Re: 2018A33 step up converter

In article <p50p3khhstse6vfn0u4hepdagvv83c5enq@4ax.com>,
john larkin  <jl@glen--canyon.com> wrote:

On Sun, 01 Jun 2025 17:25:16 +0200, albert@spenarnc.xs4all.nl wrote:
>

I am experimenting with the 2018 step up converter.
The circuit is available from aliexpress , most everywhere.
>
There is a inductance, a Skottky diode, and capacitance, and the
circuit. The 2018 cuts the coil short to earth. The diode fill the
capacitor and the output is measured for a feedback.
Textbook step up. Rock solid 5 Volt.
>
Now I have this (apparently) wild idea. I add another diode reversed
and a capacitor, to prey on the output. The circuit is not phased at all,
solid 5.08 V as far is it original function.
But I get a couple of negative millivolt out.
>
What am I doing wrong? Or should this work?
I checked this over and over again.
>
Groetjes Albert

>
That's a lot of words. Can you post schematics?
>

    The IC is not drawn. (it connects A B and ground)

    Vi                               Vo
   --------UUUUUU-------I>|----------+
                    A         B      |
                                     |
                                     |
                                     =
                                     |
                                     |
    ---------------------------------+
      |
      _
      -
      .

   Vi and Vo are 1.5 V and 5 V.
   The switch is connected to A (connect to ground)
   and the voltage is sensed at B.
   Now I want to add a negative voltage.

Now I want a negative voltage.
On second thought I came up with this addition:

   A
   --------II-----------|<I------+----+
                                 |    |
                                 |    |
                                 -    |
                                 A    =
                                 |    |
                                 |    |
    -----------------------------+----+
      |
      _
      -
      .

Can this work?
P.S.
I have 10 of those tiny boards.
The funny thing is I can remove the ic from one board, reverse the
diode and replace the coil with a capacitor.
What remain is add the extra diode over the capacitor and
connect grounds.

Groetjes Albert
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