Question about diodes - which one should I use?

Question

I'm right now attempting to reverse-engineer a computer memory card. It is basically a SRAM card with a battery backup.

+5VDC is taken from the host system's expansion slot, and basically powers everything up, including the SRAM modules. When the +5VDC is no longer avai lable (i.e. the computer is turned off,) the battery saves the contents of the SRAM modules.

The battery is used to protect the contents of the SRAM modules from gettin g lost. It is a 3V lithium battery, and is rechargable.

Between the VCC pin on the SRAM modules and the +5VDC rail from the host sy stem, there sits a diode I can only partially identify. On the diode, I can only read "3A" and "ITT". The cathode end connects to the SRAM VCC pin, wh ile the anode connects to the +5VDC rail. I believe the diode is being used to avoid the battery voltage from flowing into the host system.

What would be a good diode to use in this situation?

John Larkin · Accepted Answer

The classic (practically only) ITT part was the SD103 schottky diode. That may be it. --  John Larkin         Highland Technology, Inc lunatic fringe electronics

groink1 · Answer

is basically a SRAM card with a battery backup.

rs everything up, including the SRAM modules. When the +5VDC is no longer a vailable (i.e. the computer is turned off,) the battery saves the contents of the SRAM modules.

ting lost. It is a 3V lithium battery, and is rechargable.

system, there sits a diode I can only partially identify. On the diode, I can only read "3A" and "ITT". The cathode end connects to the SRAM VCC pin, while the anode connects to the +5VDC rail. I believe the diode is being u sed to avoid the battery voltage from flowing into the host system.

Thank you! I'll check the SD103 out.

Michael Black · Answer

And of course, a schottky diode has a lower voltage drop than a silicon  diode.    Michael

John Larkin · Answer

Sometimes. --  John Larkin         Highland Technology, Inc lunatic fringe electronics

Tim Wescott · Answer

Higher leakage, too -- so it's not necessarily a slam-dunk. --

Question about diodes - which one should I use?

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