Design example of signal interface using phototransistor coupler
The figure below shows an example of an interface circuit that converts a 5 V signal into a 10 V signal using a phototransistor coupler.
How should we design the resistor RIN on the LED input side and the resistor RL on the phototransistor output side?
And how should we select CTR of the phototransistor coupler?
We will explain from the next page with the following steps.
Step 1. Design of LED input-current IF and input-side resistor RIN
Step 2. Calculate output current from IF and CTR
Step 3. Design of output-side resistor RL
Step 4. Check each designed constant