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Old 23rd February 2012, 07:17 PM   #151
tomchr is offline tomchr  United States
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Another option for higher output currents would be to use the LM22679. It's the same pin-out and footprint so it'll fit on my regulator boards just fine. As long as the inductor can fit on the board and handle the peak output current (use WebBench to find this) it should be plug-n-play.

~Tom
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Old 23rd February 2012, 08:00 PM   #152
wicked1 is offline wicked1  United States
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The inductor specified on the 2.5A parts is rated to up to 4amps. So would the LM22679 be the only change? Or does that different part require a different inductor? (fyi, I think I'll be using a 6.3-0-6.3 trafo (radioshack) OTOH, this can be changed.. I just happen to have a few of those)

Whoa.. I just opened webbench.. It looks like it wants to design for me..

--Nevermind.. I figured out I start w/ the part you link to above, and it's simple!

Last edited by wicked1; 23rd February 2012 at 08:22 PM.
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Old 24th February 2012, 06:21 PM   #153
tomchr is offline tomchr  United States
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My intent for the regulator was to power it with two 6.3 V windings. Your RatShack trafo will work just fine provided it can handle the power. You can leave the center tap disconnected and just use the end points of the secondary.

The input to the filament regulator board should be rectified DC so you'll need an external diode bridge and cap.

As long as the current in the output inductor doesn't reach the saturation current of the inductor, you should be fine. Webbench will tell you... The Coiltronics inductors I use are listed in Webbench. As are the electrolytic caps if I recall correctly.

~Tom
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Old 24th February 2012, 08:41 PM   #154
wicked1 is offline wicked1  United States
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Ok, I've been struggling to get webbench to match your schematics, but I guess it's because my requirements are a bit different.

Looks like I will have to use a lower value inductor.. It doesn't give me the option for anything more than 15uH w/ the lm22673, and 10uH is the max w/ lm22679. There's some ripple on the output.. 33mv vs your 3.

actually, I used a 22uH inductor w/ a different footprint and ran the sim, and still get 30mv ripple. Is that simply a result of pulling 3A vs your 1.5?

Last edited by wicked1; 24th February 2012 at 08:56 PM.
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Old 25th February 2012, 02:04 AM   #155
tomchr is offline tomchr  United States
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The voltage ripple on the output is the ripple current through the inductor multiplied by the ESR of the output capacitor. The ripple current of the inductor is set by the inductance (lower L --> higher Iripple) and the input, output voltages.

What happens is that energy is stored in the inductor when the main switch inside the IC is on, then while the switch is off, this energy is dissipated in the load (OK, handwavy explanation, but you get the idea). As the amount of energy supplied to the load is constant, the amount of energy stored in the inductor per cycle is constant as well. The on-time, Ton, of the switch is Ton = Vout/(Vin*Fswi), where Fswi is the switching frequency. So a higher Vin means the switch has less time to dump the required energy into the inductor. So the ripple current goes up. As Vripple = Iripple*ESR, to get lower ripple voltage, you either need to pick a capacitor with very low ESR (watch for stability issues) or a higher inductance, thereby, reducing the ripple current. Whatever inductor you pick needs to be able to fit on the footprint and be able to handle the peak current without saturating.

WebBench seems to pick some optimum values. "Optimum" in this case is some combination of the total BOM cost, board area, etc. I find that I can trick it into using my values by either hand-picking them in the component list or by typing them in as custom components.

Notice the Phase Margin in the Operating Point spreadsheet? That needs to be MINIMUM 45 degrees - I tend to not go below 60 degrees. At 0 degrees PM the circuit is unstable, but with PM < 45 deg, expect some severe ringing on the transient response.

~Tom
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Old 25th February 2012, 10:12 PM   #156
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I've updated the Known Good BOM spreadsheet to reflect the options tested thus far. Also, as I ran out of boards (I have one left!) I decided to add a footprint for a tantalum cap (case size 6032-28 and 7343-31) on top of the footprint for the SMD electrolytic cap (C11). This actually works quite well. Aside from this small modification, Rev. 3.1 and 3.2 are identical. And, actually, it is possible to solder a tantalum cap to the Rev. 3.1 board. It's just not as easy or pretty as with a footprint designed for it...

Universal Filament Regulator : Neurochrome.com : : Audio

Rev. 3.2 boards are available for pre-order. I expect to have boards in stock in about 10 days.

~Tom
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Last edited by tomchr; 25th February 2012 at 10:15 PM.
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Old 25th February 2012, 10:36 PM   #157
wicked1 is offline wicked1  United States
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Thanks!
Success.
I couldn't get rid of the ripple w/ the lm22673 part, but it works well w/ the lm22679.
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Old 27th February 2012, 01:44 AM   #158
tomchr is offline tomchr  United States
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Yeah, the internal compensation circuitry is probably different (optimized for the higher output currents) in the LM22679. This allows you to pick more optimal external components, resulting in better performance. The same is the case between the -ADJ version and the -5.0 and is why I use the -5.0 for output voltages 5 V or higher.

~Tom
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Old 29th February 2012, 06:08 PM   #159
tomchr is offline tomchr  United States
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Latest Known Good BOM has been uploaded. This includes WebBench calculations of the values for the lower voltage options for use with tubes such as 26, 4P1L, 2A3, and the like.

I should have more boards in stock by the middle of next week. If you want to be first in line to get yours, pre-order through my website.

~Tom
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Modulus-86: Composite amp achieving 0.00018 % THD. Damn Good 300B, Novar Spud, 21st Century Maida Reg., Filament Reg., etc.
Neurochrome : : Audio - http://www.neurochrome.com/audio - Engineering : : Done : : Right
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Old 8th March 2012, 04:41 PM   #160
tomchr is offline tomchr  United States
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Universal Filament Regulator Rev. 3.2 boards are now in stock.

Universal Filament Regulator : Neurochrome.com : : Audio

~Tom
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