Schematic review
Schematic review
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.
This looks like the web simulator falstad...
Proto on Android.
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.
Looks fine to my eyes, but the last time i made a motor driver it caught fire so i wouldn't take my word for it if i was you
Haha. I do not want this one to catch fire.
DC motors have high inductance, meaning that the current going over it will resist to change. When you turn off a pair of nmos, current will likely start flowing over the the other pair, from source to drain. Depending on the spec of your nmos, you may consider using diodes in parallel to nmos to carry this current. Obviously these diodes should be reverse biased during normal operation.
Are you trying to run your motor at 5v? that's what it reads to me.
If your current draw is under like 700ma, Consider a bridge driver like the L9110, it'll get you the with minimal effort. There are other drivers out there as well. https://www.adafruit.com/product/4489
Between 4 and 8V. I'm driving a pump with a 12V rated 775 motor. Running it at full power makes the pump go too fast and with a lot of noise.
It's kind of an overpowered motor for this project but I have a couple of spare ones.
Is it okay that there is no stop state? It can only drive the motor in either direction, bit there is no OFF state with your inputs.
The off state is with both inputs at 0.
Obviously. No idea what I was thinking.