Transformer step down configuration....

[nt_authority]

i hav 230V to 12V step down transformer.... according to the datasheet provided, the output will be 12V in 0A and 16V in 0.45A....what does it mean by that? i need only 12V to power up my circuit..how will i draw just 12V?does it need to construct a 0.45A circuit at load to draw the 12V?or just simply put the resistor?

thanks...

@uthority

 

[picgak]

you just plugin the transformer to 230v side to 230v AC and measure the output voltage that will be your output voltage

 

[nt_authority]

hi picgak...

i hav directly connected the 230V line to the primary and measure the output in secondary.the value is 16V instead of 12V...i just need 12V for my circuit....i just want to know how or what configuration to draw out 12V...

thanx for the reply...

 

[FoxyRick]

All transformers will give a higher voltage if not fully loaded. They are specified to give their rated voltage at their maximum current. The voltage will get lower as you draw more current.

Does your circuit need 12V DC, or 12V AC? DC would be more usual.

If it needs DC, then you need to use a bridge rectifier, smoothing capacitor, and perhaps a 12V regulator (like a 7812) if the 12V needs to be accurate.

What is your circuit; what are you powering with the transformer?

 

[picgak]

hi picgak...

i hav directly connected the 230V line to the primary and measure the output in secondary.the value is 16V instead of 12V...i just need 12V for my circuit....i just want to know how or what configuration to draw out 12V...

thanx for the reply...

It was 16v Ac on the output am i right then you have got the wrong transformer 16v when rectified and filtered will give nearly 22 v which is very high, so you will have to use the voltage regulator IC 7812 to get the required 12v DC

 

[FoxyRick]

picgak, if the transformer that nt_authority has is rated as a 12V transformer, and it sounds like he has in the first post, then he has the correct one. It is normal for a transformer to read high when lightly loaded. This is to account for the drop in output voltage when the transformer is loaded up to its rated current, the variation in mains supply voltage and tolerance in manufacturing the transformer. 16Vrms for an unloaded 12V transformer sound reasonable to me.

nt_authority, how much current does your circuit need? That information is vital to enable us to suggest a regulator to use. If it is less than 1A, then the 7812 should do it, although you will probably need a small heat sink attached to it. The closer you get to 1A, the hotter the 7812 will get. If you need 1A or more, then a different regulator will be needed.

 

[nt_authority]

hi foxy rick..

after several configuration of 1A bridge ic,regulator7812 IC and capacitor i manage to get back 12V...i actually hav loaded the primary with capacitor coupling circuit..but the output is still 16V.i suspected the 0.45A load not achieved to get back 12V..so at output i use the IC regulator that u mention and now it works.i think the problem is solved now...

thanks all...

 

[picgak]

Hi FoxyRick,
As you have rightly mentioned it is normal to have 10-15 percent voltage more than the mentioned voltage but 33 percent more can damage sensitive devices unless the circuit load is heavy enough to bring the voltage down to the required limits.
regards ani

 

[FoxyRick]

Yes, 33% does seem high, although small transformers are less well regulated and you will find them specified with 25% regulation.

nt_authority, just check that the regulator does not get too hot to touch confortably. If it does you will need a small heatsink. As I said earlier, I think you will need one unless you only have a very low current requirement.

 

[nt_authority]

hi,

it seems i have the problem to power up device at 12V 1.5A rated.even after i regulate the output voltage of my transformer to 12V DC...attachment is the datasheet of transformer...is it capable enough to use the transformer?or need to find another transformer that rated at 1.5A?

thanks

 

[FoxyRick]

If you look at the datasheet's tables, you will find the RMS current rating.

Assuming you have paralleled the output windings (which will give the most current) the highest for the 12V transformer is still only 0.5A

If you try to draw 1.5A from them, the voltage will drop a lot and the transformer will overheat and eventually (possibly quickly) suffer damage.

You need a bigger transformer.

 

[picgak]

you need a transformer rated minimum 18vA

 

[your1click]

you can use bridge rectifier then use capacitor and you can regulate the voltage by using 7812 ic or also can use 12V Zaner diode on parallel mode....

 

[nt_authority]

hi...

thanks for all replies..if i use the 18Va transformer will it be able to power up another two device which is 12V & 9V 0.45mA? my plan is to reduce the use of transformer..sorry if keep asking question as i'm in the field of communication engineering, not having much knowledge about electric power..

regards...

 

[picgak]

thanks for all replies..if i use the 18Va transformer will it be able to power up another two device which is 12V & 9V 0.45mA? my plan is to reduce the use of transformer..sorry if keep asking question....
regards...

you will be able to power both devices with 18vA. If so far you did not buy the transformer you can keep a margin of 2vA and buy a 20vA transformer. you are always welcome to ask questions.