hi there,
i need 17 volts dc after the lt1085/1033 regulators, but how big a trafo (ac) can i actually use with good and safe result....?
(i have a 225va, 2 x 18volts ac - perhaps its too big?)
best regards,
troels
i need 17 volts dc after the lt1085/1033 regulators, but how big a trafo (ac) can i actually use with good and safe result....?
(i have a 225va, 2 x 18volts ac - perhaps its too big?)
best regards,
troels
2 x 18 V AC is a good choice for + and - 17 V DC. It will give you roughly + and - 25 V on the filter caps. Use 35 or 50 V electrolytics.
It depends of the load of course how many (milli)Watts the regulators will dissipate. You can calculate this if you know the load. Be sure to use big enough heatsinks. Each regulator will have to dissipate the 8V voltagedrop x Iload.
Please see the datasheet for details: http://www.iapp.de/~trogisch/work/chips/lt1083adj.pdf
Regards,
Jean-Paul
It depends of the load of course how many (milli)Watts the regulators will dissipate. You can calculate this if you know the load. Be sure to use big enough heatsinks. Each regulator will have to dissipate the 8V voltagedrop x Iload.
Please see the datasheet for details: http://www.iapp.de/~trogisch/work/chips/lt1083adj.pdf
Regards,
Jean-Paul
No. I assume you're talking about a 2 x 15V transformer.
Since you use low drop regulators you maybe can get away with it with low loading but it certainly is not well designed if you do.
Keep the 2 x 18 V transformer for this purpose. You will have some "headroom" left for extra RC filtering before the regulators if you like.
I want to emphasise to read the datasheet carefully concerning how to connect the resistor network from the Adjust pin to the load ! Load regulation will be much better if you do it like this.
Regards,
Jean-Paul
Since you use low drop regulators you maybe can get away with it with low loading but it certainly is not well designed if you do.
Keep the 2 x 18 V transformer for this purpose. You will have some "headroom" left for extra RC filtering before the regulators if you like.
I want to emphasise to read the datasheet carefully concerning how to connect the resistor network from the Adjust pin to the load ! Load regulation will be much better if you do it like this.
Regards,
Jean-Paul
Troels, this thread can be very inspiring and it mentions the Kelvin point connection and the errors that will come up if you do it the wrong way:
http://www.diyaudio.com/forums/showthread.php?threadid=985&perpage=15&pagenumber=3
http://www.diyaudio.com/forums/showthread.php?threadid=985&perpage=15&pagenumber=3
yes alw is very inspiring....
but i was looking for some experience concerning the voltage before and after the regulator - does it work better with a big drop or should the drop be as small as possible ?
perhaps some found a "golden rule"
thanks again,
troels
but i was looking for some experience concerning the voltage before and after the regulator - does it work better with a big drop or should the drop be as small as possible ?
perhaps some found a "golden rule"
thanks again,
troels
Hi Troels, I thought I shared some experience with you about the subject. There is no golden rule, there are golden rules better described as mathematics. Please look in an electronics book for all the formulas and the do's and don't's. There's no voodoo in here.
A too big voltage drop will generate useless heat and we don't want to throw away precious energy, don't we ? A too small voltage drop will cause your supply to be unstable and behave erratically.
Maybe a rule of thumb could be to use a transformer with the same AC Voltage as the desired DC Voltage at the output of the regulator. If the AC Voltage is below the desired DC output Voltage you better not use that transformer. I admit this is a too simple view of the matter.
A link that may be of some use:
http://www.duncanamps.com/psud2/
A too big voltage drop will generate useless heat and we don't want to throw away precious energy, don't we ? A too small voltage drop will cause your supply to be unstable and behave erratically.
Maybe a rule of thumb could be to use a transformer with the same AC Voltage as the desired DC Voltage at the output of the regulator. If the AC Voltage is below the desired DC output Voltage you better not use that transformer. I admit this is a too simple view of the matter.
A link that may be of some use:
http://www.duncanamps.com/psud2/
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