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Triac control for a Step Down Transformer ?

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Swaroop 21:
Hi, I am looking forward to design a 30V/5A Lab Power Supply. I have a 48V 5A transformer a EI cored one. I have looked up on the internet found out that they use a Pre Regulator before the main Linear Pass Element to step the voltage down before the main element to decrease the heat dissipation and I also found out the Switching Pre regulators in one of Dave's video about the PSU where he did the teardown, I don't quite remember the manufacturer (Rigol or R&S). My question was can I use TRIAC to control the output voltage of the transformer so the series pass element doesn't have to dissipate so much heat and power. If yes what method ? and on the Secondary of the transformer or the primary would be better ? As I have many of those BTB16 TRIACs around. Please Guide me on this topic I am not so used with the TRIACs or the many of the methods of controlling a highly inductive load.
EDIT: Is there any other way to limit the power before the main linear pass element ? I also have SCR will making a SCR Rectifier to control the dc work ?

moffy:
That's not really the best way to do it since a triac only switches at the mains frequency and you would need a large LC filter etc. It works well for lights or DC motors which can filter out the ripple. If you want a preregulator it would need to be PWM followed by a linear stage to reduce the noise, some would with justification say to just use a linear regulator for noise reasons but that would dissipate a lot of heat at full load current.

soldar:
I would not try that. It's not going to work well in practice.

armandine2:
see link for triac application note, used as a basis for the Elektor 400W  pre-regulator type power supply. Not widely adopted, I think.

https://www.st.com/resource/en/application_note/an308-triac-analog-control-circuits-for-inductive-loads-stmicroelectronics.pdf




Benta:
Horrible idea.
You'll have immense peak currents in the transformer and rectifiers as they try to charge your storage capacitors. And it only makes (a little) sense to use this scheme during the last half of the line cycle.
Don't go there.

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