HP Power Supply Unit (PSU) schematics & Pspice simulation

[Jacques Laporte]

On my site this month :

http://www.jacques-laporte.org/HP35%20power%20unit.htm

the HP-67 & 97 Power Supply Unit (PSU) schematics with a Pspice simulation of the switching DCDC converter.

Enjoy.

[Steve Simpkin]

Wow! Thanks for the investigative work. I always wondered how the switching power supply design worked in my HP-25. It was probably the first product I owned that used a true switching power supply.
It is a shame HP did not put a bit more design effort into the charging system on the Woodstock series (HP-21, HP-25, etc). Relying on the presence of the NiCad batteries to avoid destroying the calculator is NOT good design practice. Worn out cells, poor connections or the user simply removing the battery pack during charging could result in a failed product. I wonder why HP engineering let this design compromise (defect) get into a finished product?