12vdc to 5vdc using L7805

Thread Starter

ATM

Joined Oct 8, 2009
31
Hello guys.

I plan on dropping 7v from a 12v car battery down to 5v to operate a sensor. The sensor requires a current of 6mA. So if my calculations are correct the 7805 will need to dissipate 42mW. I have a couple of questions:

1. If I use the typical circuit below:



Will I need the caps? Also, I can disregard a heat sink if only 42mW needs to be dissipated right?

Thanks.
 

Thread Starter

ATM

Joined Oct 8, 2009
31
In this instance what are the caps for if you don't mind me asking? I presume the 0.1 is to help smooth the output?
 

bertus

Joined Apr 5, 2008
20,564
Hello,

The capacitor are there to prevent the regulator from oscillating.
It is a stability question.

Greetings,
Bertus
 

t06afre

Joined May 11, 2009
5,934
More precise 0.33u is required if the regulator is located more than 3" from the power supply filter. Will prevent regulator from oscillating. But I have never experienced a oscillating 7805 even in my most "quick and dirty" prototype boards. The 0.1u is the recommended minimum load capacitance to limit high frequency noise. I like to combine this with a 10U tantal cap
 
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