A circuit solution called "galvanic isolation" is found quite often in electronic and electrical engineering. For this reason, it is important to familiarize the user with what it is. In addition, it will be interesting to understand the existing varieties of "untie" knots and the principle of their action.
What it is?
Galvanic isolation is a method of transferring electricity or information between input and output circuits, in which parts of the circuit are not directly connected to one another. The need for it arises in cases where it is required to ensure the safety of work in the secondary circuits while maintaining the transmitted power.
In addition, thanks to this technique, an independent circuit is formed in the secondary circuit, which allows:
- partially reduce the influence of interference acting in the primary circuit;
- to improve the accuracy of taking readings in measuring circuits;
- improve load matching.
Finally, decoupling reduces the likelihood of damage to equipment connected to the secondary.
Operating principle
It is most convenient to explain the principle of operation of galvanic isolation using the example of a transformer, in which the secondary winding is not electrically connected to the primary.
Most often, the difficulty arises in understanding the reduction of the risk of electric shock when the input and output circuits are independent. The fact is that if an accident (breakdown of insulation and hitting a dangerous potential on the case) occurs directly in the supply line, the power of the entire network acts on the person who touches it.
In the presence of decoupling, the current strength will be limited not only by the resistance of the human body, but also by the power of the transformer (or other element used in this capacity). If the device case connected to the secondary circuit is grounded, the risk of injury will be reduced to a minimum.
Types of galvanic isolation
There are several known methods for artificially separating supply and load circuits.
Most often used for this:
- Inductive (or transformer) circuit.
- Optoelectronic pairs of semiconductor elements.
When implementing the first method, a separating unit is used - a transformer, which does not require a core in this case. Its transmission coefficient is usually unity, that is, the voltage in the secondary winding is equal to the input.
The disadvantages of this option include:
- bulkiness of the design;
- the possibility of using only in alternating current circuits;
- partial retention of interference from primary circuits.
It is possible to get rid of these disadvantages due to the use of a special type of decoupling, called optoelectronic.
Optoelectronic pairs
The main elements of such decoupling are optocouplers, implemented in circuits based on diodes, thyristors, as well as on transistors and other electronic components that are sensitive to light. The function of the primary element of the assembly is performed by an emitting light-emitting diode, and the medium transmitting the useful pulse is a light-conducting field created inside the optoelectronic pair.
In these devices, the electrical neutrality of the luminous flux allows you to organize an effective decoupling of input and output circuits, as well as to ensure coordination of nodes with different complex resistances. The advantages include the compactness of the device and a significant reduction in the level of noise at the output.