Quote Originally Posted by pminmo View Post
Where do I say you can sub a LM138..LM338?

As far as I know the LM138..LM338 are only available in TO-3 packages. The pcb for the L297-8, the LM317 is a TO-220. Two entirely different mechanical packages.
PMinMO, my apologies. I was reading through various PDF's covering open source boards today, and obviously I mistook the PDF as being one of yours. I'm trying to find the one I read where it stated that if our amperage requirements are higher than 2.5A or so we should consider going the route of LM150/350 or LM138/338, but for the life of me I can't find it now. I know I read it today while browsing through the PDF's but I can't remember where! I was using my work PC at the time and i'm using my home PC now so I can't even check my IE history.

Anyhow, I too realise that the TO-3 package is vastly different to the TO-220 package, but apart from the obvious issues mounting a TO-3 with heatsink to the PCB, it is still an easy task to substitute the LM338K if it will work in the circuit.

I'll try and find the relevant PDF when i'm at work again in the morning.


EDIT: Oh bugger! I remembered where I read it, and it wasn't even a relevant PDF. It was in the datasheet from National Semiconductor! Clearly i'm getting old! Quoted below.

For applications requiring greater output current, see LM150
series (3A) and LM138 series (5A) data sheets. For the negative
complement, see LM137 series data sheet.

FURTHER EDIT: In support of my other question, here is another quote regarding the fact that the max voltage handling capabilities of the LM317 refer to the differential between the input and output voltages, and not the maximum voltage above ground that the regulator can handle -

Besides replacing fixed regulators, the LM117 is useful in a
wide variety of other applications. Since the regulator is “floating”
and sees only the input-to-output differential voltage,
supplies of several hundred volts can be regulated as long as
the maximum input to output differential is not exceeded, i.e.,
avoid short-circuiting the output.