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need to make a 3v ac adapter

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xer0

New Member
its for my digital camera, so it has to be at least 1500mA
i have a 24vac adapter that a took from a garage door opener
can i use that?

i dunno how many mA it puts out, theres no labels on it
thanx
 

Sebi

Active Member
In this case not recommend for use any analog (dissipative) regulator, because the dissipation about 35...40W! Use a simple switcher SMPS regulator from Nat*ional Semi*conductor with very low dissipation (LM2576-adj).
On NSC website You can find applications.
 

bogdanfirst

New Member
yes, think that means you would need to get 1.5 amps from the transformer, wich if you would use a switching regulator, you would need about 300-400A instead, so it would be better. if you were to use a LM317 regulator at full power it might be very possible to destroy it and certainli after a few minutes the termal protection will lower the voltage. i used it to power a 1.5Amp fan/6V from a 36 voltage suply and even with a large heatsink after a few minutes, 10-20, it stopped.
so the simple regualtor is out of the question
 

kinjalgp

Active Member
LM723 IC can work as SERIES, SHUNT, SWITCHING OR
FLOATING regulator. So you can use that too.
 

bogdanfirst

New Member
but it has current limiting to 150mA, so it needs an external transistor, so still you loose much heat and its not a switching suply
 

kinjalgp

Active Member
If you are using the IC in switching mode then ofcourse the circuit along with external transistor is going to be in switching mode too. And finally the output of a any switching regulator is in form of DC pulses which is fileterd and converted to pure DC using an external capacitor. S I don;t think in swithhing mode the external transistor is going to dissipate additional power.
 

Sebi

Active Member
One problem with 723 as SMPS: the low switching frequency requires relative big inductivity 1...1,2mH.The simply switchers uses only 47....330uH.
 
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