Or how about something like this?...
http://www.mouser.com/ProductDetail/International-Rectifier/IRS2003STRPBF/?=
qs=3DsGAEpiMZZMvQcoNRkxSQkuprlmO3q%2f%2f34UdbtrJfWmo%3d

At a quick glimpse it seems I should be able to use 2 of these with 4=20
NFETs and little else to get a decent H-bridge.
These are some options I have for NFETs...
http://www.infineon.com/dgdl/Infineon-IPD50N04S4_08-DS-v01_00-en.pdf?fileId=
=3Ddb3a304328c6bd5c01291c847b245e45&ack=3Dt

http://www.mouser.com/ds/2/149/FDD8453LZ-38955.pdf

Cheers,
-Neil.


On 12/16/2014 4:50 PM, IVP wrote:
>> Other things being equal, N-fets are better (lower RDSon) than P-Fets,
>> but they are a PITA to use on the high side, because their gates must be
>> ~10V *above* the uper rail to switch on properly
> Depending on the application (ie power being switched -> gate drive
> needed) a voltage doubler made with a 555 will get you 24V for the
> high side. It should be able to supply enough current to turn the FETs
> off/on quickly and hard, and a 555 has fairly good current drive. Still
> short of the (at least) 1A for big FETs though
>
> Good hard and fast gate drive (both on and off) is the key
>
> You could make a little buck SMPS with the PIC's PWM module (if
> you're using a PIC that is), or any available/simple oscillator
>
> You should also consider dead-time. This is built in to a good driver IC
> and prevents both the high- and low-side FET on the same side being on
> at the same time.
>
> If they do happen to be on at the same time (even briefly, as one turns
> on whilst the other is still turning off) at best it means excess
> dissipation
> and at worst destruction. But that largely depends on which is tougher,
> the FETs or the power supply
>
> The gates should have protection against EMF, hash etc from the motor.
> A 15V zener paralleled with 270 ohm from gate to source is usually
> sufficient. A fast Schottky diode across drain (cathode) - source (anode)=
..
> A reverse-series (back-to-back) 15V zeners (suitably rated) across the
> motor terminals with 0.1uF ceramics from terminal to grounded case
> will suppress a lot of hash at its source. If noise is really bad you may
> have to add a couple of ultrafast diodes too.
>
> FETs are very good at switching power but they can be quite frail
> electrically.
>
> Joe
>
>
>
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