[Efi332] HW Question (for JC)

[Paul Helmuth]

Jeff,

Thanks!

I found the Panasonic devices at Digikey - they appear to be ideal for the application. The only problem for me is they also appear to be available in SMD only. After some searching, I found some units by Xicon (at Mouser) which are low ESR and come in an old fashioned package (with legs). The only thing is, I did have to bump up my capacitor value to 220 uf to be safely within the ESR at colder temperatures (not that this is really long term solution - but it doesn't hurt anything for that output cap to be bigger).

So, after everyone is back from the long holiday weekend and they ship my capacitors, I'll finally be ready to do my ignition-only testing (that is, if I have the crank trigger wheel mounted).

-Paul
  ----- Original Message ----- 
  From: bowtievette at aol.com 
  To: efi332 at diy-efi.org 
  Sent: Wednesday, June 29, 2005 8:44 PM
  Subject: Re: [Efi332] HW Question (for JC)


  Hi Paul,
  I would include the 47uF on the input side. I don't think you will have any problems with it running from the car's battery/alternator.
  On the output side, you're right, ESR values are typically not quoted in catalogs other than to say low ESR, so you usually have to dig up the datasheet(s) to get the tables for it. If you do a search for low ESR capacitor at digikey it will narrow the search to caps that advertise low ESR. Pick a 22 uF one from the selection table presented and follow it to the datasheet. For this application, aluminum electrolytics are common, and occasionally tantalums. Some folks recommend against using tantalums in power supplies since they have a tendency to blow up under rapid transient conditions. With the electrolytics, you may have to watch the temperature variation since the ESR varies quite a bit.
   
  -----Original Message-----
  From: Paul Helmuth <PaulHelmuth at SprintMail.com>
  To: efi332 at diy-efi.org
  Sent: Wed, 29 Jun 2005 16:37:06 -0500
  Subject: [Efi332] HW Question (for JC)


  Jeff,

  I managed to source a couple of National LM2940T (9volt output) regulators. I am hoping to use this part to power my Phytec development board from the car's 12v battery.

  The "Typical Application" section of the data sheet shows only two external components. 

  One is a .47 microfarad capacitor on V-in to ground. An asterisk note indicates that this is required if the regulator is located far from the "power supply filter". Which seems to imply that there should be some filtering in place between the battery and the regulator (though there is no diagram of what such a filter should look like).

  The second external component is a 22 microfarad (minimum) capacitor on V-out to ground. The interesting note on the output capacitor is that the equivalent series resistance is critical. Reading the performance characteristics table relating to the output capacitor ESR, I see that I need to use a capacitor with an ESR between .1 and 1 ohm. I have never seen ESR given for capacitors. Can you give me any pointers as to how I can determine and arrive at an acceptable ESR for the output capacitor(s)?

  Thanks,
  -Paul
_______________________________________________
Efi332 mailing list
Efi332 at diy-efi.org
http://lists.diy-efi.org/mailman/listinfo/efi332


------------------------------------------------------------------------------


  _______________________________________________
  Efi332 mailing list
  Efi332 at diy-efi.org
  http://lists.diy-efi.org/mailman/listinfo/efi332
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.diy-efi.org/pipermail/efi332/attachments/20050701/99a311af/attachment.html