741 Op-AMP help - Electronic Circuits Projects Diagrams Free

Frosty_47 · 27th April 2008, 05:46 AM

Hello,

A lot of digital IC's output 3.4V for high instead of 5V. According to my calculations, the circuit below should output 5V. Will the 741 OP-AMP below be able to conver the 3.4V TTL to 5V ?

Thanks

P.S. Vcc+ = 12V, VCC- = GND

Frosty_47 · 27th April 2008, 05:53 AM

Oh, and are there any "unusually high voltage" Op-AMPS ? Basically I want to transform a 5Vpp Sine Wave to 24Vrms (roughly 68Vpp).

Any part #'s would be greatly appreciated...

Thanks

P.S. I don't want to use a transformer...

synthius · 27th April 2008, 06:16 AM

that circuit will output 5V when a 3.4V input signal is used.

Can I ask what your application is for the 24Vrms output voltage is?

If you are trying to design a audio amplifier then the LM3886 and LM4780 are viable choices.

bananasiong · 27th April 2008, 06:33 AM

I'm not sure whether single supply works for a 741 or not. Why not use modern op amp that capable of being supplied with single supply as low as 2.7 V, with rail to rail output. So you can get 5 V at the output without feedback resistor with the supply voltage of 5 V.

synthius · 27th April 2008, 06:39 AM

he's right, you are better off using a schmitt trigger or even a comparator op amp. 741 would not work because its voltage headroom.

audioguru · 27th April 2008, 02:29 PM

The lousy old 741 opamp is 40 years old and is too slow to amplify a digital signal.
It needs a negative supply. I think without a negative supply then its low output voltage is about +1.2V which is not low enough for TTL but is OK for Cmos.

An OPA445AP opamp from Texas Instruments has a max operating supply voltage of 80V to 90V. They are sold out again. They make about 1000 at a time then they sell out in a couple of weeks.

**Nigel Goodwin** · 27th April 2008, 04:26 PM

Quote:

Originally Posted by Frosty_47

A lot of digital IC's output 3.4V for high instead of 5V. According to my calculations, the circuit below should output 5V. Will the 741 OP-AMP below be able to conver the 3.4V TTL to 5V ?

Why would you want to do this?.

ericgibbs · 27th April 2008, 04:33 PM

I would suggest that you look thru this link, reference switching levels of logic families, before you consider using any level shift/boosting..

http://www.interfacebus.com/Logic_Design_Top.html

Frosty_47 · 27th April 2008, 05:28 PM

If I redesign the circuit to output 5.7V and put a diode in series at the output, I should than have approximately 0.5V for low and 5V for high ?
I tried searching for other Op-Amps however, it turns out that there are more Op-Amps than empty beer bottles at my place on a Saturday night...

Oh, and a BIG thanks to Audioguru for OPA445.

Frosty_47 · 27th April 2008, 05:36 PM

Quote:

Originally Posted by synthius

he's right, you are better off using a schmitt trigger or even a comparator op amp. 741 would not work because its voltage headroom.

74LS14 Schmitt Inverter outputs 3.4V for high....

ericgibbs · 27th April 2008, 05:37 PM

hi,

Quote:

Perhaps If I redesign the circuit to output 5.7V and put a diode in series at the output, I should than have approximately 0.5V for low and 5V for high ?

Are you sure this idea is going to give you what you are expecting.???

**Nigel Goodwin** · 27th April 2008, 05:42 PM

Quote:

Originally Posted by Frosty_47

74LS14 Schmitt Inverter outputs 3.4V for high....

You still haven't answered my question?.

"Why do you want to do this?"

Frosty_47 · 27th April 2008, 05:57 PM

Quote:

Originally Posted by Nigel Goodwin

You still haven't answered my question?.

"Why do you want to do this?"

Because I am crazy thats why

Basically I want a 5V TTL to go into a MAX7400 that will output a nice 5Vpp Sine wave that I can further boost to 24Vrms with OPA445 (assuming I get one). The minimum High input Voltage for MAX7400 is VDD-0.5V which means it has to be at least 4.5V if VDD = 5V. Thus the typical output of 3.4V will not due for MAX7400 (please correct me If I am wrong)...

Frosty_47 · 27th April 2008, 05:59 PM

Quote:

Originally Posted by ericgibbs

hi,

Are you sure this idea is going to give you what you are expecting.???

Eh, if I was sure I wouldn't be asking you guys questions

ericgibbs · 27th April 2008, 06:13 PM

Quote:

Originally Posted by Frosty_47

Eh, if I was sure I wouldn't be asking you guys questions

Hi Frosty,
Do you have a electronics/logic simulation program in your PC.?

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27th April 2008, 05:46 AM	(permalink)
Frosty_47	741 Op-AMP help Hello, A lot of digital IC's output 3.4V for high instead of 5V. According to my calculations, the circuit below should output 5V. Will the 741 OP-AMP below be able to conver the 3.4V TTL to 5V ? Thanks P.S. Vcc+ = 12V, VCC- = GND __________________ "The people who cast the votes don't decide an election, the people who count the votes do." -Joseph Stalin Last edited by Frosty_47; 27th April 2008 at 05:48 AM.

27th April 2008, 05:53 AM	(permalink)
Frosty_47	Oh, and are there any "unusually high voltage" Op-AMPS ? Basically I want to transform a 5Vpp Sine Wave to 24Vrms (roughly 68Vpp). Any part #'s would be greatly appreciated... Thanks P.S. I don't want to use a transformer... __________________ "The people who cast the votes don't decide an election, the people who count the votes do." -Joseph Stalin Last edited by Frosty_47; 27th April 2008 at 06:04 AM.

27th April 2008, 06:16 AM	(permalink)
synthius	that circuit will output 5V when a 3.4V input signal is used. Can I ask what your application is for the 24Vrms output voltage is? If you are trying to design a audio amplifier then the LM3886 and LM4780 are viable choices.

27th April 2008, 06:33 AM	(permalink)
bananasiong	I'm not sure whether single supply works for a 741 or not. Why not use modern op amp that capable of being supplied with single supply as low as 2.7 V, with rail to rail output. So you can get 5 V at the output without feedback resistor with the supply voltage of 5 V. __________________ Superman returns..

27th April 2008, 06:39 AM	(permalink)
synthius	he's right, you are better off using a schmitt trigger or even a comparator op amp. 741 would not work because its voltage headroom.

27th April 2008, 02:29 PM	(permalink)
audioguru	The lousy old 741 opamp is 40 years old and is too slow to amplify a digital signal. It needs a negative supply. I think without a negative supply then its low output voltage is about +1.2V which is not low enough for TTL but is OK for Cmos. An OPA445AP opamp from Texas Instruments has a max operating supply voltage of 80V to 90V. They are sold out again. They make about 1000 at a time then they sell out in a couple of weeks. __________________ Uncle $crooge

27th April 2008, 04:33 PM	(permalink)
ericgibbs	I would suggest that you look thru this link, reference switching levels of logic families, before you consider using any level shift/boosting.. http://www.interfacebus.com/Logic_Design_Top.html __________________ Eric "Good enough is Perfect" PIC tutorials: Gramo's: www.digital-diy.net/ Bill's: www.blueroomelectronics.com/

27th April 2008, 05:28 PM	(permalink)
Frosty_47	Thank you folks for your expertise on this matter. If I redesign the circuit to output 5.7V and put a diode in series at the output, I should than have approximately 0.5V for low and 5V for high ? I tried searching for other Op-Amps however, it turns out that there are more Op-Amps than empty beer bottles at my place on a Saturday night... Oh, and a BIG thanks to Audioguru for OPA445. __________________ "The people who cast the votes don't decide an election, the people who count the votes do." -Joseph Stalin Last edited by Frosty_47; 27th April 2008 at 05:35 PM.