# Help needed building power supply

J

#### Jerry Lynds

Jan 1, 1970
0
Hello,

I need some help in building a 12V dc power supply. I can find lots of
documentation on building one from scratch and selecting a transformer for
the initial AC supply voltage, but this is my problem. I wish to impliment
this 12 Vdc into an audio amplifier and draw from its current transformer. I
do not want to introduce another transformer. So, I am confused as there is
not much documentation/theory for me to learn from. The exact requirements
are 12Vdc @ 600 ma...no idea as for a max ripple voltage...LCD back light
supply

I measured a +-38V dc after the rectifier diodes. I have a 12V regulator
but I need to know how to get the 38V dc to a usable level for the regulator
and have it filtered. Normal theory tells me to use a capacitive filter
rated at twice the voltage of the supply. But, the regulator has a max input
rating of 34Volts....so now I am lost.

Please, someone help or point me to some www.com where I can
learn...again...every place I find assumes building a power supply based on
a ideal transformer rating for the intended output voltage

Jerry

G

#### GregS

Jan 1, 1970
0
Hello,

I need some help in building a 12V dc power supply. I can find lots of
documentation on building one from scratch and selecting a transformer for
the initial AC supply voltage, but this is my problem. I wish to impliment
this 12 Vdc into an audio amplifier and draw from its current transformer. I
do not want to introduce another transformer. So, I am confused as there is
not much documentation/theory for me to learn from. The exact requirements
are 12Vdc @ 600 ma...no idea as for a max ripple voltage...LCD back light
supply

I measured a +-38V dc after the rectifier diodes. I have a 12V regulator
but I need to know how to get the 38V dc to a usable level for the regulator
and have it filtered. Normal theory tells me to use a capacitive filter
rated at twice the voltage of the supply. But, the regulator has a max input
rating of 34Volts....so now I am lost.

Please, someone help or point me to some www.com where I can
learn...again...every place I find assumes building a power supply based on
a ideal transformer rating for the intended output voltage

Jerry

The problem you have is dissapating at least 10 watts of heat. Going to need a big heat sink,
and maybe some zener diodes to soak up a little voltage. There
may be a switching device or just a plain DC to DC conveter you cn easily use.
I added a supply in an amplifier by doing what you didn't want to do.

P

#### Pooh Bear

Jan 1, 1970
0
Jerry said:
Hello,

I need some help in building a 12V dc power supply. I can find lots of
documentation on building one from scratch and selecting a transformer for
the initial AC supply voltage, but this is my problem. I wish to impliment
this 12 Vdc into an audio amplifier and draw from its current transformer. I
do not want to introduce another transformer. So, I am confused as there is
not much documentation/theory for me to learn from. The exact requirements
are 12Vdc @ 600 ma...no idea as for a max ripple voltage...LCD back light
supply

Jesus Christ !

Graham

J

Jan 1, 1970
0
J

Jan 1, 1970
0
J

#### JeffM

Jan 1, 1970
0
Jesus Christ !
No, he does carpentry -- not circuit design.
Tim Wescott

Actually, the turkeys who translated from the Greek texts
to make the KJV did a lousy job.

*Tekton*, properly translated is **hand-worker**.
generally thought to equate to the modern *itinerate day-laborer*.
NOTE: Neither of these fools can make a proper HTML page:
http://validator.w3.org/check?uri=http://www.voiceofjesus.org/extremelanguage.html
1438 errors (The actual page is 72kB.)
http://validator.w3.org/check?uri=http://www.tektoonics.com/parody/crackedvoice02.htm
Failed validation

It makes perfect sense.
If Joseph and his sons were cooped up in a carpenter shop in Nazareth,
Jesus would not have been quite so able to spread his dogma widely.

K

Jan 1, 1970
0
join

J

#### Jerry Lynds

Jan 1, 1970
0
Thanks for the replies,

I was just doing some reseach and educating myself on switchers such as
LM2576HV-12. I will try the circuit (fixed output voltage version) on page

http://www.ecom.cz/novinky/lm2576.pdf

Sorry for the dual posts/topics...my newsgroup server is not getting
messages to quicly so I thought no one was responding...

Jerry

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