If I need to low down a +58VDC/1.5A straigth down to 3.3V - diyAudio
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Old 20th September 2007, 08:28 AM   #1
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Join Date: May 2005
Location: HK
Default If I need to low down a +58VDC/1.5A straigth down to 3.3V

Which IC should I try to use?
1) LT3010-ADJ or LT1030-5 then with a zener
2) LM2936HV-3.3

Since I am not sure about the heat problem, although I have try to read and understan the pdf files, but if this straight step down will generate high temp., then the IC should become can't withstand the high input voltage, since themaximum voltage inout should only under the conditions of 25 degree general room temp., anyone have expereince with these (or any other SMD mount, simple/easy connections suggest) wide input range voltage regulator?
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Old 20th September 2007, 08:55 AM   #2
ssanmor is offline ssanmor  Spain
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Join Date: Jan 2002
Location: Madrid
It all depends on what you are going to feed with 3.3V (its max. current demand, Iout), and how much power you can dissipate.

The total power you are going to dissipate is: (58-3.3)*Iout

If that's only some watts, you can simply use a LM317 (TO220) with a 27V zener in series with its input so it doesn't see more than aound 31V. This way, the zener will dissipate Iout*27V watts (again, make sure that you choose a suitable power rating for the zener), and (58-27-3.3V)*Iout in the LM317.

In practice, if you require more than, say, 100mA in your 3.3V device, I would go for a separate transformer or a switching regulator, taking great care of noise, of course.

Best regards,
Sergio Sanchez
www.coldamp.com
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Old 20th September 2007, 11:19 AM   #3
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The loading will need to draw only around 30mA maximum, but problem is I must need to use SMD device since the area possible to fit in this regulator section is only as a finger tip, plus this will be a totally encapsulated section, therefore I am worry about the heat problem.

Pdf files have stated the maximum voltage input of this regualtor chips will be drop against heat increase, but I have no idea how hot will be in my case.

Thoeratically as my unerstanding, this should only base on the loading current draw, but I did done some test by simple resistors and zeners, since the source of +58V DC/1.5A is non-regulated and non-current limited, even I use over 1W resistors and zeners, the heat will increase when input source can deliver higher currents, NOT loading draw higher current, the loading always keep draw only maximum 30mA.

That's why I am asking to see if anyone have experience with these kind of SMD wide voltage range regulator chips, if they already very easy work hot against input voltage, then no matter how much current draw on loading, there should be nothing could fit me......
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Old 20th September 2007, 11:56 AM   #4
ssanmor is offline ssanmor  Spain
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Not sure if I understand you: if you keep output voltage (+58V) constant, and the 3.3V circuit load constant, the heat in your regulator will be constant, no matter what the load is in the 58V output.
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