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LM338K equivalent?

D

Dan K

pfm Member
Is there a better/ more modern equivalent that's not in the TO-3 package?

I'm thinking of building a regulated PSU for a Class A amp.

Looking for something that has 3 legs and can easily bolt to a heatsink with a single screw.

Thanks :)
 
Righty-o.

I think the only issue you may run into, will be dissipation in the regs as above.
The easiest way to halve that, would be to use a pair of regs for each amp channel, so that the standing current through each of them is only that of one half of one channel. These could all share the same raw +/- transformer rectifier and say 22Kuf reservoir DC supply of course. Just add at least 100uF from each reg input pin to the reg 0v output as a local bypass to ensure stability and best performance.

As you say - nice and simple as a clean supply. Also it adds current-limiting, too.
 
That shouldn't be necessary. Drop out of 1.5V max and will be lower at the current used here. Use big smoothing caps in a C-R-C arrangement to give low ripple into reg and then make some allowance for low mains voltage. It should be possible to get dissipation down to no more than 5W tops.

LT1084 or LM1084-ADJ are 5A and much easier to get than the 7.5A version.
 
DoctorRad said:
Where would you look to get them from at the moment?
Click to expand...

Try the usual sources.... I looked yesterday and RS and/or Farnell had them. IIRC one of them had only 20 left...
I couldn't find the 7.5A version but didn't spend much time searching less orthodox sources (If something is only available from ebay I consider it unavailable. I won't buy components from ebay. Period.)
 
gingermrkettle said:
Even from people like Nikko who are not exactly fly by night operators?
Click to expand...

For me, yes. Obviously I was referring to private sales and "never heard of 'em" shops but personally if a business shuts down its website and ordering telephone number etc and sells only on ebay I will not deal with them any further. A small number of companies have done just this...

I'll redesign circuitry to not need the unobtainium part where possible.
 
I've bought quite a bit of 'bits-n-bobs' stuff off eBay without any real problems as it's useful for small order values / small qtys.
If you are a business offering guarantees on work it's a different matter though.
A nice place for the hobbyist is bitsbox: Bitsbox Electronic Components, Electronic Component Suppliers UK
Decent prices, decent range and reasonable postage costs for hobby work. No personal affiliation.
Switch electronics is very similar; Electronic Components Supplier | Switch Electronics
 
My next stupid question is: How many volts will I have to loose across the reg (LT1083) and still get the full performance?

It's either going to be 0.5V or 3V depending on the traffo that I use (9V vs 11V secondary). Using a pair of 'Prasi' active rectifiers with 0.2V drop

Looks like I'll need a drop out voltage of 1.5V, but perhaps it will function perfectly with less, or maybe 3V will cause too much heat and I'll have to put a CR in front and loose another 1.3V or so across a 4R7 (more cost/complicated)
 
Dan K said:
My next stupid question is: How many volts will I have to loose across the reg (LT1083) and still get the full performance?

It's either going to be 0.5V or 3V depending on the traffo that I use (9V vs 11V secondary). Using a pair of 'Prasi' active rectifiers with 0.2V drop
Click to expand...

As I said above about 1 to 1.5V but you may want to allow a little more for mains voltage being low at times. The really important thing is that you have enough smoothing before the regulator.
 
Arkless Electronics said:
As I said above about 1 to 1.5V but you may want to allow a little more for mains voltage being low at times. The really important thing is that you have enough smoothing before the regulator.
Click to expand...

Yep, I just added a line to my question about that.

0.5V won't do it and 3V looks like too much

Intention was to use a pair of 16V 33,000uF Samwha FC. They seem to me to be quite comparable to Kendeils, but generally at different voltages and cheaper
 
Dan K said:
If using a CRC I can see how it would be done on the +ve rail (with the 1083), but will that work on the negative? I was simply going to follow the below PSU, but with a single cap on each side.

https://www.flickr.com/photos/kleenair/27558285865
Click to expand...

It's exactly the same on the neg rail. That's one of the least of your problems. Alarm bells should have gone off when you mentioned Le Monstre but as there had been recent discussion of single rail amps lately...

OK there is no negative version of these regulators and although it can be bodged to give a neg supply I would forget the whole idea and use LM317 and LM337 with series pass transistors etc as the simplest way. Not low drop out though so will run hotter and prob need higher voltage mains TX. There are suitable designs in app notes.
 
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