Author Topic: 1) Hello y'all -- 2) spice simulation - ESR of caps  (Read 10090 times)

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Offline madworm

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1) Hello y'all -- 2) spice simulation - ESR of caps
« on: October 17, 2009, 03:26:11 am »
Hi,

I've been lurking for a few days now. So here I am :-)

Some background: I'm a physicist (vacuum/fs-laser/xray stuff) and got addicted to electronics (again) by my arduino boards. I like to tinker and get my hands dirty, so obviously I'm not one of the theory guys who do "real numerical experiments".


Now back to what this blog is about:

Currently I'm struggling with LTSpice and a circuit for a boost converter (LT1618). It turns out that the output current of said thing is quite sensitive to the ESR of the output cap. I use pretty much the standard circuit shown in the data sheet with output current and voltage limiting.

2 problems:

- Where the heck can I get low ESR caps ? I've tried mouser and farnell and either I'm a bit thick in the head or there are simply no 4.7µF caps that come with less than 0.3 Ohm. I could of course just parallel many many normal ones, but size does matter. Oh and I need through hole parts only, as this is supposed to grow into a DIY kit.

- The LT1618 only comes in an MSOP10 package, and DIP adapters (for prototyping and DIY kit purpose) are priced hilariously. I'm at the verge of having a life time supply of 500 or so made, just so I won't have to shell out 3$ for a PCB the size of my thumbnail. Using toner transfer or the usual UV/etch stuff just doesn't cut it. I need silk screen and solder mask. Any cheap source for these out there ?


later,

robert
 

Offline EEVblog

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Re: 1) Hello y'all -- 2) spice simulation - ESR of caps
« Reply #1 on: October 17, 2009, 03:49:54 am »
Why stick with the LT1618 if it's not in a package that suits you?
Have you looked for alternatives?
Seems like too much hassle to use an adapter if this going to be a kit or product.

Farnell have 4 suitable electro RB caps, I just searched for 4.7uF and sorted by ESR.
Here's one:
http://au.farnell.com/sanyo/16sh4-7m/capacitor-4-7uf-16v/dp/9189300
Normally you'd use a multi layer ceramic for something like this, but low ESR electro is suitable too.

Dave.

 

Offline madworm

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Re: 1) Hello y'all -- 2) spice simulation - ESR of caps
« Reply #2 on: October 17, 2009, 07:08:02 am »
Yes, I've looked for others. The LT1618 is not the first IC I've considered. The first one was an LM3410, which is SMD only too (like most of the good stuff). The LT has some nice features compared to all the others I've seen and I can get it locally in small quantities. It seems perfect for what I want, expect for the package (at least for prototyping). 20 years ago I didn't have any of these problems...

Farnell is an absolute no-go in Germany. They've quit selling to non business individuals directly and have outsourced that to a smaller dealer. This of course comes at a hefty premium. I call that daylight robbery :-(

Seems like I'll have to investigate some more.
 

Andrew

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Re: 1) Hello y'all -- 2) spice simulation - ESR of caps
« Reply #3 on: October 18, 2009, 10:08:01 pm »
Where the heck can I get low ESR caps ?

From every self-respecting electronic component shop. It is pretty standard stuff these days.

Quote from: madworm
I've tried mouser and farnell and either I'm a bit thick in the head or there are simply no 4.7µF caps that come with less than 0.3 Ohm.

Nowhere in the datasheet it says 0.3 ?.  If this is the result of your simulation, forget the simulation. There are times when you have to actually build something, instead of trusting a SPICE simulation - even if the SPICE simulation comes from the IC's vendor.

http://br.mouser.com/ProductDetail/TDK/FK22X7R1E475K/?qs=sGAEpiMZZMuAYrNc52CMZAWzPNiQZc%2f%2fZMp6o9xkQ%252bE%3d should be a cap according to the datasheet. Also note the datasheet lists some cap vendors.

Quote from: madworm
- The LT1618 only comes in an MSOP10 package, and DIP adapters (for prototyping and DIY kit purpose) are priced hilariously. I'm at the verge of having a life time supply of 500 or so made, just so I won't have to shell out 3$ for a PCB the size of my thumbnail.

$3 is cheap for an MSOP-10 adapter. You can easily pay more than double.

Quote from: madworm
I need silk screen and solder mask. Any cheap source for these out there ?

Chinese manufacturers like http://www.goldphoenixpcb.biz/ or Eastern Europe manufacturers like http://www.bilex-lp.com/
 

Offline madworm

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Re: 1) Hello y'all -- 2) spice simulation - ESR of caps
« Reply #4 on: October 19, 2009, 01:57:20 am »
Thanks for the input! So I'll just build the circuit, hope it doesn't oscillate where it shouldn't and measure the output current ripple on my scope. Crossing my fingers.

3$ may be cheap compared to other ones that dare ask more for such a tiny thing. It still feels like a massive rip off. 50¢ would be a fair price.

I feared that I'd get forwarded to pcb fab houses, so I've already created the gerbers for my adapter. Soon I'll have a life-time's worth supply of them and maybe I'll even have my coffin lined with them some day. Still better than feeding the vampiristic adapter mafia. Imagine you'd have to pay 3$ for a simple 7404!

If anybody wants some MSOP10/TSSOP8 DIP adapters (12mil traces, thermal pad under the chips), I'll be swimming in them in a few weeks :-)

Goldphoenix is acceptable and fast, I've used them before. But for this I'll use a different house (ultra slow, but low prices). I don't know about European companies. In terms of price per board, they're on lost ground.


Later,

Robert
« Last Edit: October 19, 2009, 02:06:30 am by madworm »
 

Offline EEVblog

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Re: 1) Hello y'all -- 2) spice simulation - ESR of caps
« Reply #5 on: October 19, 2009, 03:09:48 am »
I use www.pcbcart.com

Dave.
 

Offline madworm

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Re: 1) Hello y'all -- 2) spice simulation - ESR of caps
« Reply #6 on: October 19, 2009, 05:04:01 am »
I've placed my order at makepcb.com. They're not fast but deliver good quality for little money. Let's see what they say about the amount of routing required for the little 14x12mm boards ;-)

In case you want the gerbers to build a little stash (or heap) of your own, you can get them >>here<<.

 

Offline qno

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Re: 1) Hello y'all -- 2) spice simulation - ESR of caps
« Reply #7 on: October 22, 2009, 03:16:24 pm »
Hi Robert,

I have used a 8 pin DIL MC34063 in the past. You can still order them. You can buy them from ON semi or ST micro.
Quite cheap.
Why spend money I don't have on things I don't need to impress people I don't like?
 

Offline madworm

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Re: 1) Hello y'all -- 2) spice simulation - ESR of caps
« Reply #8 on: October 22, 2009, 05:04:26 pm »
That IS a nice chip, and cheap. I can get it for about 30¢. I should have known about it before I got my box of MAX756 ;-(

For such a low price I can risk burning a few and see if I can get an ATtiny13 to dim my big fat LED.
 


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