Definition of an "old-school" SMPS

[japlytic]

Since around the early-80s (possibly even earlier), there were switching power supplies which had two 200/250V primary electrolytics which form an artificial centre-tap (with a polyester capacitor (usually 1uF+) between the aforesaid artifical centre-tap and the transformer primary), has a two NPN transistor push-pull stage, with a drive transformer (later becoming a current transformer as well) controlled witl a TL494, KA7500, IR3M02 or equivalent.
Earlier units had a auxiliary AC transformer for supplying the TL494 with its control voltage; this was later dispensed with in later units, but an auxiliary supply (with a +5VSB rail) was reintroduced only in ATX power supplies.

Now this is what I would consider an "old-school" SMPS - circuits of a few units are not hard to find.

[PeteS in CA]

Re: Definition of an "old-school" SMPS

You can add SG3524 to your list of vintage voltage mode PWMs.

Taking "old school" back a few more years, the Boschert Two-Stage:

* Buck converter followed by a self-oscillating 50% duty cycle (set by a saturable reactor) square-wave inverter; slightly newer designs used a square wave half bridge inverter;

* Switch devices were TO-3 Motorola 2N654x Switchmode series transistors (possibly 2N6308 in earlier designs?);

* A uA723 used as a controller (an internal reference, an error amplifier and a driver transistor);

* Feedback from the secondary side utilizing an optocoupler as an isolated amplifier rather than an isolated switch;

* "Current limit" for some secondary outputs was the diodes overheating and desoldering themselves from their leads.

This design was my intro to SMPSs. A week later I was introduced to self-oscillating discontinuous flybacks that used the TL431 as the reference and error amplifier; the switch transistors were TO-220 Motorola MJE1300x Switchmode series.

[eccerr0r]

Re: Definition of an "old-school" SMPS

How about 78S40 designs? This is an ancient SMPS chip...
Were there any on-line designs with this chip? I've only seen DC-DC converters with this chip...

[ben7]

Re: Definition of an "old-school" SMPS

Check out this old PSU I have

https://www.badcaps.net/forum/showthread.php?t=30458

I haven't a clue how it works, it looks much different than modern PSUs.

[pdavid]

Re: Definition of an "old-school" SMPS

I'd like to contribute to this nostalgia with some old PC XT units from '98 '92.

CHUNTEX MPS-4220. Sadly it's case and cover rusted beyond restoration, so its just the guts. It's a single transistor forward, very overbuilt for 200 Watts. Looks like the fan has it's own supply circuit. It has cool Teapo caps from prehistoric times. It works.

Temero TP-2200. Looks like half bridge to me. Has much more space then the previous one, but still decent. This one is working too.

There is a 180W Enemax too somewhere, but it's no big deal, except the very long cables. Also, some various beefy AT units.

[senz_90]

Re: Definition of an "old-school" SMPS

here we go

Ancient PC PSU found in my warehouse. I have tested it a months ago and needs a dummy load on 5V rail to fire it up. Recall it has Rubycon/Chemicon(forget) 3300uF on secondary !! Her looks nice and pretty after washing it and tested again
Forget the chip, transistor/Fet, schottky number because i don't know what i will do with her and just lay it down near the ceiling.

[senz_90]

Re: Definition of an "old-school" SMPS

CHUNTEX MPS-4220. Sadly it's case and cover rusted beyond restoration, so its just the guts. It's a single transistor forward, very overbuilt for 200 Watts. Looks like the fan has it's own supply circuit. It has cool Teapo caps from prehistoric times. It works.

Temero TP-2200. Looks like half bridge to me. Has much more space then the previous one, but still decent. This one is working too.

It looks bloody on the 1st pict, what is that has red coating??

[domas]

Re: Definition of an "old-school" SMPS

here we go

Ancient PC PSU found in my warehouse. I have tested it a months ago and needs a dummy load on 5V rail to fire it up. Recall it has Rubycon/Chemicon(forget) 3300uF on secondary !! Her looks nice and pretty after washing it and tested again
Forget the chip, transistor/Fet, schottky number because i don't know what i will do with her and just lay it down near the ceiling.

hey, that first picture of yours, it looks kind of unclear, wasn't there enough light or why it is so grey?

[senz_90]

Re: Definition of an "old-school" SMPS

hey, that first picture of yours, it looks kind of unclear, wasn't there enough light or why it is so grey?

it is a bit dusty huh?

look at last picture, I have clean it and looks sexy

[pdavid]

Re: Definition of an "old-school" SMPS

It looks bloody on the 1st pict, what is that has red coating??

I'm sure it's some kind of insulation coating. You know, I've seen this red paint stuff method in soviet electronic equipments too. Strangely that was smeared on mostly of the ics and other silicone to prevent the "enemy" to know what it is...

I'm just going to take some pics of the other ancient psus I have. Maybe we'll see some more bloody guts

[jamesbo]

Re: Definition of an "old-school" SMPS

The red "stuff" looks like Glyptal, a GE product used to fix the position on potentiometers and other adjustable controls. It was like a pigmented transformer varnish. In this case it appears to used to mask the identification of some of the components and to possibley encapsulate that coil/transformer.

[budm]

Re: Definition of an "old-school" SMPS

SENZ90, the board has brown glue problem also.

[senz_90]

Re: Definition of an "old-school" SMPS

SENZ90, the board has brown glue problem also.

I know that is a glue,didn't know made from what chemicals composition but i means what is this?

well, it look like i made mistake so we have misunderstanding because my bad english, i means about what component is there? it looks like an old caps maybe?
because it is not late yet to edit this post, i am just edit this post for reply

[budm]

Re: Definition of an "old-school" SMPS

http://www.alliedelec.com/search/pro...2#tab=overview