ugghh school was too long ago

[too_long_ago]

Ok,

I lost the low voltage power supply in my computer monitor. Caps look good, transistors test ok.
Still only get out 3 v where should be 12.

Time and money are in short supply, so I found this old external power supply I was going to wire in.
But....It puts out 19v and only 2.3 a.

Could I put a resistor in line somehow and make this thing work. I was thinking of putting a 1.4 ohm 35w resistor in there to drop the voltage , but just realized my current is also to low.

Thanks

 

[Hero999]

It won't work because you don't know how much the monitor takes from the 3V supply.

The current specified on the PSU is just the current capacity, the actual current depends on the resistance placed across the PSU.

The chances are a resistor woudn't work anyway because the current taken by the monitor probably varies depending on the brightness of the screen or the image being displayed..

 

[crutschow]

You might try a 7812 regulator at the output of the 19V supply. Depending upon the current, you may need to attach it to a heatsink.

Edit: That probably won't work since the 7812 is only good for 1A.

 

[Reloadron]

I agree with crutschow but there is another possibility you need to consider. Is the existing power supply only delivering about 3 volts as a result of power supply problem or is it being loaded down excessively as a result of a problem further up the line from it?

Ron

 

[Hero999]

Yes, that's right, I misread the post, it's the 12V that doesn't work, not the 3V. A simple linear regulator should do the job, as long as the current taken by the monitor isn't too high.

 

[too_long_ago]

I had the power supply removed from the monitor, it was only outputting 3 v.
I said heck with it anyway. Monitor is very old, and I need a new one anyway, so not a lot to lose.

I wired up the external 19v 2.5 a power supply into the monitor. Power it up, works fine......for now :>)
We'll see how long it lasts before it overheats.

Thanks for all the replies.

 

[Hero999]

It might be fine with 19V but don't be surprised if it overheats.