Design Guidelines for Optocoupler Safety Agency …

1 vishay SEMICONDUCTORSO ptocouplers and Solid-State RelaysApplication Note 43 Design Guidelines forOptocoupler Safety Agency ComplianceAPPLICATION NOTE Rev. , 07-Nov-111 Document Number: 83743 For technical questions, contact: DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENTARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT TO ELECTRICAL SAFETYT raditionally, electrical isolation from hazardous voltageshas been the most common application for optocouplerdevices. Other applications for optocouplers includereducing EMI through the elimination of common-modecurrent loops, which are the greatest contributors toradiated emissions in high-speed digital systems. However,isolation is still the predominant role for optocouplers intoday's electronics isolation is important in modern electronics designas a way of minimizing the likelihood of exposing an enduserto injury from hazardous currents.

2 The currents at whichharm or even death can occur are far lower than mostpeople think. In certain invasive medical operations,currents as low as 80 A can be fatal and have anacceptable Safety limit of 10 A. These thresholds areoutlined in figure 1. Fig. 1 - Shock Hazardous LevelsElectrical isolation is typically achieved by one of threemethods: magnetic, capacitive, or electrooptical. All threehave their pros and cons. Magnetic isolation (using anisolation transformer) is probably the longest-establishedmethod of electrical isolation, providing high levels ofisolation at high frequencies in a robust package. Among thedownsides of this method of isolation are a large devicefootprint when compared with other methods and suitabilityonly for AC signal coupling. Due to these characteristics,magnetic coupling is for the most part limited to high-powerAC applications. Fig. 2 - Magnetic IsolationThe second common method of electrical isolation iscapacitive coupling.

3 The advantages of capacitive couplingare high switching speeds and a relatively small packagefootprint, but to eliminate the need for a floating powersupply on the secondary side, a large capacitance isrequired to transfer energy from the primary to thesecondary side. Thus, the electrical isolation value of thistechnique is greatly diminished by the need for efficientenergy coupling. Consequently, most capacitive couplingisolation schemes have isolation values in the hundreds ofvolts rather than the thousands of volts achievable withother methods. Fig. 3 - Capacitive IsolationAnother potential isolation method involves the use ofmagneto-resistive sensors. These sensors are able to detectDC as well as AC magnetic fields. However, this is anemerging technology and is susceptible to induced noisefrom extraneous external magnetic fields. 17348 Pain, respiratory paralysisBurnsVentricular fibrilliationLet go currentPerception1 mA10 mA100 mA1 A10 A100 A60 Hz current RMS17349V-isolationV-primaryV-secondary1 7350 Voltagetofrequency+ Frequencytovoltage+ + CouplingcapacitanceSecondarysidevoltageP rimarysidevoltageDesign Guidelines forOptocoupler Safety Agency ComplianceAPPLICATION NOTEA pplication Note Semiconductors Rev.

4 , 07-Nov-112 Document Number: 83743 For technical questions, contact: DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENTARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT isolation has many of the best aspects of the formermethods without the drawbacks. Mainly, optical isolationoffers high electrical isolation values, an effective line in thesand barrier that hazardous voltages are incapable ofpenetrating. In the case of vishay s couplers, these valuesare as high as 8000 V, the highest level in the industry. Thisis achieved with small-footprint packages and high speed;moreover, it is equally effective with AC or DC signals. Fig. 4 - Electro-Optical IsolationSAFETY Agency STANDARDS OVERVIEWT here are several widely accepted industry standards thatgovern the manufacture and testing of electronicequipment. Probably the most widely known of these inNorth America is Underwriter's Laboratories (UL).

5 UL hastwo types of basic approvals: UL Listing andUL-recognition. The difference is simple but often a subjectof much confusion. The UL Recognized mark, optionallyinscribed on the devices themselves, refers to componentsthat have been evaluated to a certain extent by UL and willbe re-reviewed by UL for proper incorporation into theend-use equipment. A UL Listed mark is placed oncomplete equipment. For example, a computer would be aUL Listed, while the component hard drive would be a ULRecognized part. As seen in the next page, UL wasconcerned enough about potential confusion between themeanings of these two marks that it intentionally made themdistinct from one another. Fig. 5 - UL Listed/UL RecognizedUL has Safety standards for everything that is or possiblycan be manufactured; however, to simplify things, thesestandards can be divided into two groups: systemstandards and component standards.

6 The systemstandards are beyond the scope of this document toaddress in their entirety. Arguably, the most commonlyapplicable system standard in the electronics industry isUL60950, which governs the electrical Safety requirementsfor the broad category of information technology equipment(ITE). In addition to information technology, there are alsostandards that deal with other specialty fields of productelectrical Safety . Of particular interest to Optocoupler designis IEC 60601-1, which governs the Safety of medicalequipment. IEC 60601-1 was generated by those in themedical field worldwide, and it is the basis for manycountries national standards, such as UL2601-1 in theUnited States. Similarly, UL 60950 has been based on theinternationally generated IEC 60950 and adopted withchanges due to unique national conditions in the UnitedStates, including the National Electrical Code (NEC).

7 The European Union adopted the IEC-based version asEN 60950. As is the case for all components, optocouplersdo not necessarily need to meet all particular end-usesystem standards, such as IEC 609050 or IEC 60601-1. Intrying to meet any of the specific system standards, it isimportant to know which component parameters createdesign limitations. For Safety purposes, these parametersinclude creepage (along a surface) distances, clearance(through air) distances, maximum isolation voltages, andinsulation thicknesses. For the most part, this documentwill deal with standards exclusively dealing with themanufacture and testing of optocouplers. These arecovered under two standards, UL1577 and IEC 60747-5-1,which incorporate and supersede the earlier DIN EN60747-5-5. In addition to these standards, which explicitlydeal with optocouplers, the latest version of IEC 60950-1clauses, , , , ANEX , and ANEX ,also address issues that deal with optocouplers directly.

8 UL 1577 The main UL component standard, addressingoptocouplers in the United States is UL 1577, which coversthe Safety specifications that pertain to optocouplers inNorth America. This document offers an outline of thespecification and points out the highlights that deal withelectrical , all tests classified as type tests refer to thosetests performed to validate a particular Design to a are conducted by qualified testing laboratories, oftenonly once before serial production begins. This is in contrastto routine tests, also known as 100 % production line tests,which are intended to prevent manufacturing defects fromever leaving the factory. In other words, 100 % production17351+ V-secondaryRLRFI solation barrierV-primaryVisomin. msup to kVOperational characteristicsHigh isolation voltageHigh CMRRS mall package footprintIntrinsic secondary floating supplyHigh CMRRS mall package footprintUL ListedUL Recognized17356 CUS Design Guidelines forOptocoupler Safety Agency ComplianceAPPLICATION NOTEA pplication Note Semiconductors Rev.

9 , 07-Nov-113 Document Number: 83743 For technical questions, contact: DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENTARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT tests are designed to assure that products coming offthe line are confirmed to be constructed as those evaluatedduring the type tests. The first sections of UL1577 deal withpackage construction issues, materials, corrosionprotection, spacing, thermal testing, section of greatest interest is section , whichspecifies rated dielectric insulation voltage testing. Itspecifies a test at the rated dielectric insulation voltage for60 s; however, it gives the manufacturer the option of testingat 120 % of the rated dielectric insulation voltage for only1 second. For obvious efficiency concerns, the 1 s test ismuch more desirable. Thus, on a vishay Optocoupler datasheet, a minimum isolation test voltage , or isolationvoltage for 1 s , is actually 120 % of the rated dielectricinsulation voltage.

10 Consequently, the actual rateddielectric insulation voltages are arrived at from Table 1,where they are identified by system type (family of relatedcomponents).In addition to the general Optocoupler standards listedabove, there is one additional component classification, thatof double-protection optical isolators, which is a fairlyunique evaluation specific under UL 1577. This is oftenconfused with the more commonly used IEC-based terms of double insulation and reinforced isolation . Both terms,explained in great detail in IEC60950, are briefly defined asfollows:Reinforced insulation: A single, robust level of insulationthat meets a high level of constructional and performancerequirements at a single point. This can be thought of as ahigh-integrity component, such as a power transformer withlow-voltage outputs or an Optocoupler with at least mm minimum insulation thickness to fulfill thisrequirement.