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1、Capacitive Isolation A Technical Overview,Temperature,The Real World,Pressure,Position,Speed,Flow,Humidity,Sound,Light,TRANSCEIVERS RS-485/ CAN,Signal Isolation,What is Isolation?,Galvanic isolation: Although Circuit 1 and Circuit 2 exchange signals, no current (electrons) pass from Circuit 1 to Cir
2、cuit 2. Why is isolation required in electrical systems: Break ground loops Reduce common mode noise Safety from high voltages,Why Isolation? Ground Loops,More than one conductive path between two circuits creates a ground-loop Multiple ground paths may lead to unintended equalization currents,Groun
3、d loop can be broken by Disconnecting the grounds Common-mode chokes Frequency selective grounding Differential amplifiers Galvanic isolators Only galvanic isolation provides protection for very large potential differences,Why Isolation? Common Mode Noise,Signals referenced to GND1,Basic/Functional
4、Isolation vs. Reinforced Isolation,“An improved basic insulation with such mechanical and electrical properties that, in itself, the insulation provides the same degree of protection against electrical shock as double insulation. It may consist of one or more layers of insulation material.” UL-60950
5、-1,Basic/Functional Isolation vs. Reinforced Isolation (contd),When is Reinforced required: 6kVpp systems (e.g. 600V IGBTs/FETs) Today: all Medical applications (5kVrms!) Future: Medical applications for isolation from the patient Note: this is not complete and subject to change. Exceptions may appl
6、y!,Applications utilizing Isolation,Primary Task: Isolation between High-Power and Control Signals Isolation of Bus-Nodes to prevent Corruption of the complete Bus & Common Mode Rejection,Industrial: Robotics PLC input/output isolation Industrial networks Motor control Power supplies,Applications ut
7、ilizing Isolation,Communications: PBX (Private Branch Exchange) and central office Telephone terminal equipment Telephone switching equipment Modems ISDN Ethernet / PoE,Medical: Microwave therapy Patient monitoring Electrocardiographs Defibrillators,Primary Task: Medical: Isolation between Power and
8、 Patient Communications: Isolation between Power and Caller Isolation of Bus-Nodes to prevent Corruption of the complete Bus,Consumer Electronics: Video (TV, VCR, etc.) Plasma displays Electronic gaming Home appliances,Applications utilizing Isolation,Computers & Office Equipment Isolated I/O Printe
9、rs and plotters Fax machines,Primary Task: Isolation between High-Power and User,Nomenclatures / Definitions (1/3),Operation Voltage: Voltage that may be applied continuously across the Isolation barrier, mostly 560Vpk or 890Vpk Transient Voltage: Voltage that may occur temporarily across the barrie
10、r (tested per VDE for 1 minute), mostly 4kVpk (relates to 3kVrms per UL, as tested for 10s only) or 6kVpk Surge Voltage Single event surge, with the assumption that all effects have been recovered from prior to another surge-event, mostly rated for a 10kV single peak.,Nomenclatures / Definitions (2/
11、3),Basic / Functional Isolation: Assumes a single level of isolation with a certain strength. Applicable for most applications in industrial for fieldbusses and AC-equipment up to 400Vrms, and for consumer electronics. Mostly rated at 560Vpk continuous, 4kVpk transient voltage. Reinforced / Double I
12、solation: Double Isolation assumes a two-level isolation with a certain strength each. Reinforced addresses a single level of isolation that, however, provides the same reliability as the two-layer. Applicable for most medical applications and AC-equipment above 400Vrms. Mostly rated at 890Vpk conti
13、nuous, 6kVpk transient , 10kV surge voltage. Medical needs 5kVrms transient. Intrinsically safe Applications demand double isolation. Note: the End-equipment-standard (e.g. IEC-60950 for communications or IEC-60601-1 for medical) dictates what is needed on silicon level,Nomenclatures / Definitions (
14、3/3),Common Mode Transient Suppression: Discusses the quick change in Reference potential primary to secondary. Its given as the dU/dt up to which no false toggeling of the output will occur (e.g. 35kV/us). Usually scales linearly with Vcc. Creepage and Clearance Discusses the surface-distance that
15、may conduct if wet/polluted, respectively the air-distance. For 560V/4kV mostly 4mm is sufficient, for 890V/6kV mostly 8mm is needed. Depends on pollution degree,5 Questions, to allow educated solution-proposals Isolation strength: basic/reinforced? Isolation voltage: 4kVpeak, 560Vpeak continuos / 6
16、kVpeak, 890V peak continous? Stand-alone isolation or integration (Transceiver, Gate-Driver, Data-Converter)? Supply Voltages? Channel-count?,New Generation Capacitive Isolation,High voltage capacitor,Isolator construction,Creepage distance: Shortest distance between two conductive input to output leads measured along surface of insulation.,Clearance distance: Shortest distance between two conductive input to output leads measured through air (line of sight).,Note: Pac
