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invert amplifier using TL072

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arash rezaee

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Hi everyone.
I am quiet new and I want to design amplifier for my project. I have sinusoidal signal with amplitude of 2.4V(P-P) and i want to amplify it to 12V(P-P). Power supply I used is +12 and -12 volt for TL072 Ic. How can I amplify it and does the power supply has effect on the output voltage.
Please help me.
Regards
Arash
 

One example of the circuit:

A= R1/R2
R3= R1||R2
Vin = 2.4V
Vout=12V
A = Vout/Vin= 12/2.4= 5
so we first choose
R1 = 10 k
R2= R1/A = 10k/5=2k
R2= 2k

R3= 1.66k~ 1.5k
Of course you can chose any values for R1, and the result for R2, R3 to be different…:-D
 

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Thanks. how about not having R3. I mean non-inverting pin connecting to GND? I have 2 more question if you don`t mind.
1. can I have amplifier and lowpass together with op-amp. lowpass filter I need must have cutoff of 30KHz.
2. power supply has effect on the output or not?
 

1. One way to combine to low pass filter (first order low pass filter) is to place a capacitor in parallel with the feedback resistor .
The value of the capacitor can be determined with the formula used to calculate the cut-off corner frequency
f =1 / 2 pi RC
For R= 10K, f= 30Khz, C= 530pF

**broken link removed**
https://www.physics.unlv.edu/~bill/PHYS483/op_amp_filt.pdf



2. In theory if the supply of an op amp changes, its output should not, but it does.
The specification of power supply rejection ratio (or PSRR) is defined as if a change of X volts in the supply produces the same output change as a differential input change of Y volts, the PSRR on that supply is X/Y.
The TL072 has a PSRR of 100dB (typical).
This means that any low frequency signal on the supply (or supplies) is attenuated by 100dB before finding its way to the opamp's output pin, but this does vary with frequency though.
https://www.ti.com/lit/ds/symlink/tl072.pdf
 

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Hi,
The R3 is often considered good practice, so depending on your opamp and application, you may or may not wish to include it. It helps to reduce the offset, but can introduce noise, so it really
depends on your use-case. (If for example this is for an audio app, then you may be using a DC blocking capacitor anyway). I think you can safely remove it here if you like.
For a lowpass, you could use a conventional RC network (or are you looking for a particular filter response?).
Power supply does have an effect, same as most ics you'd need to refer to the data sheet for the particular op-amp to see the requirements. Also, ensure there is a decoupling cap
near the ic.
 

sky_123 : Thanks. I want lowpass filter in project to remove any frequency over 30KHz. I design function generator with FPGA and used DAC with I2S format to convert. But when the frequency is above 15KHz I have some undesired frequencies. It`s ok because my sampling rate is over 96KHz and so the DAC filter cannot remove all the frequencies. So I need a good lowpass filter to remove frequencies over 30 without changing amplitude of 20Hz to 20KHz. Do you have any idea?

---------- Post added at 14:14 ---------- Previous post was at 14:14 ----------

It's effectively useless for a TL072 FET OP. Just omit it.

Ok. Thanks
 

Sounds like a custom DDS type of function generator? If so, yes you need to filter (I take it you're talking about sine waves, right?), and sometimes people
use (say) third or much higher order filters.
I'm no expert on active filters, but if you used (say) passive LC types of filters then you'd need inductances of several hundred uH, so entirely feasible. There
are free tools to help you design filters. I'm sure there are free tools for active filters too.
Regarding changing amplitude, you can pick the type of filter to determine what will occur over the pass bandwidth, but sometimes signal generators
use an automatic gain control type of feature, to try to keep the signal level constant (at least for RF generators, not so sure about LF generators).
Of course, that is more work, and you may not find it worthwhile if you can calculate it, or allow the user to adjust the amplitude, etc..
 

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