optocouplers safely isolate integrated power modules

Posted on Feb 7, 2014

An interface circuit based on optocouplers provides galvanic isolation and common-mode noise rejection between low-voltage microcontroller units and high-voltage integrated power modules in motor-drive applications. Optocouplers provide high-voltage isolation between a low-voltage device like a microcontroller or a pulse-width modulation (PWM) gen

optocouplers safely isolate integrated power modules
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erator and a high-voltage device like an intelligent or integrated power module (IPM). The optocoupler is a key interface device because every high-voltage circuit must be compliant with equipment safety standards, such as IEC 60950 for IT equipment and IEC 60335 for household appliances. In testing for these standards, a high voltage is usually applied between low-voltage and high-voltage ports of the equipment. In these systems, the optocoupler isolates the low- to high-voltage interface to meet safety and protection standards. Some common semiconductor component electrical safety standards applicable to optocouplers are IEC 60747-5-2 and UL 1577. A designer can select the appropriate optocouplers based on the relevant equipment safety standards. The table lists the characteristics of some optocouplers intended for high-voltage isolation. The key optocoupler parameters related to equipment safety ratings are working voltage, polluting degree, installation class and insulation level. Various safety standards for industrial, home, office and IT equipment require a reinforced insulation level for electrical equipment powered by the ac line. Some parameters specified by equipment safety standards include external clearance, creepage, distance through insulation (DTI) or internal clearance, and comparative tracking index (CTI). Fig. 1 shows a diagram of a motor-drive circuit between a microcontroller unit (MCU) and an IPM....

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