Column: Optical isolation
VIN
can be subjected to electric surge
or electrostatic discharge on the external terminal connections; the TVS (transient voltage suppressor) protects it. Te operational amplifier LM358P-1A,
with bipolar supply voltages, provides a high input impedance and is connected as a buffer amplifier (voltage follower). +5V and R1, VIN
LM358P-2A, with +6.26V supply voltage, acts as a voltage limiter and is connected as a buffer amplifier. Te output of the LM358P-1A is
and R2, and LM358P-1B,
with bipolar supply voltages, act as a non- inverting summing amplifier. Diodes D3 and D4 ensure that -12.00V ≤ VIN VOUT
= 0.00V. Te operational amplifier < -5.00V,
connected to the input of the PUPIA1, which limits its input voltage. In this design, the PUPIA1 consists of the following: 1. Input section: R3, R4, C3, LM358P-3A. 2. HCNR201 high-linearity analogue optocoupler.
3. Output section: P1, R5, C4, LM358P-4A. Te input and output are powered by isolated +12V power supplies.
It is assumed that VIN
+5.00V, VOUT +5.01V ≤ VIN
= −12V to
+12V. When −12.00V ≤ VIN VOUT
≤ +12V, VOUT
= 0.00V. When −5.00V ≤ VIN = (VIN
< −5.00V, ≤
+ 5V) / 2. When will be
a value from 5.01V to 5.07V, due to the electrical characteristics of the LM358P-2A. See the relationship between VIN
and VOUT
in Figure 3, and
some example voltages in Table 1. For proper operation ensure R1 = R2, R7 = R8, and R10/(R9+R10) = 62.62%.
Figure 6: Module 2’s connections
Figure 7: Module 2’s prototype circuit board
www.electronicsworld.co.uk June 2022 15
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