EEVblog #440 - Atten PPS3205T-3S Triple Output Power Supply Teardown

Inside the Atten PPS3205T-3S 3 output precision laboratory bench power supply.

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[ChipGuy]

Double thumbs up for shooting that teardown twice. Thanks for the effort.

[uvxecqy]

Its good to know I am not the only person who has to do complex operations twice. Thanks for the vent...makes me feel better.

[ForViewingOnly]

Excellent video Dave, I learned a lot. Thanks. You recovered from the camera disaster pretty quickly... sign of a true pro.

[Doompro]

Remember, copper traces (or wire even) has resistance and inductance, so if you chain the grounding, then all the components connected to it will get different impedance's and inductance's to ground.

The difference between one component's ground and another might be several hundred mV, and the inductance causing ground oscillations (ringing).

If you connect them all at a common point (aka a star, with leads radiating outward) then it is almost guaranteed they are all seeing the same ground!

[juliusski]

Nice review, just as a tip: you could try to short thermostat contacts to see what happens once heatsink(s) reach 80C point.

[riakata]

Good enough depends on the application. SMPS are good enough for basically everything even digital oscilloscopes use SMPS and onboard DC-DC regulators without issue. But if you want to test something without needing to worry about your PSU being good enough for something then a precision linear supply is pretty much as good as you can get normally. You want to test things one at a time not all at once in a lab setting.

Wall adaptors are almost all SMPS due to modern energy efficiency standards.

[nemanjatodorovic]

Looks like a decent power supply for the money! Solder is a little home-made but it's cheaper than the others, survived a shorts, no overshots and is quite precise what is most important! I did not expect this much!

[Paarrad]

I wanted to ask at #439 why you turn it on before you take it apart. Tadaaa... there is the teardown. Thumbs up.

[riakata]

I think the linear regulator will help with noise to a degree but linear regulator's ripple rejection rating is frequency dependent. So while you will reject the LF ripple, higher frequency noise (the switching noise) will still get through the regulator and depending on your application this can be undesirable.

I think you can make a ultra-low noise SMPS supply it will just require a lot of filtering, post-regulators, better components, cost ... (And then making it adjustable and stable)

[aptsys]

Dave, the relay on the serial board switches the RS232 RX/TX lines between the FT232 and the MAX202. The FT232 has an output which in this case is used to drive the relay when a USB cable has been connected to a host

[CalenCarabajal]

I'm pissed for ya too, Dave. I can only imagine how much damn time it takes to shoot these. Still, vastly helpful videos so we appreciate all your hard work. Thanks, mate!

[HamishMilne]

Linear supplies have a much better noise characteristic than switch-mode stuff.

[TheExtremeXS]

Great job on the reshoot - thanks for all the extra effort! Must of been very frustrating.

[donpalmera]

>where good coders can squeeze out enough
>performance gains to make it worthwhile

I doubt the many people bother optimising standard code with inline assembly these days.. anything that could be optimised should already be optimised in your toolchain. You might see it in places where special processor features like SIMD are used but even GCC can do automatic vectorisation. With your "byte swap" example I would actually check the code GCC generates. You would be surprised at how much GCC does.

[superdau]

I had problems with several SMPSs when the load is pulsed/oscillating (e. g. PW modulating LEDs/motors).
The PSUs weren't even close to their theoretical limits (e. g. drawing 100W from a 500W PSU), but using PWM on 100Watts worth of LEDs totally freaked them out. And that example was with a dedicated 24V/20A SMPS and not an "abused" PC-PSU.
Same setup with a "simple" linear 200W PSU: no problems at all.

[riakata]

SMPS won't have the low noise a linear supply has. If you have something critical that is sensitive to noise you don't want a SMPS. Plus normally SMPS are used to power digital circuits which don't care as much and you can just use a PC power supply and get upto 1500W of "clean" power.

[riakata]

It might actually be to make it have a slow response. The part is rated to a maximum junction operating temperature of 150C so there is likely still some margin of safety. If they put it above the transistor it would have to use a higher temperature cut off. Ideally you would have those directly shutting down the supply relays and a temperature sensor monitoring it actively to do fan regulation and have a soft-cutoff for redundancy.

You can also just get power transistors with thermal limiting

[wesz]

I used to be  a lead technician on a electronic manufacturing line for over 10 years and I've seen soldering messes like what you show in your videos. One thing that made this seem to me to be more of an isolated case is that you had other boards in the PS which showed decent soldering. I've seen every cause of soldering problem issues from dunking boards in the WAVE solder to just a little chatter on the guides shaking components out of the pre-paste. All those defective cards get put aside and eventually wind up in a re-work and then it can be" solder sucker to the rescue" scenarios. I've seen the "tale-tale" signs of these defective cards in your videos,  they had whisps and slivers of hair fine solder on the boards and also solder balls. So I think these cards were re-worked and were just not cleaned properly after the re-work. That left-over solder on the surface is just an accident waiting to happen. Over time, heating/cooling/vibration can dislodge those hair-fine solder strings and they can short out between component leads, etc.
I agree with you, it was a pretty crummy job of quality control on that soldering, I can understand why it is that way, however it is unacceptable. My point is that I feel the soldering is more of an isolated case and not respective of the continued over-all process. But I've seen stuff like this get thru and with all the manufacturing quality control safeguards, it only takes one person out of hundreds not doing their job for something like this to slip thru.

[riakata]

If the power supplies are designed to be floating then you need isolation from the building ground referenced (earth) circuits or you'll tie the floating circuit's reference ground to building ground which isn't desirable in many applications.

Another big reason to have opto-isolation is for protection in case something horrible happens in the isolated section, the isolator has high withstand ratings and will protect you/other circuits/parts from damage.

[timramich]

Is that cap going to get that hot? That part of the heat sink should be pretty cool because it's getting fresh air, and the cap itself should also have some airflow over it.