Motor Mosfet Driver - design considerations

[averafter]

Mosfet Driver

I have built a set P and N mosfet (full bridge) array to drive a motor, and I am going to but a mosfet driver to drive the mosfet, can anyone give me some suggestion? What kind of consideration should I make? Because I am a fresh man in electronics, hope someone can help me. Thank you.

 

[karesz]

Mosfet Driver

Hi,
Search for appl notes i.e. by IR & read "similar topics" (right down corner on your screen) too pls...
Maybe most important is to have a good driver IC/solution, what has garanted no "through shoting" (dead time controling)!!
K.
Here only to sample it...

 

[siongboon]

Hi,

The basic parameter to look out for when driving
your motor should be the current.

1st you need to know that maximum current your
motor will draw out from power supply.
If you do not have datasheet,
you can use a lab power supply or multimeter to measure.
The power supply equipment current rating
should be higher than that of your motor.
If you don't know, just try.
Supply the motor with the recommended voltage.
Grab or lock the motor shaft.
By locking the shaft, you are forcing the motor to draw
the maximum possible current from the power supply.
Measure or note down this current rating.
This is the max current you could expect out of the motor.
Choose the transistor with a current rating more than
the motor max current.
Preferably 1.5 to 2 times accordingly to my own standard.
The same current would be flowing through the motor
and the transistor. A higher current rating of the transistor
is better as you can expect less heat to be generated.
Cons may be bigger in size and higher in price.

Transistor has many other parameter like breakdown voltage,
gate voltage, many many more etc....
However they are usually insignificant unless you are working on higher voltage.
Which is why on most transistor datasheet,
the first information you usually see would be the current rating,
followed by the breakdown voltage, and the pin out information.
As a beginner, the rest of the parameter you might just leave it out first.
Until you encounter circuit problem, you can take your time
to understand more about the other parameters of the transistor
that might make your circuit fail.
Learn as you hands-on along. This is the way it is.

I have a simple write up on my understanding
on using transistor as a switch.
Hope it helps you.

**broken link removed**

Best Regards,
Soing Boon

 

[Tahmid]

Hi,
For P-channel and N-channel MOSFET full-bridge, there are some considerations:

1) Preventing shoot-through or cross-conduction by applying "dead-time" which may be incorporated in your controller, or your driver.

2) Driving can be done with transistors or ICs, like TC426/TC427. Take a look specially at TC428.

3) Switching frequency, speed and current. P-channel MOSFETs have high RDS, so switching at high frequency at high current will produce great heat.

4) Use FETs with at least 1.5x current capability than required for safety.

5) If your supply voltage is greater than 20v, you need level-shifting for the P-channel MOSFETs.

6) For safety, use gate-to-source resistors (about 1k) to prevent accidental turn-on of MOSFETs.

7) For safety, you may include level-shifting for the P-channel MOSFETs and place zeners from gate to source of N-channel MOSFETs anyways to prevent gate breakdown due to excessive voltage from voltage spikes or transients or such, etc.

8) Of course, add a fuse at the input for protection.

9) For minimal heat, choose MOSFETs with minimum RDS.

10) Provide appropriate heat-sinking for MOSFETs.

Hope this helps.
Tahmid.

 

[averafter]

Hi,

First at all, I would like to thank you all for replying the topic. Thank you very much^^!

My motor is the power window motor which used in the car to drive up the window of the car. I test the motor with the power supply under 12V, I found that it need about 0.9 to 1A to drive it without load, when I try to hold the shaft of the motor, the current can shoot up to 2.8 to 3A.

I found an IC which consists of the driver and the mosfet, and I have attached it, can anyone tell me is it suitable for my application? By the way, what does it mean by 3A continuous current, 6A pulsed? Is it the current of the driver to charge up the junction capacitance or the max current flow through the drain of the mosfet? And it does not have the feature that control the dead time. Is it suitable for my application?

Are there any other ICs that contain both the driver and the mosfet inside a single chip? Do you all have any suggestion? Because I found that if I buy 2*p-mosfet, 2*n-mosfet and a mosfet driver is very expensive. Otherwise, are there any alternative way to drive the motor in both clockwise and anti-clockwise?

Thank you.

 

[karesz]

Hi,
Generelly is a usability of components with DC(continouos Current) a thermal problem, but if you need some higher power_you must (or can) give for short time! i.e. double of the nominal current/pwr; these means "pulsed operation"...Average power must be maximal the same as by DC, than in other case you have a bourning out...
In your case is these 3A what your driver can deliver for the motor.
K.

 

[siongboon]

Yes. The transistor can only support 3A.
If you switch the transistor on then off, then on then off quickly (pulsed)
You can try your luck up to 6A, as the transistor should be about to take more overload current if the current is not continous.

Integrated driver is reasonable to cost more then using only transistor.

Try to hold the shaft stall and check the current.
It would be the max current you motor can draw.
If it is 3A, try to use a sriver or transitor that can take at least of about 4.5A.

Have Fun,
Siong Boon