Issue link: https://resources.mouser.com/i/1525523
| 34 switching frequencies to increase efficiency and decrease system size. If the low-voltage portion of the circuit is not sufficiently protected from the high-voltage side, voltage spikes and surges can propagate through to the low-voltage side and cause safety hazards, data corruption, and permanent damage to components. There are several ways of isolating the circuit's areas, and the best solution will depend on each application's size, performance, longevity, and reliability requirements. These solutions can include relays, optical isolation, capacitive isolation, and magnetic isolation. Relays Mechanical relays can be one of the simplest ways of protecting sensitive circuits from high-voltage anomalies. They have contacts that physically separate and connect to isolate the circuit, giving high protection. Relays are also capable of switching high levels of power. However, as they are mechanical, they degrade over time and need to be replaced regularly. Relays are also slow to act, which is not ideal for the fast-switching circuits used for modern motor control. Optical Isolation Optical isolation is a technique that converts electrical signals to photons and back to electrons to provide isolation. In optical isolation devices—called optocouplers—an LED generates a photonic representation of the control signal, and a photosensitive device, such as a phototransistor, converts it back to an electrical signal. The two optical components are housed in a single package, separated by a transparent, non- conductive barrier. These packages can be small enough to provide a compact solution if there are not too many conductor traces. It isn't easy to house more than one optocoupler in the same package, as the light from one optocoupler can interfere with adjacent devices. Optocouplers can provide isolation at levels up to several kilovolts. The speed at which data can be transmitted is limited by how fast the LED can switch, but today's optocouplers can operate at tens of megabits per second (Mbps), which is sufficient for almost all motor designs. Optocouplers also have several drawbacks. They can be relatively expensive and require external biasing, which makes them less efficient than other isolation techniques. Also, high currents and temperatures can lead to the diffusion of atoms out of the LED's active region, creating defects that reduce the quantity of light emitted and leading to a degradation in performance over time. Capacitive Isolation As the name suggests, capacitors are also used for isolation purposes. These devices are manufactured from two conductive plates separated by a dielectric material. The capacitor is made to act like a transformer by coupling the voltage on one conductor to the other. Capacitive isolation is generally used in circuits with high frequencies, as they can operate up to several gigahertz. However, they can provide only low levels of protection, in the range of tens of volts. They also suffer from Figure 1: The motor system's current path often needs isolation for both safety and circuit functionality. (Source: Mouser Electronics)