230AC to 24DC Linear Power Supply - No sink, no nothing

Thread Starter

StrongPenguin

Joined Jun 9, 2018
253
I was trying to see if I could fix this linear power supply, and lo and behold, my multimeter probes slipped causing it to short "totally".

The top red circle is where the mains come in, and at the bottom red circle, they convert to 24DC (or so, didn't really get a decent measure..)

Now how in the world does it go from 230 AC to 24V DC through that little IC, and without a sink? The numbers in the chip are too damaged to read anything, all I can see is a sine wave on the left side and a +/- on the right.

This circuit looks overly complicated, too, with all these IC's and tiny transistors. Could someone give a shot in the dark as to how it works, just overall? Like what is the large inductor for, and what is the large cap for. Maybe someone has experience with this.

I was going to repair this, until I broke it. Now I wan't to make something that just does the job in a good-enough manner. Just for fun, I guess.

This LPS is feeding a CCTV station, I don't know anything about amp usage, sadly.
 

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garce

Joined Apr 10, 2017
1
Hello, this a switching power supply. Thats how you get away with no heat sinking, the efficiency of the high frequency switcher has low losses, therefore requires little or no heat sink.

The AC is first full wave rectified and filtered by the large electrolithic cap (probably rated 400VDC or more) before it is converted again to AC at high frequency and fed to the transformer primary. The secondary of the transformer is again rectified and filtered to generate the 24VDC. There is an optical isolator IC that is used to provide feeback between the low and high side to regulated for 24VDC
 
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djsfantasi

Joined Apr 11, 2010
6,787
A linear power supply uses a large transformer and a regulator to drop the voltage.

Whereas a switching power supply switches the input off and on rapidly, so that the average output is much lower. If a source is switched on for only 10% if the time, the output will only be 10% of the input.

Roughly

That’s why you don’t need as powerful components, in general.
 

MisterBill2

Joined Jan 23, 2018
6,989
I was trying to see if I could fix this linear power supply, and lo and behold, my multimeter probes slipped causing it to short "totally".

The top red circle is where the mains come in, and at the bottom red circle, they convert to 24DC (or so, didn't really get a decent measure..)

Now how in the world does it go from 230 AC to 24V DC through that little IC, and without a sink? The numbers in the chip are too damaged to read anything, all I can see is a sine wave on the left side and a +/- on the right.

This circuit looks overly complicated, too, with all these IC's and tiny transistors. Could someone give a shot in the dark as to how it works, just overall? Like what is the large inductor for, and what is the large cap for. Maybe someone has experience with this.

I was going to repair this, until I broke it. Now I wan't to make something that just does the job in a good-enough manner. Just for fun, I guess.

This LPS is feeding a CCTV station, I don't know anything about amp usage, sadly.
That "little IC" probably used to be a bridge rectifier. And why do you think that it is a linear power supply, and not a switch-mode supply? And what was the problem that you were hoping to fix? The component beneath that large white tag is probably the inductor. And the supply voltage being listed as 100 to 240 volts tells me that it is absolutely a switching mode supply. THAT is why it is so complicated. Even if you had the parts needed for the repair in hand, it would be a very big challenge to even unsolder the failed component and install the replacement.
With a failed switch mode supply that has had another component destroyed by a random short circuit I recommend replacing it, and learning about the dangers of probing items free to move when touched.
CONDOR brand supplies are still available, and with the number on the tag you should be able to find the specifications for a replacement. And with a really good magnifier you may even be able to see an output voltage next to the terminal strip. Otherwise you will need to investigate the information on whatever it used to power to see what the voltage and current requirements may be.
 
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Thread Starter

StrongPenguin

Joined Jun 9, 2018
253
@Alec_t Because I googled a number I found on the supply, which led me to a bunch of PSU's from the company, all of them listed as Linear. I've ordered a bridge rectifier. It's just that I thought when I measured it, that the output voltage was way lower than the input.

@garce Sounds like an inverter, sorta. I just assumed a SMPS had no transformer, never. Like this one. What is the purpose of going back to AC?

@djsfantasi Like PWM? I just don't see where the MCU is that controls all of this. Well, you could probably get a "all in one" chip to do the trick, I guess.

@schmitt trigger Yes, I've ordered a set from Ebay. Going to try that. But I was also thinking about building a new one, my "own design", just for practice and experience.

@MisterBill2 You are probably right, but me buying some supply does not teach me a whole lot, other than buying a supply. The device comes from the ship I am on. It was thrown away, but it costs like 3000$, so if I could fix it for a few bucks, that would be epic.

Does anyone know what the black box in the top left corner is?
 

MisterBill2

Joined Jan 23, 2018
6,989
That device still looks like a switching power supply, and you will not find a linear power supply that has that wide an input voltage range without some sort of switch for the different ranges. And the $3000 price must have included the CCTV station, because that is much to small a package to sell for that much.
As for that black box in the corner, it probably has a designation on the PCB that we can't see because of the camera angle. My guess is that it is a transformer. It is a surface mount part, with a heavy heat shrink cover.
There is some text next to it that is obscured by the shadow. And on the bottom of the PCB is another company name along with an assembly number. So it was not made by Condor.
 
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Delta prime

Joined Nov 15, 2019
484
googling the PCB came up with SL Power electronics open frame switch mode power supply. They have schematics what they don't have is hot air .download9.jpg
 
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Thread Starter

StrongPenguin

Joined Jun 9, 2018
253
I had no idea they made trafo's so small. Oh well, I've ordered a bunch of parts, going to try and build a crude one myself. I can always find a spot for the CCTV controller on the spareparts shelf. Just in case.
 

MisterBill2

Joined Jan 23, 2018
6,989
Worst case you can build a linear regulated power supply and get the system playing, and probably nobody will realize that you did not duplicate the original supply. My success with repairing switchmode supplies has not been good, mostly because of never having a circuit and never having a source for the failed parts. Usually the failed part has been a custom IC or unmarked semiconductor device.
It may make a lot of sense to first verify that the rest of that system is still working. On occasion failures cascade from one area to another.
 

MaxHeadRoom

Joined Jul 18, 2013
21,387
My success with repairing switchmode supplies has not been good, mostly because of never having a circuit and never having a source for the failed parts. Usually the failed part has been a custom IC or unmarked semiconductor device.
Just One of the reasons I never use them (SMPS) if at all possible. :p
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
21,387
They are smaller, lighter, and often cheaper, and a lot more efficient. And best of all, mostly they are regulated. The small cheap transformer supplies are seldom regulated.
Tell that to a customer with an assembly line down waiting for a replacement!
I would rather pay a little more and keep him happy!
Max.
 

MisterBill2

Joined Jan 23, 2018
6,989
The last time I had to deal with a customer who had a line down and needed a replacement, the purchasing folks at that company, a small division of Delphi, refused to buy an in-stock substitute of better quality. So the customer went a week with one machine not working doing tests. I left that company because I can not stand that level of stupidity.


And in many applications any suitable replacement can work. I always tried to use components with multiple suppliers.
 

MaxHeadRoom

Joined Jul 18, 2013
21,387
The time taken to obtain a replacement could be a problem for most customers.
The linear ones I put together, mostly toroidal transformer are easily customizable, I don't really recall a call back due to a failure, but if there was, the inventory of parts I carried would often carry the day if necessary.
Max.
 

MisterBill2

Joined Jan 23, 2018
6,989
This may help your understanding.
https://www.learnabout-electronics.org/PSU/psu30.php
And another thing, Please be very careful when playing around with the mains driven switch mod supplies. (At least, use a mains isolation transformed to make it a little safer.)
They are pretty dangerous!
Indeed, one section of all mains fed switching power supply is at both mains voltage and the rectified filtered mains voltage, and so it does offer a whole lot of quite unsafe high voltages. That section includes the feedback controlled drivers for the higher frequency feed to the power transformer. Since that transformer operates at a much higher frequency, often over one megahertz, it can be much smaller and lighter. The downside is that many of those components on the primary side of the transformer are rather highly stressed. Thus there are failures that are not obvious to the eye, or even to simple testing. If you read some of the publications about designing switching power supplies it will become clear that the actual design process is far more difficult than for an analog-linear regulated supply. They are indeed a lot more efficient, and so they generate much less heat, with the result that the components get packed much tighter. All of this makes the tolerances of replacement parts tighter, and the parts themselves more challenging to obtain and replace.
 
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