Thread: Is this the right type of capacitor to use for a regulator circuit

The only advantage in paralleling multiple capacitors is to lower the effective ESR (equivalent series resistance). If you have them laying around, use them, otherwise your better off going with one Low ESR capacitor specifically designed for regulator outputs. I'm assuming that you have the rest of the circuit designed to regulate the voltage because capacitors do little to regulate. They will only filter the input and output voltages.

Hope that helps
Walter Farmer
http://www.safossils.com/mp3car.html

Originally Posted by waltsongs

The only advantage in paralleling multiple capacitors is to lower the effective ESR (equivalent series resistance). If you have them laying around, use them, otherwise your better off going with one Low ESR capacitor specifically designed for regulator outputs. I'm assuming that you have the rest of the circuit designed to regulate the voltage because capacitors do little to regulate. They will only filter the input and output voltages.

Hope that helps
Walter Farmer
http://www.safossils.com/mp3car.html

Yes I am using 12 volt regulators to get my output. I was under the assumption that the more capacity the capacitators had the better. Could you please explain why just getting one real low ESR one will help.

It really depends on your regulator design. If you are using linear regulators, a big capacitor is not necessary. If you have some type of switching supply, the capacitor/inductor will be carrying the load while the switching FET is in the off state. A low ESR capacitor will be able to discharge into the load with more efficiency. There will be less stress on it, and less heat generated. As I said though, it all depends on your regulator design.

Walt

Originally Posted by waltsongs

It really depends on your regulator design. If you are using linear regulators, a big capacitor is not necessary. If you have some type of switching supply, the capacitor/inductor will be carrying the load while the switching FET is in the off state. A low ESR capacitor will be able to discharge into the load with more efficiency. There will be less stress on it, and less heat generated. As I said though, it all depends on your regulator design.

Walt

I am using Low Drop Out regulators that can be found here http://rocky.digikey.com/WebLib/Shar...a/pq05rd21.pdf
What type of capacitors do I need and how much uF do I need on the in and out of it. Oh, I'm using 8 of them. Thanks.

Those are linear regulators; just about anything will do. The ones you have posted above will be fine. Linear regulators, are inefficient, but are also very stable as long as the input voltage remains above 13 volts or so. The spec sheet shows them tested with a V in of 14 Volts. Even when I've had brown outs, my hard drives would simply spin down and my computer would crash. It always came back when power was restored. I've blown up lots of stuff, but I have never been able to attribute a failure to a linear device. Of course the downside there is they generate lots of heat. If you are pushing these at their full 2 amps, they'll need a good heat sink.

best of luck
Walter Farmer

Originally Posted by waltsongs

Those are linear regulators; just about anything will do. The ones you have posted above will be fine. Linear regulators, are inefficient, but are also very stable as long as the input voltage remains above 13 volts or so. The spec sheet shows them tested with a V in of 14 Volts. Even when I've had brown outs, my hard drives would simply spin down and my computer would crash. It always came back when power was restored. I've blown up lots of stuff, but I have never been able to attribute a failure to a linear device. Of course the downside there is they generate lots of heat. If you are pushing these at their full 2 amps, they'll need a good heat sink.

best of luck
Walter Farmer

Ok, so my capacitors will work fine ok. Um... lets see, I didn't realize these were linear regulators. Um... my concern now is will they provide enough power when I turn the power to the car off and the voltage in drops to 12volts or less. I'm not planning to run it, but need enough time for the system to properly shutdown. As far as heatsinks go I'm planning to use some 5 watt rated ones and I can use a fan if need be. Considering you said that linear regulators don't need a high uF capacitor rating what would you use? Could I get away with not using any at all?

I would put a larger filter to the input of the regulator, 2000 uF is probably sufficient. I would use 470 uF on the output. I'm no engineer though. I have enough old junk lying around that I usually go overboard with these types of things. I am running computers that are close to 10 years old as well so my schematics are probably no good to anyone here. Here is my latest Power Supply design it is a combination of switching and linear supplies. The twelve-volt section can supply only about 1 amp. I have the CD RW drive on a low drop out regulator like the one you posted: works fine. I have used low drop-out regulators to run hard drives, and if your battery is in good shape, they will stay spun up even with the engine off. They will not survive engine cranking though.

Hope that helps
Walt