Diode ratings in push pull converter

[Frithiof Andreas Jensen]

"Fritz Schlunder" <me@privacy.net> wrote in message
news:39qkgkF64u2k4U1@individual.net...

Indeed you have been swindled.

O.T.O.H.:

That power supply probably costs less than USD 5,00 per piece in lots of
1000 at the dockside, which is, I suspect, The *Real* Requirement.

PeeCee equipment is notoriously shitty - it's amazing how often it happens
to work in the general case while anyway near the "edge" - Boom!
(literally)!! Probably the very same principles are used here as in the olde
days with power transistors for switchmode: Everybody *knows* that the
salesperson lies through his teeth, after all his lips are moving, so we
just de-rate by 60% to compensate.

 

[Terry Given]

Fritz Schlunder wrote:

"Franc Zabkar" <fzabkar@optussnet.com.au> wrote in message
news:3gif31p1998ctmcp4ijo9et7becpkt4gq3@4ax.com...

I have a generic "400W" ATX PSU which I suspect is a fake. This is its
circuit diagram:

"LC-B250ATX ch. Y-B200-ATX ver. 2.9 JNC Computer Co."
http://electro-tech.narod.ru/schematics/power/JNC_Y-B200-ATX.zip

The label on the cover reads as follows:

L&C Technology Inc
Model: LC-B400ATX

+3.3V +5V +12V -12V -5V +5VSB
28A 40A 17A 0.8A 0.3A 2A

+5V & +3.3V combined load 220W
+5V & +3.3V & +12V combined load 380W
Total output is 400W max.

The +3.3V and +5V rails are each rectified by a S10C40C dual diode,
and the +12V rail is rectified by two FR302 fast recovery diodes.

According to their datasheets, the FR302 is rated at 3A, and the
S10C40C is rated for 10A.

http://www.mospec.com.tw/pdf/fast/FR301-FR307.pdf
http://www.mospec.com.tw/pdf/schottky/S10C30CE-S10C60CE.pdf

Printed on the PCB is the following legend:

F5A/250V (for 180W -- 235W)
F7A/250V (for 300W -- 350W)
F6.3A/250V (for 250W)

The fuse is 5A. :-(

The PCB is labelled "Y-B200 ATX Ver 2.8" which also suggests a 200W
rating.

Can anyone offer an opinion as to the real rating of this PSU? How do
the diode ratings in the push pull converter affect the PSU spec? Can
one assume that the total wattage is close enough to ...

Pt = (3.3 x 10) + (5 x 10) + (12 x 6) + (5VSB x 2) + (-5/-12 wattage)
= 175W approx


- Franc Zabkar



Indeed you have been swindled. Unfortunately you are not the first nor
surely the last person who will be swindled by "L&C Technology" power
supplies. That company clearly has no moral standards, they simply slap
stickers on their products with whatever fanciful ratings they want with no
regard to the actual powersupply construction.

As I write I have a L&C technology so called "300W" powersupply sitting in
my lap. I might add the powersupply failed after maybe 3000 hours of
operation (at much less than 300W output). The powersupply has three
substantially discolored regions on the PCB indicating prolonged extreme
heat. This powersupply also uses the same basic output rectifiers as yours
does (two 10A center tapped TO-220 schottky diodes and two 3A FR302
devices). It has two 330uF 200V input capacitors.

To be within specification of just the output rectifiers both of our
powersupplies should be rated for an absolute maximum of no more than 10A
5V, 10A 3.3V, 6A 12V, for a combined total on these rails of only 155W.
This assumes perfectly ideal duty cycle, perfect cooling, no other
significant diode losses, and no component derating of any kind.

Now adays I don't normally buy computer powersupplies unless I get a chance
to at least peek through the holes in the side with a flashlight first.
Signs of reasonably decent construction I specifically look for are large
input capacitors (two 470uF or more for 250W, 680uF or more for 300W+), and
a large main power transformer that uses a round center post. Transformers
that use a round center post are inherently superior to those that use
rectangular center posts. For a given cross sectional area the circle has
the smallest perimeter, which directly translates into better copper wire
utilization. These types of cores also normally have a much taller than
wide window area which also improves proximity effect losses for high
frequency operation.

Jolly good points.

I have a mate who has several hundred videogame machines. He has used pc
smps for a long time, as they are cheap and readily available. About 6-7
years ago he stopped buying really cheap ones, and started buying
(comparatively) expensive ones from a reputable manufacturer. His smps
failure rate plummeted to almost zero (his techs were replacing one
every week or two), and the logic board failure rate likewise became
negligible.

I think the answer to "how can you make a good smps for so little money"
is simply that you cant. Cheaper is invariably nastier.

Cheers
Terry

 

[Winfield Hill]

Fritz Schlunder wrote...

Franc Zabkar wrote ...
...
The label on the cover reads as follows:
L&C Technology Inc
Model: LC-B400ATX
+3.3V +5V +12V -12V -5V +5VSB
28A 40A 17A 0.8A 0.3A 2A

The +3.3V and +5V rails are each rectified by a S10C40C dual diode,
and the +12V rail is rectified by two FR302 fast recovery diodes.

According to their datasheets, the FR302 is rated at 3A, and the
S10C40C is rated for 10A.

http://www.mospec.com.tw/pdf/fast/FR301-FR307.pdf
http://www.mospec.com.tw/pdf/schottky/S10C30CE-S10C60CE.pdf

As I write I have a L&C technology so called "300W" powersupply sitting
in my lap. I might add the powersupply failed after maybe 3000 hours of
operation (at much less than 300W output). The powersupply has three
substantially discolored regions on the PCB indicating prolonged extreme
heat. This powersupply also uses the same basic output rectifiers as
yours does (two 10A center tapped TO-220 schottky diodes and two 3A
FR302 devices).

When Franc made his post, I questioned his determination of the
FR302 diodes, but now you confirm it in another L&C Technology PS.
Two 3A half-wave rectifier diodes could be claimed to deliver 6A
continuously (although without a proper temperature derating). The
L&C Technology 17A rating doesn't speak well for company's honesty.

The diodes would appear to drop nearly 2V at 17A, at 25C, less when
hot. Let's call it 1.5V; that's about 13W dissipation (50% duty).
It's doubtful they can do this for more than say 30ms, starting cool
from a current *much* lower than 6A. Perhaps this is long enough to
do something useful, spin up a disk drive, etc., but the discrepancy
between the 6A datasheet and 17A L&C spec'd numbers boggles the mind.

Another thing that boggles the mind is using el-cheapo $39 power
supplies with thousand-dollar processors, display monitors, etc.


--
Thanks,
- Win

 

[Fritz Schlunder]

"Terry Given" <my_name@ieee.org> wrote in message
newssQZd.10175$1S4.1066850@news.xtra.co.nz...

the diode drop is a large chunk of the 3.3V output power - say 1V at
10A, so the actual power from the 3V3 winding would be 4.3V*10A = 10W
more than you calculate.

Well okay, but a low voltage schottky diode operated at reasonably decent
current density has a typical forward voltage more in the range of 0.4-0.5V.
In your typical computer power supply which uses a half bridge topology the
secondaries are center tapped. So rectification for each rail is normally
achieved using a single TO-220 or TO-247 packaged dual diode in the typical
full wave rectifier (for center tapped secondaries) configuration. So only
one diode is effectively in series with the output at any given moment in
time. The 12V rail usually uses a TO-220 packaged 100-200V ultrafast
recovery diode with a forward voltage approaching 1V.

 

[Fritz Schlunder]

"Franc Zabkar" <fzabkar@optussnet.com.au> wrote in message
news:3gif31p1998ctmcp4ijo9et7becpkt4gq3@4ax.com...

I have a generic "400W" ATX PSU which I suspect is a fake. This is its
circuit diagram:

"LC-B250ATX ch. Y-B200-ATX ver. 2.9 JNC Computer Co."
http://electro-tech.narod.ru/schematics/power/JNC_Y-B200-ATX.zip

The label on the cover reads as follows:

L&C Technology Inc
Model: LC-B400ATX

+3.3V +5V +12V -12V -5V +5VSB
28A 40A 17A 0.8A 0.3A 2A

+5V & +3.3V combined load 220W
+5V & +3.3V & +12V combined load 380W
Total output is 400W max.

The +3.3V and +5V rails are each rectified by a S10C40C dual diode,
and the +12V rail is rectified by two FR302 fast recovery diodes.

According to their datasheets, the FR302 is rated at 3A, and the
S10C40C is rated for 10A.

http://www.mospec.com.tw/pdf/fast/FR301-FR307.pdf
http://www.mospec.com.tw/pdf/schottky/S10C30CE-S10C60CE.pdf

Printed on the PCB is the following legend:

F5A/250V (for 180W -- 235W)
F7A/250V (for 300W -- 350W)
F6.3A/250V (for 250W)

The fuse is 5A. :-(

The PCB is labelled "Y-B200 ATX Ver 2.8" which also suggests a 200W
rating.

Can anyone offer an opinion as to the real rating of this PSU? How do
the diode ratings in the push pull converter affect the PSU spec? Can
one assume that the total wattage is close enough to ...

Pt = (3.3 x 10) + (5 x 10) + (12 x 6) + (5VSB x 2) + (-5/-12 wattage)
= 175W approx


- Franc Zabkar

Indeed you have been swindled. Unfortunately you are not the first nor
surely the last person who will be swindled by "L&C Technology" power
supplies. That company clearly has no moral standards, they simply slap
stickers on their products with whatever fanciful ratings they want with no
regard to the actual powersupply construction.

As I write I have a L&C technology so called "300W" powersupply sitting in
my lap. I might add the powersupply failed after maybe 3000 hours of
operation (at much less than 300W output). The powersupply has three
substantially discolored regions on the PCB indicating prolonged extreme
heat. This powersupply also uses the same basic output rectifiers as yours
does (two 10A center tapped TO-220 schottky diodes and two 3A FR302
devices). It has two 330uF 200V input capacitors.

To be within specification of just the output rectifiers both of our
powersupplies should be rated for an absolute maximum of no more than 10A
5V, 10A 3.3V, 6A 12V, for a combined total on these rails of only 155W.
This assumes perfectly ideal duty cycle, perfect cooling, no other
significant diode losses, and no component derating of any kind.

Now adays I don't normally buy computer powersupplies unless I get a chance
to at least peek through the holes in the side with a flashlight first.
Signs of reasonably decent construction I specifically look for are large
input capacitors (two 470uF or more for 250W, 680uF or more for 300W+), and
a large main power transformer that uses a round center post. Transformers
that use a round center post are inherently superior to those that use
rectangular center posts. For a given cross sectional area the circle has
the smallest perimeter, which directly translates into better copper wire
utilization. These types of cores also normally have a much taller than
wide window area which also improves proximity effect losses for high
frequency operation.

 

[Winfield Hill]

Franc Zabkar wrote...

I have a generic "400W" ATX PSU which I suspect is a fake. This
is its circuit diagram:
"LC-B250ATX ch. Y-B200-ATX ver. 2.9 JNC Computer Co."
http://electro-tech.narod.ru/schematics/power/JNC_Y-B200-ATX.zip

Did you trace the drawing yourself to know it matches your supply?

The +3.3V and +5V rails are each rectified by a S10C40C dual diode,
and the +12V rail is rectified by two FR302 fast recovery diodes.

You know this how, from taking apart your power supply?

Can anyone offer an opinion as to the real rating of this PSU? ...

Most Pacific Rim PC supplies are NOT rated for continuous power,
especially for the +12V line, etc. The reasoning is because in
actual use the power-consumption peaks when the HD motor spins up,
etc., and you want to know it won't sag under the transient.

They are also not rated for simultaneous full load on all outputs.
Again, that would be an unrealistic application.

So, who knows exactly what the PSU rating spec means? Ask them.


--
Thanks,
- Win

 

[Alan Turner]

Hi,

On Wed, 16 Mar 2005 19:35:27 +1300, Terry Given wrote:

the diode drop is a large chunk of the 3.3V output power - say 1V at
10A, so the actual power from the 3V3 winding would be 4.3V*10A = 10W
more than you calculate. not so bad for the 5V, even less so for 12V.
But its a good start. And you can see why people use synchronous
rectifiers (ie FETs) for really low output voltages like 1.5V.

This does raise the interesting question of whether the power rating
stamped on the PSU is the input power or the output power.

If it's the input power then 200W power supplies can easily be
upgraded with a resistor

Regards,
Alan




--
Alan R. Turner | Live never to be ashamed of anything you do or say.
To reply by email, remove Mr Blobby.

 

[Franc Zabkar]

I have a generic "400W" ATX PSU which I suspect is a fake. This is its
circuit diagram:

"LC-B250ATX ch. Y-B200-ATX ver. 2.9 JNC Computer Co."
http://electro-tech.narod.ru/schematics/power/JNC_Y-B200-ATX.zip

The label on the cover reads as follows:

L&C Technology Inc
Model: LC-B400ATX

+3.3V +5V +12V -12V -5V +5VSB
28A 40A 17A 0.8A 0.3A 2A

+5V & +3.3V combined load 220W
+5V & +3.3V & +12V combined load 380W
Total output is 400W max.

The +3.3V and +5V rails are each rectified by a S10C40C dual diode,
and the +12V rail is rectified by two FR302 fast recovery diodes.

According to their datasheets, the FR302 is rated at 3A, and the
S10C40C is rated for 10A.

http://www.mospec.com.tw/pdf/fast/FR301-FR307.pdf
http://www.mospec.com.tw/pdf/schottky/S10C30CE-S10C60CE.pdf

Printed on the PCB is the following legend:

F5A/250V (for 180W -- 235W)
F7A/250V (for 300W -- 350W)
F6.3A/250V (for 250W)

The fuse is 5A. :-(

The PCB is labelled "Y-B200 ATX Ver 2.8" which also suggests a 200W
rating.

Can anyone offer an opinion as to the real rating of this PSU? How do
the diode ratings in the push pull converter affect the PSU spec? Can
one assume that the total wattage is close enough to ...

Pt = (3.3 x 10) + (5 x 10) + (12 x 6) + (5VSB x 2) + (-5/-12 wattage)
= 175W approx


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[Terry Given]

Franc Zabkar wrote:

I have a generic "400W" ATX PSU which I suspect is a fake. This is its
circuit diagram:

"LC-B250ATX ch. Y-B200-ATX ver. 2.9 JNC Computer Co."
http://electro-tech.narod.ru/schematics/power/JNC_Y-B200-ATX.zip

The label on the cover reads as follows:

L&C Technology Inc
Model: LC-B400ATX

+3.3V +5V +12V -12V -5V +5VSB
28A 40A 17A 0.8A 0.3A 2A

+5V & +3.3V combined load 220W
+5V & +3.3V & +12V combined load 380W
Total output is 400W max.

The +3.3V and +5V rails are each rectified by a S10C40C dual diode,
and the +12V rail is rectified by two FR302 fast recovery diodes.

According to their datasheets, the FR302 is rated at 3A, and the
S10C40C is rated for 10A.

http://www.mospec.com.tw/pdf/fast/FR301-FR307.pdf
http://www.mospec.com.tw/pdf/schottky/S10C30CE-S10C60CE.pdf

they probably parallel both diodes. in theory this gives twice the
current rating, if they share equally (which they probably do as they
are on the same die so at the same temperature)

Printed on the PCB is the following legend:

F5A/250V (for 180W -- 235W)
F7A/250V (for 300W -- 350W)
F6.3A/250V (for 250W)

The fuse is 5A. :-(

The PCB is labelled "Y-B200 ATX Ver 2.8" which also suggests a 200W
rating.

Can anyone offer an opinion as to the real rating of this PSU? How do
the diode ratings in the push pull converter affect the PSU spec? Can
one assume that the total wattage is close enough to ...

Pt = (3.3 x 10) + (5 x 10) + (12 x 6) + (5VSB x 2) + (-5/-12 wattage)
= 175W approx

the diode drop is a large chunk of the 3.3V output power - say 1V at
10A, so the actual power from the 3V3 winding would be 4.3V*10A = 10W
more than you calculate. not so bad for the 5V, even less so for 12V.
But its a good start. And you can see why people use synchronous
rectifiers (ie FETs) for really low output voltages like 1.5V.

read the diode drop off the datasheet (taking account the individual
diode current where 2 are paralleled) and add it to each supply voltage
in your calc, and you'll be a lot closer. It doesnt account for xfmr and
choke Cu losses, switching losses or any primary FET conduction losses,
but you'll be fairly close.

- Franc Zabkar

in a push-pull or forward or half- or full-bridge converter the average
diode current is the output current.

I have no idea where you got your current values from....

without specifying the input voltage, it is not much use looking at the
fuse rating. Even then its not too helpful (unless you take into account
the pulsating nature of a rectifier/diode filter, not that hard if you
like maths)

but if its a 5A fuse it probably wont like more than 3Arms long term -
the fuse will eventually fail at any more than that.

Cheers
Terry

 

[Franc Zabkar]

On Wed, 16 Mar 2005 19:35:27 +1300, Terry Given <my_name@ieee.org> put
finger to keyboard and composed:

Franc Zabkar wrote:
I have a generic "400W" ATX PSU which I suspect is a fake. This is its
circuit diagram:

"LC-B250ATX ch. Y-B200-ATX ver. 2.9 JNC Computer Co."
http://electro-tech.narod.ru/schematics/power/JNC_Y-B200-ATX.zip

The label on the cover reads as follows:

L&C Technology Inc
Model: LC-B400ATX

+3.3V +5V +12V -12V -5V +5VSB
28A 40A 17A 0.8A 0.3A 2A

+5V & +3.3V combined load 220W
+5V & +3.3V & +12V combined load 380W
Total output is 400W max.

The +3.3V and +5V rails are each rectified by a S10C40C dual diode,
and the +12V rail is rectified by two FR302 fast recovery diodes.

According to their datasheets, the FR302 is rated at 3A, and the
S10C40C is rated for 10A.

http://www.mospec.com.tw/pdf/fast/FR301-FR307.pdf
http://www.mospec.com.tw/pdf/schottky/S10C30CE-S10C60CE.pdf

they probably parallel both diodes. in theory this gives twice the
current rating, if they share equally (which they probably do as they
are on the same die so at the same temperature)

No, the anodes of each diode attach to opposite ends of a center
tapped winding. The rated average forward current is 5A per diode,
giving a total rating of 10A for the package. As each diode only
conducts during alternate half cycles of the oscillator, the rating of
that particular rail would be 10A.

Printed on the PCB is the following legend:

F5A/250V (for 180W -- 235W)
F7A/250V (for 300W -- 350W)
F6.3A/250V (for 250W)

The fuse is 5A. :-(

The PCB is labelled "Y-B200 ATX Ver 2.8" which also suggests a 200W
rating.

Can anyone offer an opinion as to the real rating of this PSU? How do
the diode ratings in the push pull converter affect the PSU spec? Can
one assume that the total wattage is close enough to ...

Pt = (3.3 x 10) + (5 x 10) + (12 x 6) + (5VSB x 2) + (-5/-12 wattage)
= 175W approx

the diode drop is a large chunk of the 3.3V output power - say 1V at
10A, so the actual power from the 3V3 winding would be 4.3V*10A = 10W
more than you calculate. not so bad for the 5V, even less so for 12V.
But its a good start. And you can see why people use synchronous
rectifiers (ie FETs) for really low output voltages like 1.5V.

I'm not concerned with the power output from the *winding*, except
insofar as it reflects the efficiency of the PSU. Instead I'm trying
to determine the power available to the external load, ie I'm
comparing this figure to the one on the PSU's rating sticker.

read the diode drop off the datasheet (taking account the individual
diode current where 2 are paralleled) and add it to each supply voltage
in your calc, and you'll be a lot closer. It doesnt account for xfmr and
choke Cu losses, switching losses or any primary FET conduction losses,
but you'll be fairly close.



- Franc Zabkar

in a push-pull or forward or half- or full-bridge converter the average
diode current is the output current.

That's what I've always thought, but after seeing several "200W" PSU's
with 150W parts I was left to wonder whether there was something I
didn't understand.

I have no idea where you got your current values from....

I'm not sure which current values you mean, but one set was printed on
the ratings sticker, the others came from device datasheets.

Here is a diagram of a push pull converter:
http://www.hills2.u-net.com/electron/pushpul1.gif

A diode rated at X amps should be able to carry 2X amps during each
half cycle of the oscillator. The other diode carries 2X amps during
the alternate half cycle.

without specifying the input voltage, it is not much use looking at the
fuse rating. Even then its not too helpful (unless you take into account
the pulsating nature of a rectifier/diode filter, not that hard if you
like maths)

The fuse ratings were printed on the PCB. I included this information
to confirm that this particular configuration of the PCB was intended
for a 180W-230W application. The suitability of the fuse was of no
particular concern to me.

but if its a 5A fuse it probably wont like more than 3Arms long term -
the fuse will eventually fail at any more than that.

Cheers
Terry

- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[Franc Zabkar]

On 16 Mar 2005 04:57:39 -0800, Winfield Hill
<hill_a@t_rowland-dotties-harvard-dot.s-edu> put finger to keyboard
and composed:

Fritz Schlunder wrote...

Franc Zabkar wrote ...
...
The label on the cover reads as follows:
L&C Technology Inc
Model: LC-B400ATX
+3.3V +5V +12V -12V -5V +5VSB
28A 40A 17A 0.8A 0.3A 2A

The +3.3V and +5V rails are each rectified by a S10C40C dual diode,
and the +12V rail is rectified by two FR302 fast recovery diodes.

According to their datasheets, the FR302 is rated at 3A, and the
S10C40C is rated for 10A.

http://www.mospec.com.tw/pdf/fast/FR301-FR307.pdf
http://www.mospec.com.tw/pdf/schottky/S10C30CE-S10C60CE.pdf

As I write I have a L&C technology so called "300W" powersupply sitting
in my lap. I might add the powersupply failed after maybe 3000 hours of
operation (at much less than 300W output). The powersupply has three
substantially discolored regions on the PCB indicating prolonged extreme
heat. This powersupply also uses the same basic output rectifiers as
yours does (two 10A center tapped TO-220 schottky diodes and two 3A
FR302 devices).

When Franc made his post, I questioned his determination of the
FR302 diodes, but now you confirm it in another L&C Technology PS.
Two 3A half-wave rectifier diodes could be claimed to deliver 6A
continuously (although without a proper temperature derating). The
L&C Technology 17A rating doesn't speak well for company's honesty.

I was careful not to say that this was actually an L&C PSU. The
sticker says L&C, but who knows who really made it? I posted several
links to what may be the real (?) L&C unit. These look entirely
different. Even the low wattage L&C enclosures look different to mine.

The diodes would appear to drop nearly 2V at 17A, at 25C, less when
hot. Let's call it 1.5V; that's about 13W dissipation (50% duty).
It's doubtful they can do this for more than say 30ms, starting cool
from a current *much* lower than 6A. Perhaps this is long enough to
do something useful, spin up a disk drive, etc., but the discrepancy
between the 6A datasheet and 17A L&C spec'd numbers boggles the mind.

Another thing that boggles the mind is using el-cheapo $39 power
supplies with thousand-dollar processors, display monitors, etc.

Who knows what a quality PSU really costs to make, especially in the
PRC, and by prison labour? One wonders if a genuine 400W generic PSU
is really significantly inferior to a branded product. Remember, mine
a 180W PSU with a 400W label, so it never really had a chance.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[Franc Zabkar]

On 16 Mar 2005 02:50:25 -0800, Winfield Hill
<hill_a@t_rowland-dotties-harvard-dot.s-edu> put finger to keyboard
and composed:

Franc Zabkar wrote...

I have a generic "400W" ATX PSU which I suspect is a fake. This
is its circuit diagram:
"LC-B250ATX ch. Y-B200-ATX ver. 2.9 JNC Computer Co."
http://electro-tech.narod.ru/schematics/power/JNC_Y-B200-ATX.zip

Did you trace the drawing yourself to know it matches your supply?

Yes, I did. In fact I'd traced it before I found the online circuit.
I'd even determined the pinouts of the mysterious combo PWM
controller/supervisor/3V3 regulator IC. Any differences in my
implementation of the circuit are in unpopulated sections (missing
filter caps, linked inductors), and in the wiring of the fan. My fan
is fed directly from the +12V rail, whereas the circuit diagram shows
a thermistor controlled version (this is available on my PCB, but not
used).

The +3.3V and +5V rails are each rectified by a S10C40C dual diode,
and the +12V rail is rectified by two FR302 fast recovery diodes.

You know this how, from taking apart your power supply?

Meticulously.

Can anyone offer an opinion as to the real rating of this PSU? ...

Most Pacific Rim PC supplies are NOT rated for continuous power,
especially for the +12V line, etc. The reasoning is because in
actual use the power-consumption peaks when the HD motor spins up,
etc., and you want to know it won't sag under the transient.

They are also not rated for simultaneous full load on all outputs.
Again, that would be an unrealistic application.

So, who knows exactly what the PSU rating spec means? Ask them.

Yeah, right.

The PSU label has a separate C-tick certification number. I've emailed
the relevant authority.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[Franc Zabkar]

On Wed, 16 Mar 2005 04:45:18 -0700, "Fritz Schlunder" <me@privacy.net>
put finger to keyboard and composed:

Indeed you have been swindled. Unfortunately you are not the first nor
surely the last person who will be swindled by "L&C Technology" power
supplies. That company clearly has no moral standards, they simply slap
stickers on their products with whatever fanciful ratings they want with no
regard to the actual powersupply construction.

As stated previously, this PSU does not look like any of the L&C PSUs
in the URLs I posted elsewhere in this thread. Maybe it's a fake L&C
unit put together by a third party. After all, a fake version of a
generic brand would not be subject to the same scrutiny as a fake
Enermax, for example.

As I write I have a L&C technology so called "300W" powersupply sitting in
my lap. I might add the powersupply failed after maybe 3000 hours of
operation (at much less than 300W output). The powersupply has three
substantially discolored regions on the PCB indicating prolonged extreme
heat. This powersupply also uses the same basic output rectifiers as yours
does (two 10A center tapped TO-220 schottky diodes and two 3A FR302
devices). It has two 330uF 200V input capacitors.

To be within specification of just the output rectifiers both of our
powersupplies should be rated for an absolute maximum of no more than 10A
5V, 10A 3.3V, 6A 12V, for a combined total on these rails of only 155W.
This assumes perfectly ideal duty cycle, perfect cooling, no other
significant diode losses, and no component derating of any kind.

I believe the various diodes are good for their rated current up to 75
degC.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[Terry Given]

Franc Zabkar wrote:

On Wed, 16 Mar 2005 19:35:27 +1300, Terry Given <my_name@ieee.org> put
finger to keyboard and composed:


Franc Zabkar wrote:

I have a generic "400W" ATX PSU which I suspect is a fake. This is its
circuit diagram:

"LC-B250ATX ch. Y-B200-ATX ver. 2.9 JNC Computer Co."
http://electro-tech.narod.ru/schematics/power/JNC_Y-B200-ATX.zip

The label on the cover reads as follows:

L&C Technology Inc
Model: LC-B400ATX

+3.3V +5V +12V -12V -5V +5VSB
28A 40A 17A 0.8A 0.3A 2A

+5V & +3.3V combined load 220W
+5V & +3.3V & +12V combined load 380W
Total output is 400W max.

The +3.3V and +5V rails are each rectified by a S10C40C dual diode,
and the +12V rail is rectified by two FR302 fast recovery diodes.

According to their datasheets, the FR302 is rated at 3A, and the
S10C40C is rated for 10A.

http://www.mospec.com.tw/pdf/fast/FR301-FR307.pdf
http://www.mospec.com.tw/pdf/schottky/S10C30CE-S10C60CE.pdf

they probably parallel both diodes. in theory this gives twice the
current rating, if they share equally (which they probably do as they
are on the same die so at the same temperature)


No, the anodes of each diode attach to opposite ends of a center
tapped winding. The rated average forward current is 5A per diode,
giving a total rating of 10A for the package. As each diode only
conducts during alternate half cycles of the oscillator, the rating of
that particular rail would be 10A.

Paralleling a pair of diodes is not uncommon. If I was sneaky I would
have said "possibly" not probably

as you have discovered, the rail "rating" doesnt have bugger all to do
with the diode rating. And the rated average current is given at some
(unspecified) setup having a thermal resistance which keeps the diode at
a suitable temperature. Depending on how you cool the device, it is
possible to run at much higher currents than the data sheet suggests
(Ifsm being the single-shot limit, usually constrained by adiabatic
heating, or perhaps bond wire fusing). Conversely if you did a dreadful
job of cooling the diode, reliable operation (now theres the snag) would
mandate a lower-than-rated current. My experience with cheap smps is
that they beat the snot out of the diodes, which often fail.

Printed on the PCB is the following legend:

F5A/250V (for 180W -- 235W)
F7A/250V (for 300W -- 350W)
F6.3A/250V (for 250W)

The fuse is 5A. :-(

The PCB is labelled "Y-B200 ATX Ver 2.8" which also suggests a 200W
rating.

Can anyone offer an opinion as to the real rating of this PSU? How do
the diode ratings in the push pull converter affect the PSU spec? Can
one assume that the total wattage is close enough to ...

Pt = (3.3 x 10) + (5 x 10) + (12 x 6) + (5VSB x 2) + (-5/-12 wattage)
= 175W approx

the diode drop is a large chunk of the 3.3V output power - say 1V at
10A, so the actual power from the 3V3 winding would be 4.3V*10A = 10W
more than you calculate. not so bad for the 5V, even less so for 12V.
But its a good start. And you can see why people use synchronous
rectifiers (ie FETs) for really low output voltages like 1.5V.


I'm not concerned with the power output from the *winding*, except
insofar as it reflects the efficiency of the PSU. Instead I'm trying
to determine the power available to the external load, ie I'm
comparing this figure to the one on the PSU's rating sticker.

for a reputable manufacturer, its what the label says. For a cheap
manufacturer, its often a lot less - depends on how long you want it to
live for, and under what conditions. Cheap smps ratings are a bit like
audio amp power ratings in that regard - wildly optimistic if not
complete fiction.

when a design is "optimistically spec'd" (thats being kind) like this,
its the losses that determine the medium- and long-term power available
to the load, because they are the bits that will die. But you cant
really calculate that, you pretty much have to measure it. I have done
that on several occassions when evaluating OEM parts - the results are
sometimes pleasing, often horrifying.

cap ripple current ratings affect long-term operation too, and are
usually woefully inadequate. These are wonderful for techs, they are a
never-ending source of income.

read the diode drop off the datasheet (taking account the individual
diode current where 2 are paralleled) and add it to each supply voltage
in your calc, and you'll be a lot closer. It doesnt account for xfmr and
choke Cu losses, switching losses or any primary FET conduction losses,
but you'll be fairly close.



- Franc Zabkar

in a push-pull or forward or half- or full-bridge converter the average
diode current is the output current.


That's what I've always thought, but after seeing several "200W" PSU's
with 150W parts I was left to wonder whether there was something I
didn't understand.

the mentality of the lying bastards that wrote the label. But as Fritz
pointed out, dynamic and static loads are often quite different, and
marketers usually use the former in place of the latter.

I have no idea where you got your current values from....


I'm not sure which current values you mean, but one set was printed on
the ratings sticker, the others came from device datasheets.

Here is a diagram of a push pull converter:
http://www.hills2.u-net.com/electron/pushpul1.gif

A diode rated at X amps should be able to carry 2X amps during each
half cycle of the oscillator. The other diode carries 2X amps during
the alternate half cycle.

maybe. depends on overall thermal performance. The S10C40C datasheet
gives 0.48V@5A = 2.4W and 0.6V@10A = 6W, so the peak die temperature
rise is 2.5 times larger with a 2x increase in current. again, thermal
considerations dictate whether or not this is a terribly bad thing, but
it will probably decrease the life of the part, due to the effect of
temperature cycling on the die-Cu interface.

without specifying the input voltage, it is not much use looking at the
fuse rating. Even then its not too helpful (unless you take into account
the pulsating nature of a rectifier/diode filter, not that hard if you
like maths)


The fuse ratings were printed on the PCB. I included this information
to confirm that this particular configuration of the PCB was intended
for a 180W-230W application. The suitability of the fuse was of no
particular concern to me.

if you know the ac input voltage and dc bus capacitance, you can
calculate the 100/120Hz ripple and diode conduction angle, then
calculate the rms current it will draw - assuming a diode/cap rectifier.
I doubt a cheesy smps like this will have a UPF universal input.

but if its a 5A fuse it probably wont like more than 3Arms long term -
the fuse will eventually fail at any more than that.

Cheers
Terry



- Franc Zabkar

Cheers
Terry

 

[Terry Given]

Franc Zabkar wrote:

On Wed, 16 Mar 2005 04:45:18 -0700, "Fritz Schlunder" <me@privacy.net
put finger to keyboard and composed:


Indeed you have been swindled. Unfortunately you are not the first nor
surely the last person who will be swindled by "L&C Technology" power
supplies. That company clearly has no moral standards, they simply slap
stickers on their products with whatever fanciful ratings they want with no
regard to the actual powersupply construction.


As stated previously, this PSU does not look like any of the L&C PSUs
in the URLs I posted elsewhere in this thread. Maybe it's a fake L&C
unit put together by a third party. After all, a fake version of a
generic brand would not be subject to the same scrutiny as a fake
Enermax, for example.


As I write I have a L&C technology so called "300W" powersupply sitting in
my lap. I might add the powersupply failed after maybe 3000 hours of
operation (at much less than 300W output). The powersupply has three
substantially discolored regions on the PCB indicating prolonged extreme
heat. This powersupply also uses the same basic output rectifiers as yours
does (two 10A center tapped TO-220 schottky diodes and two 3A FR302
devices). It has two 330uF 200V input capacitors.

To be within specification of just the output rectifiers both of our
powersupplies should be rated for an absolute maximum of no more than 10A
5V, 10A 3.3V, 6A 12V, for a combined total on these rails of only 155W.
This assumes perfectly ideal duty cycle, perfect cooling, no other
significant diode losses, and no component derating of any kind.


I believe the various diodes are good for their rated current up to 75
degC.

belabouring the point: 75C case temperature. Add to that the drop across
the heatsink, then internal ambient, which will likely be a fair bit
hotter than external ambient.

- Franc Zabkar

Cheers
Terry

 

[legg]

On Thu, 17 Mar 2005 08:46:32 +1100, Franc Zabkar
<fzabkar@optussnet.com.au> wrote:

The +3.3V and +5V rails are each rectified by a S10C40C dual diode,
and the +12V rail is rectified by two FR302 fast recovery diodes.

You know this how, from taking apart your power supply?

Meticulously.

Can anyone offer an opinion as to the real rating of this PSU? ...

Most Pacific Rim PC supplies are NOT rated for continuous power,
especially for the +12V line, etc. The reasoning is because in
actual use the power-consumption peaks when the HD motor spins up,
etc., and you want to know it won't sag under the transient.

The schematic indicates that a dual diode body is to be laid out for
the 12V rail at D14 - not FR503s. FR503s might be used in the negative
rectifier, as these are inicated as being discrete.

A lot of power is easily deliverable by the higher voltage rail, with
a TO220 dual rectifier employed. This is also where the extra power is
usually needed.

An SB1040 is also not necessarily a Mospec S10C40 - this could be an
autocad designation simply identifying a footprint or bin number.

I suspect that the correspondence between the schematic and the unit
you're disassembling is not as perfect as you believe.

A single schematic can easily represent a number of models that differ
in power rating - just as the same board art can be populated with
components producing different total output ratings - you'd realy need
to read the BOM in question or identify individual parts present in a
correctly labelled unit.

RL

 

[Franc Zabkar]

On Sat, 19 Mar 2005 21:45:45 GMT, legg <legg@nospam.magma.ca> put
finger to keyboard and composed:

On Thu, 17 Mar 2005 08:46:32 +1100, Franc Zabkar
fzabkar@optussnet.com.au> wrote:



The +3.3V and +5V rails are each rectified by a S10C40C dual diode,
and the +12V rail is rectified by two FR302 fast recovery diodes.

You know this how, from taking apart your power supply?

Meticulously.

Can anyone offer an opinion as to the real rating of this PSU? ...

Most Pacific Rim PC supplies are NOT rated for continuous power,
especially for the +12V line, etc. The reasoning is because in
actual use the power-consumption peaks when the HD motor spins up,
etc., and you want to know it won't sag under the transient.

The schematic indicates that a dual diode body is to be laid out for
the 12V rail at D14 - not FR503s.

The artwork can accept either a TO-220 package or the bigger TO-3P. It
appears the PCB can be configured for 180W operation or 350W,
depending on the choice of caps, inductors, transformers, and power
semis. Another difference is that my PSU has 4 rectifier diodes at the
AC input whereas the circuit diagram shows a bridge. The artwork is
designed to accommodate either. If anything, the circuit diagram of
the LC-B250ATX PSU shows a fully populated PCB - my "LC-B400ATX" has
missing parts.

FR503s might be used in the negative
rectifier, as these are inicated as being discrete.

That should be FR302, and they *are* used in the +12V rectifier. Do
you know of any PC PSU that uses 3A diodes on an 0.8A rail?

A lot of power is easily deliverable by the higher voltage rail, with
a TO220 dual rectifier employed. This is also where the extra power is
usually needed.

An SB1040 is also not necessarily a Mospec S10C40 - this could be an
autocad designation simply identifying a footprint or bin number.

An SB1040 is a single diode in a TO-220 package. An SB1040CT is a dual
diode.

I suspect that the correspondence between the schematic and the unit
you're disassembling is not as perfect as you believe.

I traced most of the circuit before I discovered it on the Net. The
circuit references appear to be identical. Even the transformers bear
similar part numbers, ie EI-33ASG, EE-19N, EE-16(TOP). The former is
shown on the schematic as an EL-33ASG - I don't know if this is
significant, or if it is a typo.

A single schematic can easily represent a number of models that differ
in power rating - just as the same board art can be populated with
components producing different total output ratings - you'd realy need
to read the BOM in question or identify individual parts present in a
correctly labelled unit.

RL

Agreed. I've identified the parts and they clearly cannot come within
a bull's roar of the spec claimed on the label.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.