Question about linear voltage supply transformers and current

Thread Starter

hunterage2000

Joined May 2, 2010
487
Hi,

If you have a chassis mount transformer with specs:

Primary V = 230Vrms
Secondary V = 24Vrms
S = 6VA

Does this mean the maximum rms current that can flow through the transformer is 250mArms?

Just wondered if you used this transformer to get a rectifed 25.9V DC input to a LM317 linear regulator. you could only get a maximum load current of 250mA DC before the output voltage drops?
 

MaxHeadRoom

Joined Jul 18, 2013
19,485
The Va of the transformer applies to both primary and secondary, IOW if you have a 6va version then yes, the load placed on the secondary is limited to 250ma.
Max.
 

Thread Starter

hunterage2000

Joined May 2, 2010
487
I see. I'll get a higher VA rated transformer. Anyone know of any good sources for variable linear power supplies i.e books, sites etc?
 

dl324

Joined Mar 30, 2015
9,351
Anyone know of any good sources for variable linear power supplies i.e books, sites etc?
Datasheets usually have application suggestions.

The National Semiconductor Voltage Regulator handbook has a wealth of information. Including how your choice of rectification/filtering will impact transformer current requirement:
upload_2017-4-7_8-54-0.png
 

crutschow

Joined Mar 14, 2008
23,826
you could only get a maximum load current of 250mA DC before the output voltage drops?
The VA rating is not where the voltage drops, since there is typically a 10-15% voltage drop from no-load to full-load due to winding resistance.

The VA rating is determined by the heating of the transformer.
Beyond that VA rating the transformer can overheat.
 
Top