Low ESR capacitor???

[victorf]

I want to use a LE33c voltage regulator to convert 5VDC to 3.3VDC. The data sheet calls for a 22uF output capacitor with a ESR of 0.1 to 10 ohms. I have been searching the distributors, Jameco, Mouser and Digikey, to find a suitable source with no luck. I need a thru-hole solution at a reasonable price. Probably don't need more than 20. Thats all the LE33Cs I have. I don't need more than 100mA for the application.

Is there a another regulator I should consider? How about just a simple voltage divider?

Any enlightenment will be appreciated.

Vic

[dkinzer]

Many of the capacitors listed at Digi-Key don't have their ESR specified. However, I suspect that a decent tantalum capacitor will have an ESR less than 10 ohms (at the "normal" 100KHz specification frequency). Note that ESR decreases as working voltage goes up so you're better off choosing a 35V capacitor over a 10V capacitor for example. The downside of this is that the physical size increases with working voltage.

If your application must operate in cold temperatures, you'll probably want to avoid aluminum eletrolytic capacitors because typically their ESR rises significantly at cold temps (< 10*C).

A voltage divider is generally not a useful solution for a power supply. The problem is that in order to get a low source impedance for the supply you have to use low value resistors so you end up wasting a lot of energy.

[victorf]

Don,

Thanks for the quick reply. I'll order up some tantalums from Digikey or Jameco and give them a whirl.

Vic

[spamiam]

Another way to do this is use a bunch of parallel smaller caps. When paralleling caps, their capacitance is additive, but their ESR is calculated the same as resistors: 1/Total ESR = 1/ESR1 +1/ESR2+1/ESR3....

So a bunch of less expensive caps or lower profile caps can sometimes do job