power supply for TL074 filter

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RajeshDutta

New Member

• Mar 8, 2010

• #1

Im making a low & high pass filter using TL074, circuit attached. Can someone help me
what should be the supply at Vcc/2 shown in the circuit .Is it (- 12v ) & if it is , then
pin 11 should i connect to ground ?.

 

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RCinFLA

Well-Known Member

• Mar 8, 2010

• #2

Take Vcc , div by 2. Also known as half supply.

 

MikeMl

Well-Known Member

Most Helpful Member

• Mar 8, 2010

• #3

RCinFLA said:

Take Vcc , div by 2. Also known as half supply.

Click to expand...

It is a little more complicated than that.

Your Vcc/2 needs to have a low AC impedance at the lowest audio frequency you want to pass through your filters. The normal way to do this is to use a fifth opamp as a voltage follower to buffer the voltage from a two-resistor voltage divider wired between Vcc and Gnd. Another way is to use the voltage divider, but bypass the mid point to Gnd with a large electrolytic capacitor. 10Ks and a 220uF capacitor would probably work...

 

Hero999

Banned

• Mar 9, 2010

• #4

The trouble with that, is it would require another op-amp.

Since C4 is AC coupled is can go to either 0V or +V.

Yes, I agree, a potential divider is probably the best way to go. The minimum DC resistance to the half the supply is is 800k so I'd just use a potential divider consisting of two 10k resistors, one bypassed with 100nF; this will have an output impedance of 5k which is 1/160th of 800k.

 

MikeMl

Well-Known Member

Most Helpful Member

• Mar 9, 2010

• #5

Actually, using Hero's idea of grounding C4, that leaves only bias current for three opamps being drawn from the voltage divider tap. This means that the two resistors in the voltage divider can be ~100K. Bypass the tap to Gnd with 4.7uF, which will produce a time constant of 0.2s, meaning that it is bypassed down to ~10Hz.

 

R

RajeshDutta

New Member

• Mar 11, 2010

• #6

Power supply for Tl074

RajeshDutta said:

Im making a low & high pass filter using TL074, circuit attached. Can someone help me
what should be the supply at Vcc/2 shown in the circuit .Is it (- 12v ) & if it is , then
pin 11 should i connect to ground ?.

Click to expand...

Thanks for the the reply .but i need more help please.
Imean could you draw the resistor & the capacitor with proper values & where to connect in the circuit .
Also i would like to make a note that without connceting Vcc/2 ,the low pass part is working fine.

 

Last edited: Mar 16, 2010

R

RajeshDutta

New Member

• Mar 24, 2010

• #7

Thanks for the the reply .but i need more help please.
Imean could you draw the resistor & the capacitor with proper values & where to connect in the circuit .
Also i would like to make a note that without connceting Vcc/2 ,the low pass part is working fine.

 

Hero999

Banned

• Mar 24, 2010

• #8

Have a go at drawing on the components I suggested and I'll tell you if you've got it right.

 

S

schmitt trigger

Well-Known Member

Most Helpful Member

• Mar 24, 2010

• #9

In the past, I've used succesfully the TLE2426 precision ground splitter.
It may be an overkill in this particular application, but it is nevertheless a very useful circuit for exactly this sort of applications.

"Also i would like to make a note that without connceting Vcc/2 ,the low pass part is working fine. "

You mean, not connected anywhere?

 

Last edited: Mar 24, 2010