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Registered Member #61406
Joined: Thu Jan 05 2017, 11:31PM
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Posts: 268
Hi, I've drawn up one leg of a H bridge, and I'm trying to workout if it will fry the MOSFETs. The battery in the top right is 56V. The digital source bottom left is 12V. The zener is 12V and R1 and R2 is selected to make 12V in the bottom right fet.
Registered Member #61406
Joined: Thu Jan 05 2017, 11:31PM
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Posts: 268
I don't have a computer anymore, but I do use ltspice. I've tryed Tesla driod on the cellphone but the free trail finished. I was hoping the zener would limit it to 12V. How do other people do it?
Edit If the zener are 12V I think this might work?,missed the ground on the right gate.
Registered Member #2939
Joined: Fri Jun 25 2010, 04:25AM
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M1 and M5 wont turn off, or if they do it will be very slow. Why not just use a high-side gate driver - all these issues would just go away, and you can use N-ch for the high-side mosfets (better RDSon)
Registered Member #61406
Joined: Thu Jan 05 2017, 11:31PM
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Thank you 2Spoons, looking at it that does make sence. I'll add a resistor in parrellel to the zener, and get the voltage divider as close to 12V. About high side gate drivers I have bookmarked works up to 80V for one leg. I will do some more looking but might test the above circuit, just need 6 MOSFETs then it will be complete.
Registered Member #2939
Joined: Fri Jun 25 2010, 04:25AM
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You run the risk of both upper and lower fets being on at the same time - you need them to turn off faster than they turn on, otherwise you will get shoot-through, and all the magic smoke will escape.
Registered Member #61406
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Would And/or/xor IC work, Should be able to not turn on the upper gate if the lower one is on. I think they have 15V supply not sure if the current is enough though.
Registered Member #61406
Joined: Thu Jan 05 2017, 11:31PM
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2Spoons would adding a gate resistor and a diode to bypass the resistor during turn off work? Could this explain why I get 6V instead of 12V which is the supply voltage? If the current path is doubled.
Registered Member #61406
Joined: Thu Jan 05 2017, 11:31PM
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Looking on Google one person said to add a gate resistor, and a diode to bypass the resistor during turn off, that just added heat on the FETs. I found making them switch faster helps, but it still seems like a 50% voltage divided is affecting the H bridge. Just to state, the data sheet for the P FETs says 123,GDS so I connected the Source to the 12V rail and had drain go to the lower FETs. I scvanged them from old projects, and tested them by putting positive rail to source with one lead from the DMM, the gate was grounded, the other DMM lead went to drain. It went infinity on the resistor setting, but that might be back to front leads.
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56V bridge question
