What is this potentiometer job

MisterBill2

Joined Jan 23, 2018
18,928
In some versions of PC power supplies there was enough variability in components so that an adjustment was required to set the output to within the specified voltage.
 

Dodgydave

Joined Jun 22, 2012
11,318
Yes it adjust 12V out put but the range is from 10.5V to 12.5, How increase it ranges to 16V?
It uses a KA75008 chip, which uses pins 1+2 and 15+16 as reference inputs to compare and adjusts the output. The preset will adjust one of those inputs and will probably increase in resistance to increase the output voltage, ideally you need to reverse the circuit diagram to see what the other inputs are doing, any shutdown is usually on pin 4, by pulling it high, putting pin 4 low keeps it running.
 

Tonyr1084

Joined Sep 24, 2015
7,943
I have a 12V power supply modified to output 13.6V. I changed that by adding an external pot to adjust the reference voltage. I don't have that file any longer as I did not think I'd need it. It's something I did some decade or so ago and is still working just fine. It is low power and maintains a 12V car battery at float charge. That car battery plays a car radio. At first it was an accoutrement in the garage for the sake of having music while working on a car. Wife drove an 87 Celica. Good car but I spent more time under the hood than I did in the driver seat. But then again it was her car. That PS/battery charger and radio migrated into my wood working workshop where it gets played every day. And the PS has been plugged in easily over 10 years. When first building it I was advised to change the output caps because they were rated for 16 volts. I never did change them and they're still working just fine.

In my case I had to find a chip, a 431 I believe was the chip along with a couple 1% resistors. I then determined I needed to change the value of one of those resistors to a lower resistance, thus changing the reference point. I added in a series resistor to prevent accidentally shorting the original resistor. Got it done. Still enjoying the fruits of my labors. All thanks to the great advice I received here on this website and the many great and experienced experts who know a thing or two. And a lot more. If I manage to come across that illustration I'll post it. But it won't be like your PS. But it may give you some ideas.
 

MisterBill2

Joined Jan 23, 2018
18,928
To learn if it is even possible to adjust the output voltage higher you will need to trace out the circuitry related to that voltage adjust variable. In some arrangements the variable has additional resistors on one side or the other so that it's adjustment range can be limited. In that case, changing the external series resistor may allow raising the output to what you seek.
One caution is that often the POWER out is the limiting factor, meaning that as the output voltage is adjusted higher, the output current available would be reduced.
 

ThePanMan

Joined Mar 13, 2020
800
Keep in mind also that 1 amp at 12 volts is 12 watts but as you go up in voltage there's a balancing act where the amperage goes down. So if you go up to 18 volts; 12W ÷ 18V = 0.66(2/3) amps. No free lunches. We can call that 667mA.
 
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