has anyone used a CLC + voltage regulator (like LT1083) in their project?

[jarthel]

I am thinking of something like 2.5mH 10A Hammond chokes.

I know that the use of choke in a filter is somewhat "old" tech but has anyone used it? I believe a choke has some benefits to power supply filtering.

Thank you for the feedback

[gootee]

I use a modified C-L-C filter (actually C-LR-C) between an LT-1270A-based boost-mode SMPS and a linear post-regulator. It works astonishingly well.

In my case, I'm filtering mostly 60 kHz switching spikes, with an average of only up to about 1.5A (at 38V). So I'm using a JW Miller 10 uH toroidal inductor (11.2A DC, .014 DCR, $1.95ea/10).

I found that adding a 0.5 Ohm 5W resistor in series, between the L and the following C (which goes to ground), made quite an improvement. (In this case, it degraded the roll-off from about 20 dB/decade to about 18.6 dB/decade, but lowered the cutoff frequency from about 1 kHz to about 140 Hz, and also eliminated a 7.3 dB peak at the cut-off frequency [and confined the phase to <= 90 deg.])

Before the L, I have the smps's output cap, a 2200 uF 50V Nichicon UHE-series, with a 2.2uF 63V AVX BQ-series Polyester cap in parallel, to ground. After the L and series R, I have another identical 2200uF 50V cap to ground, just before an LT-1084 5A regulator (output at 35V). (Actually, I use the LT-1084 for simulation, but usually use LD-1084 for production units, since it's much cheaper.)

This filter knocks the 60 kHz spikes down from the 300 mV p-p range to the 300 uV p-p range.

- Tom Gootee

http://www.fullnet.com/~tomg/index.html

[jarthel]

Originally posted by gootee
[B]I use a modified C-L-C filter (actually C-LR-C) between an LT-1270A-based boost-mode SMPS and a linear post-regulator. It works astonishingly well.....

In my case, I'm thinking of a CLC then a linear regulator.

I have not built an SMPS PSU before but from what I have read here, a PCB is a must and I do not know how to design PCBs nor do I have the time/equipment to do so. Is this correct?

Thanks again

[gootee]

Well, that's basically what I have. I started with a CLC followed by a linear regulator, but later modified the CLC to CLRC. What's upstream will just mean different CLC values.

You can get LTspice free from linear.com, and simulate what you're thinking of doing, which will help in picking or adjusting the component values, too.

Just remember to include the ESR (at your frequency of interest) for the capacitors, and the DC resistance for the inductor.

Regarding switchmode power supplies.... I've never tried one without a PCB. But I see no reason it couldn't be done. However, you DO need to know which wires to keep short and fat. (There are appnotes about that, at linear.com, national.com, et al.)

If you ever DO decide that you want to make a PCB, see http://www.fullnet.com/~tomg/gooteepc.htm . You can do it for almost nothing, in about an hour, after your layout is done at least. I used to do my layouts with MS Paint. But there are lots of free PCB-layout software packages, and free functional demos. Check out http://www.fi.uib.no/~bruce/eda.htm . For blank PCB stock, either search for FR4 on ebay.com, or get some from mouser.com. You'd probably want to use FR4 with at least "1 oz" copper, and thickness of .062" or so.

By the way, both LTspice and National.com's on-line Webench will automatically design an SMPS for you.

- Tom Gootee

http://www.fullnet.com/~tomg/index.html