Hi there
The purpose of this schematic is to control a DC motor that runs at 8V max. That is why I chose 4 N-channel mosfets in the H bridge. P-channels would not fully activate at voltages above -10Vgs but the N-channels can handle 18V at the gate.
The 5v switches represent an Arduino’s digital output pins. One to turn forward, one for reverse. To prevent a failure scenario where both pins are HIGH I added a transistor that prevents current from flowing through the optocoupler on the second half bridge.
Does this circuit make sense? I’m not an electronics engineer, just a hobbyist and have doubts about how effective the gate driving circuit is of the mosfets.
Thanks!
Please don’t use non perpendicular lines and draw in a clearer software if possible. Its quite hard to read.
What is the point of the push-pull BJTs? With the optocoupler you could drive the nmos gates directly. If you need more current to drive the gates (unlikely for a small motor), I suggest you buy dedicated gate drivers. They are tested and not expensive. If you have the 18V available already, using the optocouplers directly would be a lot simpler.
Right, sorry about that. I made the simulation on my phone with the Proto app.
I figured the push pull part is good practice with mosfets. It’s partially the learning experience and if the motor stalls it could draw several amps.
I won’t be doing PWM, just on and off so maybe just the optocoupler is good enough.
I’d have to order dedicated gate drivers and have a lot of 547 and 557 transistors in stock at home.
In that case I would omit the extra transistors and use only the optocouplers.
What sort of application is this? Having 18V somewhere and a 5V supply too that can output several amps is quite unusual.
Thanks again for the advice. I made a working prototype and attached it to my pump. The PCB is also made at home which is something I’m trying to learn.
For now I’ve used just optocouplers to drive the mosfets, since pulling p-type gates down to above -24V seemed like a hassle. I’ve ordered some IR2210 gate drivers and intend to use those with PWM later to not have to use a buck converter.
Here’s a video of the pump. https://drive.google.com/file/d/1qKDBLTbYi2Fbu3UOXpxqSoj00oueWK-K/view?usp=sharing
And the pump in action. https://drive.google.com/file/d/1--HyeJGtYS5dgsjgelE6CrOm2vbBmwXU/view?usp=sharing This version has a stepper motor instead of a DC motor. Stepper motors have low speed limit which is why I’m trying to change it to DC motors.
Well, the whole setup is a semi automatic greenhouse. It has a 12 channel peristaltic pump, grow lights, heater and a plant shaker for pollination. I’m attempting to grow indoor tomatoes and chili’s. Not weed although I have learned a lot from weed growers.
The system runs on a 24V power supply so that is easily accessible. The 18V comes from an LM7818 and the motor speed will be regulated with a buck converter module.