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Old 28th January 2005, 09:15 PM   #1
csl113 is offline csl113  Romania
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Default variable power suply

i need a schematic for a variable power suply , ajustable between 12-50V and between 0.5-5(6)A....and i need bothe pozitive and negative regulators, becaude i need +,gnd,- .....

i found something, but not more then 30V....something like lm317,(i think) + one or 2 power transistor....problem is that i need to be up tu 50V...and i need also to be able to control what the curent is going trough....

i don't need a small riple, about 50,or even 80-90-100 mV will do fine...

can someone help me...????
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Old 28th January 2005, 10:07 PM   #2
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you can use the LM317HV (high voltage version of the LM317) with a pass transistor -- but for +/0/- you will need a transformer with two independent secondary windings -- the negative supply is regulated in its ground return (which is, after all, positive) .
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Old 28th January 2005, 11:03 PM   #3
csl113 is offline csl113  Romania
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yes,jackinnj i did not know about the LM317HV ,only about the LM317....

i found this schematic in the datasheet, what do i need to change for this to work with hier suply voltage...let's say a 50-55V input and stil deliver a 5 A at the output,or even better a 6 A....or it will work as it is at this voltage...???(also i will double the output tranzistor, 2 are better then one, and at 50V and 5 or 6 A one will be not enaugh...)
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Old 29th January 2005, 12:17 PM   #4
sss is offline sss  Israel
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try lm350 , its an old but good regulator and i can get 'em with no problems, the max voltage is 33V i think but it can be floating - the max voltage is the input to output voltage on the regulator , so u can use 50V supply but u can go down to 50-33= 17V
there is schematic in the datasheet how to parralel em'
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Old 4th February 2005, 07:51 AM   #5
d3imlay is offline d3imlay  United States
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You better have a lot of heat sinks and fans. If you really want 5-6 amps over that voltage range you're going to have a lot of heat to dissipate. This application begs for a switching supply, not a linear.

One possible solution would be to use a transformer with dual primaries and have a high/low range. Use the primaries in parallel for the high range, and in series for the low range. Note that you'd have to derate the available current from the transformer at least 50% on the low range to avoid burning up the primaries. Make sure that the power supply is stable over a wide input voltage range. 108-132 VAC is standard.
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Old 4th February 2005, 09:16 AM   #6
UrSv is offline UrSv  Sweden
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Take a look at:

http://www.a-and-t-labs.com/K2_Lab_P...pply/index.htm

If you need that output current when using low voltages you will, as mentioned, need serious heatsinking. Try and use pre-regulation by either switching the charging of the reservoir caps or by switching different transfomer windings depending on voltage needed.

Janneman presented a circuit for this while back.
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Old 4th February 2005, 01:48 PM   #7
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Quote:
Originally posted by d3imlay
You better have a lot of heat sinks and fans. If you really want 5-6 amps over that voltage range you're going to have a lot of heat to dissipate. This application begs for a switching supply, not a linear.

One possible solution would be to use a transformer with dual primaries and have a high/low range. Use the primaries in parallel for the high range, and in series for the low range. Note that you'd have to derate the available current from the transformer at least 50% on the low range to avoid burning up the primaries. Make sure that the power supply is stable over a wide input voltage range. 108-132 VAC is standard.
Hewlett Packard provided a series of linear power supplies which would do 250 watts -- the rails were +/- 75V -- so you can imagine the amount of heat being dissipated. I bought a number of them during the technology crash in the US -- the least expensive was $1.00 but I had to drive to Bethpage, Long Island to pick it up.

Note the fan and "wind tunnel" heat sink.

Click the image to open in full size.

and

Click the image to open in full size.

Today's bjt transistors can take a lot more punishment, the error amplifiers are better and we seem to know a bit more on how they should be compensated. You will be pretty surprised at how well an LM317HV works with a couple external pass transistors. (unfortunately, there isn't an LM337HV -- that's why you need a trannie with two independent windings -- not too difficult to find, however.)
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Old 5th February 2005, 03:19 PM   #8
csl113 is offline csl113  Romania
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exacly what i need!!!

thanks a lot!!!
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