Column: Optical isolation


Optically- isolated 0-5V analogue


output module


By Professor Murat Uzam, Department of Electrical and Electronics Engineering, Yozgat Bozok University, Turkey


F


igure 1 shows the optically- isolated 0-5V analogue output module, to be used with a 5V microcontroller through its DAC


output, with its connections shown in Figure 2. Te circuit contains a Positive Unipolar


Photovoltaic Isolation Amplifier 3 (PUPIA3 – explained previously), with HCNR201 high-linearity analogue optocoupler for photovoltaic isolation. Due to its limited current drive


capability, the buffer amplifier (a voltage follower) LM358P-1A must be used on the DAC output. Its output is connected to the input of PUPIA3, which consists of R1, R2 and LM358P-1B as its input, P1, R3, C3 and LM358P-2A as its output, and, of course, the HCNR201 optocoupler. PUPIA3’s output is connected to the non-inverting input terminal of LM358P-2B. Provided


PUPIA3’s input voltage is limited to 5.00V, its output will also be limited to 5.00V. Dual series Schottky barrier diodes


D1 and D2 divert any overcurrent coming from the terminal VOUT


to the


power supply or ground. A ferrite bead connected in series with the output path adds isolation and decoupling from high-frequency transient noises. A transient voltage suppressor (TVS) is used to filter and suppress any transients coming from VOUT


. The circuit can supply up to 20mA.


It is powered by +12V, with another +12V powering the optically-isolated circuit output. When 0.00V ≤ VIN 5.00V, VOUT


≤ = VIN


Table 1. Set VIN


; see Figure 3 and P1, ensure that VOUT


to +5.00V and, by adjusting = +5.00V.


Figure 1: Optically-isolated 0-5V analogue output module


Figure 2: The module’s connections 16 October 2022 www.electronicsworld.co.uk


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