Column: Optical isolation
transient noises. A TVS (transient voltage suppressor) is used to fi lter out any transients coming from VOUT
. This circuit is capable of supplying up to 20mA. Its input
is powered by +12V, whereas its output by +5.00V, +12V and −12V isolated from its input. When 0.00V ≤ VIN
≤ 5.00V, VOUT therefore VOUT = 4VIN − 10. VIN = −10.00V to +10.00V; see Figure 3. Table 1 provides some example voltages for this signal
converter, with the circuit’s prototype board shown in Figure 4. To calibrate this circuit with S1 open:
1. Set VIN
2. Set VIN VOUT
make VTP1
to +5.00V and, then, by adjusting the value of P1, = +5.00V.
to +5.00V and then by adjusting P3 make = +10.00V.
To calibrate the circuit with S1 closed: 1. Set VIN
to +5.00V and, by 2. Set VIN 3. Set VIN
adjusting P1, make VTP1 to +5.00V and, by
adjusting P3, make VOUT make VOUT = +5.00V. = +10.00V.
to 0.00V and, by adjusting P2, = −10.00V.
Module 2 Figures 5, 6 and 7 show Module 2, with its connections to the DAC output of a 5V microcontroller. As with Module 1, this circuit is also PUPIA3 based, with a high-linearity analogue optocoupler (HCNR201) providing photovoltaic isolation. Module 2 operates exactly the same way as Module 1, so
it has all the same components, but with the addition of R8, D3 (10V Zener diode) and C5 to provide a 10.00V reference voltage from a +12V supply. This 10.00V reference voltage is then divided by resistors R9 and R10 to obtain a +5.00V reference voltage. This +5.00V is connected to the non- inverting input of buffer amplifier LM358P-2B, whose output is fixed at +5.00V and capable of sourcing up to 20mA. Unlike Module 1, in Module 2 the circuit’s output is
powered with only +12V and −12V, isolated from the circuit’s +12V input. For its proper operation, make R9 = R10.
1. Set VIN 2. Set VIN
To calibrate the module with S1 open: to +5.00V and, by
adjusting P1, make VTP1 to +5.00V and, by
adjusting P3, make VOUT 1. Set VIN 2. Set VIN 3. Set VIN = +5.00V. = +10.00V.
To calibrate the circuit with S1 closed: to +5.00V and, by
adjusting P1, make VTP1 to +5.00V and, by
adjusting P3, make VOUT to 0.00V and, by
adjusting P2, make VOUT = +5.00V. = +10.00V. = −10.00V. Figure 7: Module 2’s prototype board = 0-5V,
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 fi lter out
any transients coming from VOUT
www.electronicsworld.co.uk February 2023 17
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