Need help protect burn Mosfet H bridge circuit

Thread Starter

mpcotuong

Joined Aug 26, 2010
170
Hi All,

I am using Mosfet P and N channel for H bridge circuit, once my Motor stuck the whole circuit has burned. Do you know how to make protect Mosfet H bridge circuit? Please let me know. The Voltage is 12VDC for Motor.

Thanks,
Kevin
 

Kermit2

Joined Feb 5, 2010
4,163
There is an ancient device made from a low temperature fusible metal.

It's called a fuse. It might help protect your motor from large current flows, and in the process it will keep your H bridge from bursting into flames :)
 

SgtWookie

Joined Jul 17, 2007
22,210
MOSFET internal diodes won't protect against overcurrent.

When a motors' rotor is locked/stalled, current flow is perhaps 10x as much as when it is running no-load.

Another option is to use a chopper driver, which limits the maximum current without a fuse; however a fuse is always good protection against other circuit failures.
 

thatoneguy

Joined Feb 19, 2009
6,359
What is your MOSFET Peak Current rating?

Add a fuse inline with the motor of an automotive blade type, say 10 Amp or whatever, and you have that part covered.
 

SgtWookie

Joined Jul 17, 2007
22,210
Then use a 2A fuse rated for 32v or higher.

I don't know why you're using such high-voltage MOSFETs, unless you just can't find any that are lower voltage. Your Rds(on) is quite high at 0.6 Ohms.
 

Thread Starter

mpcotuong

Joined Aug 26, 2010
170
I am using the high Mosfet because would like to use strong motor of 12VDC. How to connect the Fuse. Is that connect it before the input of 12VDC?

Thanks,
Kevin
 

SgtWookie

Joined Jul 17, 2007
22,210
I am using the high Mosfet because would like to use strong motor of 12VDC.
You would get a much lower Rds(on) if you used lower Vdss rated MOSFETs. 20v to 60v would be much lower.

How to connect the Fuse. Is that connect it before the input of 12VDC?
You can put it on either power supply/return wire to the H-bridge. My personal preference would be to interrupt the positive side.
 

SgtWookie

Joined Jul 17, 2007
22,210
If you have other Mosfet please recommend.
I would not use a P-ch MOSFET. The gate charge is 2.5 times higher in order to get the same Rds(on) for the same Vdss rating as an N-ch power MOSFET.

I would use a high and low-side driver IC for each side of the H-bridge, and use identical N-ch power MOSFETs for all four.

The IRLR8721/IRLU8721 would be a far better match for your application. Rds(on) is 0.0084 Ohms vs 0.6 Ohms for the P-channel you're using now; your power dissipation is over 71 times as high as it would be with these MOSFETs.

The total gate charge at 8.5nC is ~half your current 16nC-22nC total gate charge; but as an added benefit the MOSFETs I'm suggesting are logic level rather than standard level.

As I said though, you will need to use a high & low side driver IC for both sides of the H-bridge.
 

thatoneguy

Joined Feb 19, 2009
6,359
The motor may actually move faster due to lower resistance internal to the MOSFETs. The motor is still only supplied 12V, even if the MOSFETs are rated for 600V or more, 12V is all that is available.

An H-Bridge driver IC may be the ticket, some include current sensing and shutdown as well.
 

SgtWookie

Joined Jul 17, 2007
22,210
The VNH2SP30-E by ST Microelectronics is a very capable Automotive Fully Integrated H-Bridge Motor Driver, capable of up to 30A @ 41V (maximum), 19m Ohms per leg; 20kHz PWM, really too many great features to mention in one post, all for about $10/ea - if you can find any. For some reason, they appear to be sold out virtually everywhere, and new stock won't be arriving for a month or two.
 
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