[sdiy] 1S2473 vs. 1N4148 diode specs

[Happy Harry]

I do not agree....

In a LOT of japan designed battery back up circuits... they run
the RAM one diode drop below the 5V rail. So the normal memory
voltage is about 4.3V.

That is a LOT of headroom loss...

There are two ways to eliminate this...
Raise the supply voltage to 5.7V... and supply the 5V circuit via a single 
diode drop... and then use a similar connection to the RAM... so the diode 
drops cancel.

This is the way it SHOULD have been designed from the start... its only ONE 
extra diode.

Method #2... use a SHOTTKY DIODE such as 1N5817, with very low forward drop.

Do not worry about reverse leakage... it will NOT harm the battery. The 
reverse leakage is very low (I admit it is orders of magnitude higher than 
the 1N4148... but it is still too low to harm the battery)

The reverse leakage only gets bad at high temperatures... which the synth 
will never see for any length of time... maybe at an all day concert, in the 
sun, in the desert, near the equator, with high line voltage... you get the 
idea. Even then its only 12 hours max...right.

OK maybe a three day concert as above....  ;^)

Also note that reverse current is only possible with the synth ON... mine is 
off more often than on.... ;^(

I have done this on all my synths and get less memory corruption, and am 
still running on the same batteries....

The Shottky diode has a drop (in memory use... almost zero current) of about 
.25V

H^) harry


>From: "Synthusiast" <synthusiast at gmx.net>
>Reply-To: "Synthusiast" <synthusiast at gmx.net>
>To: "Synth DIY" <synth-diy at node12b53.a2000.nl>
>Subject: Re: [sdiy] 1S2473 vs. 1N4148 diode specs
>Date: Fri, 8 Jun 2001 22:13:35 +0200
>
>Hi again all,
>
>Thanks for all the responses. :)
>
>I was reverse engineering the battery backup circuit of the Roland 
>Jupiter-6
>and wanted to know if the 1S2473 diodes Roland used for this circuit could
>be replaced by commonly available 1N4148 diodes. And the answer to that is
>yes, though the path is a little long. I was told the 1S2473 is compatible
>with the ECG519 diode and I found out the ECG519 is compatible with the
>1N914 diode, which is compatible with the 1N4148 diode ;) So the 1S2374 is 
>a
>plain normal diode and couldn't even be a Schottki diode, as I learned the
>reverse current leakage of those diodes would ruin the non-chargeable
>Lithium cell when used in a battery backup circuit.
>
>Why I wanted a battery backup circuit in the first place? Well, I performed
>Old Crow's battery replacement for my Polysix and was wondering if the
>voltage drop could be reduced by using different diodes than the 1N4148 I
>used. But as even Roland used these kind of diodes, I'll keep my 1N4148 in
>the circuit and be happy with it :-)
>
>Cheers,
>Martijn
>

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