When designing an optocoupler, the CTR value is important and must be considered. The CTR value is affected by ambient temperature, collector current, and forward current. As shown in the left curve diagram, the ambient temperature affects the relative CTR value and the applied collector-emitter voltages. This must be taken into account in the system. Not only does the temperature change the CTR value, but also different forward current provides different CTR ranges. Customers can drive the infrared LED with various forward currents, but it should be considered that the CTR changes with the forward current.