Inductor whine/noise on a dc circuit?

RayRay1132 · Dec 16, 2021

I was messing around with a few mini fluorescent tubes and connecting one up in series with a ballast choke/inductor to my dc bench power supply. The tube is small enough that 30 volts is enough to keep it lit up however I notice a whining noise coming from the inductor choke. The supply I use had a very filtered dc output when I bought it and it’s not a switch mode supply (I initially thought the ripple in the dc might have some effect, but there doesn’t seem to be much according to my oscilloscope) What would cause this?

Thanks in advance - Raymond, KD2JID

rjenkinsgb · Dec 17, 2021

It may be oscillating, strobing at a high frequency.

Neon lamps have been use for oscillators and timing in the past, just with a resistor and capacitor - the cap charges until the neon strikes, then the neon discharges the cap until the voltage drops to the point it extinguishes, then it repeats.

It could be a similar effect with the initial strike of the tube causing a voltage transient across the ballast and making it ring, which the tube extinguishing and striking maintains?

Note that a ballast will only have the correct current limiting effect with an AC supply; on DC (and without the oscillation), it's just a chunk of wire.

RayRay1132 · Dec 17, 2021

rjenkinsgb said:
It may be oscillating, strobing at a high frequency.

Neon lamps have been use for oscillators and timing in the past, just with a resistor and capacitor - the cap charges until the neon strikes, then the neon discharges the cap until the voltage drops to the point it extinguishes, then it repeats.

It could be a similar effect with the initial strike of the tube causing a voltage transient across the ballast and making it ring, which the tube extinguishing and striking maintains?

Note that a ballast will only have the correct current limiting effect with an AC supply; on DC (and without the oscillation), it's just a chunk of wire.

I was thinking that it was self oscillating but it must be doing it at several kHz because it sounds like an old tv flyback transformer, however it’s not flickering or acting weird at all. Regarding the ballast being a chunk of wire on dc, I was just using it to strike the bulb with a hv pulse.

RayRay1132 · Dec 17, 2021

rjenkinsgb said:
It may be oscillating, strobing at a high frequency.

Neon lamps have been use for oscillators and timing in the past, just with a resistor and capacitor - the cap charges until the neon strikes, then the neon discharges the cap until the voltage drops to the point it extinguishes, then it repeats.

It could be a similar effect with the initial strike of the tube causing a voltage transient across the ballast and making it ring, which the tube extinguishing and striking maintains?

Note that a ballast will only have the correct current limiting effect with an AC supply; on DC (and without the oscillation), it's just a chunk of wire.

I also don’t think it’s oscillating because the power supply by itself doesn’t make enough voltage to reignite the lamp, I would have to do that manually

rjenkinsgb · Dec 17, 2021

It will get a back EMF pulse every time it extinguishes, which may strike it again...

Inductor whine/noise on a dc circuit?

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Inductor whine/noise on a dc circuit?

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