On Tue, 14 Sep 2004, Alexandre Guimaraes wrote:

> Hi, Dave
>
>>> Hi,
>>>
>>>    I am still in the quest for making my pick and place table work...
>>>
>>>    Can I put 2 LM317 configured as current sources in parallel ?
>>
>>
>> Why not go LM338?
>
>    This is one of those times that I fell embaressed to live in a
> developing country... I can buy any parts in quantity down here. We have
> arrow, insight and Future with offices in Brazil but.... I can not find a
> simple LM338 in a street store and we do not have mail order distributors
> down here !! And this thing is a one of project. It does not justify to buy
> from digikey and pay shipping and huge taxes... Oh well... I really live in
> a weird country.... It is very advanced in some stuff and extremely "third
> World" in other things..

You can supplement the output of the lm using a pnp pass transistor 'in 
parallel' with the lm. Look at the lm applications used as voltage 
regulators with external transistor for clues. The scheme is exactly the 
same (collectors of pnps connect to lm output, before the current setting 
resistor). To make the thermal protection work all must be connected to 
the same heatsink. Building a 10A, 24V pass device is relatively easy (but 
requires a huge heatsink). This used 1 LM317T and 3 2N2955T and two Dale 
heatsinked power resistors. The emitters of the 2N2955s had 0.22 ohm 
equalising resistors.

Peter
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