Joule Ringer!

[conradelektro]

@ xee2, 1 Ohm shunt between collector coil and collector of transistor:


Good idea xee2, that confirms that the transistor opens two times in a row (within about 2 μsec).

I guess it is the 200pF capacitor over the 500K resistor.

Green is ground line. Cyan is the measurment over the 1 Ohm shunt. Probe B is at coil, ground of probe B is a collector of transistor.

Again the white line is the lamp (without connecting to scope ground, kind of floating).

I will make the same kind of measurements at my next circuit.

A nice fact: using a 100pF - 80K combination in this circuit makes a 15 Watt spiral CFL shine a pleasant yellow light with about 15 mA at 12 Volt. (The measurements were done with 200pF-500K and a 120 mm long blue cold cathode tube.)

Greetings, Conrad

[hartiberlin]

Many thanks Conrad for all your help.
Yes, as Xee2 says, the transistor seems to switch on 2 times
in this interval.
Now it would be interesting to see, if one could
find out a circuit variation, that makes it only switch on 1 time
in this interval as this will consume less current from the cap
and see, what this will get us for the light output.

P.S: Are you saying you get a 15 Watt light bulbs fully lit up
with just 12 Volts and 15 mA which is just about 0.18 Watts ?

How bright is it ?
What is then the frequency of these burst pulses ?

Many thanks.

Regards, Stefan.

[xee2]

@ Conrad

Well, I think that is pretty clear that the transistor is turning on twice. Interesting results. Thank you for posting all of these great measurements.

[xee2]

I guess it is the 200pF capacitor over the 500K resistor.

I think it is probably the current induced in the base coil by the collapsing magnetic field. The time delay is most likely the turn on time of the transistor (even longer for a darlington). But, why does it not happen again when the transistor turns off the second time? Still not fully clear, but great progress. Thanks again.

[conradelektro]

15 Watt spiral CFL, 100K-100pF, about 2200 Hz, 12 Volt about 12 mA

The 15 Watt CFL is not very bright, I call it a "pleasant yellow". To read a book, the lamp has to be at 200 mm from the book. So, it is not even a decent reading lamp. I like to see it as an "atmosphere" lamp to chill out.

It looks like that:

The circuit is very sensitive to the capacitor-resistor combination between trigger coil and +12V.

It is mostly the frequency that gets changed. Higher resistor ---> lower frequency.

Varying the capacitor is more tricky and there the double triggering comes in. Higher capacitor ---> double triggering but also lower frequency.

One has to analyse this capacitor-resistor pair in order to get more insight and to avoid the double triggering.

The capacitor is necessary, without capacitor there is no oscillation. May be there could be oscillation without capacitor if one biases the transistor.

Also the 4700 uF cap plays a role. The circuit behaves completely different if one disconnects the 4700 uF cap, the power consumption shoots up, also the brightness of the lamp.

The really low power consumption around 1 mA at 12V (and a rather dim lamp) starts with 500K or 1M and 200 pF at about 200Hz to 300Hz. There is also erratic flickering at this low power.

Greetings, Conrad