Computer science & math major here.
I'm designing a linear power supply to introduce myself to electronics. To keep things cool and cheap, I am trying to limit the amount of power dissipated in the LDOs when delivering high currents (1 amp) at low voltage.
My plan is to use a relay (or maybe a pair of traics) to switch which tap of my center tapped transformer feeds my rectifier and filtering caps to reduce the voltage drop across my LDOs.
Is this a totally misguided idea and need I be concerned about transients caused by the change in current of the secondary coil of my transformer when I switch from the center tap (12 VAC) to the outer tap (24 VAC)?
I've read some articles and done some modeling of the behavior of a transformer feeding into a full-wave bridge rectifier and then into filtering cap as a pre regulator for my LDO (image not mine).
Because, as I understand it, kickback transients are proportional to the current flowing across the inductor; I've started to design an "interrupter" using an opto (to detect 0 points of the AC wave) and a couple of logic gates to force the transition to happen when the capacitors are supplying current. Is this enough precaution to protect my puny circuit from high voltage transformer transients?
Imgur link to pdf output from kicad for those interested of schematic without "interrupter".
Wolfram alpha output of "interrupter" logic also for those interested.
Where U is high when user needs to use the outer tap, O is the opto (high when AC is near 0v), and C is high when the outer tap is in use.
[edit 1] changed a word.
Best Answer
Is this any good?
from a:-
It's circuit diagrams for the Korad (US) /Tenma (UK) series of bench PSUs. Thousands of people have them. They switch the windings as you change output voltage, which you can actually hear quite easily. With two SPDT relays, it might be able to switch in four tap settings. They also automatically switch off the output as you change level. This might be the key to your question.