# MOSFET Driver HIP4081A with a square wave input to change direction of an electromagnet help

#### kmr33

Joined Apr 10, 2018
1
I was tasked by one of my professors to create a device to change the direction of current flow through a solenoid in order to change the direction of the magnetic field it produces. He gave me a partially completed H-Bridge design using 4 MOSFETs which I completed and told me to drive them using a HIP4081A. However, the whole thing is supposed to be driven by a square wave from a function generator and I am unsure how to make the inputs of the HIP4081A work with this since normally the BLI and ALI are inverted versions of each other.

H-Bridge schematic the load (M) would be a coil to act as a magnet.

My current design is using diodes to rectify the square wave into the positive amplitudes and the negative amplitudes. My main problem is that I would then need to make the negative amplitudes positive to have out of phase inputs into ALI and BLI (i.e. ALI high while BLI is zero and vice versa) and I am not really sure how to do this.
If there is also a better way to do all of this let me know.

Note: I also have BHI and ALI sharing the same input and BLI and AHI sharing the same input.

I have uploaded the datasheet for the HIP4081A.

This is my first post and I am a physics student so I don't know a whole lot about this kind of stuff so go easy on me.

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Joined Mar 10, 2018
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#### shortbus

Joined Sep 30, 2009
8,044
You can buy gate drivers that take care
of this as an issue. Google "MOSFET Gate Drivers",
That is what the HIP4081 is. But instead of it being a half bridge driver, it is a full bridge driver.

#### shortbus

Joined Sep 30, 2009
8,044
My current design is using diodes to rectify the square wave into the positive amplitudes and the negative amplitudes. My main problem is that I would then need to make the negative amplitudes positive to have out of phase inputs into ALI and BLI (i.e. ALI high while BLI is zero and vice versa) and I am not really sure how to do this.
If there is also a better way to do all of this let me know.
One way would be to use a SPDT switch, to change the inputs to the HIP4081 from the square wave generator to the appropriate inputs on the driver. Both directions are only looking for the high/positive part of the square wave.

#### ebp

Joined Feb 8, 2018
2,332
I think you are grossly complicating the problem. As I interpret the requirement, when the input from the function generator is HIGH the current flows one way through the solenoid and when it is LOW it flows the opposite way. This requires just a bit of simple gating at the driver inputs. The gating is different if you require a DIRECTION input and an ON/OFF signal, but that has not been mentioned.

EDIT - When I say "gating" I mean the use of ordinary logic gates (AND, OR, NAND, NOR, etc.) from any logic family appropriate to the signal voltage from the generator and as required by the gate driver. Suitable parts might be found in the 4000 series, or in 74HC, 74HCT, 74AC or 74ACT families. The 4000 series has the advantage of operating from a wide supply voltage range. The others are much faster but the maximum supply voltage is much less.

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