Inductor specs in threeneuron's HV PSU

[Morten Mønsted]

Hi,

I'm building a nixie clock "from scratch", designing the circuit (with great inspiration from other projects) and the PCB etc. Just for my own entertainment, not for selling or anything. I'm a hobbyist, not a professional :)

I want to have the power supply on the board, and was inspired by threeneuron's high voltage supply, which can be seen here: https://threeneurons.wordpress.com/nixie-power-supply/hv-supply-kit/

My problem is that I can't source the inductor L1 with the correct combination of 100uH and 1.4A. The closest I can get are:

1. 68µH / 1.4A
2. 220µH / 1.4A
3. 100µH / 1.0A
4. 100µH / 1.6A

Now my question is, would I be able to use one of the four above mentioned inductors, without switching other parts? On the page linked above it says that you can increase the output power of the PSU by using an higher current inductor, but it also says that it's necessary to change some other parts like resistors and a capacitor.

My thoughts so far:

1. I could go with inductor #4 and not change other parts, because I know I won't ever get over 3 watts total (but I'm not sure if this is safe or not)
2. Go with inductor #3, not changing other parts, knowing that I won't use up the current capacity (but again, is that really safe?)
3. Use inductor #1 or #2 — but again my lack of knowledge plays in, as I have no idea how significant the 100µH is, and would would happen if you increased/decreased it.

I know I can probably get exactly the correct inductor from the right supplier, but I have to stick with a few who don't charge an arm and a leg for shipping (to my country), whilst still selling in low quantities. Also, I'm hoping to learn something here, by not simply throwing money at the problem!

Any help is much appreciated!

[Nick]

A higher-current-rated inductor of the same uH value and same type will be fine - inductor #4 is likely as good as the original...

Nick

[Morten Mønsted]

Thanks for your answer.

All right, it does make sense, my concern was with the rest of the circuit only being designed for 1.4A. But I guess the key here is that it's "up to 1.4A", which I will never reach, even thought the rating is higher.

[Tomasz Kowalczyk]

You're right. The current rating for an inductor is an "up to" value, as it states the maximum current you can pass through that part without saturating the ferrite core. A saturated inductor in a boost converter will heat up and the converter won't reach designated voltage.

Btw. I've read somewhere, that for boost converters you shouldn't use inductors with "o" shaped core or any closed loop core inductors, as they are much easier to saturate. I've done only very short tests, and it was true - but maybe the peak current of the inductor was too high, I can only measure average, which was 3x lower than that coil max specified current. Can anyone confirm if it is possible or not to use closed loop ferrite cores for converter coils?

[threeneurons]

The coil issued with the kit is a Bourns RLB9012-101. All major distributors (Mouser, Digikey, ...)  are currently out of stock, and back ordered to May. That coil is a tad overkill for what the supply is rated to output. The RLB0914-101 will also work to more than the posted maximum specs. So will a RLB9012-082 (82uH).

[Morten Mønsted]

Thanks for your answer :)

As I read you, I could use either RLB0914-101 or RLB9012-082 instead?

I just checked and I can get the RLB0914-101 from my supplier of choice!

[threeneurons]

Yep, when I saw the stock situation, I order some 82uH parts, and tested them, in excess of the recommended load. Worked great. I had already tested the RLB9014-101, way back when, but routinely ordered the RLB9012 part due to the extra safety margin.