Isolation 101: How to find the right isolation solution for your application

“Although you may have a clear idea of ​​what quarantine is, you may still have questions about the various types of quarantine. In this technical article, I will define the four main types of isolation and explain how engineers can benefit from TI’s new fully integrated transformer technology, which has multiple advantages over other reinforced isolation solutions .

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Although you may have a clear idea of ​​what quarantine is, you may still have questions about the various types of quarantine. In this technical article, I will define the four main types of isolation and explain how engineers can benefit from TI’s new fully integrated transformer technology, which has multiple advantages over other reinforced isolation solutions .

Simply put, isolation can prevent abnormal DC and AC currents between different parts of the system while transmitting the required signals and/or power. Designers will use isolation technology in many applications to supply power to the high-voltage side gate driver in the power supply or motor drive Circuit, protect the low-voltage circuit in the high-voltage system (such as the processor in the electric vehicle system), and separate different voltage potentials. Communication between systems, or to prevent electric shock to end users of high-voltage equipment. There are many different levels of isolation, including functional isolation, basic isolation, dual isolation, and reinforced isolation.

Functional isolation, as the name suggests, only provides functions. It transfers a signal or power source from a system of one potential to another system of a different voltage with one electric potential. It does not prevent electric shock.

The next one is basic isolation. It is a kind of functional isolation, but adds protection from electric shock. Class I equipment uses functional isolation and ground connections to protect users. Figure 1 shows a typical Class I device.

shell

Grounded

Shell ground

Figure 1: Typical Class I equipment

Double isolation adopts a system with basic isolation (basic-level electric shock protection), and an auxiliary insulating layer is added between the electrical components and the end user to reduce the possibility of electric shock when the basic isolation fails. Type II products require double isolation. These products are equipped with AC plugs without grounding pins, which improves the safety of the product because it does not rely on external wiring to ensure the safety of users. Examples of terminal equipment with dual isolation include grid asset monitoring systems, portable medical equipment (such as intravenous pumps), and electrical equipment (such as mixers or mobile phone charging power supplies).

The second layer physically isolates the internal metal parts (which may be live) from the external housing, or uses a non-conductive external housing, such as plastic. Compared with Type I equipment, Type II equipment does have a certain degree of safety because they do not rely on external wiring to provide redundant protection. Figure 2 shows a typical Class II device.

Double isolation-the entire system protects customers from electric shock

The insulating layer prevents any current from being conducted to the housing.

shell

Grounded

Insulation

Basic isolation C provides level 1 protection and any functional isolation required by the system

Reinforced isolation has the same effect as double isolation using a single layer. Equipment with reinforced isolation provides basic isolation; in addition, it is used to ensure physical isolation between printed circuit board traces, magnetic cores, windings, pins, etc., while meeting safety creep and gap distance (referring to two voltages The physical distance between systems). The reinforced device adopts a double isolation design, but it can only be tested as a single piece.

Safety standards define the values ​​that must be achieved for certification. For example, the International Electrotechnical Commission (IEC) 60950-1 requires a creep/gap distance of 3.2 mm for basic isolation, and a creep/gap distance of 6.4 mm for reinforced isolation and double isolation. The rated voltage requirements for basic isolation are 2,500 VRMS (1 minute) and 3,000 VRMS (1 second); the rated voltage requirements for reinforced isolation and double isolation are 5000 VRMS (1 minute) and 6,000 VRMS (1 second). You can see that the reinforced/double isolation is exactly-twice the basic isolation. As shown in Figure 3, the double isolation device is marked on the label with the double box logo.

This type of equipment is represented by a two-wire plug and an indicator light on the power supply.

Once you decide to build Class II equipment, you will need dual isolation or reinforced isolation. Why choose this type instead of other types? The answer lies in the size and cost of the solution. As you can imagine, if one device can complete the work of two devices, a smaller solution can be produced. You can save costs not only by integrating into a single device, but also by reducing the amount of work required to meet isolation safety standards.

The fully integrated, reinforced isolation solution comes in a small package and is easy to implement. Compared with other solutions, this device has multiple benefits. For example, Texas Instruments UCC12050 integrates all controllers, drivers, field effect transistors and magnetic components into a single package. You only need to place the device on a circuit board with some bypass capacitors, and follow the correct circuit board layout instructions to design an enhanced isolation solution, which can be offset in an ultra-small footprint. Set power application. All engineering work has been completed: no magnetic element design, no power controller selection.

Standards such as the German Institute of Electrical Engineers (VDE) 0884-10 and the International Electrotechnical Commission (IEC) 60747-17 provide minimum requirements for the certification of reinforced isolation equipment. UCC12050 meets all the requirements of reinforced isolation, the minimum isolation protection is 7 kVPK (1 second, after production test) and 5 kVRMS (1 minute).

All in all, functional and basic isolation electrically isolates one voltage rail from another, while dual isolation and reinforced isolation provide an interchangeable solution for the same design goal-unplug the ground pin from the plug.

Reinforced isolation provides a better advantage than double isolation by reducing two insulating devices to one. Compared with other isolated bias power solutions, it is an ideal choice to save time, energy, space and cost in your system.