Site Search User. Share Contact author Subscribe by email More Cancel. Similar topics. Optocouplers and silicon-based galvanic isolation technology — how do they work? How does an optocoupler work? Figure 1: Optocoupler with pinout diagram Communication within an optocoupler occurs when an applied CMOS logic input generates an input-side current, which then creates a proportional LED output for transmission through the molding compound barrier to the receiving photodetector and output. How does a silicon-based isolator work?
It may also occur when two similar conductors come in contact with each other via dissimilar electrolytes the former is the more common condition. The intensity of galvanic corrosion is affected by certain factors they are the potential difference between the metals or alloys and the nature of the environment.
What is isolation and How does a galvanic isolator work. Isolation is one of the most critical issues in process control. It is used to prevent unwanted current loops, ground loops, protection of delicate equipment and ensuring the safety of human operators when high common-mode voltages are to be expected.
Galvanic isolation can do the physical separation of the input and output. Galvanic isolation is of three types signal isolation, power level isolation, and capacitors as an isolator. Galvanic isolation of the measuring signals can be done with the help of isolation amplifiers. These amplifiers need an external power supply.
The most common example of a galvanic isolator would be the transformer. The primary and secondary windings of a transformer are insulated from one another.
Transformers buffer or change voltages by stepping them up or down. A transformer allows its secondary windings to be offset from a ground reference on the primary side.
Thus, breaking potential ground loops between the primary and secondary circuits. Because it involves the mutual inductance of magnetic fields from coils, it can be more susceptible to magnetic interference.
Further, unless properly shielded, it can also be a source of magnetic interference to adjacent circuitry inductive and radiated emissions. Transformers are traditionally bulkier than optical or capacitive isolators.
These DC currents can accelerate galvanic corrosion on underwater metals of boats and cause extensive damage; metal in hulls, zinc anodes, prop, drive-shaft, etc. Galvanic isolators are used because boats plugged into shore power at marinas each act like giant batteries; contributing DC voltage to the power signals via the ground wires. This produces corrosive electric currents through all the metals that contact the water.
The metal and water form a giant battery, causing the metals to corrode in galvanic fashion; the way terminals and plates of a battery corrode as current passes through them. It allows AC fault current to pass through it while blocking DC current. Thus, AC faults are transmitted back to the power source, where they can safely trip a breaker or open a fuse.
This enables the zinc anodes of your boat to help protect its underwater metals and not those of other vessels that surround it; as they act to control the corrosion of the metal attached to your own boat. Most galvanic isolators are designed to be fail-safe; meaning that if they fail, they do not also open the path to ground for fault current.
The ground wire must be present to carry fault current back to the dock power source or transformer. Otherwise, if you accidentally contacted the shore power AC line by some type of wiring fault, you could become the medium to carry fault current back to the transformer; this could be fatal.
Optical devices transmit information through their medium or across their barriers using varying levels of light intensity; with no direct electrical conduction path. A light source transmitter, typically an LED sends light waves to a photo-sensitive device receiver, typically a photo-transistor.
The combination is often held in place with insulating plastic, like that of an integrated circuit IC. Alternatively, transmit and receive functions are separated using a transmitter linked to a remote receiver via fiber optic cable. One major benefit of optical isolation is its inherent immunity to EMI Electro-Magnetic Interference or electrical and magnetic noise.
Remember that capacitors generally allow AC current to flow, but block DC current. Thus, they efficiently couple AC signals between circuits, at different DC voltages, via a varying electric field. There are many capacitive isolation devices available, and it is a common technology of digital isolators.
Many modern devices will even use isolation-rated capacitors to connect between grounds on each side of an isolation barrier. This provides a conduction path for transient signals; perhaps to earth ground also helpful in quelling radiated emissions. Capacitive isolation is faster than optical isolation. Unfortunately, capacitors are more prone to failure when stressed by voltages above their voltage rating. And for some capacitors, this failure mode can result in a short circuit condition; abruptly ending its isolation-ability, as well as possibly rendering its circuit unsafe or hazardous.
Safety rated Y-type capacitors are used in line to ground applications and are designed to fail open; while X-types are used in line-to-line filtering applications and may fail short. Also bothersome when used to isolate digital signals; often the first bit transmitted after power-up using capacitive digital isolators is used to setup the data stream, and must be ignored only the trailing bits contain useful data.
An explanation of GMR isolation is beyond the scope of this paper. Briefly: GMR refers to an isolation scheme that relies on the property of a material to change the value of its electrical resistance, when an external magnetic field is applied to it.
However, it does this to linearly alter the DC resistance of a physically isolated sensing element. We have two principal reasons for introducing isolation into an electric circuit:. We use isolation to prevent the transfer of high or hazardous voltages between circuits. We typically block these voltages using isolation for safety reasons and protection from electric shock; but also to block high common mode voltage present in our signals, which can prevent its measurement and damage equipment.
Isolation can also block transient voltages for the same reasons. High voltage may drive injury via electric shock and the unintended flow of electric current through the body. Additionally, it may also drive damage to an electrical circuit because of unintended electric current flowing between conductive circuits. One reason we isolate a circuit is to help prevent electrical shock. That is, by introducing isolation between conductive bodies, we minimize or eliminate the potential for unintended current flow.
With no shared common reference or conductive path between two conductors or circuits you cannot complete a circuit for current to flow. Consider the above image. A popular optoisolator PC is isolating two independent circuits. Circuit 1 is the power source with a switch, circuit 2 is a logic level output connected with a different 5V supply. The logic state is controlled by the left circuit.
When the switch is being closed, the LED inside the optocoupler lights up and turns on the transistor. The logic state will be changed from High to Low. The circuit 1 and circuit 2 are isolated using the above circuit. Galvanic isolation is very useful for the above circuit.
There are several situations where the high potential ground noise induced in the low potential ground and creates a ground loop which further responsible for inaccurate measurements. Similar to PC there are many types of Optocoupler for different application requirements.
Optoisolators are useful for DC signal isolation , but electromagnetic isolators such as small signal transformers are useful for AC signal isolation. Transformers like audio transformer have their primary and secondary sides isolated which can be used for different audio signal isolation.
Another most common use is in network hardware or Ethernet section. Pulse transformers are used to isolate the external wiring with internal hardware. Even telephone lines are used transformer based signal isolators. But, as transformers are isolated by electromagnetically, it only works with AC. Above image is the internal schematic of RJ45 jack with integrated pulse transformer for isolating MCU portion with the Output.
Power level isolations are required to isolate low power sensitive devices from high power noisy lines or vice versa. Also, power level isolation provides proper safety from hazardous line voltages by isolating the high voltage lines from the operator and other parts of the system.
The popular power level isolator is again a Transformer. There are enormous applications for transformers the most commonly usage is to provide low voltage from a high voltage source. The transformer does not have connections between primary and secondary but could step down the voltage from high voltage AC to low voltage AC without losing the galvanic isolation.
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