Linear Voltage Regulator filter caps in a battery application.
Linear Voltage Regulator filter caps in a battery application.
(OP)
While using a genaric LVR such as a 7805 where the supply is from a battery is it typical practice to use a filter cap on the input. I'm looking at an application where I'll be suppying 100mA peak with a typical operating current of 3mA to a few Digital Panel Meters. The input will be coming from 5AA batteries (7.5V) regulated to 5V. The spec sheet calls for a 33uF cap on the input but I'm not sure I see a need, maybe the .01uF it calls for on the output ....
Thanks,
Mark
Thanks,
Mark





RE: Linear Voltage Regulator filter caps in a battery application.
RE: Linear Voltage Regulator filter caps in a battery application.
If less then use a smaller or no cap.
RE: Linear Voltage Regulator filter caps in a battery application.
RE: Linear Voltage Regulator filter caps in a battery application.
Let the manufacturers application notes be your guide, they have already been through all this. Better safe than sorry.
RE: Linear Voltage Regulator filter caps in a battery application.
Dan
Owner
http://www.Hi-TecDesigns.com
RE: Linear Voltage Regulator filter caps in a battery application.
RE: Linear Voltage Regulator filter caps in a battery application.
RE: Linear Voltage Regulator filter caps in a battery application.
http://www.national.com/ds/LM/LM78L05.pdf
RE: Linear Voltage Regulator filter caps in a battery application.
For example, I use one regulator by Zetex which has a max out of 50mA in an SOT-23 package... I think the quiescent current is about 50uA. The last project I designed with it used high brightness LEDs tuned down significantly. Still quite bright, but the processor and crystal took 8mA, 11 LEDs another 5mA, and everything else was negligible. If I had used a high quiescent current regulator (as I accidentally did for the prototype), my current draw would have been about 30% higher, and that's significant for a battery project.
Dan
Owner
http://www.Hi-TecDesigns.com