I'm looking at designing and building my own DC power supply as a project, and got a bit stuck on finding an appropriate transformer. All of the ones in the correct voltage/current range don't look like the ones I know (that have fewer pins!).
Here's the pinout of one:
https://www1.elfa.se/data1/wwwroot/assets/large/5617907-11.jpg
Some of the specs:
"With 1 or 2 secondary winds that can be parallel or series connected.
Connections secondary: pins 9-13
Connections primary: pins 1-7
Secondary: 16 VA, 1 x 6...18 VAC / 2x 6...15 VAC
Secondary voltage: 15 VAC(1x)
Data sheet: https://www1.elfa.se/data1/wwwroot/assets/datasheets/EI54_eng_tds.pdf
"
(The exact model doesn't matter since I picked this transformer semi-randomly from a pool of similar ones. The same principle should apply to all of them.)
So... What do I make of this? My goal is first and foremost to step down 230 V to roughly 20 V, but I have a secondary goal which is center tapping, or something to that effect, so that I can choose between ~10 and ~20 volts, perhaps even more than 2 choices... The point of this being to limit the input voltage to the regulator (LM317) to avoid wasting those excess volts as heat (via (Vin - Vout) * I = heat in watts) when using low output voltages.
Would this be possible with the above style transformer?
If not, why are there more than 4 pins?
Here's the pinout of one:
https://www1.elfa.se/data1/wwwroot/assets/large/5617907-11.jpg
Some of the specs:
"With 1 or 2 secondary winds that can be parallel or series connected.
Connections secondary: pins 9-13
Connections primary: pins 1-7
Secondary: 16 VA, 1 x 6...18 VAC / 2x 6...15 VAC
Secondary voltage: 15 VAC(1x)
Data sheet: https://www1.elfa.se/data1/wwwroot/assets/datasheets/EI54_eng_tds.pdf
"
(The exact model doesn't matter since I picked this transformer semi-randomly from a pool of similar ones. The same principle should apply to all of them.)
So... What do I make of this? My goal is first and foremost to step down 230 V to roughly 20 V, but I have a secondary goal which is center tapping, or something to that effect, so that I can choose between ~10 and ~20 volts, perhaps even more than 2 choices... The point of this being to limit the input voltage to the regulator (LM317) to avoid wasting those excess volts as heat (via (Vin - Vout) * I = heat in watts) when using low output voltages.
Would this be possible with the above style transformer?
If not, why are there more than 4 pins?