Plus and Minus 9V from one 9V Battery

Discussion in 'The Projects Forum' started by iONic, Jul 14, 2008.

  1. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
    1,420
    68
    I have recently the circuit below and powered it with a Lithium battery rated at 9.6VDC. The actual voltage was measuring at 10.4V, but the negative output was measuring at 9.35V. If I were to run a dual supply IC I would want the +/-
    voltages to be as close as possible... How might I achieve this in this circuit?
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    Linear regulators, that or create a pseudo ground using a voltage divider and a op amp w/ driver.

    There are probably better ways, do you have the data sheet for that IC?
     
    Last edited: Jul 14, 2008
  3. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,677
    900
    There are several options. The ICL7660 is popular. You may also want to consider the MAX 1680. The MAX768 provides dual regulated outputs. With an op-amp, you may not need a regulated supply.

    John
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    There are naturally going to be minor losses in the switched-capacitor inverter.

    You could use a couple of forward-biased diodes in the + output. 1N5817's are Schottky diodes with a low Vf; much lower than a standard rectifier diode. You could use one of those with a 1N4100 rectifier diode to get pretty close to the same voltage.

    Cheap and simple.

    Otherwise, look for low-dropout regulators for both the + and - supplies. That'll probably cost you somewhere around $8 for the pair.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Bill's idea of using a power opamp to create an artificial ground is a good one.

    See National's datasheet for the LM675.

    If your load is low, you might use Fairchild's KA334 or L272 dual power opamps; much cheaper than the LM675.

    [eta] Actually, scratch the power opamps - that IC is only going to put out 10mA anyway. You could use just about any opamp.
     
    Last edited: Jul 14, 2008
  6. theamber

    Active Member

    Jun 13, 2008
    318
    0
    I think your battery is not providing enough current to the IC.
     
  7. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
    1,420
    68
  8. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The MAX1440 and ILC7660 are on the same datasheet! They are pretty much equivalent parts, except for the MAX1440's BOOST pin (pin 1), which is N/C on the ILC7660.

    Download Maxim's datasheet for the MAX1440/ICL7660.

    LTC1440 is another similar IC.
     
  9. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,677
    900
    You made me think I was crazy there for a minute when I read your comment. My datasheet for ICL7660/7660A is the official Intersil datasheet , rev. 1999. It makes no mention of the Maxim chip. I had actually never looked at the Maxim datasheet, and when I first saw it today, I wondered how I had missed such an obvious thing.

    The Maxim data sheet for the Max1044 is dated 1994 and shows them to be the same. Does Maxim in fact make the ICL7660?

    A quick look at the history shows each company is traded separately on the stock market. Maxim was formed in 1983 by some people from Intersil, which was owned by GE at the time.

    So, how can Maxim claim to produce the ICL7660? Was there a settlement of a lawsuit that allows it to do that?

    BTW, I use the ICL7660A, and in one application power it with a single 12V alkaline battery cell. The ICL7660A has a 12V limit instead of 10V. The Max 1044 is also 10V.

    John
     
  10. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The line between crazy and genius is often rather difficult to define ;)

    Well, I don't know if Intersil got absorbed by Dallas/Maxim, or if Dallas/Maxim is merely making an equivalent part with the ICL7660 part number.

    Please re-read the datasheet! My Maxim datasheet, Rev 1, dated 7/94, shows on page 1 that Pin 1 is "(N/C) BOOST" - and in a footnote, it states that "() ARE FOR ICL7660". So, the ICL7660 does not have the BOOST function.

    Interesting. A similar thing occurred when TRW was started by former Hughes Aircraft Co. executive by the name of Thompson, then merged with Ramo-Wooldridge.

    Well, it seems to be an industry standard IC. When it's an industry standard, falling into common use, then it's pretty much up for grabs. Look at the ULN2xxx series, everyone makes them with the exact same part numbers.

    Years ago, Xerox Corporation was terrified that they were going to lose their trademark name "Xerox" because people would instead of saying "Make a copy of that would you?" would say "Make a Xerox of that would you?" When a trademark falls into such common usage, it's not a trademark anymore.

    Interesting. I hadn't read that part.
    The BOOST function of the MAX1044 increases the switching speed, to get the boost out of audio range. I figure that would play in heavily as to why it's a lower voltage part.
     
Loading...