Question on a 7805 Voltage Regulator

[BCHurricane89]

So I actually have two voltage regulators that I will be using to create a 5v and a 3.3v rail. Here is the application circuit from the 5v regulator:
**broken link removed**

The question I have is what type of capacitors to use? I have seen some people use two electrolytic caps, some use one electrolytic and one ceramic. The schematic seems to show ceramic caps, since I don't see polarity shown. What is the best combination to use to get fairly clean power?

I will probably be using a 9v 650mA ac adapter, and I have did some research, and came across ripple currents etc, and how the caps smooth it out. I've also read something regarding the ESR, and using both an electrolytic and ceramic as each capacitor can do different things with the different frequencies? If you need any more information on what im doing, just ask. Thanks.

 

[ericgibbs]

hi,
The caps shown in the circuit, ie: Ci and Co can be unpolarised ceramic, general purpose types, rated at 25V or higher.

I would add a 470uF 25V electrolytic cap across Ci and a a 220uF 10V across Co.
Note: most electrolytics are polarised and are marked +/-/

For a simple linear regulator I would not worry about ESR..

NOTE: 9v 650mA ac adapter, with your circuit the adaptor must be DC out not AC

 

[BCHurricane89]

Oh, so different rated caps than the diagram. So a 470uF 25V electrolytic cap, and a 220uF 10V ceramic cap.

How about for a 3.3v voltage regulator with the same 9v 650mA AC Adapter - and yes, my output is DC.
**broken link removed**

 

[alec_t]

So a 470uF 25V electrolytic cap, and a 220uF 10V ceramic cap

Er, that's not what Eric suggested. He was suggesting a 220uF 10V electrolytic cap connected in parallel with ceramic cap Co.

 

[ericgibbs]

hi,
Like this.

 

[BCHurricane89]

Ahhh ok, thanks for the info!

 

[Nigel Goodwin]

It's really VERY non-critical, I usually just use a couple of small electrolytics (1-10uF) depending what's on hand - they should be as close to the IC as possible.

As Eric has mentioned, the input side should also has a good sized electrolytic as well, as should any power supply.