Hugo Holden
Veteran Member
One very interesting thing is to look at the way a 110/220V switched option SMPS was implemented in the 5155 computer.
It also answers an interesting question, which could perhaps be posed in an electronics exam question:
How can you run the 110V primary of a small line fed power transformer from 220V, without using a dropper resistor, series capacitor or a step down transformer ?...might leave a few exam candidates stumped might it not ?
How about doing it with a bridge rectifier and two large value capacitors and creating a virtual mid point rail from the 220V supply ?
This is exactly what IBM (or at least the Zenith contractors) did with the dual voltage IBM5155 supply. I took a little time in the article to explain how they did it:
http://worldphaco.com/uploads/The_IBM_5155_POWER_SUPPLY.pdf
Once these principles are understood, it easy to convert SMPS supplies to dual voltage.
It also answers an interesting question, which could perhaps be posed in an electronics exam question:
How can you run the 110V primary of a small line fed power transformer from 220V, without using a dropper resistor, series capacitor or a step down transformer ?...might leave a few exam candidates stumped might it not ?
How about doing it with a bridge rectifier and two large value capacitors and creating a virtual mid point rail from the 220V supply ?
This is exactly what IBM (or at least the Zenith contractors) did with the dual voltage IBM5155 supply. I took a little time in the article to explain how they did it:
http://worldphaco.com/uploads/The_IBM_5155_POWER_SUPPLY.pdf
Once these principles are understood, it easy to convert SMPS supplies to dual voltage.