inductors?

[jrz126]

Where is a good place to get some inductors? I'm looking into building a driver circuit for my 3W LEDs https://www.electro-tech-online.com/custompdfs/2006/01/00874b.pdf
and I need some inductors.
I'm eventually going to build about 10 of these drivers, and maybe more down the road, so a cheap source would be great.

oh yeah, I havent finalized all of my calculations yet, but I need the inductor to be in the range of 50-100 microhenreys, or possibly 700-800 microhenreys.

 

[chemelec]

How about Digi-Key in the USA or Electrosonic in Canada.

You don't say where you live.

But Before you buy any of these inductors, Make Sure they can handle the Current and Frequency.
I've found that Hi Q type Hash Chokes usually work well in these applicaions.

 

[Russlk]

Mouser and Allied do not have a minimum order, so check them out for small quantities.

 

[Styx]

or be cheaky and see if you can blag some samples

 

[jrz126]

I was able to find a site that has samples, but they would need an email from my professor saying that the samples are for a school related project. (which they are not).

I wonder if I can convince one of my professors to send them an email.
or I wonder how well they follow up on it. maybe I could fake it.

 

[justDIY]

check out Jameco if you're in the states ... they have a line of 'nock-off' torrid power inductors with pretty good ratings, best part is most are under $2 each

 

[jrz126]

I think Jameco is one of the few places that I didnt look. I'll give them a shot.

and I am in the states. Located by one of those 'great' lakes. There really isnt anything all that great about it.

 

[Oznog]

The best inductor for this job is in the Bournes SDR surface mount series. And only $0.85.
https://www.electro-tech-online.com/custompdfs/2006/01/686.pdf

Most likely one in the SDR1806 series will do it:
https://www.electro-tech-online.com/custompdfs/2006/01/SDR1806.pdf

If you need higher inductance or current, the JW Miller toroids are good deals:
https://www.electro-tech-online.com/custompdfs/2006/01/697.pdf

What's your power source for this project? I found the HV9910 was a lot better device for driving these than the PIC.

 

[jrz126]

I was looking at the DR0608-684L from coilcraft.
https://www.coilcraft.com/dr0608.cfm would those work?

I'm probably going to end up using these in my car, so I'll have a 12-15V supply (with a 5v reg for the pic of course). Although that 12V source is rather noisey, but Ill burn that bridge when I come to it.

I'm planning on making a sound to light type thing with these. I'm going to modifiy the micro so that it will vary the brightness with the voltage on pin3? (originally set up to monitor the battery level)

 

[Oznog]

I was looking at the DR0608-684L from coilcraft.
https://www.coilcraft.com/dr0608.cfm would those work?

Likely too small. Need more inductance and current capacity.

I'm probably going to end up using these in my car, so I'll have a 12-15V supply (with a 5v reg for the pic of course). Although that 12V source is rather noisey, but Ill burn that bridge when I come to it.

Isn't that PIC design made only for a high side switch? You'll need to build a driver because +5v will leave the PMOS on.

The noise gets to be a problem with this type of design because the PIC can't respond right away to changes in source voltage. If the LED takes 4v, the input is at 12v and then spikes to 16v, the LED and inductor current go up 66% until the PIC can correct it. If this exceeds the inductor's saturation current, you have a real problem!

LEDs tends to be good at taking brief overcurrents like that, though not so much in the Luxeon. The thermal mass versus the dissipation is not so great so its gap between safe peak current and average current is lower than most LEDs.

 

[jrz126]

I dont think I'll need a driver. The app note at Microchip says it will work, so I'll trust them.

I'm going to use the 680 uH. I figured that would be enough (based on the calculations in the app note).

Is there some sort of simple filter I can use to limit the spikes?

 

[Russlk]

You don't need any filter, the inductor does not produce spikes because it is supposed to be conducting all the time and the flyback is captured by the diode to ground.

 

[audioguru]

I found some nice inductors inside expired Compact Fluorescent bulbs that oscillate at around 40kHz that I'll try with a TL497 driver IC for a voltage stepper-upper. Silicon Chip mag has a project that uses it. It can probably drive a Mosfet for higher current and as a voltage stepper-downer.
Go to Google and enter: Silicon Chip Never Buy Another 9V Battery. The 1st link is the entire article for free.

 

[Oznog]

I dont think I'll need a driver. The app note at Microchip says it will work, so I'll trust them.

Is there some sort of simple filter I can use to limit the spikes?

OK, now I'm laughing... if Microchip says it works, it must work!
Microchip has released flawed app notes before. A few even qualify as infamous. Actually on the whole they're pretty good, better than most mfgs, but one can't assume they must be correct because they came from uC.

An LC filter can help filter the input, but the inductor and cap will need to be fairly large.

680uF is probably large enough, maybe even excessive. The thing to watch is the average current limit- exceeding this will cause the inductor to overheat just from I^2*R heating- and the saturation current, which cannot be exceeded even briefly, even during input spikes. Exceeding it will cause LED current to go very high and may damage the device.
The current for a 3W Luxeon is fairly substantial and beyond the capacity of many cheap/tiny devices. You'll want to shop for new stuff that you can get specs on.

 

[Russlk]

This circuit is only going to light an LED, so it does not need to be filtered.