best capacitors for dc low voltage smoothing

[danrogers]

hi im trying to find out what caps to get to smooth some T092 regulators.

looking on farnell, and typing what i need (0.1,0.33,22 & 47uF) i get a crazy amount of results.

what would be the best and the most cost effective choice?

 

[Hero999]

You haven't said what the input and output voltage is or the current draw.

It sounds like the capacitors specified are too small.

 

[crutschow]

For less than 1µF, ceramic or film capacitors are typically used. Above that use aluminum electrolytic (cheapest) or tantalum electrolytic (more expensive but smaller and better performance).

 

[danrogers]

the voltage wont be more than 9v and current draw on the regulators is 100ma

cheers crutschow

 

[Hero999]

You still haven't mentioned the transformer voltage.

What regulator are you using? What's the dropout votlage?

 

[danrogers]

**broken link removed**

will be those devices or similar mate.

hmmm drop out voltage looks like 1.7v, i'm not sure what that means?

 

[Hero999]

It means that if the input voltage drops below the output plus 1.7V the output voltage will become unregulated and start to fall.

Again what's the transformer voltage?

This is hard work.

 

[danrogers]

what transformer? the regulators will be battery powered, probably a 9v

 

[danrogers]

oh and thanks for explaining drop out to me by the way

 

[Hero999]

If you'd told me that in the first place, then I would've said that the capacitor value is fine.

You'll probably want to use regulator with a lower drop-out voltage to get more life out of the battery.

 

[joemcder]

the voltage wont be more than 9v and current draw on the regulators is 100ma

cheers crutschow

With a 9v battery this is a routine application. Use a 50 - 100 uF aluminum electrolytic. An additional 1-10 uF Tantalum is often added for noise supression. The Tantalum is faster acting. Is the load noisey, such as a small motor? If its just LED's etc, then anything will work. If the circuit includes a microcontroller than noise suppresion is essential.

Note that a 1.7 drop out may somewhat limit battery life. You can get low dropout regulators < 1 volt, for example the LM2940.

Joe

 

[danrogers]

i know the values were fine, i took them from the datasheet. i was just enquiring as to the best type of caps to use, thanks anyhow.

thats cool cheers Joe, the load will be rf modules and encoders etc so should take it pretty smooth. thanks for the heads up on the regulator

 

[Hero999]

Is the load noisey, such as a small motor?

I wouldn't recommend powering a motor from the regulator.

I take it, you mean powering the motor directly from the battery and the control circuit from the regulator?

 

[joemcder]

I wouldn't recommend powering a motor from the regulator.

I take it, you mean powering the motor directly from the battery and the control circuit from the regulator?

Yes you are correct. However even a motor on the battery will inject noise into the electronics. Apparenltly no motors are involved so the issue is theoretical.