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12.6V from ATX instead of 12V?  Any ideas?
12.6V from ATX instead of 12V?  Any ideas?
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Old 30th October 2017, 05:48 PM   #21
kodabmx is online now kodabmx  Canada
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Quote:
Originally Posted by JMFahey View Post
Well, you *should*
Voltage is never absolute but relative to another point.

* If you touch (accidentally or on purpose) the "+380V" node with a fingertip (or elbow or wrist or any other body part) but nothing else in that supply, specially its chassis or supply ground, nothing happens.

* if you touch *any* point in the *hot/live* side of that supply, you die , for the very good reason that already, always, you are touching "another point" : ground/earth/the floor.

You think both situations are the same?


If you are "tinkering" with the secondary side, you are handling/touching/holding one way or another a single board, palm sized, where you will be soldering/desoldering/modding on the admittelly safe secondary, 1 inch away from half the board which is live/hot.

The potential for error is there.

No need to connect secondary to primary, fully exposed hot parts are there at your fingertips.


You are comparing apples to oranges.

Standard power supplies are:

1) very simple, you only have to pay attention to power switch contacts, fuse ones, and little else, and they are "all together" on a separate, easy to avoid place, wires carrying mains voltage into the transformer are insulated, while *all* components and tracks on an SMPS primary side are hot and exposed.

2) when building an amplifier, mains wiring is made with everything unplugged and never touched again, while when tinkering with the board as needed here, you are handling and touching it and to adjust it must be on.

Again:
You think both situations are the same?
If what you say was actually true I'd be dead long ago. Death is POSSIBLE, not GUARANTEED.

Adjust it, power it, test it, unplug it, wait for the caps to discharge, adjust and test again.

Also when working with high voltages smart people keep one hand in their pocket or behind their back. Getting a 500V shock across a finger tip sucks but it won't kill you, having that same current go through your body across your chest can easily kill you.

BTW I measured only 330VDC in the ATX (momentarily powered, no load), not 380V. Furthermore you certainly DO feel it if you brush the HV even without touching anything else. It's just nowhere as bad.

In any case I was hoping it might be as simple as adding a diode between the regulation and ground to "lift" it .7V like you can with a 7812...

In any case it seems as it's more complex than that, and I can live with 12V.

This 12V SMPS powers 20 tube heaters and two boost inverters... One that outputs 380VAC at 20kHz, and one that outputs 280VDC. The AC is rectified with HER208 and fed to the plate circuit of a class A push pull 6550 amp. The 280V is used for the line/driver/headphone and buffer stages. I'm thrilled with it's performance. It's stiff, efficient, smaller and cheaper than a linear supply with similar ratings... Plus it's hard to find a transformer that outputs 12V@20A, and 350-250-0-250-350@1A This entire power supply cost me less than $100 to build. My rough math suggests the linear version would cost over $300.

Last edited by kodabmx; 30th October 2017 at 06:06 PM.
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Old 30th October 2017, 11:12 PM   #22
TonyTecson is offline TonyTecson  Philippines
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12.6V from ATX instead of 12V?  Any ideas?
you said you wanted to get 12.6v instead of just 12, your question have been answered and more....

with tubes, filaments can be wired in series, so that high currents can be avoided...
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Old 30th October 2017, 11:58 PM   #23
kodabmx is online now kodabmx  Canada
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Heaters need to be rated for series connection, and I am putting them in series hence 12V instead of using a buck converter for 6.3V. Without knowing more about SMPS design I can't begin to modify it.
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Old 31st October 2017, 12:29 AM   #24
TonyTecson is offline TonyTecson  Philippines
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12.6V from ATX instead of 12V?  Any ideas?
why not post the schematic of your target psu so we can see what can be done,
the pwm chip, what is the part number?
there is the ka7500, TL494, UC3852 etc...

http://www.ti.com/lit/ds/symlink/tl494.pdf
http://www.ti.com/lit/ds/symlink/uc2852.pdf
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Old 31st October 2017, 02:23 AM   #25
kodabmx is online now kodabmx  Canada
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It uses a TNY177PN.

Here's the datasheet.

http://dalincom.ru/datasheet/TNY176PN.pdf
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Old 31st October 2017, 03:18 AM   #26
kodabmx is online now kodabmx  Canada
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Quote:
Originally Posted by Chris888 View Post
Take care with the hot side of a switching PSU.
There can be a lot of energy stored in the caps. The residual current breaker on your bench isn't going to stop that hurting.

If the OP wants more than his PC supply will give, step up switchers are available on ebay for the price of a beer. But I'm sure many attics still contain PC supplies where loading the 5V will boost the 12V a little. Or you can buy a 15V smps for the price of two beers.


There is no "residual current breaker" on my bench. The North American electrical system is hub and spoke, not ring, so in my case I have fuses in a fusebox in the closet for all the circuits in the house. Agreed though 15A won't save you from a shock, however "mains" is much less dangerous here simply because we use 120V 15A branch circuits.

An old PC supply is only 200W-300W, and then mostly 5V and 3.3V whereas this one is 700W and claims to be able to put out 55A@12V

Either the 15V supply for the price of two beers is an underpowered piece of junk or beer is bloody expensive where you are Besides that is it was 15V instead of 12V then 360V would become 450V, and I'd have to use a buck converter for the heaters...
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Old 31st October 2017, 03:22 AM   #27
TonyTecson is offline TonyTecson  Philippines
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12.6V from ATX instead of 12V?  Any ideas?
that is a chopper type pwm circuit,
output voltage controled by feedback from an opto isolator,
so my guess is lowering the value of the opto diode shunt resistor will increase output voltage, perhaps at 20k ten turn bourns trimpot can be used here to vary the voltage,
go slow.....stay safe.....

quick question, what is the brand and make of atx psu you are using?
can you post the label of that psu so we can get more info?
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File Type: png smpsNG.PNG (55.9 KB, 84 views)
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Old 31st October 2017, 03:26 AM   #28
TonyTecson is offline TonyTecson  Philippines
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12.6V from ATX instead of 12V?  Any ideas?
Quote:
Originally Posted by kodabmx View Post
It uses a TNY177PN.

Here's the datasheet.

http://dalincom.ru/datasheet/TNY176PN.pdf
strange but this chip is low powered, perhaps this is for the 5 volt standby ckt to power USB devices and for starting the psu...

700 watts ATX require a double or even more mosfet choppers...
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Old 31st October 2017, 03:45 AM   #29
kodabmx is online now kodabmx  Canada
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It's a Deepcool DA700. I can't find the same model even on their website... I can't see which mosfets is uses (it's a tight squeeze with 4 devices on one sink, and 5 on the other facing inwards. And there are 3 4 pin DIP chips which I can't read the writing (it's tiny).

I'll just leave it alone since it is working. 6V is still in spec for the heaters anyway.

Thanks for your assistance though.
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Old 31st October 2017, 04:27 AM   #30
TonyTecson is offline TonyTecson  Philippines
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12.6V from ATX instead of 12V?  Any ideas?
there are quite a number of brands, but there are not many OEM for atx psu,
there is pc and power cooling, then delta electronics and a few others...

i will bet that that atx has an active power factor correction circuit....

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