Power supply fail head's up

[Robindonne]

If someone finds time to explain to me(us). 
 

if you choose the battery solution from corncrake, do you advice to just use your existing powerbrick? And does the battery needs to meet a number?(amps or you name it what else) 

if you go for a crowbar, can it be build in a 60x100x30 housing, a housing just for this circuit!  And can You explain or advice what components to use when planning to implement it in a 12v 5a setup?  Or is this a question for a more electric dedicated forum?  
 

thx.  

Edited June 23, 2020 by Robindonne

[symmetal]

Rather than using a brute force approach to disable the power supply I would personably go for a more subtle approach of a separate unit on the PSU output which just cuts its output if the input voltage range exceeds preset limits. Something based on the LTC4365 or similar. With suitable mosfets the output current can then be higher than the 3A circuit shown in the examples.

There are also modules available which use a relay to disable the output like this or perhaps this which may be worth looking into. 

Switch mode PSUs normally have over-voltage protection built in. The Mean Well ones certainly do.

Alan

Edited June 23, 2020 by symmetal

[NickK]

On 21/06/2020 at 14:48, StuartJPP said:

If people knew how Switch Mode Power Supplies operate then they'd think twice about using them.

Think of a Switch Mode Power Supply as a nest full of angry wasps buzzing away, until something (anything) upsets them.

I am of course being a bit facetious, and allegedly they can be designed properly.

On the flip side, a freshly charged 12V leisure battery can deliver at most about 14V, give or take. It can deliver a lot of current, so it can melt wires and set fire to things if wired incorrectly, but it will never deliver more voltage than chemically possible.

Now if only the manufacturers would put an "idiot" diode in line with the circuit board or better yet a FET and derate the component operating voltages/currents then it would be practically impossible to blow a board up by plugging it in, except for actual component failure on that board.

 

I've recently been heavily involved in producing a 24Vdc -> 240Vdc boost converter for a valve amp. Let's ignore the topology discussion for now but - you're right that SMPS are an inherently noisy way of either stepping down or stepping up power. One or more switches are flipping anything from 50,000-1M times a second depending on design and configuration. It's the reason why the components are smaller (due to the high frequency switching). Also SMPS that plug into the mains typically convert from 240Vac to 390V before bucking down to the intended 24V or 12Vdc.

Meanwell produce good supplies - including medical. just ensure that (a) the supply is "isolated" and (b) has over/under and short curcuit protection. A lot of the meanwell also have PFC which makes them very efficient. Their 24V supplies only have around 150mV peak-to-peak for the 24V supply. There's some noise but for audio shifting the noise up in frequency is a great way to make things quieter (easier to filter).

Now to my point. It is possible to post regulate (ie using a maida regulator with an LT3080 instead of the old LM317 for example) with 1A max to 1mV ripple or below which means you're at least down to -60dBv and the supply I'm working on is around -120dBV at 240Vdc but also be efficient. That lower ripple (regardless of frequency range) means low noise for cameras - traditionally this is why APers have used linear regulated power supplies as they don't have switching noise.

I have a meanwell supply on my koi pond filter controller. I've had it blow due to water ingress but it's dependable and works. New controller box to solve the water leak and no problem since.  I'd certainly recommend meanwell supplies.

As always - careful of humidity and water ingress ;)