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| Help with op amp OP07 |
 Posted: Sat Oct 08, 2005 4:26 pm |
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I have an op07 (LOW OFFSET) with negative voltage + - 12 Volt.
I need to measure a shunt 0 to 10mv and i need to amplify it.
But the power source is a batery of 9 volt, and dont have negative voltage.
What can i do?
Change the amp op?
Is any chip that convert the 9 volt positive on negative?
Thank, excuse me for my english! |
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kender
Joined: 09 Aug 2004
Posts: 768
Location: Silicon Valley
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| Re: Help with op amp OP07 |
| Posted: Sat Oct 08, 2005 4:44 pm |
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| Anonymous wrote: | | Is any chip that convert the 9 volt positive on negative? |
Yes, there is. You can generate the negative supply voltage with a charge pump power supply such as Microchip TC7660. |
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SherpaDoug
Joined: 07 Sep 2003
Posts: 1640
Location: Cape Cod Mass USA
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| Posted: Sat Oct 08, 2005 7:34 pm |
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Does your project have an RS232 converter chip like the MAX232? If so you may be able to use the negative supply of the RS232 driver.
_________________
The search for better is endless. Instead simply find very good and get the job done. |
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kender
Joined: 09 Aug 2004
Posts: 768
Location: Silicon Valley
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| Posted: Sat Oct 08, 2005 7:40 pm |
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| SherpaDoug wrote: | | Does your project have an RS232 converter chip like the MAX232? If so you may be able to use the negative supply of the RS232 driver. |
How can one tap into the negative supply of MAX232? |
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Guest
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| Re: Help with op amp OP07 |
| Posted: Sat Oct 08, 2005 8:28 pm |
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| Anonymous wrote: | I have an op07 (LOW OFFSET) with negative voltage + - 12 Volt.
I need to measure a shunt 0 to 10mv and i need to amplify it.
But the power source is a batery of 9 volt, and dont have negative voltage.
What can i do?
Change the amp op?
Is any chip that convert the 9 volt positive on negative?
Thank, excuse me for my english! |
If you want only amplify to 0...10 mV then you need -4 VDC.
Not need -12 VDC. |
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dyeatman
Joined: 06 Sep 2003
Posts: 1924
Location: Norman, OK
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| Posted: Sat Oct 08, 2005 8:33 pm |
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| I personally wouldn't recommend using the max232. The voltage is too noisy and unstable to use with an opamp. Try the MAX850 or similar, it's regulated and only 1mv of ripple on the output. |
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SherpaDoug
Joined: 07 Sep 2003
Posts: 1640
Location: Cape Cod Mass USA
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| Posted: Sun Oct 09, 2005 4:57 pm |
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| kender wrote: | | SherpaDoug wrote: | | Does your project have an RS232 converter chip like the MAX232? If so you may be able to use the negative supply of the RS232 driver. |
How can one tap into the negative supply of MAX232? |
Pin #6 of the MAX232, from figure #5 of the Maxim datasheet.
This supply is noisy but a good op amp like the OP07 has a power supply noise rejection of 5 or 10 uV/V. So a 1V ripple on the supply gives a 5 or 10 microvolt ripple on the output. For most applications that isn't too bad for a free negative supply. If in doubt use bigger caps on the MAX232 to reduce the supply ripple and add a 100 ohm series resistor and a 0.1uf decoupling cap to feed the op amp, but even that may be overkill.
_________________
The search for better is endless. Instead simply find very good and get the job done. |
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kender
Joined: 09 Aug 2004
Posts: 768
Location: Silicon Valley
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| Posted: Mon Oct 10, 2005 7:08 pm |
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| SherpaDoug wrote: | | Pin #6 of the MAX232, from figure #5 of the Maxim datasheet. |
Thanks! This info goes to the "[spam]-saving knowledge" file.
I guess, conversely, Pin #2 could potentially act as a free +10V supply. |
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sseidman
Joined: 14 Mar 2005
Posts: 159
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| Re: Help with op amp OP07 |
| Posted: Tue Oct 11, 2005 6:55 am |
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| Anonymous wrote: | If you want only amplify to 0...10 mV then you need -4 VDC.
Not need -12 VDC. |
Wouldn't that depend upon how much you wanted to amplify? |
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