Inductors, Lightbulbs As Current Sources

[Michael Rothacher]

I've seen a number of single-ended designs in old solid state circuit textbooks which employ an inductor as a current source for the output rather than a resistor or active current source.

1. Would anyone be willing to offer an explanation for this approach? Is the idea to present a low impedance at audio frequencies? How would one calculate the appropriate inductor value?

2. As many of the inductor values I've seen in these old circuits are large, would it be possible to use a smaller inductor in series with a lightbuld ala ZenLite?

3. Is the larger inductor in ZenLite (power supply) used because the lightbulb itself is intrinsically noisy or because it presents a low impedance to the power supply.

Your advice is most appreciated. As I've been unable to divine the ansers from the old texts.

Thanks

Mike

[Nelson Pass]

No, we want a high impedance at audio frequencies.

Inductors work great. I have built a Zen with a 1 Henry
air core coil (...alright, a spool of magnet wire) and it had
about 40% efficiency and good low distortion. Of course it
has very low resistance, and so the Zen's original bias
network cannot be used to set the DC current.

As seen in ZV1, light bulbs work pretty well too, but at much
lesser efficiency.

[Michael Rothacher]

Thanks Mr. Pass

I like the spool of magnet wire idea.

[till]

what is magnet wire?

[Jocko Homo]

Light bulbs are used in the telephone industry as current limiting devices. But they do not like contiuous DC being passed through them. Unless you like replacing them frequently.

Jocko

[Tall Shadow]

Originally posted by Jocko Homo
Light bulbs are used in the telephone industry as current limiting devices. But they do not like contiuous DC being passed through them. Unless you like replacing them frequently.

Jocko

I had always thought that Lamps run better & longer with DC. Here in Detroit We have Tommy Edison's original Light(Running on DC) still running. There were even quite a few "Add-On" diode sets for consumer lamps a few years back. I also thought that much of the power used in the telecom industry was still AC.

Anyone know about this??

Tall Shadow

[Nelson Pass]

Originally posted by Jocko Homo
But they do not like contiuous DC being passed through them.

I haven't had any problems, but then I have run them
very much below their ratings.

[paulb]

Originally posted by mrothacher
I've seen a number of single-ended designs in old solid state circuit textbooks which employ an inductor as a current source for the output rather than a resistor or active current source.

Could the designs be referring to RF circuits?

[Michael Rothacher]

Paul:

No, they're audio circuits. I've seen them in very simple demonstration circuits in old transistor books. I guess the idea didn't have much appeal because of the size of the inductor required since, from a cost and weight standpoint, a 1 Henry inductor doesn't offer much over a transformer-coupled output.

Of course, this is of little consequence to us fanatics!

Mike

[halojoy]

Originally posted by Nelson Pass
I haven't had any problems, but then I have run them
very much below their ratings.

LIVSTID= lifespan
LJUSSTYRKA= strenght of light
ARBETSSPÄNNING= work voltage
MÄRKSPÄNNING= mark voltage (nominal)
STRÖM= current
the picture is from www.elfa.com pages with facts
It is on how the lifespan in ordinary lightbulbs correlates to working voltage