10 mH inductor (28R)

[J4e8a16n]

Does that make sense?

The inductor charges and discharge when the base is closed?
The ringning can occur because of the 1 uf cap. See Reply #18




JP

[rvof11]

It is more an energy balance. You put energy into the magnetic field in the coil when the transistor is on, and when you turn off the transistor you have to dissipate the energy somehow. If there is no load the voltage rises until the energy is dissipated. Whether it goes into a resistor, capacitor or killing the transistor is immaterial, the energy is going to be going somewhere.

Isn't this suppose to be an exact science?

[TerminalJack505]

Does that make sense?

The inductor charges and discharge when the base is closed?
The ringning can occur because of the 1 uf cap. See Reply #18




JP

That ringing might be due to something else.  Notice how the voltage at the base is ringing as well.  This might be causing the ringing at the collector since the transistor would be quickly switching off and on.  The ringing at the base might be due to the probe's capacitance along with some parasitic inductance (the probe's ground lead and other wiring, for example) creating an (unwanted) tank circuit.

You might try using the probe's low inductance ground attachment (the little spring) to see if the circuit behaves differently.

[J4e8a16n]

That ringing might be due to something else.  Notice how the voltage at the base is ringing as well.  This might be causing the ringing at the collector since the transistor would be quickly switching off and on.  The ringing at the base might be due to the probe's capacitance along with some parasitic inductance (the probe's ground lead and other wiring, for example) creating an (unwanted) tank circuit.

You might try using the probe's low inductance ground attachment (the little spring) to see if the circuit behaves differently.

Great idea.

JPD

[J4e8a16n]

Only a small ringning at the base... from the 555 probably...

[TerminalJack505]

Those waveforms look a lot better.  It was the probe then?

I'll have to built one of these for myself.  I bet a joule thief circuit can be modified to get the same functionality.

[J4e8a16n]

Not the probe.

The pcb was directly on my bench and there was weak join between the zener and the output.

I bet a joule thief circuit can be modified to get the same functionality.

Interesting.


JP