Lesson 14/1782%
MODULE 14

Applications

Sector-by-sector application patterns: industrial automation I/O, medical patient-connected electronics, motor drives and inverters, solar and wind power conversion, EV charging infrastructure, battery management systems, and precision instrumentation front ends.

Learning Objectives

After completing this module, you will be able to:

Recognize standard isolation architectures per industry
Map sector-specific standards to optocoupler requirements
Analyze reference designs from each application domain
Anticipate environmental stresses per sector
Select appropriate device families per application
Where this fits. Modules 3–13 built the toolkit; this module shows where it is used. Each sector gets its isolation architecture (click the numbered isolation points), the governing standards (Module 16), the device-family choice and why (Module 5, Module 15), environmental stresses, a reference-design calculation and the classic pitfalls. The design details are in Module 10.
Illustrations and animations are original teaching drawings, not to scale. Values marked representative are typical of common parts; always confirm against the current datasheet or standard you design to.

Isolation requirements cluster by sector: a PLC input card and a SiC traction inverter both use “optocouplers”, but almost every number that matters differs by an order of magnitude. Start by placing your product in the envelope below.

Table of seven sectors with representative working voltage, CMTI need, signal speed, temperature range and key standard
Figure 1. Representative envelopes per sector.

Interactive: Sector Comparison Matrix

Filter by group and click a column header to sort. Values are representative upper envelopes for teaching, not requirements.

Sector ⇅Max working V ⇅CMTI need ⇅Data rate ⇅Max T ⇅StandardTypical families

A PLC or remote I/O module is the classic optocoupler application: dozens of slow 24 V signals, a noisy cabinet, long field cables and a price per channel measured in cents.

Interactive: System Map — Industrial automation

Click a numbered isolation point for the recommended family, a representative part and the rationale.

Industrial automation: PLC I/O module architecture: blocks with numbered isolation points

Standards

IEC 61131-2 (input types, immunity), with safety via IEC 61010-2-201; generic EMC IEC 61000-6-2. Field I/O and logic are usually both SELV/PELV, so the isolation is functional: for noise and ground loops. Relay outputs switching mains need reinforced spacing.

Family choice

Quad phototransistor couplers for inputs (cost, no field supply); PhotoMOS or opto-driven high-side switches for outputs; fast optos or digital isolators for fieldbus.

Environment

−25…+70 °C cabinet, pollution degree 2 (PD 3 in harsh plants), EFT bursts on cables (±1–2 kV), surges on long lines, 10–20 year life at 24/7 duty.

Reference snippet — RS-485 fieldbus at 1 Mbps through a TLP2361-class coupler
  1. Bit time = 1 µs. A common rule keeps total pulse-width distortion below ~10 % of the bit: 100 ns.
  2. Coupler PWD (representative max) ≈ 30 ns, plus transceiver skew ~10 ns: 40 ns, which is within budget.
  3. At 12 Mbps (PROFIBUS DP max) the bit is 83 ns: 40 ns is 48 %, so use a digital isolator or an isolated transceiver (Module 15).
Design trap — designing inputs at 24 V. IEC 61131-2 type 1/3 inputs must switch ON at 15 V and tolerate the full current band. Design the CTR at the 15 V threshold with end-of-life margin (Module 10, Example 3), or the card fails after a few years in a hot cabinet.

Medical equipment connected to a patient needs the highest isolation margins in this course and the tightest leakage limits: the patient may be anaesthetised, and a cardiac catheter makes microamps dangerous.

Interactive: System Map — Medical

Click a numbered isolation point for the recommended family, a representative part and the rationale.

Medical: patient-connected monitor architecture: blocks with numbered isolation points

Standards

IEC 60601-1: 2 MOPP between mains and the applied part; 2 MOOP to operator-accessible parts; B/BF/CF applied parts with patient-leakage limits (representative 100/100/10 µA in normal condition).

Family choice

Wide-lead reinforced couplers (≥ 8 mm creepage, VISO ≥ 5 kVrms) or reinforced digital isolators for data; medical-grade DC-DC with low interwinding capacitance for power; PhotoMOS for nurse-call contacts.

Environment

Benign temperature (+10…+40 °C), but cleaning agents, defibrillator pulses on ECG leads (defibrillation-proof applied parts) and strict EMC (IEC 60601-1-2).

Interactive: MOPP / MOOP Requirement Helper

Representative values commonly quoted for working voltages up to 250 Vrms — verify with the IEC 60601-1 tables for your edition, pollution degree and material group.

Dielectric test voltage–
Creepage–
Clearance–
Leakage limit–
–

Reference snippet — patient leakage through the isolation

A BF ECG front end is isolated by a data coupler (CIO ≈ 1 pF) and a medical DC-DC (10 pF interwinding). Test at 110 % of 240 V, 60 Hz: 264 V.

  1. Total barrier capacitance: 11 pF.
  2. I = 2π × 60 × 11 pF × 264 V = 1.1 µA, which is well below 100 µA (BF) and even 10 µA (CF).
  3. Replace the DC-DC with a generic 100 pF module and add a 470 pF Y-cap: I ≈ 2π × 60 × 571 pF × 264 = 57 µA, which fails CF and eats most of the BF budget.
Design trap — reusing ICT parts. A 3.75 kVrms, 5 mm SO-4 coupler that is fine for IEC 62368-1 reinforced insulation cannot provide 2 MOPP. Choose the package for the 8 mm creepage first.

Drives are the high-dV/dt world. Every switching edge on the DC link drives displacement current through each barrier that bridges the switch node, and the control electronics must be protectively separated from hundreds of volts.

Interactive: System Map — Motor drive / inverter

Click a numbered isolation point for the recommended family, a representative part and the rationale.

Motor drive / inverter architecture: blocks with numbered isolation points

Animation of a switch-node voltage waveform, the resulting common-mode current spikes at each edge, and arrows of displacement current crossing the barrier of a gate-drive coupler
Figure 2 (animation). Common-mode current through the gate-drive barrier at each switching edge.
Standards

IEC 61800-5-1 (DVC classes, protective separation), IEC 61800-3 (EMC), IEC 60204-1 for the machine.

Family choice

Opto gate drivers (HCPL-3120, ACPL-332J with DESAT/Miller clamp, TLP250) for IGBTs; high-CMTI isolated gate drivers for SiC/GaN; isolated amplifiers or ΔΣ modulators for current sensing; IL300/HCNR201 for slow voltage sensing.

Environment

Heat from the power stage, vibration, conductive dust (pollution degree 2–3), regeneration overvoltage, long motor cables that multiply dV/dt reflections.

Reference snippet — CMTI requirement for IGBT vs SiC
  1. IGBT, 560 V DC link, 100 ns edge (10–90 %): dV/dt = 0.8 × 560 / 100 ns = 4.5 kV/µs. Target ≥ 2× = 9 kV/µs; classic opto gate drivers rated in the tens of kV/µs are comfortable.
  2. SiC, 800 V bus, 16 ns edge: 0.8 × 800 / 16 ns = 40 kV/µs. Target ≥ 80 kV/µs: only the highest-CMTI opto drivers or digital-isolator gate drivers qualify (check the datasheet minimum, not the typical).
  3. Barrier current at 40 kV/µs with 1 pF: 40 mA per edge, returned through the gate-driver supply: keep that loop small (Module 11).
Design trap — forgetting the aux supply feedback coupler. The auxiliary SMPS that powers the control board often straddles the DC-link-to-control barrier. Its TL431 + PC817 feedback coupler then carries the reinforced requirement and full dV/dt too.

Solar and wind converters combine drive-like dV/dt with very high DC working voltages (1000 V and increasingly 1500 V PV strings), outdoor installation, altitude and 20-year life expectations.

Interactive: System Map — Renewable energy

Click a numbered isolation point for the recommended family, a representative part and the rationale.

Renewable energy: PV string inverter architecture: blocks with numbered isolation points

Standards

IEC 62109-1/-2 (PV converter safety), IEC 62477-1, grid codes; insulation coordination via IEC 60664-1 including altitude.

Family choice

Reinforced gate drivers with high VIORM (often digital-isolator based at 1500 V), isolated amplifiers for string voltage/current, PhotoMOS for insulation-resistance measurement, optos for relay feedback.

Environment

−25…+60 °C ambient with solar heating, humidity and condensation, altitude up to 4000–5000 m, lightning surges on long DC cables.

Reference snippet — is a 1140 Vpk coupler enough at 1500 V DC?
  1. Working voltage across a gate driver referenced to the negative rail: up to 1500 V DC plus switching overshoot (~10 %): about 1650 Vpk.
  2. 1650 > 1140 VIORM: the coupler is not suitable, whatever its UL 1577 VISO.
  3. Options: a driver with VIORM ≥ 2 kVpk class, a topology that halves the voltage across each barrier (three-level/split DC link), or two barriers in series.
  4. Altitude: clearances need the altitude correction (e.g. about 1.14 at 3000 m, 1.29 at 4000 m, 1.48 at 5000 m, representative per IEC 60664-1).
Design trap — using VISO as the working-voltage rating. A 5 kVrms UL 1577 rating says nothing about continuous 1500 V DC. Only VIORM/VIOWM from IEC 60747-5-5 (or -17) answer that question.

EV chargers range from 230 V AC wallboxes (a smart contactor with a control pilot) to 1000 V DC fast chargers that are, in effect, large isolated power converters. Both must keep the user interface, the control pilot and the communications safely separated from mains and the DC output.

Interactive: System Map — EV charger (AC wallbox / DC fast charger)

Click a numbered isolation point for the recommended family, a representative part and the rationale.

EV charger (AC wallbox / DC fast charger) architecture: blocks with numbered isolation points

Standards

IEC 61851-1 (general) and IEC 61851-23 (DC chargers), IEC 62196 connectors, national installation rules; UL 2202 / UL 2594 in North America.

Family choice

H11AA1 or PC817 with resistor chains for mains/welded-contact detection; fast optos for pilot PWM readback where isolated; isolated gate drivers and amplifiers inside DC power modules; digital isolators for CAN/PLC communication.

Environment

Outdoor enclosures (−30…+50 °C), condensation, pollution degree 3, surges, 24/7 duty for public DC chargers.

Reference snippet — mains-presence sensing with H11AA1

Two 100 kΩ resistors in series with the H11AA1 input at 230 Vrms.

  1. LED current ≈ 230 V / 200 kΩ = 1.15 mArms (1.6 mA peak).
  2. Power per resistor: (1.15 mA)2 × 100 kΩ = 0.13 W. Use ≥ 0.25 W, pulse- and voltage-rated (≥ 400 V each) parts.
  3. H11AA1 CTR (min, representative 20 %) at 1.6 mA gives IC ≈ 0.32 mA peak: a 22 kΩ pull-up from 3.3 V (0.15 mA) is pulled low near each peak. Firmware sees 100/120 pulses per second when mains is present.
  4. The resistor chain crosses the barrier distance on the PCB: its layout must respect the same creepage as the coupler.
Design trap — a single resistor in the sensing chain. One resistor spanning mains is a single point of failure for both creepage and power. Use two or more in series so a single short keeps the current and voltage stress limited.

Battery management systems measure every cell of a 400–800 V stack and report to a 12 V vehicle controller. The isolation problem is both many potentials (each module at a different voltage) and automotive qualification.

Interactive: System Map — Battery management system (EV / ESS)

Click a numbered isolation point for the recommended family, a representative part and the rationale.

Battery management system (EV / ESS) architecture: blocks with numbered isolation points

Standards

ISO 6469-3 and OEM specifications for HV/LV isolation; AEC-Q100 (ICs), AEC-Q101/Q102 (discretes/optoelectronics); ISO 26262 for functional safety (Module 16).

Family choice

Capacitive/transformer daisy chains between cell monitors; AEC-Q100 digital isolators between stack and master; automotive optos for contactor feedback; automotive PhotoMOS for insulation monitoring.

Environment

−40…+85/+125 °C, vibration, thermal cycling, 15-year vehicle life, low quiescent-current budgets when parked.

Reference snippet — insulation-monitoring accuracy

An 800 V pack must flag an insulation fault below a representative 100 Ω/V (80 kΩ) and warn earlier (e.g. 500 Ω/V = 400 kΩ). Two PhotoMOS relays switch measurement resistors to chassis.

  1. PhotoMOS off-state leakage (representative 1 µA at rated voltage) looks like 800 V / 1 µA = 800 MΩ in parallel with the insulation.
  2. 800 MΩ against a 400 kΩ threshold is a 0.05 % error, which is negligible.
  3. A standard phototransistor opto would leak more when hot and cannot switch the measurement path; PhotoMOS (or HV MOSFET + isolated driver) is the usual choice.
Design trap — parked-car current. An opto LED at 5 mA left on while parked drains 120 mAh per day. BMS designs prefer isolators with near-zero static current, or duty-cycle the LED.

Instrumentation isolates for accuracy and safety: ground loops corrupt microvolt signals, and a measurement input may sit on a CAT III mains conductor. The choice is between isolating the analog signal or digitising first and isolating data.

Interactive: System Map — Instrumentation

Click a numbered isolation point for the recommended family, a representative part and the rationale.

Instrumentation: isolated measurement channel architecture: blocks with numbered isolation points

Standards

IEC 61010-1 and IEC 61010-2-030 (measurement categories), IEC 61326-1 EMC. Channel-to-channel isolation is rated like any other barrier.

Family choice

IL300/HCNR201 servo-linear couplers for moderate-accuracy analog; isolated ADC + digital isolator for high resolution; isolated DC-DC per channel.

Environment

Laboratory or panel (0…+50 °C) but high common-mode voltages, fast common-mode transients on power measurements, and precision drift requirements.

Reference snippet — is a linear opto good enough for 12 bits?

±10 V signal, 12-bit target (1 LSB = 0.024 %). IL300-class transfer gain K3 drift (representative) ≈ 50 ppm/°C.

  1. Over a 30 °C span: 50 ppm × 30 = 0.15 % gain error, about 6 LSB at 12 bits.
  2. Initial K3 tolerance is several percent: a one-point gain calibration is mandatory.
  3. For ≤ 10-bit accuracy with calibration a linear opto is fine; for 16–24 bits place the ADC on the sensor side and isolate SPI.
Design trap — channel-to-channel via shared supply. Isolating the signal but powering all channels from one non-isolated rail defeats channel-to-channel isolation. Each isolated channel needs its own isolated supply.

Across all seven sectors the same few questions decide the design:

QuestionWhere it bites hardestModule
What is the peak working voltage, including overshoot?PV, drives, BMS6, 16
What insulation class and how many means of protection?Medical, EV, PV16
What dV/dt appears across the barrier?Drives, PV, DC chargers6, 13, 15
Is CTR at end of life still enough at the worst threshold?PLC, SMPS feedback9, 10
What are the leakage limits?Medical, instrumentation13
Which environment: temperature, pollution degree, altitude?PV, EV, BMS8, 11
Opto or digital isolator?Everywhere above ~1 Mbps15
Pro tip Keep a one-page “isolation profile” per product (working voltages, classes, dV/dt, environment, standards). It makes part selection, layout review and certification much faster, and is the input for the capstone in Module 17.
Industrial

Functional isolation, cost per channel, 15 V threshold design, EFT/surge robustness.

Medical

2 MOPP, 8 mm creepage, µA-level leakage: package and capacitance first.

Drives

CMTI ≥ 2× dV/dt; gate drivers with DESAT; aux supply feedback shares the barrier.

Renewables

VIORM vs 1000–1500 V DC, altitude correction, outdoor life.

EV chargers

Mains sensing chains, pilot accuracy, surge and condensation.

BMS

Many potentials, AEC-Q parts, low static current, PhotoMOS for insulation monitoring.

Instrumentation

Analog (IL300) vs digital (isolated ADC) isolation; per-channel supplies.

Method

Build a per-product isolation profile before choosing parts.

Design checklist

Tick items as you review a design. Your ticks are saved in this browser only; use your browser’s print function for a sign-off copy.

Four parts: multiple choice, true/false, a matching exercise and engineering scenarios. Score 80 % on the multiple choice to pass the module.

Part A — Multiple Choice

Question 1 of 10  •  Score: 0/10

Part B — True or False

Score: 0/8

Part C — Match the Term to Its Meaning

Drag each term onto its definition, or click a term and then click a definition.

Placed: 0/6

Part D — Engineering Scenarios

Scenario 1 — The PLC card that fails in summer
A 16-channel input card passes all tests but, after two years, inputs in a hot cabinet (60 °C inside) intermittently miss 18 V signals. Design: PC817 rank A (80–160 %), IF = 2 mA at 15 V, 10 kΩ pull-up from 3.3 V.
Analysis. Required IC ≈ 3.3 V / 10 kΩ = 0.33 mA, so CTR ≥ 16.5 % at 2 mA. Worst case: 80 % (bin min) × ~0.6 (low-current CTR factor at 2 mA) × ~0.8 (60 °C, representative) × 0.5 (end-of-life ageing) ≈ 19 %, only just above the requirement with no margin for tolerances. Fix: raise the pull-up to 47 kΩ (if the speed allows), use a higher rank, or increase IF at threshold; re-run the Module 9 margin stack.
Scenario 2 — Medical upgrade
A monitor moves from BF to CF classification (cardiac use). Measured patient leakage is 35 µA, dominated by the isolated DC-DC.
Analysis. CF allows ~10 µA (representative, normal condition). 35 µA at 264 V, 60 Hz implies C ≈ 35 µA / (2π × 60 × 264) ≈ 350 pF. Fix: a medical DC-DC with < 20 pF interwinding capacitance, remove Y-caps across the patient barrier, and check that data couplers (≈ 1 pF each) and PCB stray capacitance stay within budget.
Scenario 3 — SiC retrofit
An IGBT inverter is upgraded to SiC MOSFETs with 15 ns edges on an 800 V bus. The existing opto gate driver (CMTI min 15 kV/µs, representative) now produces random shoot-through faults.
Analysis. dV/dt = 0.8 × 800 / 15 ns ≈ 43 kV/µs, nearly 3× the coupler’s minimum rating. Fix: a gate driver with ≥ 100 kV/µs CMTI (high-CMTI opto driver or isolated gate-driver IC), negative turn-off bias, Miller clamp, tight gate loop and low-capacitance isolated gate supplies. Verify with the CMTI bench test in Module 13.

Additional Resources

Sector standards

IEC 61131-2 • IEC 60601-1 • IEC 61800-5-1 • IEC 62109-1/-2 • IEC 61851-1/-23 • ISO 6469-3 • IEC 61010-1/-2-030 (details in Module 16).

Vendor application material

Gate-driver coupler application notes (DESAT, Miller clamp, CMTI) from Broadcom, Toshiba and others; linear-coupler application notes for IL300/HCNR201; medical isolation guides from DC-DC and isolator vendors.

Keep learning

Module 17 turns these architectures into labs and a capstone project.