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Old 12th January 2005, 11:19 AM   #11
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Might be able to chop out the power-on circuit (probably easier to build from scratch). It uses (I belive) a +12v pulse to power on. Could be +5v, I'll check. Might be a good use for my extra low-voltage leads from my current transformer.... I have an old PS right here.

hmmm
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Old 12th January 2005, 02:57 PM   #12
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Default Radio amateurs, in my country, use those PC supplies to power transceivers.

Transceivers need 12 to 15 volts with 20 amperes.

I am not sure the method, but i heard that they found one 5 volts zener somewhere, as 5 volts output has enormous current capacity, this one is used....they put a 5 watt, with 22 ohms in series resistor in series wit the main 5 volts reference zenner and Ready!!!...there's a 13.8, 20 amperes perfect supply...using 250 Watts PC supplies.

To radio, there's a problem, there are some oscilators that create some "beating" of frequencies with the transceiver oscilators...this way...people use some LC small filtering to the output to avoid that...and put the supply 10 feet away to avoid radio frequency interference.....this rises the "idea" price, as the wire must be special and really heavy gauge, as with that current.... every ohm is a tragedy!

To make plus 14 and minus 14....or even bigger voltage...lets see....hummmm 22 plus and 22 minus, you will have to put bigger zenner related their voltages and discover the protection...the over voltage protection must be switched off...if not...supply will not go on with bigger voltage than maximum alowable by the over voltage internal protection.

I do not know how to instruct you, as i never done....but hundreds of guys are doing that here, and thousands are working in many radio amateur stations in this country.

Those switching supplies, PWM supplies created the class d Amplifier, that is some modified supply only, with double greek "P" letter filter in the output...the filter is passive.

They are wonderfull... small, lightweigth, reliable...but have one terrible defect:

- "I do not dominate them, i do not know exacty how they work", this way i stay alike an indian watching one airplane..... Yeahh..big silver bird.... God of the winds may be...Yuuuugahhh!

Maybe can put two in series to have positive , ground and negative...but really...only Eva can answer that question with 100 percent guaranteed answer quality.

If you had received some money playing cards....if some airplane fall down around you and not hitted you..... if you crash your car against some wall at 150 miles per hour, and no damage in your skin...you will be lucky enough to find this guy...sorry...this girl...EVA.

Carlos
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Power supply; ripple, filter, noise, stability and the use of capacitance multiplier... Portuguese and English; https://www.youtube.com/watch?v=sSm0ku1eIgg
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Old 13th January 2005, 01:50 AM   #13
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+13.5V 14Amp cont. 20 A for 20 sec.
See the link,Tried it 2 years back it works fine...Still used as a battery charger.
http://www.webx.dk/oz2cpu/radios/psu-pc1.htm
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Old 13th January 2005, 08:41 PM   #14
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Default On the target...100 point to you man, thank you.

The complete service...told us all he needs, and all i need too.

thank you

Carlos
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Power supply; ripple, filter, noise, stability and the use of capacitance multiplier... Portuguese and English; https://www.youtube.com/watch?v=sSm0ku1eIgg
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Old 21st January 2005, 08:13 AM   #15
Rahul is offline Rahul  India
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Hi!

As a amateur radio operator I have also looked into this conversion. Most PC SMPS are noisy in one of them I measured about 50mV - 100mV peak high frequency ripple.

While using with HF ie shortwave transceivers the radio goes CHuuurrrr every 40 Khz. For VHF radios operating on 144-146Mhz the noise is not noticeable. One such converted supply gave about 11amps at 13.6V . This was good enough for normal 25-40W VHF transceivers.

Here is another link describing such Mod:

http://www.qsl.net/aa3sj/Pages/PC-Supply.html

BTW Icom kenwood and many other companies manufacture such supplies a search over the net can provide their schematics. PS 85 is one such PSU.

Regards

Rahul ( Wireless call VU3WJM)
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Old 28th January 2005, 06:52 AM   #16
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Rahul !!!
Thanks for ur input. Switching supplies produce noise and the harmonics may even extend to HF Range, and even upto 250Mhz.U may notice this only in AM ie in HF,and not
in 2 meter amateur VHF band the sound is Freq Modulated.
I noticed noise in picture of TV,Which was solved by using a high PYE filter at the output of SMPS and a double PYE @ the mains input end.(filter from an old TV was used successfully.
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Old 7th February 2005, 03:01 PM   #17
Rahul is offline Rahul  India
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Dear Sivan,

Hi!

Sorry for late reply was out of town. I have come to conclusion after going thru many ckts that common mode at AC as well as DC out put is solution to the noise problem along with extensive lead screening using high mu ferrite cores.

Recently while at N Delhi I have procured ferrite cores as well as powdered iron torroids to make a 25amp 13.6V supply. Small double section bobbin and cores have been also procured for input filtering as you suggest.

I would be obliged if you can give some tips for the same specially on choise of transistor. Topology used is half bridge as in common PC supplies.

Regards

Rahul
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Old 8th February 2005, 12:38 AM   #18
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Rahul !!!
BUH1215 Transistor = 600watts SMPS A/C i/p =250volts
IFR840= Hexfet= 500 watts SMPS A/C i/p =250volts.
both in half bridge config.
My choice IRF840, Can use the same EE16 core (as in PC SMPS) for gate driving but with modiified turns ratio.

PS: I was really amazed to see ur web site..congrats and 73's.
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Old 8th February 2005, 04:24 AM   #19
Eva is offline Eva  Spain
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I've tried BUH1015 and BUH1215 and they are very slow so switching losses become quickly unacceptable. Don't waste money with them

I've also tried MJE18008, that worked much better, and MJE13009 that is the best I've ever tried. Note that these devices were originally made by On Semiconductor but have been cloned later by a lot of companies. I've not tried the clones but I have reports stating that they show inferior performance in comparison with the originals, making them unusable in high power SMPS

I've succesfully used four MJE13009 in a full-bridge configuration to produce 1000W of continuous output at an Ic of 6A. Now I'm gathering more parts and redesigning the prototype to use two power transformers instead of one and three pairs of MOSFETs instead of one for synchronous rectification of the 14.4V output. My target is 1500W [Ic=9A] or more if the MJE13009 allow them reliably. This is 14.4V 108A while the current prorotype produces only 72A

Base-drive transformer design is very tricky. I'm using its own magnetizing inductance to borrow some Ib at the end of the cycle for faster turn-off and get that Ib returned back in the beggining of the next cycle to speed up turn-on saturation process

This works very well and makes redundant the saturation-helping circuit I was previously using,
that provided 1A of additional Ib during the first 1uS of each cycle. The difference is easily felt on the heatsink

When finished, this project will also make a nice and simple high efficiency SMPS for audio amplifiers [with suitable transformer secondaries] and it does not require expensive nor exotic parts. Only SMPS transformer winding skills will be required to build it

I'm also planning to use a PFC front-end to power the full bridge with 340V or 420V pseudo-regulated and get up to 2.8KW output with just four MJE13009 or MJE18008 bipolar switches
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Old 8th February 2005, 05:27 AM   #20
Rahul is offline Rahul  India
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Thanks Sivan & Eva,

Most of the commercial supplies that I have gone thru in this class I found using transistors in TO247 type of casing. In one of them the transistor was 2SC2625. I will have to check its specs and availibility in local mkt.

Eva as you have rightly noticed the driver transformer design is very critical specially where saturation at start up is concerned. A recent article in Dec 2004 QEX deals with this issue and component wise detailed analysis and modification of an ATX power supply. It has been found that ones used have more than the required inductance so a replacement has been designed using ferrite torroid.
If needed drop a line for that article, its about 1.4meg.

I do remember repairing a small 40Kv unit for xray using IRF840 in half bridge configration, remember tracing it out will look around. This appears to be the cheapest way to go.

Regards to all.

Rahul
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