  1. ↑ Graf, p. 522.
  2. 1 2 Lee et al., p. 2.
  3. ↑ Hasse, p. 145.
  4. ↑ Joffe and Kai-Sang Lock, p. 279.
  5. ↑ Graf, p. 522; PerkinElmer, p. 28.
  6. 1 2 See Ananthi, pp. 56, 62 for a practical example of an opto-coupled EEG application.
  7. 1 2 3 4 5 6 Mims, p. 100.
  8. ↑ Hasse, p. 43.
  9. ↑ Hasse, p. 60.
  10. ↑ See Basso for a discussion of such interfacing in switched-mode power supplies.
  11. 1 2 Horowitz and Hill, p. 595.
  12. 1 2 Jaus, p. 48.
  13. ↑ Jaus, pp. 50–51.
  14. 1 2 Joffe and Kai-Sang Lock, p. 277.
  15. ↑ Joffe and Kai-Sang Lock, pp. 268, 276.
  16. 1 2 3 Mataré, p. 174
  17. ↑ Ball, p. 69.
  18. ↑ Avago Technologies (2007). ASSR-301C and ASSR-302C (datasheet) . Retrieved November 3, 2010.
  19. ↑ Bottrill et al., p. 175.
  20. 1 2 3 4 Basso.
  21. 1 2 Vishay Semiconductor.
  22. 1 2 3 4 Mataré, p. 177, table 5.1.
  23. ↑ Mataré, p. 177
  24. ↑ Weber, p. 190; PerkinElmer, p. 28; Collins, p. 181.
  25. ↑ Schubert, pp. 8–9.
  26. ↑ PerkinElmer, pp. 6–7: "at 1 fc of illumination the response times are typically in the range of 5 ms to 100 ms."
  27. ↑ Weber, p. 190; PerkinElmer, pp. 2,7,28; Collins, p. 181.
  28. 1 2 3 4 5 PerkinElmer, p. 3
  29. ↑ Fliegler and Eiche, p. 28; Teagle and Sprung, p. 225.
  30. ↑ Weber, p. 190.
  31. 1 2 Collins, p. 181.
  32. ↑ PerkinElmer, pp. 35–36; Silonex, p. 1 (see also distortion charts on subsequent pages).
  33. ↑ PerkinElmer, pp. 7, 29, 38; Silonex, p. 8.
  34. ↑ Horowitz and Hill, pp. 596–597.
  35. ↑ Porat and Barna, p. 464. See also full specifications of currently produced devices: 6N137 / HCPL-2601 datasheet . Avago Technologies. March 2010. Retrieved November 2, 2010.
  36. ↑ Agilent Technologies Introduces Industry's Fastest Optocouplers . Business Wire. December 2, 2002.
  37. ↑ Agilent Technologies (2005). Agilent HCPL-7723 & HCPL-0723 50 MBd 2 ns PWD High Speed CMOS Optocoupler (Datasheet) . Retrieved November 2, 2010.
  38. 1 2 Horowitz and Hill, p. 598.
  39. ↑ Modern Applied Science Vol 5, No 3 (2011). A Novel Approach to Analog Signal Isolation through Digital Opto-coupler (YOUTAB) .
  40. ↑ Vishay website, IL300 data (accessed 10-20-2015), http://www.vishay.com/optocouplers/list/product-83622/ Archived 2016-12-27 at the Wayback Machine .
  41. ↑ Ball, p. 61.
  42. ↑ Horowitz and Hill, p. 596. Ball p. 68, provides rise and fall time of 10 μs but does not specify load impedance.
  43. ↑ Ball, p. 68.
  44. ↑ MIDI Electrical Specification Diagram & Proper Design of Joystick/MIDI Adapter . MIDI Manufacturers Association. 1985. Retrieved November 2, 2010.
  45. ↑ Ball, p. 67.
  46. 1 2 3 4 Pease, p. 73.
  47. ↑ Ball, pp. 181–182. Shorting one side of an H-bridge is called shoot-through.
  48. 1 2 Mims vol. 2, p. 102.
  49. ↑ Photodiode opto-isolators have current transfer ratios of up to 0.2% - Mataré, p. 177, table 5.1.

Sources

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.