Barrel battery replacement

[SpidersWeb]

Yeah I don't have an explanation for that. I would've expected 0 also.

Edit: although datasheet scanning, does indicate that some variants of this part may have a reverse DC voltage rating as low as 2V - e.g. if you put 3.6V on them, it'll start leaking through. I suspect that's what Chuck may have meant. May just need to get a higher rated part.

 

[3pcedev]

As Chuck mentioned before you can use a MOSFET to protect the battery with ~0 voltage drop.

I did it on my 486 - Some details are in the thread here: http://www.vintage-computer.com/vcf...sembled)-computer-486DX2-80&highlight=3pcedev

 

[H-A-L-9000]

This cirquit helps to protect against reverse polarity, but not against reverse current. There is no way the MOSFET can turn off when the direction of current flow changes (when you power on the computer).

You can however use a P-MOS and switch that off with the 5V from the power supply:

BATT- -> GND
BATT+ -> S MOS
G MOS -> R1k -> GND
G MOS -> -1N4148+ -> R100ohms -> +5V
D MOS -> +RTC
Maybe not needed: GND -> -C100µF+ -> +RTC