Column: Optical isolation


Optically- isolated analogue


output module for a 0-5V to 0-10V signal converter


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


I


n this instalment we will cover the second optically-isolated analogue output module – for a 0-5V to 0-10V signal converter that requires two DC


power supplies: +12V and isolated +12V; see Figures 1 and 2. Tis circuit contains the Positive Unipolar


Photovoltaic Isolation Amplifier 3 (PUPIA3 – explained before) with an HCNR201 high-linearity analogue optocoupler for photovoltaic isolation. Te circuit’s input signal (to the leſt of HCNR201) is isolated from its output (to the right of HCNR201). Due to a limited current drive


capability, the buffer amplifier (a voltage follower) LM358P-1A is used on the DAC output; its output is connected to the PUPIA3 input. In this design, PUPIA3 consists of:


1. R1, R2, LM358P-1B as input; 2. Te high-linearity analogue optocoupler, HCNR201; and


3. P1, R3, C3, LM358P-2A as output. Providing the PUPIA3’s input is 0.00V ≤ VIN ≤ 5.00V, PUPIA3’s output will be limited between 0.00V and 5.00V. PUPIA3’s output is connected to the


non-inverting input terminal of LM358P- 2B. Jumper S1 (shown here as a switch for clarity) is used to choose the operating mode – either isolated 0-5V analogue output operation by opening S1, or by


closing it, 0-5V to 0-10V signal converter with isolated output operation. For the purposes of this discussion, we consider S1 closed. Te LM358P-2B op-amp is used to


obtain a non-inverting operational amplifier with the transfer function:


Aſter adjusting the value of P2, we obtain R4 + P2 = R5, therefore:


Te output gain of the amplifier becomes positive in value, so VOUT


VIN . Dual series Schottky barrier diodes


D1 and D2 divert any overcurrent from VOUT


to the power supply or ground.


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


transients. Tis circuit can


supply up to 20mA. In this design, the input is powered by


+12V, and the output by another +12V supply isolated from the input. For this module, we assume VIN


from the 5V microcontroller’s DAC comes


is in-phase with


Figure 1: Optically-isolated 0-5V to 0-10V signal converter output module 12 November 2022 www.electronicsworld.co.uk


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44