Correct capacitor choice - OT

[Christopher4187]

OK, I've taken some measurements of the circuit and here is what I found. The board is in production already (low quantities - see picture) so I measured at the fuse and my measurements were a bit different than I wrote before because I was measuring board current instead of the 5 volt regulator current. The nominal current of the regulator is ~7mA. When the alarm is in standby mode, the current will go from ~7mA to 15mA because of an LED. When the alarm activated, the current will go from ~15mA to 60mA. I looked at the regulator you suggessted but it's too expensive. The one that I want to use is $.31 for quantities of 100. However, if there are less external components required, I would think about using it because I pay $.25 for each smt component on the board. I can't use a SMPS because I have a wireless IC on the board but the entire board has a ground plane so noise should not be a problem. I currently have 30 units sold with no problems noted but I am crossing my fingers. I would like to improve the power supply circuit and I don't think I need that large cap on the output. Let me know your thoughts.

Thanks,

Chris

[mister_e]

Look you PM.

[Ron Marcus]

Many high frequency transient spikes will go right through the regulator. A .1 or even .01 uF capacitor will help, but a series chip choke type inductor will give you the best gain for the money. I have been working with switching regulators for battery boost, and they were reeking havoc with a RF receiver built into the app.. I isolated the regulator circuit using a chip inductor on B+ and tied the grounds together through another chip inductor. The high frequency noise dropped by a factor of almost 20. It meant 800 foot range as opposed to 200.

[Christopher4187]

Did you simply use a oscilloscope to measure the noise?

[Christopher4187]

What does "look you PM" mean?

[mister_e]

Private Message... top of this page at the right corner bellow your name.