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 Author Topic: ZTEX USB-FPGA Modules 1.15x and 1.15y: 215 and 860 MH/s FPGA Boards  (Read 181388 times)
SgtSpike
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 December 02, 2011, 12:12:30 AM

What power supply was used, anyway?  Brand/model #?
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ztex
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 December 02, 2011, 01:04:39 AM

What power supply was used, anyway?  Brand/model #?

It seems to be an unregulated supply with an idle mean voltage of 13.5V. The peak voltage should be about 21V, see https://bitcointalk.org/index.php?topic=49180.msg637394#msg637394 (2112, thanks for your calculations)

fizzisist
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 December 02, 2011, 08:54:11 AM

I'm only asking in the name of science here, not to slander ztex or his design or to take the side of the customer.
In the name of science I'm answering:

1) cheap multi-meters measure the average voltage
2) int sin(t),t=0..pi = 2
3) thus peak to average ratio for a full-wave rectifier is pi/2 ~= 1.570
4) 12V * pi/2 ~= 18.9V, 13.5V * pi/2 ~= 21.21V
5) unregulated but filtered power supply will charge its filtering capacitors to the peak voltage in (4)
6) a silicon device designed for 16V maximum input may release its magic smoke if supplied with the unfiltered rectified waveform with peaks as high as (4)
7) if the power supply was first plugged in to the mains side and then to the load side then the filtering capacitors will get partially discharged from the state (5) to their designed average
the safer way of powering up is first to plug in the load side of the supply to the device then plug in the supply to the mains outlet.

The above is what science says.

But the whole thread is an example why selling electronics to consumers demands sandbagging: both financial markups to cover losses caused by pissed of consumers and to safeguard devices from the accidental abuse by the uneducated consumers.

This calculation only applies to an ideal full-wave rectifier. With filtering it is very different situation. If you have an output capacitor, then the average will be much closer to the peak.

ztex
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 December 02, 2011, 09:17:09 AM

This calculation only applies to an ideal full-wave rectifier. With filtering it is very different situation. If you have an output capacitor, then the average will be much closer to the peak.

see 5)

That is why I'm assumung Gusties power supply has no filter capacitors, i.e. an unregulated 12 V power supply with filter cpapcitors would have an much higher idle voltage (and a regulated power supply would deliver about 12V).

fizzisist
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 December 02, 2011, 09:22:46 AM

This calculation only applies to an ideal full-wave rectifier. With filtering it is very different situation. If you have an output capacitor, then the average will be much closer to the peak.

see 5)

That is why I'm assumung Gusties power supply has no filter capacitors, i.e. an unregulated 12 V power supply with filter cpapcitors would have an much higher idle voltage (and a regulated power supply would deliver about 12V).

First of all, whether or not it has a large capacitor on the output, it is not an ideal full wave rectifier.

Second, it either has an output capacitor and the ratio of the peak to average voltage is much smaller than pi/2, or it doesn't have an output capacitor and 5 is irrelevant. It can't be both. Or am I missing something?

Like I said before, I'm just trying to understand the cause of the problem and whether or not I need to be worried about something like this happening to our boards. Thanks for your help with this.

ztex
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 December 02, 2011, 09:30:50 AM

Second, it either has an output capacitor and the ratio of the peak to average voltage is much smaller than pi/2, or it doesn't have an output capacitor and 5 is irrelevant. It can't be both. Or am I missing something?

I meant 5) said what you said: If there is an output capacitor the mean voltage will be close to the peak voltage.

fizzisist
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 December 02, 2011, 12:25:13 PM

I just did a quick survey of all the "wall wart" power supplies I could find laying around my house. I looked at 6 different ones all from very different backgrounds. It appears that 5 out of the 6 were regulated, and output a voltage right near the rated voltage with no load. On a scope, the ripple is basically 0.

The odd one was rated for 9V and 600 mA, but the open circuit voltage measured was 12.85 V, so I assume it is unregulated. On the scope, the ripple was on the order of a half volt, and the peak voltage was at most about 13.1 V. I didn't measure it under load.

Without being able to measure gusti's power supply, we can't really conclude anything from this, but it was an interesting experiment!

Second, it either has an output capacitor and the ratio of the peak to average voltage is much smaller than pi/2, or it doesn't have an output capacitor and 5 is irrelevant. It can't be both. Or am I missing something?

I meant 5) said what you said: If there is an output capacitor the mean voltage will be close to the peak voltage.

To me, the dangerous thing is that charged up output capacitor. If that is sitting at a relatively high voltage and has a high capacitance, I could see that potentially causing some damage.

On the other hand, if it has an output capacitor, then the maximum voltage that the capacitor could be charged up to when gusti plugged in the board is not much higher than his measured 13.5 V. This doesn't seem like a dangerous situation.

If it doesn't have an output capacitor, then the higher voltage (definitely not higher than 21 V) will be applied for an incredibly short time. This doesn't seem dangerous to me, either.

I'm no expert on these power supplies, though. Is there someone reading that might have some experience with these and can correct me if I'm wrong?

ztex
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 December 02, 2011, 01:15:46 PM

Quote
To me, the dangerous thing is that charged up output capacitor. If that is sitting at a relatively high voltage and has a high capacitance, I could see that potentially causing some damage.

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.)

Quote
On the other hand, if it has an output capacitor, then the maximum voltage that the capacitor could be charged up to when gusti plugged in the board is not much higher than his measured 13.5 V. This doesn't seem like a dangerous situation.

If it doesn't have an output capacitor, then the higher voltage (definitely not higher than 21 V) will be applied for an incredibly short time. This doesn't seem dangerous to me, either.

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.

gusti
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 December 02, 2011, 04:22:19 PM

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

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2112
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 December 02, 2011, 09:41:40 PM

If that is sitting at a relatively high voltage and has a high capacitance, I could see that potentially causing some damage.
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.

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Enigma81
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 December 03, 2011, 01:32:30 AM

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..

gusti
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 December 03, 2011, 01:39:16 AM

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..

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

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Enigma81
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 December 03, 2011, 01:43:34 AM

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..

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

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
gusti
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 December 03, 2011, 01:49:53 AM

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..

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

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

Excelent explanation.
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)

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Enigma81
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 December 03, 2011, 02:04:21 AM

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
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 December 03, 2011, 02:17:12 AM

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

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.

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DeathAndTaxes
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 December 03, 2011, 02:18:10 AM

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

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.
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 December 03, 2011, 02:28:45 AM

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

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.

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 ?

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DeepBit
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 December 03, 2011, 03:28:45 AM

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
Is that 3com switch protected?  God no.  Plug the wrong supply into that and see what majick smoke comes out.
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.

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Enigma81
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 December 03, 2011, 04:11:17 AM

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

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 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...
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