Topic: ZTEX USB-FPGA Modules 1.15x and 1.15y: 215 and 860 MH/s FPGA Boards - page 45. (Read 182450 times)

For those in the US, these might be a good choice.  Maybe even outside the US with an appropriate adapter, not sure about shipping $$.  They're cheap and well regulated, mainly meant for powering arduino-type projects.  Both are $5.95 USD with low volume discounts.

I'm not sure of the current requirements, these are rated about 600-650mA  I'm not sure if that's measured at 9/12V DC or 110/220V AC - I'd assume the measurement is AC since 0.6A @ 12V is very little power.  I could be wrong, someone should correct me who knows better.

9V @ 650mA - http://www.sparkfun.com/products/298

12V @ 600mA - http://www.sparkfun.com/products/9442


The SparkFun guys are a great bunch, I've gotten lots of hobby supplies from them.

If you search on ebay, you may also come to this 12 vdc power supply. Same as I used.

You may also add to your wiki : "Manufacturer now warns that this boards have absolutely no protection, so any problem with power supply will fry the boards themselves, with no recourse or warranty at all".

Thanks.

I reworked the Power supply selection guide again.

I think if I write "The peak voltage of the power supply must be less than 16 V (absolute maximum: 18 V) and the minimum voltage must be at least 4.5V" and "Power supplies from unused consumer electronics, e.g. routers, switches" are "Possible sources of supply" it should be clear, that a 20V(-peak) PSU from a router is a bad choice.

Furthermore I wrote, that switching supplies are always regulated. I.e. if one wants to be absolutely sure, one purchases a "12V switching power supply" e.g. from Ebay

I suppose this one has no switchable output voltage.

If the voltage is switchable the power supply needs voltage regulators.

This is the way of future customer losses. I think you should only advice PC power supplies with your boards.

"Universal power supplies (the ones with switchable output voltage) from the supermarket or electronic stores. These supplies should be stabilzed since they have to work with a wide range of consumer electronics" - one of the worst PSUs I ever had was the universal transformator-based 1A supply from the supermarket :)

A Power supply selection guide which should help to find a suitable power supply has been added to the Wiki. (A link to this description is also the Products page.)

I really believe a customer should use a reasonably good power supply on boards that cost 500 bucks each..  I also believe a customer should be directed to a safe solution when they ask, not a cheap one.  I never try to break my customers' banks, but I also suggest they spend money when it makes sense to do so.

As DeathAndTaxes mentioned, the real cost of "Protection" isn't in the manufacture of the board (their bucks) but in Watts (customer's bucks).  "Protection" can be as simple as
a diode that prevents reverse bias (3 cents)..

or get more involved, and use
a zener clamp diode (19 cents) http://www.mouser.com/ProductDetail/Vishay-Semiconductors/BZG03C16-TR/?qs=sGAEpiMZZMstCHp3EWKGl1tP683WM1O433kxgBzanSM%3d
and optionally
a PTC (40 cents) http://www.mouser.com/ProductDetail/Littelfuse/2920L200DR/?qs=sGAEpiMZZMu7EFbsM1w0nTP0ee3bziE2pcZdmj40k18%3d

So leaving it off isn't to save money, it's to save power (increase efficiency).

Now, there is a way to add protection without really costing power, and that is to use just the zener accross the power input with a PTC (no reverse protection diode).  Interestingly, because of the way a zener works, it will still protect against reverse bias (kind of.. You can still get about -0.6V before the protection kicks in.  Some circuits can survive that, some can't.) but it won't be inline burning power and creating heat.  That may be a smart thing to add, if in fact the circuit can survive -0.6V (or be made to survive it relatively easily)...

Either way, MOST "boards" that you buy do not have protection.  Motherboards?  nope.  Video cards?  nope.  Home Routers and switches?  nope.  DVD Players and Xboxes?  nope.  I'm actually a bit hard pressed to think of something you might regularly buy that IS protected from over voltage and/or reverse bias... having a hard time..
The manufacturers of these products expect that their customers will use an appropriate power supply, and therefor do not need protection.  The caveat, of course, is that in most cases the manufacturer provides the power supply that the customer should use...

Another possible reason - bad grid power (unexpected peaks or unusually high voltage for some time).
Less dangerous for switching supplies, but worse for transformer-based, non regulated ones.

I would not call "very efficient" to a board that will blow itself at the slight failure on the power side.
In my case, overall "efficiency" was 0%. You also will need to invest more in better power supplies.

I prefer a couple of more watts to be wasted instead, and sleep well for having a proper protection.
Maybe the competition manufacturers are doing that already ?

Nice summary.  The important part of "protection" isn't the capital cost it is the never ending energy drain associated with it.  This board is very efficient and that actually makes any protection even more expensive on a percentile basis.

Do you really believe that an average customer should know about peaks, RMS, oscilloscopes and sine waves ?

For sure I'd picked a lower output power supply if manufacturer told me "hey, customer, beware that our boards have no overvoltage protection at all, because we care about our bucks but not about yours, so be very very careful about that".

I'd put a 5v one, to be safe. But you see the email above, it says "supermarket" power supply.
 

I won't agree or disagree with that statement - here's what I will say..
  If that power supply is putting out a peak of less than 18 volts (I'm not talking the average of 14.5 that you Hioki is displaying) than it DID NOT hurt the board.  Something else did.  You?  Maybe.  ZTEX? Maybe.  Shipping? Maybe.

There is no way for you to know what the peak voltage of that supply is without an oscilloscope.  Your Hioki is either an RMS or Averaging meter.  A noisy supply that peaks at 19.5 but troughs at 9.5 will be displayed as 14.5 on an averaging meter.  Similar results for an RMS meter..

Rundown:
     Is the ztex board poorly designed?  No, not in my opinion.  It has a well designed regulator with a very reasonable input range.
     What voltages can it tolerate? 0 - 18
     What voltages can it operate at?  4.5-16
     Is that 3Com power supply a piece of shit?  Probably
     Did the 3Com supply damage the ztex board?  Absolutely no way to tell without an oscilloscope
     Should ztex boards be protected?  Probably not.  It costs watts and money and you can never protect against everything anyway.
     Is that 3com switch protected?  God no.  Plug the wrong supply into that and see what majick smoke comes out.

     What can be done?  Use GOOD quality power supplies on your 500 dollar boards or at least use a cheap supply that is way under volted.  A 6V 'cheap' supply is not going to put out 18V under any normal circumstances.  If it fails, it might put out wall voltage (110/220) - but under normal circumstances, it's going to be 'safe' for the ztex board.

Enigma

Excelent explanation.
ztex should have pointed the same when I asked about.
But instead I got this :

-------------------------------------------------------------------
me : Is power supply standard ?

ztex : Yes, standard DC power jack with 2.1mm center pin diameter for a supply
voltage of 5 V to 16 V. Available in Supermarkets, but most customers
have suitable AC/DC converters laying around from routers and so.
-------------------------------------------------------------------
(from a email on October 21st)

I'm convinced after looking at the circuit that the power supply design is quite good, and that there is absolutely no protection.  Most devices do not have protection because in most cases, protection costs watts.  I'm also convinced that the input of the power supply will not tolerate more than 18V for brief periods or more than 16V for extended periods - hence the reason I suggest using a 9 or 6V supply IF you're going to use cheap crappy supplies.  If you're going to power it with a good, clean, accurate, switching regulator - feel free to use one at 15.99998V if you so desire - the board will survive and operate just fine.

Enigma

That's a very good advice, I'm convinced that the boards lack a proper power design and protection.

On the ZTEX Boards, If you're going to use a cheap supply, just use a 9v one..
Even at worst case, 9v is only going to be 12.73 volts peak - still leaving PLENTY of headroom..

If you want to be ultra-cautious, use a 6V supply..

OK, I understand the mis-communication I created with my earlier post.

There are two types of filtering in a typical small-electronics power supply:

1) ripple filter designed to filter out the remnants of the mains frequency and its harmonics

2) switching noise filter designed to filter out the ultra-rapid falling-edges of the reverse-polarization current.

The proper word I should have used is "snubber capacitors" not "filter capacitors".

http://www.hagtech.com/pdf/snubber.pdf

There's a lot of other sources as well, just google "snubber" and "snubbers".

I was thinking of a wall-wart that is more of a recharging device and the ripple filtering is done not with capacitors, but with the battery. It doesn't seem like 3COM manufactures any battery-powered devices, so my assumptions may not apply here.

Some pictures of the PSU I used, and a measure of the idle voltage, it was 14.5 not 13.5, my mistake.
Sorry for the poor picture focus, my camera not doing fine on very close pictures :

http://voip54.com/fotos%20PSU/121_0454.JPG
http://voip54.com/fotos%20PSU/121_0455.JPG
http://voip54.com/fotos%20PSU/121_0456.JPG

The dangerous thing is the peak voltage, not the mean voltage.

The filter capacitors increase the mean voltage (to about the peak) but also reduce the peak a little bit, because there is always some load (maybe 30mA). This is the job of C3.
Also, especially the ceramic capacitors eliminates spikes.

Another thing that has to be considered is that the DC voltage is everything but a sine shaped. (Here in EU we have laws which try to keep the waveform beautiful.)


If it would have an output capacitor the idle (mean) voltage would be much higher than 13.5V.

Assuming a sine wave the time over 18V (absolute maximum) is not incredibly short. But it does not matter whether it is short or not.

In my opinion, Gusties power supply has no filter capacitors (else the idle mean voltage would be higher) and an idle peak voltage of about 20-21V.
If connected to the board (in idle mode) the peak voltage is reduced to about 19 V to 20 V (due to C3 and the other capacitors and due to a small load) and the mean voltage is about the same.