To protecting human and eliminating the ground loop we need a specific isolation circuit. The isolation amplifier does this job to isolating the input and output signals, providing a galvanic electrical barrier to the input, output regions.
Key Points
✔ Isolation Between input and output connections.
✔ No direct electrical connection.
✔ Input energy is transform its form to light, magnetic and capacitive.
✔ Less hazard to human and voltage sensitive circuits.
How Isolation Amplifiers Work
The isolation amplifier is working based on electrical conversion like converting the input signal into another form of energy like light, magnetic and capacitive charge. This converter energy is transferred to the output section none electrically across the isolation barrier.
This converted energy is then reversing the original form when we get it through in output. This method of isolation is safest way to protecting human and other voltage sensitive electronic devices.
Components of Isolation Amplifier
The main components of an isolation amplifier are listed below,
- Input amplifier stage.
- Modulator
- Isolation barrier.
- Demodulator.
- Output amplifier stage.
Types of Isolation Amplifiers
The isolation amplifiers are categorized based on the method of energy transferring. So there are three type of isolation amps are available, which are listed below.
- Transformer Isolation.
- Optical isolation.
- Capacitive isolation.
Transformer Isolation
The transformer based isolation using magnetic field as the isolation barrier and energy transferring through this magnetic field. This method is called as magnetic coupling of energy transferring.
Pros: High common mode rejection ratio, good linearity and can transfer isolated power across the barrier.
Cons: Lower bandwidth compared to other types (typically 2 kHz to 20 kHz) and it will produce magnetic noise.
Optical Isolation
The input signal is converted into light energy using an LED, then it transforming back to the signal at the output. This process is happening inside an optocoupler IC, the inbuilt LED and photoresistor doing this job of optical isolation.
Pros: Excellent safety and high linearity, there is no modulator/demodulator is needed for basic designs.
Cons: This design is more sensitive to temperature changes and aging effects due to the LED component.
Capacitive Isolation
Capacitive Isolation is uses a differential capacitive barrier to couple a high frequency carrier signal, often employing the digital encoding or frequency modulation of the input voltage.
Pros: Very high immunity to the magnetic noise, excellent linearity and high gain stability. It offers the highest bandwidth frequency often 70 kHz or more.
Cons: This can be more expensive and requires separate power supplies for both sides.
Applications
- In medical Equipment’s, they play crucial role for patient safety in devices like ECG (electrocardiogram) and EEG (electroencephalogram) machines. It providing a safety barrier against the accidental electric shock from the device.
- In industrial process control it is most commonly used in data acquisition systems and 4-20 mA current loops to eliminate ground loops and measuring the small signals in the presence of high common mode voltages. So this way it protects sensitive control systems from the voltage transients.
- This type of isolation is used in current and voltage sensing systems for motor control and power supply monitoring, where high noise is generated and high voltage isolation is required.
