3-phase BLDC mosfet motor driver

[celtik]

hello folks 8)! i'm in a kind of a trouble building the full electronic support platform for my bldc motor (recovered from an old hdd). i have an arduino uno plus (rev 3) board and a three phase motor driver with 6 n-ch mosfets. 2 mosfets at a time will be energised to power a single coil. here is an exapmle of one sequence for one of the three coils.
T1=high T2=low T3=low
T4=low T5=high T6=low
or
1 0 0
0 1 0 and so on...
I'm using a 3 led blinker with a potentiometer programm that generates pwm on 3 pins, enough to drive the bridge.
the PROBLEM IS :~, from what i know, that i cannot drive the mosfet bridge directly from the arduino without any protection from burning the programmer. the mosfets are powered from a sepparated power suply with over 6v. the bridge itself has 100 ohm resistors in series with the mosfets gates, but then again i don't know if that is enough to protect my arduino. i tried using opto's between ardu and bridge but the power regulator of the arduino was overheating. is there any way to use a buffer between ardu and the bridge to take the signal and amplify it or protect my programmer? any ideea? i'm stuck! =(

_3_ph_bldc_motor.ino (3.48 KB)

[MarkT]

For all n-channel MOSFETs you need a driver that generates a bias voltage above the motor supply voltage (the upper MOSFETs can only be on if their gates are held above the supply voltage enough to turn them on.) For instance a chip that can do this for all 3-phases is the HIP4086. Many drivers are available for one leg of the circuit (a half-H-bridge). Many of these driver chips require 12V, however, so be careful reading the specs.

Alternatively if the bottom MOSFETs are logic-level they could be driven directly - you will then need a supply 5V above the motor supply
and some level-shifting circuitry to drive the top MOSFETs - its gets rather complex (which is why there are many MOSFET driver chips on the market). These chips often incorporate protection features that make things much more robust (very important with higher voltages and powers).

[celtik]

good point ....but...our electronics market is either ridiculously expensive or non-existent for these kind of specialised chips. besides where is the need for an arduino, if i would use a chip that can do the power and the logic job for that bldc? i could use though the logic chips from the hdd's motherboard, but again the research/testing/time/burning of them is not really efficient and productive. p.s.-can cd4050 protect the ardu from overheating or burning? i know that they'r buffers/inverters with 12v rail supply, but is that rating used for the logic signal that goes out?