Column: Optical isolation


Schottky barrier diodes D1 and D2 divert any overcurrent to the positive or negative power supply. Te operational amplifier LM358P-1A,


with bipolar supply voltages, provides a high input impedance and is connected as a buffer amplifier (voltage follower). Diodes


D3 and D4 ensure that when −12.00V ≤ VIN < −10.00V, VOUT


= 0.00V. Te operational amplifier LM358P-2A, with a +6.26V


supply voltage, acts as a voltage limiter and is connected as a buffer amplifier. LM358P-2A’s output is connected to


PUPIA1’s input, which limits the input voltage. PUPIA1 consists of: 1. Input section: R4, R5, C4, LM358P-3A; 2. HCNR201 high-linearity analogue optocoupler;


3. Output section: P1, R6, C5, LM358P-4A.


Te input and output are powered by isolated +12V. It is assumed that VIN


When −12.00V ≤ VIN When −10.00V ≤ VIN


< −10.00V, VOUT ≤ +10.00V, VOUT


+10V) / 4. When +10.01V ≤ VIN


= −12V to +12V. = 0.00V.


= (VIN ≤ +12V, VOUT


will be a value from 5.01V to 5.07V, because of LM358P-2A; see Figure 3 and Table 1. For proper operation make R2 = R3, R1 = ½ R2, R8 = R9, and R11/(R10+R11) = 62.62%.


Figure 6: Module 2’s connections


Figure 7: Module 2’s prototype circuit board


16 July/August 2022 www.electronicsworld.co.uk


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