Post Go back to editing

Amp01 single 9V battery supply ... problems

I am using an Amp01 as a simple 200X (V/V) Op-Amp in a portable situation with a single 9V battery.

The amp circuit is as described in the data sheets, with the 1K & 10K resistors, however a single 9V battery is being used with the battery ground created with two 100K resistors each connected to a battery terminal & the common ends of these resistors connected to the Amp01 ground & pin 8(Reference). The amp works fine, but the battery life is far less than the expected two months: A fresh 9V battery(9.31V unloaded) will drop down to 8.54V within 24 hrs, and down to 6.45V within 10 days. This current draw seems too high{ for the stated ~3mA of the Amp01} and clearly it appears that excess current may be flowing through the Amp01 via substrate paths(diode & transistor). Is there a better way to power this amp via a single 9V cell ?

thanks

  • Harry;

    The A/D Amp01 circuit is same as in the A/D data sheet for the Amp01. Only difference is that it is powered by 1 single 9V battery. Across the battery are two 100K resistors (in the shape of a “Y”). the common of the pair or the resistors goes to pin 8 of the Amp01 & GND in the circuit. This is a simple method of turning the single 9V battery into a +/- battery with an ‘artificial ground’.

    Are you an Analog Devices Engineer (or Tech Support) person ?

  • photo,

      I'm having trouble visualizing your circuit.  Can you attach a schematic, preferably in PDF format?

    Thanks,

    Harry

  • hi Harry;

    The output of the Amp01 goes directly into an HP DVM. Yes, a standard new 9V battery is being used.

    It sounds like we are using an older OpAmp that is somewhat power hungry !

    thank you,

    rick

  • The gain we are using with the old Amp01 is 200X (V/V)  . We are running at near DC measuring Thermopile detector outputs. We do have a fair amount of noise, but this might be from the 9V battery split across the old Amp01 IC.

    In any event, I will try a few newer Op-Amps, any chance you can ship me a few samples to try ? I am on the A/D sample program, so my address is in the system.

    The only problem is that we are limited to IC’s that are the DIP type (8 pin DIP, 14, 16, 18, pin DIP) for fast prototyping… { the dark ages !}…

    thank you,

    rick

  • yea.. a problem….

    dips are easier to do things by hand for small jobs…

    otherwise it is SOT-23’s , a microscope & wire wrap wire and a very thin soldering iron… unless I can sneak into the coffee room & use the toaster oven…

    How come there is not a simple cheap plastic “snap-in”(press-fit) adapter for prototyping… something everyone would use ?

    If you take my idea and do it, you’ll be a hero, not to mention a multi-millionaire.

    If you are successful, just try to remember me & toss me an apple and a sweater when I am homeless & in the gutter, or perhaps a few thousand shares of the new company… whatever…

    rick

  • photodetCALIB,

      During my 35 years in applications, at both National and now at ADI, I have found that it's difficult

    to solve a problem that is incompletely stated.  There is always something that might be important

    that is left out.  But I will assume that:

    "...The A/D Amp01 circuit is same as in the A/D data sheet for the Amp01..."  is figure 29 in the rev. D data sheet, even though there are 16 other application circuits. 

      The max supply current is 4.8 mA, with 3 mA. typical.  Some of the parts will be less than typ, some will be more.  You might have one that is 4 mA, which is still within the spec limit.

      You did not state what the load is.  If you have a 100 ohm resistor on the output and the output goes to 1V,

    that is 10 mA, which would certainly drain the battery faster than expected.

    The supply voltage range is listed in the spec table as +/-4.5V to +/-18V.   The AMP01 came out in 1984, and most analog systems ran on +/-15V, so operation at low total supply voltage was not a priority.

    If you are using a 9V battery, I am assuming it is similiar to the classic MN1604 used in smoke detectors.

    Looking at a manufacturer's data sheet:

    http://ww2.duracell.com/media/en-US/pdf/gtcl/Product_Data_Sheet/NA_DATASHEETS/MN1604_6LR61_US_CT.pdf

    It looks like with a 2 mA load, the voltage drops to 7 Volts in about 50 hours.

    I think what is happening is with 8V or lower, across the part, it starts to die and maybe the supply current goes up.

    I don't know what your total requirements are WRT signal bandwidth, temp range, etc., but I would suggest looking at some of the newer parts, such as AD8420, AD8227, AD8226, AD8223, AD8220, AD8221; all of which are guaranteed to operate at 5V or in some cases, even 2.7V and all of them are less than 1 mA typical suppy current.

    Harry

  • rick,

      Yes, we develop new processes with finer geometries, so it gives us the speed we want at lower currents.

    A gain of 20 is not that high, but for high gain, or a wide temperature range, you may want to consider one

    of  the "zero drift"/chopper/autozero parts:  AD8237.  It's very slow, only runs on 2-5.5V, but is less than 150 uA.

    Harry

  • Rick,

      I'm on the technical side of the house so I don't have access to any parts. 

    If you go to the product page for a particular part, in the pricing box, on the right,

    is usually a "Sample and Buy" button that takes to the form, etc.

    DIPs only is a serious problem...... There are some companies, such as sparkfun

    https://www.sparkfun.com/products/494

    That make little adapter boards.  They have several competitors.

    Harry

    Harry

  • rick,

      Too old to do a start up;  Why don't you do one??

    Here's another idea.   Use a REF196 (micropower 45 uA, DIP) to regulate the 9V down to 3.3V

    and then use an AD8237 on an adapter board.

    Maybe you'll get six months out of a battery?

    Or use an AD627 directly? (comes in a DIP)

    Harry

  • If you want a low power low offset opamp in a DIP package, how about an OP193, which pulls 30uA and runs down to 1.7V