Hi All

I see there has been quite a bit discussed on H-Bridge stuff. I am trying to drive a 12V DC motor for a gate valve. It is anticipated that a normal automatic gate motor will be used so I guess the currents will not be more than about 20-30A.

The project manager insist on only using N channel FET's and one of the IR H-Bridge devices such as the IR2110. I have readup on the IR devices but cannot fathm out if these take care of the Vgs issue on the high side that normally would require a charge pump o sustain the say 10V Vgs when the high side FET opens up.

Do these devices do this as the tech notes are not very clear?

Are there any recommendations, examples that anyone has that I may use as a starting pont?

I am going to drive the whole system from a STM32F103CBT6 device. I also need to do some current sensing to detect shoot through faults, locked rotor etc, so will use op amps onto the AD's of the micro.

Any help greatly appreciated.

Regards

Dead Short

 

Shoot through faults have to be avoided and not detected. If a shoot through fault happens then the MOSFETs will degrade (depends on the design and MOSFET choice) in most cases. So you have to include dead time between the switching of the high and low side MOSFETs as to avoid shoot though. IR2110 does not provide this dead time delay and thus you have to take care of it with your controller (STM). If the controller cannot provide dead time then choose another gate driver which provides.

 

Hi All

I see there has been quite a bit discussed on H-Bridge stuff. I am trying to drive a 12V DC motor for a gate valve. It is anticipated that a normal automatic gate motor will be used so I guess the currents will not be more than about 20-30A.

You really need to nail down the current requirements of the motor under load. Your worst case scenario will likely be when the gate valve is closed, and current is just starting to be applied to the motor. Motors at stall will draw many times the current as they do when they are running at speed.

The project manager insist on only using N channel FET's and one of the IR H-Bridge devices such as the IR2110. I have readup on the IR devices but cannot fathm out if these take care of the Vgs issue on the high side that normally would require a charge pump o sustain the say 10V Vgs when the high side FET opens up.

Yes, they take care of the Vgs for the high side MOSFETs.

Are there any recommendations, examples that anyone has that I may use as a starting pont?

There are examples in the datasheet. Are these not sufficient?
Take a look at International Rectifier's AN-944 application note.

I am going to drive the whole system from a STM32F103CBT6 device.

Datasheets available here: http://www.st.com/mcu/devicedocs-STM32F103CB-110.html

I also need to do some current sensing to detect shoot through faults, locked rotor etc, so will use op amps onto the AD's of the micro.

You had mentioned in your E-mail that you were considering using IRF640 MOSFETs. These would not be a good choice. They are older technology, are for a much higher voltage range (Vdss=200), have a relatively high Rdson(0.18 Ohms) and high gate charge compared to more modern and more suitable MOSFETs.

For what you're doing, it sounds as something like a VNH2SP30-E "Automotive Fully Integrated H-Bridge Motor Driver" would be a far easier solution. It takes care of many of the issues you're concerned about all by itself.

Datasheet available here;
http://www.st.com/stonline/products/literature/ds/10832.htm

 

Thanks for the reposnes and advice.

I have searched IR and cannot find their App note 944???

The other thing I am hitting a snag on is a search mechanism to narrow down the choice of MOSFET - I am trying to find one with lowest Vgs Rds etc - are there search engines for these.

I am still having a snag with the half bridge devices of IR as they do not explain clearly the high side issue with ensuring Vgs is maintained. IR also seem to have a limited number of half bridges???

The ST stuff on hte micro is good as I have done quite oa bit of work on these devices and am comfortable with them. Will obviously have to write teh appropriate delays during switchover.

Must now try convince the boss that the ST H-Bridge device is the way to go rather than re-invent the wheel.

Thanks again for the help.

DS

 

i have not searched for parts like the ones you are looking for, but i know that digikey has a great filtering system which will likely allow you to sort by those two parameters.

start your search with the broadest component category to ensure you dont miss any parts.