To be deleted

[itsu]

As the percentage "power users versus input" drops from 94% with feedback to 85% without feedback (see post #100),
i was trying to find out where that missing 15% in the no feedback situation went.

I was doing that by monitoring the temperature of some components like the transformer, the potmeter and the
electrolytical cap using my laser temp. meter.

But it seems that this method is too rough for these small currents as i do see some temp. changes, but in a
irregular way, so probably due to room temp changes.

Guess i have to scope the current paths to these components to get a more accurate view.


Itsu

[nul-points]

that's a shame about the resolution issue of a low-powered circuit, Itsu - it would have been a very interesting view of what's going on where


i've repeated the 1F (nominal) cap draw-down test swapping out the original coil with a larger coil (both turns and ferrite, also a toroid rather than solenoidal)

the average runtimes (for same draw-down voltage range) are as follows:-

NO FEEDBACK: t = 68.4s

LED FEEDBACK: t = 89.6s

ratio = 89.6 / 68.4 = 1.31


thanks
np

[itsu]

I started measuring the current through the potmeter with and without feedback
and the current to the electrolytical cap with and without feedback.

We are dealing with minute currents through the potmeter, but we see a big increase of the current when feedback
is removed from 402uA with, to 636uA without,  see screenshot 1.
White is the current through the potmeter with feedback, green without.
Also to notice is that the frequency went up when feedback is removed.


The current to the elco is much bigger, but behaves the other way around, less without feedback, from 6.22mA with, to
5.04mA without, see screenshot 2.


I don't think though that this will account for the missing power in the system with feedback removed.


Itsu

[nul-points]

yes, good call Itsu


the frequency does increase with 'no feedback' (and i think this is because in the feedback case, the f/b pulse increases the cycle duration whilst the coil collapse energy performs work, charging the battery somewhat & lighting the feedback LED - in the 'no feedback' case the coil collapse energy dissipates wherever it can)

interesting about the resistor pot - after i used the pot to select a suitable operating drive level i replaced the pot with a fixed resistor

the elco behaviour seems reasonable -

with feedback, the elco is drained in 2 ways:
1) buffering the LEDs
2) completing the coil collapse current circuit back thro' the Feedback LED

without feedback, the elco is only drained as in 1) above


thanks
np

[nul-points]

QUESTION:  Is the average supply current, Isupply, equal to the difference between the current drawn, Iin, and the feedback current, Ifb?

ANSWER:  Yes it is

SCOPE TEST:  measure Isupply at a mid-range voltage (3.75V)

(With Feedback)
signal cycle = 70.4kHz, full cycle = 14.1us

DC average, across 1 ohm CSR, using scope math from traces shown below

Isupply: 8.0mA 
(full cycle)

Ifb: -5.24mA  *   (4.7us / 14.1us) = -1.67mA  (averaged over full cycle)

Iin: 14.6mA * (9.4us / 14.1us) = 9.7mA  (averaged over full cycle)

Difference between Iin & Ifb = (9.7 - 1.67) = 8.03mA