# Capacitors

#### Iodem_Asakura

Joined Sep 14, 2004
140
Hi.

I'm trying to understand all the diference between electrolitic capacitors and the non-polarized ones. I know the basic ideas, but it has been a little dificult to understand why to use the non-polarized ones (except this aplications of high frecuency). Especially when i see it in a circuit, i can't figure out why it's necesary there . Recently, i was making a circuit and it didn't work like i was expecting. I saw a similar made one, and the diference was this 0.01 microfarad capacitor. When i put the capacitor all goes ok, but i don't understad why. I'll post a schematic later, to post only the involved part, so you can see clearly what's the problem.

#### Steel

Joined Oct 27, 2004
25
Capacitors do a few different things in a circuit. The main principal of a capacitor is that it allows AC current to flow through, but blocks DC current. There are 2 immediate ways to use a capacitor.

You can use it in series with the rest of the circuit. This is generally used in Amplification. You use capacitors to prevent DC voltage from flowing into sensitive AC signal devices. If you Put a Capacitor across a DC source, it will prevent the rest of the circuit from being affected by that source, while it does maintain reading an AC Source. (keep the 24VDC from flowing backwards into your 100mV AC audio Source and blowing it up.)

You can also use it in Series with your circuit. This is most commonly used in Digital circuits, where the Capacitor runs directly to ground. Again, the Capacitor allows AC Voltage to flow through while not allowing DC through. This capacitor acts as a 'Shunt'. If there is any AC voltage, or any noise, it escapes through the capacitor to ground (the path of least resistance for AC) whereas The DC current continues on its original path, because it cannot travel across the capacitor. If you have a noisy 5V signal that can cause problems with your IC's, if you throw a cap in it to ground, the majority(if not all) of the noise will flow to ground, while you are still provided a clean 5V signal.

#### bodhisatva

Joined May 20, 2004
23
Read something about ESR (Equivalent Series Resistance). Different types of capacitors - different ESR. Some times this really matters.

#### Iodem_Asakura

Joined Sep 14, 2004
140
Thanks for your help. I like you to do that (say me what to investigate). That's good, since we almost never know all that is implicated in something (i hope you understand me). For example, i didn't now that ESR existed since 3 days ago (well, the term really, since i knew that any capacitor can be represented like a resistance (its internal resistance) in serie with the capacitor) but there are some things i didn't take in count.

I really appraise you say me the things are involved about the theme i ask.... i'll investigate it :lol: .

By the way, do you know about a circuit or technique to measure the ESR?

#### sampinoy

Joined Sep 24, 2004
31
hi everybody,

i would liky to add somemore question about capacitors, yes i have seen circuits with caps connected in series with a source and i have wondered why some use electrolytics and others use nonpolar capacitors. basing on what steel has replied and also from what i know, electrolytics hav polarity. but if its connected in series to the source how would i know which way it should be connected. :unsure: am so confused bcoz i see circuits with the electrolytics positive side connected on the source side and others the positive side is connected to the circuit side. :unsure:

#### vineethbs

Joined Nov 14, 2004
56
source in the sense ?

well , u of course use capacitors to bypass power sources but they are never put in series (of course u know why B) ) . this is to bypass noise and/or power supply variations from a sensitive ckt .

capacitors are also used to provide dc isolation , which u can very well see in a simple RC coupled amp , there u can see that capacitors (if polarized) are put in taking the dc conditions into consideration , see if u have an ac source pumping in a signal , and u also have to bias the base of a transistor to abt 2V then u clamp the ac signal onto this 2v using a capacitor . Here the capacitor would have the -ive terminal connected to the ac source ! More on this if u reply !