Calling all Circuit Wizards...

[nul-points]

now here's a nifty little New Year puzzle for you...

what happens when the switch S1 connection changes from position 3 to position 2?

try & predict without building first!

i'd be interested to hear what a Sim makes of this

cheers
sandy


(Background:
  i thought it was about time i experimentally tested my view of the old standard: 'charge two caps in parallel, feed back into the source as two caps in series'
  i was surprised to observe something rather unusual with this config

oh, and i confirmed that the battery discharges, btw - but that's NOT unusual - with conventional batteries!!)

[poynt99]

OK, here's a quick stab:

1) When S1 = 3, C1 will charge to 1.24V. C2 is previously charged to 1.24V through D1.

2) LED should be OFF.

3) When S1 goes to 2, C1's voltage may get clamped down somewhat by D1, and the battery will receive some energy back due to C1 and C2 being in series with their voltage > 1.24V.

4) Re-charging will cease when C1 + C2 has discharged to roughly 1.24V.

5) The LED should never illuminate.

.99

[nul-points]

hi poynt

in my view, that's a good - and entirely reasonable - call

i'm glad to hear that someone else has the same expectation of what should happen


strangely, the circuit seems to have something extra up it's sleeve

any other takers - or further ideas?

regards
sandy


(in case anyone's wondering why i designed the circuit exactly this way - i didn't;
i noticed something odd by accident and tailored my original 'parallel to serial cap' circuit to focus on this new behaviour)

[poynt99]

What I described above assumes S1 is a perfect switch.

As this is rarely the case with mechanical switches, there will be "switch-bounce" between the common contact (1) and the position (2) contact. As such, the L1 inductor may certainly kickback a number of times resulting in the LED illuminating for a brief moment.

.99

[gyulasun]

Perhaps sweeping the switching frequency, there can be a magic one (lol)  that (either by resonating somehow L1 and combination of C1 and C2 or hitting a favorable time constant value) may enhance voltage level in any capacitor a little?  (IF any increase shows up, voltage level in C1 is clamped by LED to 3.2V max at switch position 3.)
Diode D1 should be low barrier Schottky or Germanium to minimize its forward drop loss (it misses from the 1.24V C2 could charge up).

Looking forward to your finding too.

Gyula