Electrical Isolation Techniques are discussed with various applications, advantages and relative comparisons.

1. Compiled by: Prof. G B Rathod
EC Dept., BVM Engineering college.
Email: ghansyam.rathod@bvmengineering.ac.in
Isolation Techniques

2. Applications of Isolation Techniques
 Isolation amplifiers provide electrical isolation and an
electrical safety barrier.
 They protect the patients from leakage currents.
 They break the ohmic continuity of electrical signals between
input and output.
 Isolated power supplies are provided for both the input and
output stages.
 Used to amplify low level signals.

3. GENERAL PIN CONFIGURATION OF ISOLATION
AMPLIFIER

4. Types:
 Three types of methods are used to design isolation amplifier
 Transformer isolation
 Optical isolation
 Capacitive isolation

5. TRANSFORMER COUPLED
ISOLATION AMPLIFIER

6. TRANSFORMER COUPLED
ISOLATION AMPLIFIER
 It uses either frequency modulated or a pulse width
modulated carrier signal.
 Internally it has 20KHz oscillator, transformer, rectifier and
filter to provide supplies for each isolated stages.
 Rectifier- input to primary OPAMP.
 Transformer- couples the supply.
 Oscillator – input to secondary OPAMP.
 A low pass filter is used to remove the other frequency
components.

7. Advantages
 High common mode rejection ratio
 High linearity
 High accuracy

8. Applications
 MEDICAL
 Patient Monitoring and Diagnostic Instrumentation
 INDUSTRIAL
 Ground Loop Elimination and Off-ground Signal
Measurement
 NUCLEAR
 Input/output/Power Isolation

9. Optically isolated isolation
amplifier

10. Optically isolated isolation
amplifier
 The biological signal is converted into a light signal by LED
for further process.
 It has patient circuit which is the input circuit and a
phototransistor which forms the output circuit.
 Each circuit is battery driven.
 The input circuit converts the signal to light and the output
circuit converts the light back to signal.

11. Advantages
 Original frequency and amplitude is obtained.
 High linearity.
 No modulator or demodulator is needed as it couples
optically.
 Improves patient safety

12. Applications
 INDUSTRIAL PROCESS CONTROL
 DATAACQUISITION
 INTERFACE ELEMENT
 BIOMEDICAL MEASUREMENTS
 PATIENT MONITORING
 TEST EQUIPMENT
 CURRENT SHUNT MEASUREMENT
 GROUND-LOOP ELIMINATION
 SCR CONTROLS

13. Capacitively coupled isolation
amplifier

14. Applications:
 It uses digital encoding of the input voltage and frequency
modulation.
 The input voltage is converted to proportional charge on the
switched capacitor.
 It has modulator and demodulator circuits.
 The signals are sent across a differential capacitive barrier.
 Separate supplies are given for both sides.

15. Applications:

16. Advantages:
 Ripple noises are removed.
 It avoids device noise, radiated noise and conducted noise.
 High immunity to magnetic noises.
 Useful for analog systems.
 Has high gain stability and linearity.

17. Applications:
 DATAACQUISITION
 INTERFACE ELEMENT
 PATIENT MONITORING
 ECG
 EEG

18. Comparative Study:
 Commonly used
 Transformer isolation amplifier
 Cost
 Optical- low cost due to less components
 Transformer
 Capacitor coupled- high cost
 Isolation voltage
 Optical- low (800V)
 Transformer- medium (1200V)

19. Comparative Study:
 Isolation resistance
 Optical- 10^12
 Transformer- 10^10
 Capacitance- 10^12
 Gain stability and Linearity
 Optical- 0.02%
 Transformer- between 0.005% and
 0.02%
 Capacitance- 0.005% (best)

20. Reference
 Click Here for the National Instruments Study Material.