Neil,

Why trying to reinvent the wheel, when companies have already done the work=
 for you.
Just look at the ST device VNH5019A-E. It will handle easily the 6A RMS you=
 wanted.
I do not know what is your max voltage, but that device is fairly inexpensi=
ve, like $6 a piece.

Just my $0.02,
Jean-Paul
AC9GH


> On Jan 1, 2015, at 9:21 PM, Neil <picdude3@narwani.org> wrote:
>=20
> As I read up more on h-bridges, I understand better why you say this=20
> (about switching time and linear region).  I chose 50khz just thinking=20
> it's well outside the upper audible range) but that's not a critical=20
> parameter.  AIUI, if I drop to 20Khz, the drive requirements get much=20
> simpler.
>=20
> However, I just discovered this seemingly neat device -- VNH5019. At=20
> US$8 with minimal other support components required, is there any reason=
=20
> I should really be trying to engineer my own?  From what I see of=20
> discrete-component versions, I'm very much in the same price range alread=
y.
>=20
> Cheers,
> -Neil.
>=20
>=20
> On 12/17/2014 5:11 AM, IVP wrote:
>>> Usually you don't need vast average gate drive mA - you need
>>> around an amp while the FET is switching but most of the time
>>> the gate does not require current to hold it on or off
>> AIUI the current is needed mostly to charge the gate cap quickly to
>> keep the switching time low (ie keep out of the linear region as much
>> as possible). And once turned on, the FET is voltage, rather than
>> current, driven
>>=20
>> I PWM a 1/2HP 12V motor with 3 paralleled FETs using a BC337/
>> BC327 push-pull pair and that works fine, even though the BCs are
>> rated at only 500-800mA. Stall / start current is many times the run
>> current so I do tend to try and remember to soft start
>>=20
>> Neil, useable speed / torque might not kick in until the PWM is quite
>> high. I think mine is around 30%. Below that the energy simply heats
>> the windings without the motor turning usefully. This may or may not
>> be a problem. For example if there's fan cooling on the shaft
>>=20
>> My scrollsaw has a *proper* variable-frequency speed control
>> for the induction motor and can be run slowly enough (with good
>> torque, so it's tempting to use it too long) to cause damage if forced
>> cooling isn't used to assist the internal fan
>>=20
>> Joe
>>=20
>>=20
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4
>>=20
>=20
> --=20
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