>>         http://russell.servepics.com/temp/r100b.gif
>>
>> Criticism invited.


> Russel, wrong or right drawing this design can't be more cheaper 
> that
> a standard integrated H bridge. You forgot from the total cost of 
> this
> design the time spent with PCB design and component soldering. In 
> fact
> I think is more expensive than most of the standard H bridges 
> adapted
> for your requirements. Except maybe if you plan to produce it in 
> China
> with chinese transistors.

A number of people have said this. But nobody so far has suggested a 
"Standard H Bridge" that will meet my specs or be cheaper, let alone 
both.

Initial production is in Taiwan. If it goes to decent volume 
production will indeed be in China.

Design time is not an issue for several reasons. Soldering time is 
relevant but as it will be autoinserted/placed this is not a vast 
factor. PCB area matters but as it is part of a PCB of fixed existing 
dimensions this also is less of a factor than otherwise.

Most H bridges will not run down to say 3v supply. 5v supply is OK for 
the logic portion as long as the bridge proper is happy with less.

Most H bridges (not all) have terrible saturation voltages - 1.5v or 
worse. I require say 0.5v total in most cases.

Many H bridges do not provide the dynamic braking function that my FET 
circuit provides - but let's leave this out of cost and consideration 
unless there is a bridge which does this.

Many bridges have substantial quiescent currents.

Most H bridges do not limit the maximum motor voltage when supply is 
too high.

I looked at all the parts that people suggested previously. One came 
closer than most. I couldn't find a source of supply but I imagine it 
would have been available. But it still didn't meet all specs.

Even if I use a standard H bridge that I'm aware of I may have to eg 
add a voltage regulator or a power shut down circuit to limit 
quiescent current.

I'd be very happy to know of an H bridge that met all these specs 
(except perhaps motor braking) and sold for say under $US0.40 in 1000 
quantity.
By all means please do suggest ones that do. I'd be most grateful.




        Russell McMahon

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