vne147
Member
I have a circuit I'm working on in which I need to switch up to 25A @ 48V to a mostly resistive load that will be in the range of 0.1Ω - 10Ω. Every other time I supply power to the load, I need to switch polarity. For the prototype I have been using 2 SPDT relays to accomplish this. But for reasons of cost and reducing the number of moving parts, I'm looking to change this arrangement to an H-bridge.
I've looked around for MOSFETs that meet the operational requirements listed above and also have a very low RDSON, so they don't get too hot. I've found quite a few N-channel MOSFETs that fit the bill, but the P-channels (at least the ones I've found) seem to have a higher RDSON and have fewer options overall. For that reason, I'm going to try to employ the H-bridge arrangement using only N-channel MOSFETs.
The problem is, that the highest voltage I have in the circuit (48V) is also the voltage I'm switching. So, it won't always be possible for the high side MOSFETs to maintain the necessary VGSTH. For this reason, I started looking at using a gate driver IC for the high side MOSFETs.
Now finally to my question:
I've found a few gate driver ICs that have very high output currents. The LTC4441 for example, can output up to 6A. Why would this much current every be necessary to drive the gate of a MOSFET? I can't for the life of me imagine an instance where you'd need 6A to turn on a MOSFET, or even a bunch of MOSFETs. Knowing that the people who design these parts aren't dummies, and knowing that I don't understand why I would ever need to use the full 6A this part can source, makes me think I don't understand something about the proper use for this IC, or worse yet something fundamental about how MOSFETs work.
So, can someone please explain this to me? You can talk to me like I'm 5. You won't hurt my feelings.
Also, if you think I'm going about this H-bridge arrangement the wrong way by trying to do it with all N-channel MOSFETs, please don't be shy.
Thanks in advance for your help.
I've looked around for MOSFETs that meet the operational requirements listed above and also have a very low RDSON, so they don't get too hot. I've found quite a few N-channel MOSFETs that fit the bill, but the P-channels (at least the ones I've found) seem to have a higher RDSON and have fewer options overall. For that reason, I'm going to try to employ the H-bridge arrangement using only N-channel MOSFETs.
The problem is, that the highest voltage I have in the circuit (48V) is also the voltage I'm switching. So, it won't always be possible for the high side MOSFETs to maintain the necessary VGSTH. For this reason, I started looking at using a gate driver IC for the high side MOSFETs.
Now finally to my question:
I've found a few gate driver ICs that have very high output currents. The LTC4441 for example, can output up to 6A. Why would this much current every be necessary to drive the gate of a MOSFET? I can't for the life of me imagine an instance where you'd need 6A to turn on a MOSFET, or even a bunch of MOSFETs. Knowing that the people who design these parts aren't dummies, and knowing that I don't understand why I would ever need to use the full 6A this part can source, makes me think I don't understand something about the proper use for this IC, or worse yet something fundamental about how MOSFETs work.
So, can someone please explain this to me? You can talk to me like I'm 5. You won't hurt my feelings.
Also, if you think I'm going about this H-bridge arrangement the wrong way by trying to do it with all N-channel MOSFETs, please don't be shy.
Thanks in advance for your help.