H-bridges - what am I missing?

On Sep 20, 4:28=A0pm, Anton Erasmus <nob...@spam.prevent.net> wrote:

> >expecting - National LMD18200. Seems like a very old part though.
>
> The even older L298N might also be viable. Stil available from
> multiple sources. In stock at Digikey.

Cheap, too. But dropping 10W(ish) in the chip for a 2A load?! :)

"larwe" <zwsdotcom@gmail.com> wrote in message 
news:35ebc821-5667-422c-be1c-7b308b497b36@m1g2000vbh.googlegroups.com...
On Sep 19, 4:22 pm, Dave Nadler <d...@nadler.com> wrote:

> > I'm looking for a simple, preferably through-hole H-bridge IC, nothing
> > fancy, for PWM-controlled DC motor drive. (5A max would be plenty).
>
> Sorry if I'm being dense Lewin, but this part is for
> driving a DC motor in one or the other direction,
> for example car electric window.

I need to drive a DC gearhead motor forward and reverse, with some
speed control (2 or 3 steps in each direction). Fine control of motor
speed is not necessary, and this is open loop. It would be a low
frequency PWM signal, but the switching times mentioned in that
specific datasheet seem to imply up to maybe 30kHz is theoretically
doable. Control is from a general-purpose micro with two 10-bit PWM
outputs and various available GPIOs.

I could do what I want to do with discrete FETs but I don't want to
have to design all the shoot-through protection, etc. etc. and worry
about what I might have forgotten - much rather get a canned part.

If shoot-through is what I think it is - both ends of a half bridge being on 
together during a transition and shorting the supply - then there are plenty 
of half bridge drivers that look after that. Just connect to a pair of 
N-channel fets and drive with logic signals (typically H/L and enable). 2 
should produce an H-bridge unless I'm missing something.

I've driven FETs up to > 350 KHz using these with no problems.



> PS: careful on lead time of H-bridges - I'm having
> difficulty finding what we need that's actually

I thought it was just me - almost all the parts I want are no stock
everywhere... 

On Sun, 19 Sep 2010 17:52:46 -0700 (PDT), larwe <zwsdotcom@gmail.com>
wrote:

>On Sep 19, 8:47&#4294967295;pm, Tim Wescott <t...@seemywebsite.com> wrote:
>
>> > I thought it was just me - almost all the parts I want are no stock
>> > everywhere...
>>
>> If employers are afraid to hire even as the work picks up, I see no
>> reason that manufacturers wouldn't be afraid to stock parts, even as
>> demand picks up.
>>
>> Perhaps the "jobless recovery" is a "partless recovery" as well.
>
>We have a serious problem with this at my day job - most of the big
>guys are giving us random leadtimes. I think the recovery is uncertain
>enough that it isn't a sure thing that it's going to be worthwhile to
>fire up a new shift or bring a spare fab online or whatever it is -
>the mfrs just don't want to sign up for increased fixed costs.
>
>On a related note, I found a device that has exactly the inputs I was
>expecting - National LMD18200. Seems like a very old part though.


There are some other like the LMD18200 (approx. 40V/3Apk)  chips
aviable 

Freescale  MC33186
ST: L6203
Infineon TLE7209, TLE5205

all are more or less aviable @ digikey (Austria)

hth
-
Michael Wieser
--