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Hi. My absolutely first enclosure to MOSFET’s. After studying ”lot’s” of them in INSTR. & Arduino & elsewere of them users having problems with controlling them mosfets with logics.
Problems there seems to be: 1. To get a proper Volt-level to the gate from logics. 2. To get a NON-inverting output to the fet 3. To NOT use the same power-rail to both logic & load 4. To have a simpel, (few components), solution to all above.

I rigged up my own suggestion to try to solve these problems. And voilá, it worked like charm, (my first mosfet connection ewer). I attach here the schematics and them data of the optocoupler and the Mosfet i used. Keep in mind: My solution is just for guidelines for anyone to use. There are 100’s of different kind of optocouplers, so that’s why I don’t here go closer to the specs, same goes for the Mosfet. The principal idea is that when the switch, (or logic), is LOW, the optocoupler LED is ON. R1 is the LED current limitor resistance, (you need to dimension it to your own demands). The output is now ON thus giving 0V at pin 8 to the GATE

With the switch, (or logic), is HIGH, (or no potential at all), the output at pin 8 is OFF. Now the VDD, (your ”load” voltage), to the GATE goes via R2, voilá.

The resistor R3, (optional), is there for a voltage-divider. This is if your load voltage ower-rides the volt-level to the gate allowed, (e.g. load volt > 15V).

I haven’t tested my circuit with any heawy load’s yet. Only with 20V/ 500mA. The mosfet was colder, (after 15minutes ON), that my finger, (couldn’t get any warmth at all), There’s a ton of details to concider, delays…. etc.

Keep in mind: this is ”just” a guide-line for that I tested of curiosity them Mosfet’s

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Bio: Gee.. Me 65+ years. My first contact with them locic's was about in them mid-70's. There was allso something called "DTL-logic, and ewen ... More »
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