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How to regulate output current of a power supply

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debasisswan

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Hi,
I have a 12V DC 1500mA supply (Non regulated output) built with 1 simple step down transformer, two 5480 rectifier diodes and one 2500mFD condenser. I use it to power a heater element that protects my Telescope lens from dew deposition in outdoor works during winter. Now I want to use it to charge my Sealed Lead Acid battery of 12V 7.5Ah. too.

I have learnt from the posts of senior members of this group that the charging current for a SLA battery should be 1/10th of its Ampere hour capacity. And the charging Voltage should be battery voltage x 1.2. So, for me, it should be 700mA. 14.4V DC.

With the help of senior group members, even with my novice workmanship, I could successfully build a regulated output charger using LM341 for my 6V SLA battery. Is there any way to use LM 341 to regulate the output voltage and current both for my 12V supply that can be used safely to charge my 12V battery? Please help.
Regards and thanks in advance-
Debasisswan
 

IanP

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The voltage from the unregulated 12/1500 source is to low ..
If you don’t have alternative power source (roughly 18Vdc/1A) you can step up 12V (unregulated) to 17-18V dc using something like the LM2577 and then with the LM317 in a constant current configuration charge both 6V and 12V batteries ..

IanP
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debasisswan

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Thanks Srhoar and Ianp,

Ianp wrote- "The voltage from the unregulated 12/1500 source is to low ..If you don’t have alternative power source (roughly 18Vdc/1A)...''

I got the point.
The unregulated power supply I have gives 19V at its output without any load and the transformer is of 1500mA. Will this do? I mean can It support LM 317 circuit to deliver final regulated 12V DC?

Regards-
Debasisswan
 

IanP

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The unregulated power supply I have gives 19V at its output without any load and the transformer is of 1500mA. Will this do? I mean can It support LM 317 circuit to deliver final regulated 12V DC?

That depends on how much the voltage drops down under a load ..
The LM317 needs something like 3V between its input-and-output to work as intended, so the way to go would be to connect a load of 1A to the unregulated power supply and to measure the voltage ..
Anything around 15Vdc and above should work fine ..

IanP
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