The IL388DAA Linear Optocoupler consist of an IRLED optically coupled to two photodiodes. The emitter is located such that both photodiodes receive approximately an equal amount of infrared light. The diodes produce a proportional amount of photocurrent. The ratio of the photocurrent stays constant with high accuracy when either the LED current or the ambient temperature changes. Thus one can control the output diode current optically by controlling the input photodiode current.