What Is an Isolation Amplifier?
An isolation amplifier is an amplifier that can transmit signals while providing electrical isolation between input and output signals.
Isolation amplifiers are incorporated into the input and output circuits of printed circuit boards, such as microcontroller control boards, to provide DC isolation from incoming signals and enable accurate measurements. For this reason, they are generally used in measuring instruments and medical equipment.
They also serve to ensure the safety of users. Features include prevention of electric shock, signal branching, countermeasures against high ground potentials, and noise suppression.
Uses of Isolation Amplifier
Isolation amplifiers protect power supplies by removing reverse currents caused by high ground potentials. They can also be installed in environments with many noise sources.
Specific applications are as follows:
- Train Cars
Monitoring of overhead line voltage and current, monitoring of drive power systems, control signal interfaces between trains, etc. - Power Generation Equipment
Interface between power generation and control units, monitoring of terminal voltage of each battery cell and solar cell connected in series, transmission of power conditioner control signals, etc. - FA-Related
Interfaces between sensors and control devices, control signal transmission for large power supplies, etc. - Others
Medical equipment, semiconductor manufacturing equipment, communication equipment, measuring equipment, etc.
By incorporating them into key locations in circuits, they function as safety measures to prevent users from receiving electric shocks in the event of equipment malfunctions.
Principle of Isolation Amplifiers
An isolation amplifier is a type of amplifier that operates circuits while completely separating and isolating them so that the circuits are not affected by grounding or common power supply. The main signal transmission methods include optical, magnetic, and capacitive, of which the operation of the magnetic method is as follows.
The input signal to the Isolation Amplifier first enters a buffer amplifier1 on the input side. This amplifier has the characteristics of high input impedance and low output impedance. The output side of the Isolation Amplifier is a similar buffer amplifier 2.
There is an isolation circuit between the two buffer amplifiers, but the input side is completely isolated from the output side in terms of DC. The isolation circuit has a signal transformer, with switching elements connected to the primary and secondary coils, respectively. synchronous rectification is possible by repeating the two switching elements on and off simultaneously.
Synchronous rectification then transfers a voltage to the secondary equal to the signal voltage entering the primary. Therefore, even if the primary and secondary sides of a signal transformer are completely isolated, the signal can be taken out from the secondary side.
Characteristics of Isolation Amplifiers
An isolation amplifier has the following features.
- No leakage of current from the output side to the input side, so there is no risk of electric shock and safety can be ensured.
- Since it operates even when a high voltage exists between the input and output, signal amplification of the high-voltage section is possible.
- Operates even in the presence of extremely large noise between input and output, enabling common-mode noise elimination.
High withstand voltage. (Many products are several thousand volts)
Other Information on Isolation Amplifiers
1. Power Supply for Isolation Amplifier
Isolation amplifier isolation transformers have a power transformer in addition to the signal transformer. On the primary side of the power transformer, a square wave from the oscillator is added, and the same square wave is generated on the secondary side.
The oscillator frequency is set to match the frequency response of the Isolation Amplifier: a square wave oscillator of about 50 kHz to 100 kHz. The voltage from the power transformer drives the switching elements on both the primary and secondary sides, respectively.
The primary and secondary sides of the power transformer are also isolated from each other DC-wise, and the power supplies for the primary and secondary buffer amplifiers are also supplied from the primary and secondary sides of the power transformer.
2. Photocoupler for Isolation Amplifier
When an isolation amplifier signal transmission is optical, a photocoupler is used. This photocoupler is an optical IC used in Isolation Amplifier circuits when making an isolated circuit in which the input and output are completely floating above each other, or when detecting signals of different potentials.