My main question is how do you switch on and off a negative voltage with a n-channel Power Mosfet, because if you look at the schematic in the first post, you will see the mosfet labeled ‘M4’ whenever I applied 5 volts from the arduino to the the gate it turned negative on but sparked. I believe this is because it came in contact with the 5 volts. What is another way to turn negative on and off?
In case you or anyone else are wondering what sequence I will be using I attached a photo of it.
I also reattached the schematic.
So, for anyone following this, you replaced the 200V ,0.038 ohm, 40A N-channel Mosfets in the schematic , with 68V, 0.0082 ohm, 98A N-channel Mosfets. Which, just for the record, has no impact on the fact that you want to control it with an arduino since you may have gone from a 200V VDS to a 68V VDS , the VGS is the same +/-20V.
What we need to concern ourselves with FIRST , BEFORE even getting into the whole UNIPOLAR , BIPOLAR Power Supply issue,
is that NEITHER of the these two types of mosfets are Logic Level mosfets, which means you need voltage converter circuit for each and every one of them that converts 0V to -5V so that the device will be OFF when the arduino output is LOW (0v).
Can this be done ? Yes. Is it necessary ? I don’t know. Your opening remark about just finishing soldering your circuit suggests that these devices are not in a breadboard but a PCB and cannot be removed (easily). Do you have any spares ? (we don’t know).
Why would I ask that ? Because before you attempt to drive your motor with these devices you need to do some preliminary
lab tests on these devices to ascertain what impact using a logic level (TTL) signal to drive non-Logic Level Mosfets will have.
How much current (if any) will conduct through the load with 0V on the gate ? If you look at Fig-13 through 17 on page 3 of the datasheet there are some test circuits. some of them use 100 ohm gate resistor. I don’t know why that is. (because I am not an Electrical Engineer, I am an Electronics Engineering Tech)
Perhaps this post might shed some light on the Logic Level vs Normal Mosfet subject:
[ http://www.electro-tech-online.com/threads/logic-level-vs-normal-mosfets.91756/ ](http:// http://www.electro-tech-online.com/threads/logic-level-vs-normal-mosfets.91756/)
I should point out that all the specs in the mosfet datasheets are referenced to VSource, so converting the single supply
motor driver schematic to dual-rail (bi-polar) design involves more than just replacing the source connections with a negative supply. The gate drive signals would have to be converted from 0V/5V to +/- 10 to 15 V (max = +/- 20V)
Questions to be answered:
1-What are the consequences of driving “normal” mosfets (as opposed to “Logic Level” Mosfets) with a logic level signal ?
2-How do you convert the single ended drive signals to dual-ended (bi-polar) gate drive signals ?
3-What do you gain by converting the given single ended design to a dual-rail design ?
For the record, I did spend at least an hour searching online for a plug & play TTL to bipolar mosfet gate driver ic that has three
power pins, GND, +Vcc, & -Vee, that accepts TTL input signal and output a +/- V gate drive signal . I had no luck finding one but
I am almost certain they exist.
If we forget the whole single-ended to dual-rail conversion idea altogether and focus on how to use your schematic as is with
the drive sequence table as given, I don’t see why it should not work as is for a single ended circuit. The drive sequence should remain the same with respect to the hall sensor inputs.
The only question I have, is how were you planning on writing code to drive this ? Do you know how to do that ?
Check out this post:
Part-2: Circuit and Software
Unfortunately, that was all I was able to find.
You could try that but I seriously recommend testing the circuit and software with a variable voltage, adjustable current bench lab power supply and a small RC 3-phase brushless motor before attempting to drive the 48V motor, due to the risk of damaging something before you have tested the circuit and software. You should be able to drive a small RC brushless motor from 12V with the current limit set to a maximum of 1A using the same circuit you posted.
That’s how I would approach it. I would forget the idea of converting the circuit to bipolar for now and just focus on getting the software to work. Obviously if you repeat your previous hardware test approach of just touching two wires together then you are headed for disaster. For the sake of your project, don’t do that again. It is a reckless way to perform circuit/motor testing.
I would strongly discourage any further such actions. Get your circuit and software working before you touch that motor again unless you can get a 3-phase brushless motor controller that can handle the current rating of your motor, which , according to my calculations is about 21A @ 48V.
1000W can do a lot of damage if something goes wrong. If you used current limiting power resistors that allow enough current to pass to get the motor spinning but not enough to drive a load then you could safely test your circuit and your software with the 48V motor.