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power supply

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bmwcars

New Member
Hi i am trying to build a power supply AC220v to DC 12 to 18v.

First what kind of tranformer do i need?


bmwcars
 

Exo

Active Member
What do you mean by '12V to 18V'

Do you mean, anything between 12V and 18V is fine...
or do you mean it needs to be adjustable between 12V and 18V ?

also, how much current does it need to be able to deliver?
 

bmwcars

New Member
bmwcars

hi EXO, thanks for your reply.

I am trying to build a power supply can supply 12 to 18v DC

i am using it for my RC plane charger.

Thanks
 

semiconductor

New Member
Your transfromer would be 220VAC to 15VAC (after Bridge rectifier, the output DC voltage will be multiplied by sqrt(2))

Then, you can use LM317 to regulate your output DC Voltage. If you need more current (2A), you can add a power transistor, such as 2N3055 or 2N2955 (check in datasheet to get N-type or P-type).

For specific circuit diagram, download LM317 datasheet, it is accompanied with some useful circuit diagram!

For filter, use 2.200 uF for 1A (so 2A is 4.400 uf)
 

Optikon

New Member
semiconductor said:
Your transfromer would be 220VAC to 15VAC (after Bridge rectifier, the output DC voltage will be multiplied by sqrt(2))

Then, you can use LM317 to regulate your output DC Voltage. If you need more current (2A), you can add a power transistor, such as 2N3055 or 2N2955 (check in datasheet to get N-type or P-type).

For specific circuit diagram, download LM317 datasheet, it is accompanied with some useful circuit diagram!

For filter, use 2.200 uF for 1A (so 2A is 4.400 uf)

Oh, and you had better calcluate(or measure) what your ripply current is and make sure that your filter caps are rated for that amount of ripple current or you could have a most unpleasant surprise waiting for you.
 

Roff

Well-Known Member
semiconductor said:
Your transfromer would be 220VAC to 15VAC (after Bridge rectifier, the output DC voltage will be multiplied by sqrt(2))

Then, you can use LM317 to regulate your output DC Voltage. If you need more current (2A), you can add a power transistor, such as 2N3055 or 2N2955 (check in datasheet to get N-type or P-type).

For specific circuit diagram, download LM317 datasheet, it is accompanied with some useful circuit diagram!

For filter, use 2.200 uF for 1A (so 2A is 4.400 uf)
A 50 Hz, 15v RMS AC voltage is, as Semiconductor pointed out, 21v peak. The bridge rectifier will drop about 1.6v, leaving 19.4v peak. The ripple, with 4400uF, will be 3.5v, leaving only 15.9v at the valleys of the ripple. The LM317 needs about 3v of headroom, so you could only get about 13v maximum out of the supply. You should use an 18v RMS transformer and a 10,000uF capacitor. Be sure you pick rectifiers that can handle more than 20 amp peak repetitive current.
 
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