Using a Pololu driver, the throttle-body I'm testing with is quite loud=20
in the 2Khz-4Khz PWM range.  11khz gets noticeably lower in volume and=20
20khz is almost non-existant, though it's easy to tell it's on.  For the=20
purpose of this project, the noise is not an issue, but I want to keep=20
the noise down just cause people will think something is wrong.

Cheers,
-Neil.




On 1/2/2015 3:20 AM, IVP wrote:
>> As I read up more on h-bridges, I understand better why you say this
>> (about switching time and linear region).  I chose 50khz just thinking
>> it's well outside the upper audible range) but that's not a critical
>> parameter.  AIUI, if I drop to 20Khz, the drive requirements get much
>> simpler.
> I've not experienced it myself but my belief is that noise from switching
> in the audible range comes from the load, eg motor or coil windings
> vibrating, and some loads are better made than others. Occassionally
> I've heard the semi ringing if it's not bolted down hard enough to the
> heatsink, or like a loose transformer that hums until you give it a clout
>
> Given a fixed transition time, as the number of transitions / sec decreas=
es
> then the time / sec spent in the linear region decreases. For example if =
the
> transition time is 1us then at 1MHz ......
>
>> However, I just discovered this seemingly neat device -- VNH5019.
>> At US$8 with minimal other support components required, is there
>> any reason I should really be trying to engineer my own?  From what
>> I see of discrete-component versions, I'm very much in the same price
>> range already.
> If the cost is about the same I'd go with an IC, someone's already done
> the design work
>
> Last year I re-jigged some golf carts. The overseas manufacturer had
> put a very poor discrete driver in and the FETs were cooking and failing
> unpredictably (although it was often after user abuse - overloading etc).
> The PCB was designed for 3 FETs but another 3 (!!!) were added at
> the factory to try and spread the stress. In fact the FETs chosen were
> so big that only one was almost enough if it was driven properly. An
> inexpensive change to the driver got the FET count back to the original
> 3 and they now run barely above ambient
>
> Joe
>
>
>
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