Motor controller with full bridge

Thread Starter

mejlby

Joined Apr 26, 2013
28
Hello everyone

I have previously made a motor controller with a TL494 and uses a half bridge L6384. it can handle 40Amp without mosfet get hot. I do not use heatsink.

Now I will try to make a motor controller with a full bridge so that I can run the motor forward and reverse I have found the attached circuit. Do I understand it right, the PWM signal is either set to high or low so that the motor changes direction ?

I I hope someone can help me with this question

best regards
Mejlby
 

Attachments

MaxHeadRoom

Joined Jul 18, 2013
19,067
Yes, with a full bridge shown, the top semi on one side will conduct with the lower semi on the opposite side, applies to each direction selected.
Max.
 

MrChips

Joined Oct 2, 2009
19,280
Why duplicate the circuit? Can you drive Q1 & Q4 together from the same gate signal, and do the same with Q2 & Q3?
 

RamaD

Joined Dec 4, 2009
319
The charging path for the bootstrap cap needs to be checked.
The Left High side bootstrap cap gets charged during the left low side MOSFET turn-on and vice versa. During any one direction movement, the upper turning on mosfet's driver's bootstrap cap loses charge driving the gate. During this time, only the lower mosfet of the opposite side turns on. To be a little more clear, if
Left Top MOSFET on and Right Bottom MOSFET on - Right Top MOSFET's bootstrap cap charges and let top mosfet's bootstrap is not charged and is losing charge driving the gate!
It may be necessary to provide 2 isolated supplies for Vb. Or, Turn on both the low side MOSFETs during the off time.
Sorry, if I have not communicated well.
 

Thread Starter

mejlby

Joined Apr 26, 2013
28
Thank you Max

Then I have understand it correctly and now I will try too make a new motor controller.

Attached circuit shows how I make the half-bridge controller. Do you think I can use the same Mosfet driver L6384 to a full bridge if i use 2 x L6384 ? It has worked 100% correct and as mentioned it can handle at least 40Amp without heatsink. I use it for an electric go-kart that I made for my daughter. I use a relay to reverse.


( see on youtupe:
)

Regards Mejlby
 

Attachments

Last edited:

Thread Starter

mejlby

Joined Apr 26, 2013
28
The charging path for the bootstrap cap needs to be checked.
The Left High side bootstrap cap gets charged during the left low side MOSFET turn-on and vice versa. During any one direction movement, the upper turning on mosfet's driver's bootstrap cap loses charge driving the gate. During this time, only the lower mosfet of the opposite side turns on. To be a little more clear, if
Left Top MOSFET on and Right Bottom MOSFET on - Right Top MOSFET's bootstrap cap charges and let top mosfet's bootstrap is not charged and is losing charge driving the gate!
It may be necessary to provide 2 isolated supplies for Vb. Or, Turn on both the low side MOSFETs during the off time.
Sorry, if I have not communicated well.

Hi RamaD

Sorry i don´t understand: " It may be necessary to provide 2 isolated supplies for Vb. Or, Turn on both the low side MOSFETs during the off time."
do you have the opportunity to draw it on the circuit so I can see what you mean?
 

Thread Starter

mejlby

Joined Apr 26, 2013
28
Tonny, in your half-bridge circuit, why do you need the lower pair of MOSFETs?
Hi MrChips

This link explain the whole theory behind the moefet driver much better than I can explain it. I have make some experimenting with other forms of driver - it does not work - mosfet gets so hot that they require a very large cooling or simply burn out. This circuit I made WORKS 100%.- no problem with hot mosfet

the reason I use a L6384 mosfet driver is this driver has a Intregrated bootstrap diode and can replace an external bootstrap diode

http://www.microsofttranslator.com/BV.aspx?ref=IE8Activity&a=http://tahmidmc.blogspot.dk/2013/01/using-high-low-side-driver-ir2110-with.html
 
Last edited:

MrChips

Joined Oct 2, 2009
19,280
I do not doubt that your circuit works 100%.

What happens if you disconnect the lower MOSFETs?

I suspect the author of the article does not fully understand the operation of high-side, low-side drivers.
 

Thread Starter

mejlby

Joined Apr 26, 2013
28
I do not doubt that your circuit works 100%.

What happens if you disconnect the lower MOSFETs?

I suspect the author of the article does not fully understand the operation of high-side, low-side drivers.


Now you made me curious !!!

Tomorrow I will try to remove the 2 lower Mosfet and see what happens

I think the bootstrap capacitor vill not discharged and can not feed the upper Mosfet

What do you think ?
 

Thread Starter

mejlby

Joined Apr 26, 2013
28
Hi MrChips

Now I already have an answer for you!

In my workshop, I had a prototype of the controller and the mosfet is mounted in some terminals. I removed the 2 lower Mosfet and immediately became the 2 upper MOSFET very hot. When I mounted the two lower Mosfet again and the controller was broken.

Tomorrow I have to find the error. I think the upper mosfet is burnt of or the capacitor / diode is burnt of ...or the driver L6384 is broken

( shit - I should never have listened to you)

So now you have the answer why the 2 lower Mosfet is mounted

Let me hear your answar

correctly Max .... mr MrChips should have read tahmids blog !!
 
Last edited:

MrChips

Joined Oct 2, 2009
19,280
The charging path for the bootstrap cap needs to be checked.
The Left High side bootstrap cap gets charged during the left low side MOSFET turn-on and vice versa. During any one direction movement, the upper turning on mosfet's driver's bootstrap cap loses charge driving the gate. During this time, only the lower mosfet of the opposite side turns on. To be a little more clear, if
Left Top MOSFET on and Right Bottom MOSFET on - Right Top MOSFET's bootstrap cap charges and let top mosfet's bootstrap is not charged and is losing charge driving the gate!
It may be necessary to provide 2 isolated supplies for Vb. Or, Turn on both the low side MOSFETs during the off time.
Sorry, if I have not communicated well.
I think I follow what you are saying. I have been reading up on how the MOSFET drivers operate. Without the lower MOSFET, the charge on the bootstrap cap blows the gate on the upper MOSFET. Is that correct?

So I eat humble pie tonight!:(
 
Last edited:

Thread Starter

mejlby

Joined Apr 26, 2013
28
Yes you are absolutely right
I do not know why I tried it - in fact I already knew the outcome.
I only managed to overload the controller with about 2-amp and then the damage was done
Tomorrow I will fix it again. :mad:
 

ronv

Joined Nov 12, 2008
3,768
There are no clamp diodes in either circuit. In the half bridge the bottom FETs perform that function. I think in the full bridge you will need some, but I don't know your whole timing diagram.
 

Sensacell

Joined Jun 19, 2012
2,450
The design needs the lower mosfets only to charge the bootstrap capacitor- this cap provides the higher voltage to drive the high side mosfets.
Without the low side, the upper mosfets do not see enough gate voltage to turn on all the way.

The low side also shorts the back EMF of the motor! not a good idea!

This design is very inappropriate for driving a motor in one direction, a single low side switch would be much better and simpler.
 
Top