Column: Optical isolation
Optical isolation I used the HCNR201 high-linearity analogue optocoupler in this project for optical (photovoltaic) isolation; see Figure 3. The HCNR201 is made of a high-
performance AlGaAs LED that illuminates two closely-matched photodiodes. The input photodiode can be used to monitor – and therefore stabilise – the light output of the LED. As a result, the non- linearity and drift characteristics of the LED can be virtually eliminated. The output photodiode produces a photocurrent that is linearly related to the light output of the LED. The close matching of the photo-diodes and advanced design of the package ensure the optocoupler’s high linearity and stable gain characteristics. HCNR201 can be used to isolate
analogue signals in a wide variety of applications that require good stability, linearity, bandwidth and low cost. The HCNR201 is very flexible and, by appropriate design of the application circuit, is capable of operating in many different modes, including unipolar/bipolar, AC/DC, and inverting/non-inverting. Features of the HCNR201 include
low non-linearity: 0.01%, K3 (IPD2/ IPD1) transfer gain of ±5%, low gain temperature coefficient: -65ppm/°C, wide bandwidth – DC to > 1MHz, worldwide safety approval: UL1577- recognised (5kVrms/1min rating), CSA approved, IEC/EN/DIN EN 60747-5-2 approved, VIORM = 1414V peak (option #050), surface- mount option available (option #300), 8-pin-wide DIP package with 0.400” spacing, and flexible circuit design. Its applications include low-cost analogue isolation; in telecoms they include modem and PBX use among others; in industrial process control they include transducers, thermocouples and 4-20mA loop isolation, SMPS feedback loop and feed-forward, monitor motor supply voltage; as well as many applications in medical electronics.
Table 1: Twelve optically-isolated analogue input modules developed in this project
Table 2: Seven optically-isolated analogue output modules developed in this projects
www.electronicsworld.co.uk December 2021/January 2022 19
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