# AT supply? - Increasing output the voltage.

R

#### Rob Paisley

Jan 1, 1970
0
Would it be possible or practical to increase the output voltage on
the 12 volt line of an AT type power supply to 14 or 15 volts if the
output current was suitably de-rated.?

The affect on 5 volt and other lines is of no concern in this
question.

Thanks.

Rob.

A

Jan 1, 1970
0
some supplies have a trimmer for the output, you can try increasing it,
You may also need to remove the feedback from the +5V line. Note these
supplies sense a "mixture" of the +12V and +5V lines feeding to the
TL494 error amplifier. You need to replace with appropriate resistors
values. I made a cheap 25A variable power supply by putting a 10 turn
pot on the voltage feedback loop in a ATX supply so it gives 0 to 5V on
the "+5V" line. This is possible in a ATX supply because the PWM

B

#### budgie

Jan 1, 1970
0
Would it be possible or practical to increase the output voltage on
the 12 volt line of an AT type power supply to 14 or 15 volts if the
output current was suitably de-rated.?

Most if not all the AT supplies I have serviced have regulated ONLY the +5v
line. The other rails were derived simply by turns ratio. (This current box
has +11.42v on the +12v line but it isn't worth intervening).

As long as you are prepared to add turns to the core in series with the +12v
winding, it is straightforward. If the core doesn't have enough daylight left
in it you may have to unwind and rewind windings and re-do the +12v in a lighter
gauge wire.

Plan B would be to fiddle the +5v feedback divider to get the same end result.
This is fine as long as you don't ever want to use the +5v as a +5v source, and
assuming you can correctly identify the relevant components.
The affect on 5 volt and other lines is of no concern in this
question.

See above.

N

#### Nico Coesel

Jan 1, 1970
0
Would it be possible or practical to increase the output voltage on
the 12 volt line of an AT type power supply to 14 or 15 volts if the
output current was suitably de-rated.?

The affect on 5 volt and other lines is of no concern in this
question.

It has been done before by several people. It is not a difficult

T

#### Tam/WB2TT

Jan 1, 1970
0
Rob Paisley said:
Would it be possible or practical to increase the output voltage on
the 12 volt line of an AT type power supply to 14 or 15 volts if the
output current was suitably de-rated.?

The affect on 5 volt and other lines is of no concern in this
question.

Thanks.

Rob.
If you are trying to power a ham transmitter at ~14V, this was all hashed
out in QST months ago. Unless you actually plan to redesign the supply, you
probably shouldn't do it unless you have a very cheap radio.

Tam

M

#### mike

Jan 1, 1970
0
Nico said:
It has been done before by several people. It is not a difficult

If you're gonna do this, measure the 5V output with the other 12V output
set at it's highest setting. Then compare that voltage to the voltage
rating of the 5V filter caps. You don't want them exploding on you.
Might also look at the ratings of all the other components in the system.

If you don't change the feedback to regulate the +12, your regulation
will be crap. If you do change the fedback, do a lot of tests with
various load transients to make sure the system is stable. If the
output turns out to have a big inductive reactance, load dumps will
give you big voltage spikes.

I'll try to verbalize my assumption...the way you asked the question
leads me to the assumption that you don't have the technical expertise
or equipment to evaluate the result. Yes, it can be done. Can YOU do it?

Bottom line is economics. Compare the $20 you saved on a power supply to the replacement cost of the$2000 laptop computer you're testing. If
you like the odds, proceed.

mike
--
Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121
Bunch of stuff For Sale and Wanted at the link below.
Compaq Aero floppy,ram,battery.
MINT HP-41CV, 2-METER AMPS, 200CH SCANNER
http://www.geocities.com/SiliconValley/Monitor/4710/

N

#### Nico Coesel

Jan 1, 1970
0
mike said:
Bottom line is economics. Compare the $20 you saved on a power supply to the replacement cost of the$2000 laptop computer you're testing. If
you like the odds, proceed.

The OP stated the 5V is of no concern. He probably wants to feed
something else than a computer at a higher voltage.

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