Author Topic: What inductor to use for boost circuit?  (Read 1988 times)

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Offline j209177Topic starter

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What inductor to use for boost circuit?
« on: December 18, 2017, 01:09:56 am »
I am making a nixie tube watch.
I need to use a small height inductor than the one this guy used, and i need a max Current Rating of 700ma.
https://www.digikey.com/products/en?keywords=RLB9012-101KL-ND --  The one he used

https://threeneurons.wordpress.com/nixie-power-supply/hv-supply-kit/ -- the kit and schematic he made


this is the inductor the guy uses but it is large and it has a 1.4A max rating


could i use something like this

https://www.digikey.com/product-detail/en/bourns-inc/SDR1006-101KL/SDR1006-101KLCT-ND/2127203


is there something i missed?
 

Offline Cliff Matthews

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Re: What inductor to use for boost circuit?
« Reply #1 on: December 18, 2017, 01:44:48 am »
I'm not an engineer, but to make things smaller, try another switching regulator than the MC34063. Higher frequency = smaller size.


* Edit: Someone here (Tim?) posted this a while ago on the forum..

Suggested alternatives:
Boost or flyback, offline under 100W: - UC3842 series, TOPSwitch, FPS, etc. Buck or forward, offline over 100W: - TL494, UC3524, etc.
Buck, DC-DC, external switch: - LM5085, TLE6389, LTC3824, LTC3810, etc.
Internal switch: - TPS54231, LM2675, LM5008, etc. There are many to choose from, and you will save greatly on the cost of other components.

One of these chips may cost $1-3, but they all use much smaller support components. The huge caps and choke looming in the picture will cost more in total, plus board area. Plus, these newer chips are easier to use. And these are just a few excellent options for the most common uses.
« Last Edit: December 18, 2017, 01:50:02 am by Cliff Matthews »
 

Offline T3sl4co1l

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Re: What inductor to use for boost circuit?
« Reply #2 on: December 18, 2017, 05:56:59 am »
Yes, that inductor is probably about right. Mind that it's SMT, so you need some pads to solder it onto (or tack some pigtails onto it, so you can shove it into a board).

* Edit: Someone here (Tim?) posted this a while ago on the forum..

Yes. :P

But hey, at least it's current sensing at all, and not the stupid circuit that's open loop, with a 555 or MCU (uch) generating the square wave!

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 

Offline j209177Topic starter

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Re: What inductor to use for boost circuit?
« Reply #3 on: December 19, 2017, 12:31:00 am »
I'm not an engineer, but to make things smaller, try another switching regulator than the MC34063. Higher frequency = smaller size.

I did not know about frequency and size.
but i would like to stick with the MC34063 for now.

Yes, that inductor is probably about right. Mind that it's SMT, so you need some pads to solder it onto (or tack some pigtails onto it, so you can shove it into a board).

I am aware of the smd nature of the device i am wouried about the Frequency - Self Resonan, Q @ Freq, Frequency - Test and ect. What are these things and do i need to worry about them.

How much power do you need? If it's only less than 2W, consider MP3425+ATB322524 (5V->150V).
At 5V->150V, 1:10 turns ratio, CCM, such a flyback converter has D=0.75.
At 2W output, assuming efficiency=0.9, then input current is 0.44A, equivalent transformer current is 0.59A.
Ripple current will be 5V*0.75*0.67us/2/6uH=0.21A (at Fsw=1.5MHz), so peak current it 0.8A, which is far from saturation point of ATB322524.
Primary side RMS current will be roughly sqrt(0.75)*0.59A=0.51A, less than ATB322524's rated 0.7A RMS max current.
Primary winding power loss will be 0.51A*0.51A*0.5R=0.13W, secondary loss is [2W/150V/sqrt(1-0.75)]^2*60R=0.04W.
Total transformer loss will be 0.17W (ignoring core loss), or 8.5% output power.

If you need more than 2W output, consider parallel two ATB322524 to double the power. MP3425 can handle up to 3.5A peak current (4*ATB322524 per above calculation in parallel), providing up to 8W of total output power.

I would like to stick to the MC34063. for No other reason than someody already has desiged the circuit and knows it works, plus the time i have invested in the board layout and the likes. But thank you.

The pictures are what i am trying to improve on (because they dont work, for various reason).
The first picture is showing the inductor is the thickest component, the rest of them have the wrong footprint (or some else i did wrong), and the tubes would interfere the inductor. thats why i need a smaller one.
 
The Second picture is a top down view. Inductor is the one in the middle.

Third picture is the aluminum case i made and the tubes.

Thank you all for your response.
 


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