Insulation Basics: Choosing the Right Insulation Solution for Your Application

1 Introduction

Everyone knows what insulation is, but not much is known about the various types of insulation. In this article, we'll look at four isolation types and explain how TI's highly integrated transformer technology provides advantages over other reinforced isolation solutions.

Simply put, isolation is the transmission of required signals and/or power between discrete components in a system while blocking unwanted DC and AC currents. Therefore, insulation is used in many applications. Protecting low-voltage circuits on high-voltage systems (such as processors in electric vehicle systems) by isolating upper gate drivers that drive power supplies or motor drive circuits. Isolating communications between systems with different voltage potentials can prevent end consumers using high-voltage equipment from getting electrocuted. For this purpose, different levels of insulation are used: functional insulation, basic insulation, double insulation and reinforced insulation.

Functional isolation , as the name suggests, provides isolation functions. It carries signals or power between systems of different voltage potentials and does not provide protection against electric shock.

Basic isolation is the next isolation level. On the basis of functional insulation, protection against electric shock is added. Class I equipment uses a ground connection for functional isolation to protect the user. Figure 1 shows a typical Class I device.

Figure 1: Class I equipment

Double isolation is a secondary connection between an electrical component and the end consumer to provide a basic level of protection against electric shock by reducing the chance of electric shock that may occur if basic insulation fails in a system using basic insulation. Insulation is added. Class II products require double insulation. These products are manufactured with an AC plug that does not have a grounding prong. It improves user safety as no external wiring is used for user safety. End devices that use double insulation include grid asset monitoring systems, portable medical equipment such as IV pumps, home appliances such as blenders, and mobile phone chargers.

The second layer can be used to physically shield the inner metal parts from the enclosure, or use a non-conductive material (such as plastic) for the enclosure. Class II devices offer significant safety compared to Class I devices because they do not use external wiring for double protection . Figure 2 shows a schematic diagram of Class II equipment.

Figure 2: Class II equipment

Reinforced isolation achieves the same effect as double insulation by using a single layer. Equipment with reinforced insulation is designed to provide basic isolation and meet safe creepage and spacing (the physical distance between two voltage systems) while maintaining physical spacing between PCB traces, cores, windings and pins. Enhanced equipment is designed with double insulation, but can only be tested as a single piece.

Safety standards set out the requirements that must be met to obtain certification. The IEC 60950-1 standard requires creepage distances and spacings of 3.2 mm for basic insulation and 6.4 mm for reinforced and double insulation. Rated voltage requirements are 2,500V RMS for 1 minute, 3,000V RMS for 1 second for basic insulation , while reinforced insulation and double insulation are 5,000V RMS for 1 minute, 6,000V RMS for 1 second . As can be seen, reinforced /double insulation is exactly twice as good as basic insulation. Double-insulated equipment is marked with a double-framed mark on the label, as shown in Figure 3.

Figure 3: Double insulation markings

If we are designing Class II equipment, we will need double or reinforced insulation. The choice of insulation material depends on the size and cost of the solution. Using a single device that can perform both functions will of course physically reduce the size of the solution. Using a single integrated device not only reduces costs but also reduces the engineering required to meet insulation safety standards.

Highly integrated reinforced insulation solutions are available in small packages and can be easily implemented using these solutions. Texas Instruments UCC12030  integrates control, drivers, field effect transistors and magnetics into a single package. With just a few bypass capacitors, the device can be mounted on a circuit board according to correct board layout guidelines and a reinforced isolation solution with a minimal footprint can be designed for bias supply applications. All the engineering work has been done, so there is no need to choose magnetic designs or power controllers.

Standards such as VDE 0884-10 and IEC 60747-17 define minimum requirements for certification of reinforced insulation equipment. The UCC12050 meets all requirements for reinforced insulation with minimum protection of 7kV PK ( 1 second, production test) and 5kV RMS ( 1 minute) insulation.

In short, functional isolation and basic isolation are electrical isolation of one voltage rail from another, while double isolation and reinforced isolation are compatible solutions to achieve the same goal of removing the ground pin from the plug, just with different designs.

The advantage of reinforced insulation compared to double insulation is that it reduces two isolated devices to one. Using this isolation saves time, effort and cost compared to other isolated bias power solutions.