Brushless Controller

[CLEMENT]

HI EVERYONE

DOES ANYONE KNOW 8051 OR ATMEL AVR microprocessor CAN DRIVE THE MOSFET OR NOT? DO I NEED TO BUY SPECIAL TYPE OF MOSFETS FOR MICROPROCESSOR TO DRIVE it???
I USE P-TYPE MOSFET ON THE HIGH SIDE AND N TYPE MOSFET ON THE LOW SIDE. I USE 8051 output a signal to the gate of the mosfet. The connection is similar to the six step inverter. I CANNOT GET THE THREE PHASE SIGNAL WAVEFORM FROM THE OUTPUT OF THE SIX STEP INVERTER. DOES ANYONE KNOW WHAT IS THE PROBLEM? :confused: CAN ANYONE GIVE ME SOME IDEAS?
THX :p

[weazuul]

http://www.rcgroups.com/forums/showthread.php?t=200567

will help you find infos about bldc controllers
i think all this has already been discussed

[jeffs555]

You can drive the low side n-channel mosfets directly from the microprocessor if they are logic level mosfets. Unless your motor is powered from the same voltage as the 8051, you will need a high voltage driver for the high side p-channel. Can you post a schematic of how you have it connected? Without a diagram, it is hard to say what the problem could be.

[CLEMENT]

THIS IS THE SCHEMATIC
CAN I USE IRF 9540 P CHANNEL MOSFET FOR THE HIGH SIDE?
AND IRF 640 N CHANNEL MOSFET FOR THE LOWER SIDE?
DOES 8051 CAN DRIVE THIS 6 STEP INVERTER TO GIVE OUT THE 3 PHASE OUTPUT SIGNAL :confused:
THX :p

[Andy W]

Please don't type in CAPS - it's considered shouting.

[jeffs555]

What you show will not work for many reasons. The n-channel mosfets need +10 volts to turn on completely, and you are only driving them with 5 volts. The p-channel mosfets also need 10 volts so they will never turn on completely, but worse is that the threshold voltage is 2 volts, so they will also never turn off completely. To run off a 7.4 volt battery, you will need logic level mosfets, and will also need a driver for the p-channel that can drive the gate all the way to 7.4 volts to turn it off. The long thread in this forum "BLDC controller" has lots of suggestions for logic level mosfets, and driver circuits.

[Comatose]

That will only work if your motor voltage and your microcontroller voltage are the same, eg 5v. Otherwise you'll need high side drivers.

[CLEMENT]

Thankyou for the above reply :)
The six step inverter that i design cannot work in 7.4V.
Hi jeffs555. Do u mean that if the mosfet is not completely turn on, the three phase sine wave cannot be obtained(i.e. the mosfet must operate in the saturation region)? :confused:
I want to test my circuit on the breadboard, so I prefer to use the mosfet which is not surface mounted. Can anyone suggest some model number of the logic mosfets to me(surface mounted also OK)? :p Which type of p type driver do i need? Can anyone suggest one to me? :p
Thanks