High current H-Bridge

[ScOe]

build h-bridge 10a

Hi!

First i would like to note that i'm not EE but ME so please have patience with me

Ok, i would like to make full h-bridge to drive ~10A motor at 7.2V. I will connect two motors in parallel so it will be around 20A. Problem is that motors can drain around 200A peak.
First, i'm consider to design h-bridge with all n-fet IRFZ46. They already have build in diode which i'm not sure is enough to suppress induced voltage.
I will use uC to create PWM signal and one direction signal. So my h-bridge will have only two inputs. I'll use NOR logic to drive max4420.
For driving Mosfets i have max4420 (i know that they are not quite best choice, but i have it in my drawer so...). I saw somewhere on Net that i need to apply Vin to max4420 slowly, but im not sure why. If that is true, is it enough to use some condenser ?
Also, if i use max4420 do i need to use voltage doubler for upper mosfets to supply enough volts on gate ?

For protecting the uC circuit, do i need to use some kind of optocouplers or is it enough to use those mosfet drivers ? I'm not sure if optocouplers are fast enough.

After some confirmation, i'll draw circuit schematic for further analysis.

Thanks in advance!
Sven

P.S. i apologize for my english skills, hope everyone understand what i'm talking about

 

[chand1]

max4420 application

Yes. Better to use Opto-coupler to have isolation between micro controller and the Bridge ckt. Speed up to 25KHz is fine.
The gate voltage should be around 10 Volts or moe. ( But many MOSFETs works with about 4 Volts also).

Added after 1 minutes:

One more info. Built in diode is enough.

 

[FvM]

high current h-bridges

Hello,

I don't see the necessity of using optocouplers for low voltage motor drivers, but it depends on the application. Using high current gate drivers is necessary anyway, MAX4420 isn't a bad choice, I think. As an alternative, opto isolated MOS/IGBT gate driver IC are available from Avagotech and other companies.

But I see an issue with high-side gate driver supply. It is mandatory that gate voltage swings 5, better 10 volts above positive positive bridge supply. Typically a floating supply is used for this driver, or a specialized high-side driver with integrated levelshift. If the bridge supply is limited to 7.2V, the high-side driver negative supply could be connected to bridge supply, but you should have measures against supply transients exceeding Ugs limits.

Obviously the control timing must observe a sufficient deadtime to prevent from bridge shortcuts, but excessive deadtime would increase switchig losses by causing current flow in the slow MOS reverse diodes.

Regards,
Frank

 

[ScOe]

pwm h bridge high current

Hi,

I've decided to build H-bridge with high side and low side mosfet drivers which will eliminate need for voltage doubling (i supose high side driver will do that). I will use LTC1155 for high side and IR4426 for low. Now there are few issues about safety. I would like to limit current on around 20A, and for that i was planing to build in current sensor and uC that will be in charge for that task. uC will receive reference value for velocity and with some kind of PID algorithm and input from encoder it will generate PWM for mosfet drivers.
I will put schottkey diode in parallel with all M-FET-s. So, do i need to put opto couplers between uC and FET drivers ? Also, it is better to use some kind of logic IC to reduce from 4 to 2 outputs (PWM and direction) to control the drivers, or to use algorithm in uC. Number of output from uC is not an issue because it will be dedicated uC only for bridge and communication.

 

[FvM]

hi current h-bridge with direction control

Hello,

one point about safety is to assure break-before-make operation for the switches, it may be achieved alreaydy by driver timing, but you should check for. Another point could be not to allow a badly programmed uP to short the bridge, this would require external logic. Also, if you want to generate PWM from uP, it may be meaningful to use one pwm output for both sides.

For maximal safety, overcurrent protection should trigger independent of uP, needing an external latch. If output shorts are possible by application, you should analyze what's the maximum latency for overcurrent switchoff to protect the FETs.

Schottky diodes are not generally necessary with MOSFET bridges, but can reduce power-losses during switchover. They are however, also more sensitive to transient overvoltages than MOSFET at their DS contacts cause unlike FET they have no intrinsic overvoltage protection.

Regards,
Frank

 

[amal_s]

h bridge transient

Hi,
I'm using PIC 18Fxx31 to control a 12A 24V dc motor.
HIP4081 act as Mosfet driver and charge pump for IRF 4310.
I dont think optocouplers are necessary for this circuit.
The system is now working properly.:|