LM723 adjustable bench PSU not working

[Th3_uN1Qu3]

Re: LM723 adjustable bench PSU not working

Would definitely like to get the DC-DC supply STJ linked to....not terribly expensive and looks fairly professional....stick an UPS transformer on it and I'd have myself a decent PSU. Some of my colleagues order stuff from Ebay and Aliexpress all the friggin' time, albeit very cheap stuff, like miscellaneous tablet and phone components, so I'm not sure at what value customs tax is added...or VAT...or some stuff like that...anyway SOMETHING extra is added if the parcel's value is higher than X. Will have to do some research. If this thing costs 36 dollars, I don't know if that's the final price I'll actually pay or I'll also pay a tax twice that, at which point it's probably not worth it...:|

You won't pay VAT for $36. It's $50+ items that may give you grief, but not all the time - it depends how the seller marks the package... I have had to pay VAT a grand total of ONE time, for a stick of 8GB DDR3, back in the day when they were super expensive over here. And i've ordered higher value items than that and got away without tax.

Even if you would have to pay, for that value it would be like $8 so don't worry. Still cheaper than grabbing such a module from a local distributor - where'd you think they get them from?

[redwire]

Re: LM723 adjustable bench PSU not working

If it's a "kit" or PCB and not a finished product, it is perceived as no threat to local manufacturers, and there is no need for any regulatory approvals- it is a part not a complete assembly.

I make a PSU to learn and master it. Using chinese boards is always a hassle because of fake specs and cheap components. So it seems quicker to buy it off eBay but more time troubleshooting the cheap undersized capacitors, or cooling things etc.
So far every one I've bought needs major design rework.

[eccerr0r]

Re: LM723 adjustable bench PSU not working

Actually no. Countries like china put an import tax on everything and dont tax exports. USA makes it complicated and puts it on some things and not others...

It's a compromise.

[stj]

Re: LM723 adjustable bench PSU not working

that whole "finished" vs "unfinished" is pure u.s. bullshit - the rest of the world has no such rules.

it was probably created so u.s. company's could make everything in asia, then ship it in "unfinished" and finish it by sticking a "product of u.s.a." label on it!!!!

just like u.s. goods being taxed on the production line even if they are for export.
i wont mess with words here, the u.s. is under economic attack/sabotage from within by these treasonous rules.
and i fully understand if people try to find workarounds.

trump needs to fix this shit if he wants to create jobs.
you dont fucking tax company's for making stuff!!!!!

[eccerr0r]

Re: LM723 adjustable bench PSU not working

Sometimes I wonder, the chinese selling unfinished stuff which are "virtually" finished to other countries as "parts" ... because the whole unit if it were "finished" has a tax on it and could not sell as many due to higher price.

I know this happened to laser diodes, not because it was a trade protection tax but rather FDA approval because unprotected high powered laser pointers are illegal in the US, but if you buy the parts to make a high power laser pointer, that's your prerogative. Except that the high power laser diode can easily be incorporated into a design and you still can fry your eyes with it...

Oh well, yeah this is off topic, alas I see all this 'dumping' going on and people snapping them up...

[Dannyx]

Re: LM723 adjustable bench PSU not working

Would definitely like to get the DC-DC supply STJ linked to....not terribly expensive and looks fairly professional....stick an UPS transformer on it and I'd have myself a decent PSU. Some of my colleagues order stuff from Ebay and Aliexpress all the friggin' time, albeit very cheap stuff, like miscellaneous tablet and phone components, so I'm not sure at what value customs tax is added...or VAT...or some stuff like that...anyway SOMETHING extra is added if the parcel's value is higher than X. Will have to do some research. If this thing costs 36 dollars, I don't know if that's the final price I'll actually pay or I'll also pay a tax twice that, at which point it's probably not worth it...:|

[Th3_uN1Qu3]

Re: LM723 adjustable bench PSU not working

I have seen a lot of popular youtubers ordering from there. It is at least as trustable as AliExpress.

[sam_sam_sam]

Re: LM723 adjustable bench PSU not working

www.banggood.com

How good is Banggood about getting the stuff that you order can you trust there site

[Dannyx]

Re: LM723 adjustable bench PSU not working

The one you linked to looks interesting as heck - would like to have a go on it and it's DEFINITELY beyond anything I'd be able to design I've seen things like that before around here also, though less fancy. Of course, I could just buy a pre-made circuit like that, but to me half the fun is building stuff...or at least TRYING to I'll definitely keep it as an option though. Cheers.

[stj]

Re: LM723 adjustable bench PSU not working

black boxes matter!
so do translucent ones with leds inside - all from china!

[eccerr0r]

Re: LM723 adjustable bench PSU not working

It can also be said... know your tools... instead of having a black box.

[stj]

Re: LM723 adjustable bench PSU not working

it works - spend your time making stuff, not the tools to make stuff

[eccerr0r]

Re: LM723 adjustable bench PSU not working

Yep that seems about sums it up, no more design needed, just wire up top level stuff and make things that are just like everyone else's ...

[stj]

Re: LM723 adjustable bench PSU not working

no, you supply the dc, it does the rest.
so your transformer + rectifier & cap.(or a laptop supply??)
then a module with the apropriate max current.
they do make ones that have boost converters btw.

[eccerr0r]

Re: LM723 adjustable bench PSU not working

no, I think he meant don't bother designing a wasteful linear design and depend on the chinese to get a switching solution without needing to do anything...

[Dannyx]

Re: LM723 adjustable bench PSU not working

just use a module.
this is the top one, but there is a table of versions on the page.

https://www.banggood.com/DP50V15A-DP...p-1072236.html

I feel like something's missing in your post...you mean like a step-down module or buck converter or whatever ? If so, I think there should be a link in there

[stj]

Re: LM723 adjustable bench PSU not working

just use a module.
this is the top one, but there is a table of versions on the page.

https://www.banggood.com/DP50V15A-DP...p-1072236.html

[Dannyx]

Re: LM723 adjustable bench PSU not working

Really quick, here are some shots of the transformer I'm planning to use...not terribly huge, but still "beefy". Scale is CM (duuh)

[Dannyx]

Re: LM723 adjustable bench PSU not working

Mine starts to reek of burnt stuff when I leave it on under high load also The 2n3055 burnt out A LOT in the past (I believe this is the third one I swap in), so to stop that from happening (or at least delay the unavoidable) I added a CPU heatsink with a fan to it. The thing that last failed now was the transformer itself: small and undersized and got extremely hot...took almost an hour to cool down enough to touch it. The rectifier hasn't failed so far and it also looks pretty beefy. It's not 4 diodes, it's a proper single-piece (don't know how you call those) part and looks like something I scavenged from TV PSUs.

[Th3_uN1Qu3]

Re: LM723 adjustable bench PSU not working

I have a 2A one at work. The weak point in it is the bridge rectifier. When it died i found that it had been swapped by someone else before me.

The one i put in isn't quite optimal either, but it has been holding up so far (about 8 months IIRC). But the Chinese 2N3055 at the back runs pretty hot too. When it's been continuously running at over 1A for more than 1 hour it starts smelling funky.

A UPS transformer as the base for a lab power supply should make for a pretty solid setup if you size the other components adequately as well. The LM723 is very old tech (think 1980s) but it is simple and straightforward to use.