Here’s a
design circuit for linear opto coupler circuit that is based on MOC5010
and can be used to isolate a circuit from main grid, audio interface, in
medical electronics and many other applications. Here’s the figure of the circuit;
MOC5010
transforms an input current variation into an output voltage variation. The
linear optocoupler circuit presented here has an amplification factor of 0.75.
The input must not overcome 2 Vef while bandwidth is 118 kHz at -3 dB.
Amplifier A has a transfer resistance of 200 mV/mA resulting in a total
amplification of 0.6 … 0.8 (-4.5 … -2 dB). The output impedance is not higher
than 200 Ω so you can connect an external amplifier at pin 4. If the input
voltages are higher than 2 Vef then connect a potentiometer as voltage divider
like showing below optocoupler circuit diagram. If the global amplification is
too small use a regular transistor instead of FET T1. It is important to
mention that 2 separate power supplies are required: both the +12 V terminals
as well the 0V (ground) must be isolated from one another. In many cases it is
possible to use a 12V voltage for the transmitter part from the connected
device.
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