1 watt DC-DC power supply module reliability issues
1 watt DC-DC power supply module reliability issues
(OP)
This is my first post here but I've been involved in electronic circuit design for many decades. As part of a current design effort I take an unconditioned AC voltage, put it through a bridge and large capacitor to get maybe 9 volts, then I pass that through a linear regulator to get 5 volts, then I send that to a (typically Chinese-made) 1 watt isolated dual +/-12 volt DC-DC power converter module. (Please note I'm NOT looking for circuit design help so I'm not posting schematics or anything else that isn't relevant.) The trouble is on the (typically) second or third power cycle the device outputs will be zero and the module will be burned out, EVEN IF I HAVEN'T EVEN HOOKED UP THE OUTPUTS YET, the linear regulator (typically LD1117) is never harmed, nor is a second module across the SAME input that's generating isolated +5 for another purpose! The vendors I've identified for this type of product are aimtec, CUI, Mornsun, gaptec, Mean Well, XP and Cincon, so far I've blown out two from each of the first two vendors (I don't even have parts from all these brands, still waiting on my distributor for delivery for some of them). A representative part # (aimtec) would be AM1DS-0512DJZ. So far when I talk to any of their "support people" all I get is "what is your company name and website?" as if big customers are the only ones "entitled to" application and reliability support. It seems to me all these parts basically come out of some windowless factory in China and NONE of these vendors know anything about the product design or application! The only "clue" I have is SOME vendors say the modules OUGHT to be "protected" from "undervoltage conditions" but there isn't an actual spec at which they admit the module would self-destruct! Is there some "minimum level of product" below which it just isn't advisable nowadays to expect any level of reliability or support AT ALL? (These aren't for DOD application so I don't have an infinite budget, it's a consumer product with an extended warranty so I can't afford gold-plated stuff but it DOES have to be generally reliable.) When did the market change so that power supply modules can be so goll-darned unreliable but somehow they still meet the requirements of the market? Has anyone had the same level of frustration with this type of product, and how did you resolve it?
RE: 1 watt DC-DC power supply module reliability issues
Dan - Owner
http://www.Hi-TecDesigns.com
RE: 1 watt DC-DC power supply module reliability issues
RE: 1 watt DC-DC power supply module reliability issues
The most common failure though is for the oscillator to not start up. I think a soft supply to them causes this. I also think that that can cause burnout because unrestricted current sits there running thru only part of the switcher topography.
I suspect the problem in your case is your linear regulator. It's probably causing a soft start-up that's screwing with the DC-DCs. I bet if you switched on/off your DC-DCs after the linear they'd not fry IF there's a large bulk cap after the linear.
Keep in mind all DC-DCs have a huge startup demand. If that hammers your linear then the linear limits the inrush for a while. While it struggles to recover bad things will be happening to the DC-DCs.
Keith Cress
kcress - http://www.flaminsystems.com
RE: 1 watt DC-DC power supply module reliability issues
I have had a "largish" (47uF) cap at the linear reg output trying to kill noise and keep supply Z low. Maybe that's slowing startup.
What's "startup current" for how long and best way to meet it, I assume it can be ahead of enable FET, maybe I leave the cap in there?
Primary reason for the linear reg is the tight published spec (4.5-5.5v) for input. In the absence of other info I have to try and meet the numbers that I can see, if I don't need it it would be great to be rid of.
RE: 1 watt DC-DC power supply module reliability issues
Keith Cress
kcress - http://www.flaminsystems.com
RE: 1 watt DC-DC power supply module reliability issues
Older design, simple and cheap? Can do...
RE: 1 watt DC-DC power supply module reliability issues
Changing subjects, most of those small switchers have minimum load requirements that need to be provided. Most all designs with them I've done have needed passive loading added to meet the spec. Particularly watch the negative rail because with a +/-12V unit you frequently load the + side easily but the negative side often just negatively biases some opamp or something else light. Add resistors where needed to meet the minimums.
Keith Cress
kcress - http://www.flaminsystems.com
RE: 1 watt DC-DC power supply module reliability issues
So I spent a little while researching part #'s and data sheets. It turns out several of the vendors that I guess I wasn't looking at very hard because I didn't know them too well (XP Power, Delta, Recom, Murata, Traco) are actually quoting 3 year warranties (some of them anyway) and MIL-HDBK-217 reliability hours. And parts from these vendors are available at prices that are quite competitive with some of the ones that I had been considering (well if you can get them at all, this is all quite relative, even power converter modules are in short supply these days). And it's weird, you've got some distributors supplying low-quality parts at high markups out of one group of vendors, and a different group of distributors supplying much higher reliability at lower markups from a different group for the customers actually building something for sale. Or that's how it seems anyway! Now this doesn't mean the reliable parts don't have a turn-on surge, but it does seem like a better field to go hunting in, and they SHOULDN'T self-destruct quite as easily if they're supporting a 3 year warranty!
RE: 1 watt DC-DC power supply module reliability issues
RE: 1 watt DC-DC power supply module reliability issues
RE: 1 watt DC-DC power supply module reliability issues
If your 9V source can meet the minimum input voltage of the boost converter under these demands often reserved for batteries, that should be your source. But beware supply regulation specs must be observed and recognize there may be compromises and it may still fail.
Otherwise you are making a self destructing oscillator without sufficient awareness of requirements.
RE: 1 watt DC-DC power supply module reliability issues