Todd MAX-354-1252 Power Supply for XL1201

So, I learned something about the Todd MAX-354-1252 power supply in the Symbolics XL1201 today that I thought I'd share. Not that I understand it, mind you.

The power supply has six trim pots. Four are obviously labeled for adjusting the four output voltages:

  • 5V at 50A
  • 12V at 8A, 12A peak
  • -12V at 2A
  • -5.2V at 10A (for ECL circuits)

However, according to the expert engineers at Power Clinic "The two [remaining] trim pots in question are related to the front-end boost circuits. One is for operation frequency and the other is for boost fold. NEITHER should ever be adjusted."

As I understand it, switching power supplies work by switching the output voltage on and off extremely quickly (on the order of 100kHz) from the high input voltage, so obviously one of these tweaks that frequency. No idea what the "boost fold" is - but fortunately according to the engineers I never have to touch it.

Douglas Fields

Writing LISP and Haskell since 1990