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Author Topic: Power Mosfets for a H-Bridge?  (Read 2141 times)
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What are some good power mosfets for an arduino powered h bridge? I am looking for some "Logic Level" mosfets in order to drive them without any additional hardware.

I have been looking at the IRLZ44 and the specs seem to be enough to drive a 5A load but I can't seem to find a matching P-CHANNEL Mosfet for the high side of the h bridge.

Any help? Thanks !
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Does your motor need 5V, or something higher? if it needs more than 5V then you will have to level-shift the drive to the P-channel mosfets, in which case there is no need for them to be logic-level. If you do need logic-level P-channel mosfets, then IRLIB9343PBF, NDP6020P or MTP50P03HDLG may be suitable.
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It is hard to say what is 'good'.
I look at the specifications to see if it fits my demands. For power mosfets there is no commonly used type.

The more current a mosfet can handle, the lower the voltage drop (drain-source voltage drop if turned 'on').
For a tiny motor of 1A, I like to use a logic level power mosfet that can handle 20A.
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Does your motor need 5V, or something higher? if it needs more than 5V then you will have to level-shift the drive to the P-channel mosfets, in which case there is no need for them to be logic-level. If you do need logic-level P-channel mosfets, then IRLIB9343PBF, NDP6020P or MTP50P03HDLG may be suitable.

What do you mean exactly by level-shifting? Yes, I was expecting to use some 12v dc motors and drive them using the arduino.

Am I wrong or do I need 2xN Channel + 2xP Channel to build a H-Bridge?
« Last Edit: February 25, 2013, 03:26:52 pm by juanps90 » Logged

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What do you mean exactly by level-shifting? Yes, I was expecting to use some 12v dc motors and drive them using the arduino.

Am I wrong or do I need 2xN Channel + 2xP Channel to build a H-Bridge?

You can build an H-bridge either using 2xN + 2xP channel mosfets, or using 4xN-channel mosfets. Either way, you need to level-shift the drive to the upper mosfets, unless you are using a 5V supply and P-channel upper mosfets.

Suppose you are using a 12V supply and P-channel upper mosfets. Their source terminals are at +12V, so to turn them off, their gates need to be at about +12V too. To turn them on, their gates need to be at +7V or lower if they are logic level mosfets (i.e. 5V gate drive). The Arduino can only put out 0V and +5V, which you therefore need to turn into +7V and +12V (or the other way round). This is known as level shifting. Since it normally needs at least a transistor to do it, you may as well amplify the signal at the same time. For example, you can convert the 0V and +5V into +12V and 0V, allowing you to drive P-channel mosfets that need 10V gate drive. This gives you a better choice of mosfets. See the attached schematic for one possible way of doing it.

High current H-bridges are usually built using 4x N-channel mosfets. This is trickier because you need higher gate drive voltage for the upper mosfets (i.e. the supply voltage + either 5V or 10V). However, there are some ICs  designed for this purpose.


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Thanks for such a clear explanation.

I understand that the diagram that you posted includes one pair of N-Channel mosfets and one pair of P-Channel mosfets. The drawing is pretty clear, thank you.

So, how can I build an H bridge consisting of 4 N-Channel mosfets? because I currently have the N-Channel type so it would be nice to make use of them. I'm guessing i would need additional hardware since I would need to increase the gate voltage even more to reach the necessary Vgs.

Thank you!
« Last Edit: February 26, 2013, 05:29:10 am by juanps90 » Logged

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It is hard to say what is 'good'.
I look at the specifications to see if it fits my demands. For power mosfets there is no commonly used type.

The more current a mosfet can handle, the lower the voltage drop (drain-source voltage drop if turned 'on').
For a tiny motor of 1A, I like to use a logic level power mosfet that can handle 20A.

I can't seem to find ANY P-Channel Mosfet that is a logic level one on eBay. Are they not used at all or am I just doing something wrong?

Thanks !
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In the diagram I provided, the P-channel mosfets don't need to be logic level because they get 12V gate drive.

To use 4xN-channel mosfets, use e.g. two IRS2003 or IRS2004 driver chips, or one HIP4080A.
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Would it be possible to use transistors to drive a higher voltage to the mosfet gates?

I was just thinking that, even though you mention that the P-Channel mosfets do not need to be logic level MOSFETS, the N-Channel ones do have to unless I use some transistor to drive a higher voltage. Am I right?

Thanks for helping me !
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In the schematic I posted, the P-channel mosfets are drive by NPN transistors that level shift, invert and amplify the mosfet gate drive. So they don't need to be logic-level mosfets. It would certainly be possible to amplify the gate drive to the N-channel mosfets too. However, logic-level N-channel mosfets are readily available, so this isn't worthwhile unless you also need to reduce the switching time.
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Thanks for answering that.

The problem is that, besides running a 12v motor, I am also planning to build another robot and use 5v, same as the atmega328, so in that case I would definitely need logic level mosfets, right?

For the 12v robot that I am going to build I will take your suggestion and use standard P-Channel Mosfets using the circuit that you posted.

Thanks!
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Ebay now has fairly inexpensive h-bridges that might be of interest. If you want to DIY an h-bridge, the below discussion might be worth a read.

http://arduino.cc/forum/index.php?topic=53425.0
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I was actually trying to keep everything on a single pcb besides learning.

And yes, I had seen the post that you linked.

Thanks !
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