How to use sealed isolation amplifier for design

Optocoupler is a ubiquitous Electronic component, which can be found in almost any electrical equipment and most industries. Since its introduction 25 years ago, optocoupler isolators (also called optocouplers, optocouplers, or opto-isolators) have proven to be indispensable for galvanic isolation and isolation of ground loop noise or other EMI induced noise interference components.

Optocoupler is a ubiquitous Electronic Component, which can be found in almost any electrical equipment and most industries. Since its introduction 25 years ago, optocoupler isolators (also called optocouplers, optocouplers, or opto-isolators) have proven to be indispensable for galvanic isolation and isolation of ground loop noise or other EMI induced noise interference Components.

How to use sealed isolation amplifier for design

Abstract: Today, optocouplers are ubiquitous electronic components that can be found in almost any electrical equipment and most industries. Since its introduction 25 years ago, optocoupler isolators (also called optocouplers, optocouplers, or opto-isolators) have proven to be indispensable for galvanic isolation and isolation of ground loop noise or other EMI induced noise interference Components. These basic forms of optocouplers only consist of an LED emitter ON the input side and a bipolar photodetector on the output side, separated by a high-dielectric strength insulating film, and packaged in a small package.

Initially, these optocouplers were mainly used in digital applications. They are known for the non-Linear input-output response and require clever design techniques to “make” them work in linear applications. What is less known is that linear optocouplers can also be used now. Features such as small size, high reliability, and low power consumption make optocouplers popular with digital designers and make them a favorite component of analog designers.

Avago Technologies’ HCPL-7851 sealed analog isolation Amplifier can be used for analog current or voltage sensing applications. The analog isolation amplifier is designed to replace traditional current measurement methods, such as closed-loop or open-loop Hall effect devices or current transformers. In this article, linear sealed optocouplers such as HCPL-7851, HCPL-785K or HCPL-7850 are introduced. We also compared the performance of these sealed linear amplifiers with competing technologies such as Hall-effect devices and current transformers.

How to use sealed isolation amplifier for design
Block diagram of optically isolated analog isolation amplifier

Optically isolated sealed analog isolation amplifier HCPL-7851 series sealed analog isolation amplifier is designed to perform linear current detection or Voltage detection, with a guaranteed bandwidth of 40 kHz. The proprietary internal shielding process is designed to achieve a high common mode noise rejection (CMR) of 5 kV/μs at a common mode voltage of 1 kV. Within the complete military standard operating temperature range of -55° to 125°C and a full-scale input dynamic range of ±200mV, a non-linearity of 0.8% is guaranteed. The total power consumption of the analog amplifier is very low. The input side and output side respectively consume no more than 15.5 mA of static bias current. This low-power requirement allows the use of bootstrap technology to provide isolated power. All of these isolated analog amplifiers are based on Sigma-Delta (ΣΔ) analog-to-digital converters, which are optically coupled to an integrated output digital-to-analog converter. Analog isolation amplifiers have very high common-mode transient rejection (CMR), which is usually necessary in modern fast-switching motor control electronics. They also provide high isolation voltage through signal light transmission from input to output. The voltage is detected by the isolation amplifier input through a low value external shunt Resistor connected in parallel with the input pin. The analog linearity is guaranteed within the input range of ±200 mV. The output voltage of the isolation amplifier is an analog output voltage proportional to the input voltage.

The input is sampled at a high rate through a chopper stabilized differential amplifier that is part of the ΣΔ amplifier. Input sensing at very high rates is achieved with sampling rates usually between 6 and 10 MHz. This high-speed sensing ensures that the Nyquist criterion is always met when the input is sensed with a high-frequency signal.

Typical application circuit for current detection using HCPL-7851 isolation amplifier

In operation, the ΣΔ modulator converts the analog input signal into a high-speed serial bit stream. The average time of this bit stream is proportional to the input signal. This digital data stream is encoded and optically transmitted to the detector circuit. The detected signal is decoded and converted back to an analog signal, and then filtered to obtain the final output signal. Figure 2 shows a typical application circuit.

The Links:   DMF-50383NF-FW CM600HA-12H