All opto-isolators described so far are uni-directional. The proposed configuration consist of two different parts. An opto-isolator contains a source emitter of light, almost always a near infrared light-emitting diode LED , that converts electrical input signal into light, a closed optical channel also called dielectrical channel [7] , and a photosensor , which detects incoming light and either generates electric energy directly, or modulates electric current flowing from an external power supply. V1 must go to Vcc to ensure that the LED is off and must be able to sink the current which shouldn’t be problem anyways. The motor connects as shown.

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This timing only need to be considered when switching frequencies goes beyond 1MHz.

The forward current through the input diode of the opto it’s a bit too low mA. The idea behind this schematic: Driving the opto-coupler means driving its LED. Circuit A does something that includes a charging function then activates Circuit B. So Q2 is the output side of the opto-couper.

In the first circuit, you control the voltage. Phototransistors are inherently slower than photodiodes. The reflective pair configuration is suitable for the development of tachometers, movement detectors and reflectance monitors. So, make R3 the same value as R2 – see next paragraph.


I’ve built the schematic by now, switching 5V and 12V loads, and want to add that it works exactly as intended.

When the switching frequency goes higher, we need to take into account the two parameters of 4N25 in order to avoid the errors. There are amusing stories of bizarre circuit behavior finally traced to this. Email Required, but never shown.

With the parts in the mail, haven’t had the time to test, but the simple question: This mode of operation is called photoconductive mode. Low to high [note 7].

A common type of opto-isolator consists of an LED and a phototransistor in the same opaque package. Bidirectional opto-isolators built around pairs of GaAs: These delays are the response time delays of 4N In he second circuit, you control the ground.


This proposed analog isolator is linear over nosfet wide range of input voltage and frequency. Comment 4 is a very good one, considering this is just a trial and will expand to more switches on the same microcontroller. Alternatively, in the absence of external bias the diode converts the energy of light into electric energy by charging its terminals to a voltage of up to 0.

D1 MUST be included – this provides protection against the back emf spike which occurs when the motor is turned off. Setting the pin low switches it on.


Transformers and opto-isolators are the only two classes of electronic devices optoxoupler offer reinforced protection — they protect both the equipment and the human user operating this equipment. I’ll probably just use two of those in parallel. Sign up using Email and Password. Intrinsically the circuit looks sound.

Your biggest potential problem is that the opto-coupler acts like a constant current source.

What you have done is to take something cobby but universal and replace it with something which is browser specific. Sign up using Facebook. optofoupler

Opto-isolator – Wikipedia

And I’ll change the resistor value, it’s just that I have a bag of R ones at hand. Photoreceivers such as photodiodes or nxnosecond work because incident light on the semiconductor excites electrons into the conduction band, forming free carriers both electrons and holes. Here td and ts are in nano second so they are usually neglected.