DC filter capacitors - Electronic Circuits Projects Diagrams Free

pike · 8th October 2004, 03:13 AM

http://www.uoguelph.ca/~antoon/circ/fmt4.html

does anyone know why the capacitors (4.7uf) are needed in front of the transisitors???

i'm assuming they only allow ac or voice signals to pass into the transisitors, yes???

Roff · 8th October 2004, 03:55 AM

That's correct.

electronist · 8th October 2004, 02:29 PM

Thats right,

More precisly they act as coupling capacitors to prevent any dc voltage from the biasing ckt to pass through hence preventing a dc shift in the original signal.

krishnakanth · 8th October 2004, 04:33 PM

Correct

A coupling capacitor only allows the ac sinals and blocks the dc signals.
the one you mentioned is also a coupling capacitor.

It ensures that the source and load do not effect the biasing conditions in the circuit.A similar capacitor is neede in the output to couple the load to the load resistor.

stevez · 8th October 2004, 06:52 PM

Given that electronics is a hobby I tend to work at a more basic level. The advice already offered is several levels up from where I am at.

I tend to think in terms of DC then work my way up to light (low frequency to high frequency). Then I think about the passive device in terms of resistance.

A resistor is just that and from DC to light it's resistance to the flow of electricity is relatively constant - I emphasis relative here.

A capacitor would conduct no DC like a resistor with infinite resistance but starts to conduct to a greater degree as frequency goes up.

An inductor behaves like an upside down capacitor - at DC it's like a short circuit and it conducts less and less as frequency goes up.

Note that all of this is very simple and basic. It ignores the storage of energy, resonance, etc. It doesn't explain why the component is there - as others have explained. It does help me think thru what might be happening in the circuit so that I can figure it out - sometimes.

Dean Huster · 9th October 2004, 01:14 AM

"Coupling capacitors" as used in this application (they couple the signal to the next stage much like coupling railroad cars together) are also sometimes called "blocking capacitors" to describe their DC function -- blocking DC to prevent two different DC levels from getting into a big fight.

Dean

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8th October 2004, 03:13 AM	(permalink)
pike	DC filter capacitors http://www.uoguelph.ca/~antoon/circ/fmt4.html does anyone know why the capacitors (4.7uf) are needed in front of the transisitors??? i'm assuming they only allow ac or voice signals to pass into the transisitors, yes??? __________________ www.winpicprog.co.uk - Great PIC language tutorials.

8th October 2004, 03:55 AM	(permalink)
Roff	That's correct.

8th October 2004, 02:29 PM	(permalink)
electronist	Thats right, More precisly they act as coupling capacitors to prevent any dc voltage from the biasing ckt to pass through hence preventing a dc shift in the original signal.

8th October 2004, 04:33 PM	(permalink)
krishnakanth	Correct A coupling capacitor only allows the ac sinals and blocks the dc signals. the one you mentioned is also a coupling capacitor. It ensures that the source and load do not effect the biasing conditions in the circuit.A similar capacitor is neede in the output to couple the load to the load resistor.

8th October 2004, 06:52 PM	(permalink)
stevez	Given that electronics is a hobby I tend to work at a more basic level. The advice already offered is several levels up from where I am at. I tend to think in terms of DC then work my way up to light (low frequency to high frequency). Then I think about the passive device in terms of resistance. A resistor is just that and from DC to light it's resistance to the flow of electricity is relatively constant - I emphasis relative here. A capacitor would conduct no DC like a resistor with infinite resistance but starts to conduct to a greater degree as frequency goes up. An inductor behaves like an upside down capacitor - at DC it's like a short circuit and it conducts less and less as frequency goes up. Note that all of this is very simple and basic. It ignores the storage of energy, resonance, etc. It doesn't explain why the component is there - as others have explained. It does help me think thru what might be happening in the circuit so that I can figure it out - sometimes. __________________ stevez

9th October 2004, 01:14 AM	(permalink)
Dean Huster	"Coupling capacitors" as used in this application (they couple the signal to the next stage much like coupling railroad cars together) are also sometimes called "blocking capacitors" to describe their DC function -- blocking DC to prevent two different DC levels from getting into a big fight. Dean __________________ Dean Huster, Electronics Curmudgeon Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines). R.I.P.