opto coupler with two LEDs

On the basis of the principle that the conversion of electrical energy to light in a LED must be revers- ible, its merits for practical use were investigated. The diagram shows positive results. A logic level of at least 2 Vis applied to the input of T 1. The photo current generated in LED 2 is fed to a three-stage amplifier where it is brought to a level suitable to drive TS and T6. At very low frequencies the duty cycle varies, but this forms no objection for most applications.