Isolated outputs, while having a fixed voltage between output terminals, don't have a defined or fixed voltage relative to voltage nodes in circuits from which they've been isolated, and are said to be floating. Floating Outputs and Level ShiftingĪnother benefit to isolated converters is a floating output. Circuits that are sensitive to noise can benefit from this by having their ground broken up and separated from noisy circuits that could cause problems. Reinforced insulation: is a single barrier equivalent to two layers of basic.īecause the input and output of isolated supplies do not share a ground, they can be used to break up ground loops.Supplementary insulation: is basic insulation plus one additional barrier for redundancy. Basic insulation: provides a single layer of protection against shock.Functional insulation: is the most simple and, while providing isolation, it does not provide any protection against electric shock.The insulation grade is divided into several categories including functional, basic, supplementary, and reinforced. Safety standards should be reviewed to determine what level of insulation is required for a given application. When safety is the concern, the insulation grade must also be considered. For converters powered from high and potentially hazardous voltages (such as ac-dc converters powered from ac mains) isolation separates the output from dangerous voltages on the input. Safety requirements are a common reason to use an isolated power converter. These include safety compliance, the breaking of ground loops, and level shifting. There are several cases where an isolated power supply may be required or provide some benefit in an application. The isolation rating should not be confused with the working voltage, which is the maximum voltage that may be applied continuously across the isolation without isolation breakdown. Datasheets will usually list the isolation voltage, which is the voltage which may be applied across the isolation for a short duration without current flowing. At high enough voltages, the insulation will break down and current will flow. There are several ways to do this, but power converters generally rely on two power is transferred through electromagnetic fields using transformers or coupled inductors and signals cross the isolation using signal transformers or optically through opto-isolators. However, in an isolated converter, as shown on the right side of Figure 1, the input and output return to their own independent ground and there is no path for direct current from one to the other.įigure 1: Non-isolated buck converter (left), Isolated Flyback converter (right)Įven though current is not permitted to flow between input and output in isolated converters, power and information must still be transferred from one side to the other. In a non-isolated converter, as shown on the left side of Figure 1, the input and output share a common ground and current can flow between them. A result of isolation is that each of the isolated circuits has its own return or ground reference. Galvanic isolation (usually simplified to just isolation) is the physical and electrical separation between one section of a circuit and another. For those not familiar with power supplies this leads to additional questions: What are the benefits of isolated vs non-isolated power supplies? And how do I know which one I need for my application? Isolation Basics A non-isolated power converter has a single circuit in which current can flow between the input and output. In short, an isolated power converter isolates the input from the output by electrically and physically separating the circuit into two sections preventing direct current flow between input and output, typically achieved by using a transformer. What's the Difference Between Isolated and Non-Isolated Power Supplies?
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