Fluorecent choke for power supply

[wabun]

Can I use fluorecent choke (36W lamp )as PSU choke ? It is much cheaper and has DC resistant of ~ 80 Ohms.. I do not have a LCR meter, donno what is the Henry value.. any experience can share ?

[stormsonic]

Measured some of them, 0.3 - 1.5 H, depends on type.
You need to measure your choke, then use PSU Designer.
They can be used for low-power loads (preamps, tube gear, etc.).

[metalsculptor]

I used a 250W mercury vapour ballast (choke) for a CLC filter once and it worked fine even though it was not designed for DC. The henry value can be calculated by knowing the details of the lamp it drives.

Low loss types have a lower DC resistance and more inductance, for comparison @240V 36W, a standard ballast has a 40 ohm DC resistance and a low loss type has a 23 ohm DC resistance.

80 ohms seems like a lot of DC resistance even if the ballast were designed for a 277V supply it should have a similar or slightly lower DC resistance than the 240V 50Hz ballasts I measured.

[DF96]

DC will reduce the inductance, as these chokes won't have an air gap. You need to measure it with DC present, or just build a PSU and measure the output. What you can't do is measure the inductance at zero DC and then simulate a circuit assuming it retains that inductance.

[Elvee]

Originally Posted by DF96

DC will reduce the inductance, as these chokes won't have an air gap. You need to measure it with DC present, or just build a PSU and measure the output. What you can't do is measure the inductance at zero DC and then simulate a circuit assuming it retains that inductance.

They have distributed high reluctance sections, because they have to operate as power inductors, and are not allowed to saturate significantly within their operating range.
The fact that they operate in AC changes nothing.

The parameter to take into consideration for saturation is the instantaneous current.

I just measured a 15W ballast (for 230V). The (cold) DC resistance is 56 ohm, and the inductance is 1.56H (under small signal; at the nominal current, it is normally higher).
The maximum rms current is 0.33A --> 468mA instantaneous.
It could be used up to that current in DC, except it will overheat.

1.5H is not much, but it can be useful tough, and it could be parallel-tuned for 100Hz.

[DF96]

OK, I didn't realise they solve the problem in a different way.

[wabun]

1.5H is not much, but it can be useful tough, and it could be parallel-tuned for 100Hz.

Does it mean we can parallel the choke and ideally it should behave as follow..

50Ohms ( 1.5H ) || 50 Ohms (1.5H) = 25Ohms (3H)

and the max allowable current will double 0.33 A x 2 = 0.66A ?

[stormsonic]

INDUCTORS

[wabun]

thanks for the point out. I have mistakenly tot inductor & capacitor behave the same. In fact they aren't

[Elvee]

Originally Posted by wabun

Does it mean we can parallel the choke and ideally it should behave as follow..

50Ohms ( 1.5H ) || 50 Ohms (1.5H) = 25Ohms (3H)

and the max allowable current will double 0.33 A x 2 = 0.66A ?

No, I mean you can parallel it with a 1.69µF capacitor to increase the rejection at 100Hz (~30dB), provided you already have a conventional filter to remove higher harmonics.