"Easy" PWM driver for H bridge MOSFET motor control ( BIG )

D n T

Senior Member
Can I ask Hippy, Dippy etc to have a look at the HIP 4081 MOSFET H bridge driver chip.
It appears to be a really easy (relatively simple) way to wire up a 24 volt 20 amp( with enough MOSFETS in parallel) motor with forward and reverse direction control, of them would allow a serious skid steered unit.

It might even serve to assist in the MOSFET education of me and others.
I think I m right but I might be seeing what I want to see rather than what is in front of me.
I found it at the "Open Source Motor Controller" or OSMC site.
Could someone in the know have a look and give an opinion, I know some might see it as cheating but...

I'm bracing for replies, good, bad and ugly
Thank you


Senior Member
I used the HIP4081 many moons ago when I started dabbling in Class-D audio.

The problem I see with the HIP4081 and its sibling the HIP4080, is that they charge up the Mosfets extremely quickly. This is usually a very good thing, as one minimizes the transitions (and thus the dynamic power dissipation) of the Mosfets. The downside is that this fast switching creates large dI/dt's....in other words voltage spikes that unless you have a first rate grounding and decoupling techniques, it will wreck total and complete havoc in your remaining circuitry.

Essentially, this means the following:

1) You must at least a double layer PWB, with one layer dedicated as a ground plane. Forget about using veroboards and strip breadboards!
2) Good decoupling using Surface Mount ceramic chip and tantalum caps.
3) By the same token, to keep leads very short, it is also highly recommended that the Mosfets to be SMT.
4) You may still require to tailor the gate drive to control the rise/fall times. This takes the form of a lowly, low-value resistor in series with each gate. But you cannot do it blindly, it all depends on the Mosfet's total gate capacitance (Cgs and Miller), and you must have a very fast oscilloscope (>=200 Mhz) to verify the actual waveforms.
5) Ferrite beads may be necessary in key signal lines, to attenuate conducted noise.

Now, please do not be discouraged...you can still do it and it will be a rewarding learning experience. But follow the guidelines above, and be prepared to blow up a few Mosfets.
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Senior Member
This will help with di/dt "noise". But good board design/layout is
still very important.

See attached.

The values of R1 and R2 determine rise and fall times respectively ....
by slowing the gate charge/ discharge. The trade off is some loss
of efficiency.

Almost all commercial high current motor drivers that use FETs
or IGBTs will have some kind of gate current limiting similar to this.



Senior Member
Disregard the "not fitted" and "removed labels", they aren't mine, have a look anyway
This shows some of the techniques I talked about (conditioning of the individual gate drive) plus some additional ones (like the R-C snubber circuit and tranzorb diodes) to dampen up spikes.

It also has some good engineering practices, like having pullup/ pulldown resistors, to disable the unit in case the signals become accidentally lost.

The images also show a dual layer board. All thru-hole devices, but hey, SMT is the icing on the cake... as mentioned by the other poster, a good board layout is paramount.

Overall, this seems like a well thought-out unit.
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