Column: Optical isolation


Figure 2: Design 3’s connections


Figure 3: VOUT


vs. VIN


for design 3


optocoupler (HCNR201) providing photovoltaic isolation. Here, R4, D4 (a 10V Zener diode) and


C5, together with the buffer amplifier LM358P-4A, provide a 10.00V reference voltage from a +24V power supply. This voltage is divided by resistors R5 and R6 to obtain a +6.26V reference voltage. This voltage is connected to the non- inverting input of the buffer amplifier LM358P-1A, whose output is fixed at +6.26V, which can source current to 20mA. The TVS protects the overall circuit


from discharges, and D1 from accidental reverse polarities. In this design, PUPIA2 consists of the


following components: 1. The input: R1, R2, C3, LM358P-2A. 2. HCNR201 high-linearity analogue optocoupler.


3. The output: P1, R3, C4, LM358P-3A. In this design, the input of the circuit


is powered by a +24V power supply, and the output by an optically-isolated


Figure 4: The prototype board of design 3 www.electronicsworld.co.uk April 2022 11


Table 1: Example input and output voltages for design 3; 5.0X is a value from 5.01V to 5.07V, due to the electrical characteristics of the LM358P-1A


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