🚀 go-pugleaf

>It works, but I have heard a couple of NeXT SEs say that this will
>void your warranty.  You never know when the diode that prevents
>reverse current will fail and fry who knows what.

    IF there is an inline diode there preventing the reverse current it
    will never fail.  The reverse breakdown voltage for most standard
    diodes is a hellofalot larger then anything a battery puts out. No
    current == no heat.  For example, diodes are often used in battery
    charging circuits like this:

	+12V from supply ----*DIODE*----x----> system power
					|
	+!2V from battery --------------/

    When AC is available it charges the battery.  When AC is not available
    the battery does not try to feed the supply, the diode is reverse
    biased by 12V when the supply DC is at 0V.	This is standard operation
    and the diode will never break down for this case.	Now, shorting
    system power to ground is a different case... in that case the diode is
    forward biased and dissipates W=Ix0.7 (usually) in heat. Any diode can
    handle large forward currents for a short while, how long they last
    depends on their current rating but usually the solder melts on the PC
    board before the diode dies.  Diodes are usually rated 500mW, 1W, or 5W
    the smallest being applied to glass diodes.

    I presume that NeXT is using a similar circuit to power the real time
    clock and prevent the battery from trying to power the system +5.

					-Matt

>MUCH safer to let the capacitor sit and discharge for a few hours on
>its own.
>What's your hurry?
>:-)
>--
>David Lemson						     (217) 244-1205
>University of Illinois NeXT Campus Consultant / CCSO NeXT Lab System Admin
>Internet : lemson@uiuc.edu		   UUCP :...!uiucuxc!uiucux1!lemson
>NeXTMail accepted				    BITNET : LEMSON@UIUCVMD

--

    Matthew Dillon		dillon@Overload.Berkeley.CA.US
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