LM320 voltages?

4 replies [Last post]
Offline
Joined: Oct 15 2013
Posts: 17

Can anyone tell me what voltages they are reading on the out and in pins on the LM320 marked in the attached pic?

http://imgur.com/c1hM39d

This is an Apple I replica.

Thanks,

Win

AttachmentSize
IMG_5066.jpg1.34 MB

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.
speedyG's picture
Offline
Joined: Nov 16 2011
Posts: 2376
Re: LM320 voltages?

Hello wheagy,

The input of the -12 Volt regulator should display same voltage as the
minus output of the diodes from the small rectifierbridge depending to
the transformer you use ( - 12 Volt to - 18 Volt ) and the output of the
minus 12 Volt regulator should display a value from -11,6 volt to -12,4 volt
by datasheet. The output of the minus 12 volt regulator also feeds the
input of the minus 5 Volt regulator with the regulated output of the
minus 12 volt regulator ( displaying same value ) and at the output of the
minus 5 volt regulator there should be a value from -4,8 volt to -5,5 Volt present.

the picture below also displays the path by light orange:

remark:
besides... you should also clean away that remaining soldering resine
like that still remaining at the capacitor at bottom left side
with old toothbrush or similar tool....

sincerely speedyG

__________________

In early days I had a lot of money but no time - now I have no money but a lot of time....
the second part includes less friends but a lot more joy on life....

Offline
Joined: Jun 15 2014
Posts: 305
Re: LM320 voltages?

speedyG wrote:

remark:
besides... you should also clean away that remaining soldering resine
like that still remaining at the capacitor at bottom left side
with old toothbrush or similar tool....

sincerely speedyG

Depending on flux type. Probability is high that this cleaning is not necessary.

Offline
Joined: Jun 5 2008
Posts: 380
Re: LM320 voltages?

The input to the regulator needs to be -2 volts below the regulated voltage of -12V and since there is probably some ripple on the input, you want a little extra. Anything in the very general area of -20 volts is what I've seen with US mains power and the transformers recommended by WOZ. Minimum would probably be around -15 and max input for the regulator is -30. There is a trade off, the farther the input is from -12 volts, the hotter the regulator will run.

regards,
Mike WIllegal

Offline
Joined: Oct 15 2013
Posts: 17
Re: LM320 voltages?

That's helpful, thanks Mike.

Win