Psu Multi Voltages And Doubt About

[ct.waveform]

I saw 25V AC on the schematic, so assumed that became a 40V rail, or near enough.

 

[ct.waveform]

I saw 25V AC on the schematic, so assumed that became a 40V rail, or near enough.

Actually I had a little bit of a brain fart there and should have said 35V if I'd been thinking straight. I use rails a bit above 40V generally and was thinking that 25V was the next step down, but it's actually 28V that most people use.

 

[Newmarket]

Actually I had a little bit of a brain fart there and should have said 35V if I'd been thinking straight. I use rails a bit above 40V generally and was thinking that 25V was the next step down, but it's actually 28V that most people use.

Bit less due to the drop across rectifier bridge diodes.

 

[ct.waveform]

Bit less due to the drop across rectifier bridge diodes.

Obviously. But the bit I was embarassed about was not having 25 x sqrt(2) being ~35V - which is kinda engrained into all of us. LOL.

 

[Matt Syson]

There is often quite a bit less (or more) when you consider the rectifier, winding impedance and for manufacturers the need to be able to cope with EXPECTED tolerances of (nowadays) Plus 6% high and minus 10% low mains which goes a long way towards explaining why linear supplies are so inefficient (then add in the peak charging currents of the rectifier/capacitors and attendant poor power factor).
The LM338K (steel can) devices at arould a hundred Euros these days was a great part to use. Somehow the plastic version does not fill me with confidence that they really don't expode when faced with the same loads that the K versions are happy with. Getting the hear out of a plastic casing/tab is not so easy (although it looks like it might be) A manufacturer I worked for changed from 2N3055 in TO3 cans to the (new at the time) plastic 'wonder devices and they would burst on occasions thus requiring a doubling up to get back to what a '3055 was happy with. There is a good reason why commecial power supply makers (Coutant/advance/international Power etc) only ask the pass transistors to handle only 2 or 3 Amps even though they are nominal 15 Amp devices. one place where multiple cheap 'old school' devices really come into their own.

 

[ct.waveform]

There is often quite a bit less (or more) when you consider the rectifier, winding impedance and for manufacturers the need to be able to cope with EXPECTED tolerances of (nowadays) Plus 6% high and minus 10% low mains which goes a long way towards explaining why linear supplies are so inefficient (then add in the peak charging currents of the rectifier/capacitors and attendant poor power factor).
The LM338K (steel can) devices at arould a hundred Euros these days was a great part to use. Somehow the plastic version does not fill me with confidence that they really don't expode when faced with the same loads that the K versions are happy with. Getting the hear out of a plastic casing/tab is not so easy (although it looks like it might be) A manufacturer I worked for changed from 2N3055 in TO3 cans to the (new at the time) plastic 'wonder devices and they would burst on occasions thus requiring a doubling up to get back to what a '3055 was happy with. There is a good reason why commecial power supply makers (Coutant/advance/international Power etc) only ask the pass transistors to handle only 2 or 3 Amps even though they are nominal 15 Amp devices. one place where multiple cheap 'old school' devices really come into their own.

Eu100! That's quite a price! I'm a committed scavenger so those are going on my list! The TO-220 LM338T isn't completely insulated but I can't say I've ever really pushed one (except perhaps on a battery charger I once knocked up) but it might be reassuring that I've never blown one up. Of course you can always wrap a PNP around them, or even a CFP, if you want another current path.

It's a real shame that so many of the larger format parts are disappearing (or have gone). MT-200s came and went quickly and, along with all the low noise and precision parts, they seem to be going for anything else with any bulk, too. Funnily enough I was looking at the price of copper sheet just the other day, in the hope of mimicking what the MT200s did, and it really doesn't look a cheap option any more. Cost wise, it's somewhere either side of evens but a bigger transistor is a lot less hassle.

 

[r2d2]

Had a bit of time to check another piece of the psu and"expand" the scheme ,
to place here for opinions about always welcome,
thanks

 

[Newmarket]

Just to mention that mains (EU / UK) is -6/+10 % as stated other way round earlier in thread.

 

[Holger]

Eu100! That's quite a price!

Digikey sells them for 75€ actually. IIRC I've purchased 4 for 20€ two years ago...

 

[Rob Flinn]

Had a bit of time to check another piece of the psu and"expand" the scheme ,
to place here for opinions about always welcome,
thanks

If you only have a requirement for 1.5A from the +&-18v part of your psu as your drawing suggests by using the LM317 then personally I would just use an LM317/337 pair. You can get some pretty cheap pcb's from ebay that work with these regulators & provide quite a neat solution. It's only really when the current required is a few amps that I use the stacked psu's method, because it's difficult to find negative regulators that will do more than about 1.5A.

 

[r2d2]

If you only have a requirement for 1.5A from the +&-18v part of your psu as your drawing suggests by using the LM317 then personally I would just use an LM317/337 pair. You can get some pretty cheap pcb's from ebay that work with these regulators & provide quite a neat solution.

Much thanks for the post !
In fact, in the various schemes and pcb kits, found here and around the net
are all with the "concept":
"317" for the positive, "337" for the negative ,
(and "783" for +48v)
because the most reliable and time-tested ?

It's only really when the current required is a few amps that I use the stacked psu's method, because it's difficult to find negative regulators that will do more than about 1.5A.

reason why for large consoles the psu are multiple and divided in ch strips sections ?

another "thing" as from the "draft" scheme above
is the ground "configuration",
psu pcbs have not connected to main ground,
only the rack chassis,
more thanks !

 

[Rob Flinn]

Much thanks for the post !
In fact, in the various schemes and pcb kits, found here and around the net
are all with the "concept":
"317" for the positive, "337" for the negative ,
(and "783" for +48v)
because the most reliable and time-tested ?

One reason maybe because you can use a centre tapped transformer rather than having to have 2 isolated secondaries.