transformer basics

Thread Starter

adamclark

Joined Oct 4, 2013
472
The transformer appears to be quite small, you will be very limited as to the current capability and keep in mind that regulators consume power also.
Max.
maybe I should have gave something for reference.. the transformer is about 2.5 by 2.5 inches and give out 19.6vac full wave when measured.. I have one that's physically bigger but it only outputs 7vac...
 

#12

Joined Nov 30, 2010
18,224
It is never a good idea to use 2 regulators if one will do the job. They fight.
Better to switch resistors on one regulator to get different voltages.
The wattage rating of the diode doesn't mean much. It's the amp rating that matters.
Got any part numbers?
And, yes, bigger runs cooler, so it's a good idea, up to a point.
 

Thread Starter

adamclark

Joined Oct 4, 2013
472
It is never a good idea to use 2 regulators if one will do the job. They fight.
Better to switch resistors on one regulator to get different voltages.
The wattage rating of the diode doesn't mean much. It's the amp rating that matters.
Got any part numbers?
And, yes, bigger runs cooler, so it's a good idea, up to a point.
the big ones say sb560 1093 on them what would the ideal ones be,, I could easily go buy some
 
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Thread Starter

adamclark

Joined Oct 4, 2013
472
and in the middle of all of this info im trying to soak in, heres another newb question.. I know what +12v means and I know what - means.. but what does -12v mean and ive seen a lot of schematics with -voltage on them,, what is the importance of - voltage and should I be considering adding this into my psu?
 

#12

Joined Nov 30, 2010
18,224
Schottky 60V 5A
Plenty good enough.
Be aware: The voltage at no load will decrease as you use some power from the transformer. Very unlikely that the transformer is rated as 19.6V Probably rated at 15 volts.
 

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MaxHeadRoom

Joined Jul 18, 2013
28,619
. I know what +12v means and I know what - means.. but what does -12v mean and ive seen a lot of schematics with -voltage on them,, what is the importance of - voltage and should I be considering adding this into my psu?

If working with Op amps they often have dual supply +12 0 -12.
There is single supply types, however.
Max.
 

#12

Joined Nov 30, 2010
18,224
Yes. I would definitely make a dual polarity power supply with + 12V and -12V. Some things just can't get along without both.
 

BobTPH

Joined Jun 5, 2013
8,813
what is the capabilities of the lm338? here is something I was considering (thanks to scottwang) I also put my transformer on the page for some sort of reference
5A, and it works just like an LM317.

Are you sure that transformer is 2 1/2 in square? It looks more like 1 1/2 in when sitting on that lined paper.

Bob
 

Thread Starter

adamclark

Joined Oct 4, 2013
472
I tried to copy and paste the original from a pdf but it wouldn't let me.. what exactly is the purpose for the -voltage, all my experience comes from 12v automotive electric.. ive never had the need for negative voltage.. what exactly is the purpose for it?
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
If you intend working with various op amps, the dual supply will be handy, op amps have featured dual supplies since their inception, one reason was to enable amplifier output to reach 0v.
There are other considerations, depending on the circuit you have in mind.
There are other IC's such as DAC's and such that use -dcv.
It all depends on what circuits you intend working with, but most bench P.S.'s have the dual voltage option.
Max.
 

#12

Joined Nov 30, 2010
18,224
4 instance, audio has a waveform that goes both positive and negative. If you don't have a negative supply voltage, the amplifier can only do half the wave.
 

Thread Starter

adamclark

Joined Oct 4, 2013
472
got it on the - voltage thing.. the sound wave remark made sense.. I do believe this needs added to my psu, thank you.. and ive attached another image that I hope you can see better....
 

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Thread Starter

adamclark

Joined Oct 4, 2013
472
got it on the - voltage thing.. the sound wave remark made sense.. I do believe this needs added to my psu, thank you.. and ive attached another image that I hope you can see better....
ok on the image I attached a couple things were left out.. the transistor is a 2n2905 and the missing resistor value under the third lm317 is 100 ohms..
 
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