-Forward voltage of- -ZLLS410- S4 diode. Edited- This is NOT a Zener mod

[wight]

@Rufusbduck

I was sorry to see your frustration growing since all along I had been assuming I was going to connect the divider before the the diode. My typo was in the number I typed at the end. My original question was “what’s the voltage drop of this diode?” which I needed to know to calculate the (.5v) number and for nothing else. I’m fine with solving a simple equation for x or locating which trace to cut where. I kept picturing you banging your head saying “who is this idiot?” while with each post we were operating with different assumptions. You have been very helpful typing long posts affirming things I already knew while I couldn’t seem to make clear my question.

To get low voltage regulation to work I need to be able to show pin 7 – .5V when Vb=5.6V.

If the voltage drop across the diode is some value other than .25v then .5V is the wrong target for the divider.

This second is the sole reason for my post. We assume a certain value for the voltage drop across the diode to make the first calculation of the voltage on pin 7 on boards as they are now configured.

In post 5 I listed 4 different new values for R1 to show how a different value for D1 in the first calculation affects the value R1 in the second even though the diode is bypassed. Please note that we agreed then and still agree now that if the diode drop is ~.25v then R1 should be ~48k when bypassing the diode.

Is the .25v assumption a correct one?

Heheh. Now I get it. Looks like the proper amount of bold print can get the message across to me. Sorry for missing that key point, it’s easy to see now how we could be so close and yet so far away!

I’ve got to dig through my mess for a 105c to test with the diode in place. For the time being I used my $13 buck PSU to put 10mA across a diode I recently stripped from a FT 105c. Initially it read 0.28v but by the time I got my meter on it it read 0.30v. The meter agreed and it stayed there, I suppose that’s from the warmup at 10mA.

FWIW, my opinion is that you need to target a cutoff of 2.8-3.0v. The cell is effectively empty at 3.0v or greater, just not damaged yet. There’s no reason for precision for the actual low voltage cutoff. Step down is a little trickier and calls for more precision of course. If actual cutoff is the only concern, you have a huge target.