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What's the function of a decoupling capacitor?

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Usually decoupling capacitor is used fom VCC to GND in ICs
Can someone plz explain why is necessary to place this capacitor

What i think is it is to cater the power supply fluctuations if it is so then if i will use a normal 1.5v dry cell battery to power an IC lets say mcu.Is this decoupling capacitor is to be used

What is a typical velue for a decoupling capacitor for lets say a 5v supply
 

Re: decoupling capacitor

coupling caps are usually needed if you power your source from the grid. if you have battery, you usually don't need any caps. that's how people avoid supply glitches in their circuits. however, the bad thing about battery is that they run out.

normally you would use umm .1uF to 1uF.

it acts as a smoothing function, ie any spikes from the supply would be directed to ground, instead of to your circuit (which may blow/destroy some of your ics up). So put a cap near the supply source connection, then another near your ic Vcc/Vdd.
 

Re: decoupling capacitor

Yup, i think they are for reducing power glitches, partly due to sudden current consumption during logic transitions in CMOS digital circuits.

I always try to use MKM 100nF.
 

Re: decoupling capacitor

place decoupling cap close to the ic as possible to reduce trace inductance. if trace inductance created by pcb route is more or cap is far away from ic , it is useless
 

Re: decoupling capacitor

It is necesary to place a decoupling capacitor near Power supply conector ( usually from high density technologies, for example tantalium) and other near the load or IC to compensate PCB inductance (usually from ceramic technologies, specially designed for high frequencies). If you dont use them, ICs could not work propriety.
 

Re: decoupling capacitor

I was taught that it's used in digital chips because power supplies have certain noise that can affect the chip opperation, so in order to filter this noise we need to put this capacitors in the Vcc or -Vcc terminals of the chips. It seems like for 5V, standard value is 0.1 µF, and I always use this value, but there are some vendors that specify the value for this cap.
 

decoupling capacitor

Putting a capacitor (few nF) with low value is often used to filter the power of the IC (avoid glitches).

Putting a high value capacitor (few µF) is locally used to make an energy tank... When the IC is running and has to sink a lot of current in a short period of time, it will sink current wherever it could find it... When no big capacitor is place, it involves glitch on the power line. When there is one, the IC will "drink" the over current it needs from the capacitor)
 

Re: decoupling capacitor

Putting a capacitor 0.1 uf ceramic will be quite enough on the supply of each switching IC (whatever it is) and on the supply of high gain circuits , we use that capacitor to bypass transients that occurs during switching on or off where the small inductance of the tracks of the pcb may apear and make fluctuations on the supply of the ic during switching on or off that is why we put decoupling capacitor for each switching ic and for the regulator ic, but for the regulator you add a capacitor 4.7 uf electrolyte or 0.1 uf ceramic .
 

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