Re: 2018A33 step up converter

On Thu, 05 Jun 2025 14:15:47 +0200, albert@spenarnc.xs4all.nl wrote:

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

Yikes. Ascii art.

Given the ususal non-synchronous buck switcher, series switch with a
catch diode, you can get a modest negative voltage as I think you
suggest, namely a series cap and a DC-restore circuit, sometimes
called a "half wave voltage doubler."

Or you can add a winding to the inductor and rectify that.

One picture is worth a thousand words.