Column: Optical isolation


Optically- isolated analogue output modules for a 0-5V to –5V - +5V signal converter


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


T


his month we will discuss the third and fourth optically-isolated analogue output modules for a 0-5V to −5V - +5V signal converter, which


provide voltages from −5V to +5V. Module 1, shown in Figure 1, requires four DC power supplies: isolated +12V, +5.00V, −12V and +12V, whereas Module 2, shown in Figure 2, requires three DC supplies: isolated +12V, −12V and +12V.


Module 1 Module 1’s circuit contains the Positive Unipolar Photovoltaic Isolation Amplifier 3 (PUPIA3 – explained previously), with a HCNR201 high- linearity analogue optocoupler providing photovoltaic isolation. The circuit’s input stages to the left of HCNR201 are isolated from its output stages to its right. Due to limited current drive capability,


the buffer amplifier (a voltage follower) LM358P-1A is used on the DAC output. LM358P-1A’s output is connected to


the input of the PUPIA3, which consists of: 1. Input: R1, R2, LM358P-1B; 2. HCNR201; 3. Output: P1, R3, C3, LM358P-2A. Providing 0.00V ≤ VIN


≤ 5.00V,


PUPIA3’s output voltage will range between 0.00V and 5.00V. This output


is connected to the non-inverting input terminal of LM358P-3A. Jumper S1 (shown here as a switch for clarity) is used to choose either the isolated 0-5V analogue output, when S1 is open, or when closed, the 0-5V to −5V - +5V isolated analogue output. With S1 open, the circuit works as


explained in the optically-isolated 0-5V analogue output design. Here we will only consider the 0-5V to −5V - +5V signal converter – optically-isolated analogue output operation mode, i.e., with S1 closed. This design is used to level shift the


unipolar 0-5V input to a bipolar −5V to +5V output. When 0.00V ≤ VIN


LM358P-3A, with its bipolar supply voltages, acts with the transfer function of:


≤ 5.00V,


After adjusting P2’s value, we obtain R4 + P2 = R5, then:


A buffer amplifier (voltage follower) LM358P-3B is used on the output of LM358P-3A. Dual series Schottky barrier diodes D1 and D2 divert any overcurrent from VOUT


to the positive or negative power supply. A ferrite bead in series


Figure 1: Optically-isolated 0-5V to −5V - +5V signal converter – Module 1


12 December/January 2023 www.electronicsworld.co.uk


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