ICL 7107 electrostatic protection

Discussion in 'General Electronics Chat' started by O.K., Jan 15, 2016.

  1. O.K.

    Thread Starter New Member

    Dec 10, 2014

    I want to build a power supply unit with display. I use icl7107 ic to measure voltage. I tried it on a board, and it worked fine, but after a week when I checked it one more time it didnt work. It shows '1'. Is it because of electrostatic damage? How should I protect it? I want to make it on pcb. Thanks for reply.
  2. Willen


    Nov 13, 2015
    I don't knoe how to sure about the IC damaged or not but I know that while handling chips, Wrist-band is needed to discharge static charge of our body, seriously during winter (dry) season.

    Poor soldering iron (like I use- $1), leaks mains voltage around 25V to 30 (depends on irons types) which also can damage chips or FETs. I also had to ground its metal tip through 100k (or less) resistor, to ground the leakage to around safe level.
  3. #12


    Nov 30, 2010
    Post your schematic. Static damage to an installed part is not the usual suspect. Without a schematic, all you will get here is guessing or low quality mind reading. Even with a schematic, the answers might be guessing, but we might spot an error that can be fixed.
    absf likes this.
  4. Brevor

    Active Member

    Apr 9, 2011
    I remember some of those old 7106/7107 IC's would display "-1" when the input was open.
  5. joeyd999

    AAC Fanatic!

    Jun 6, 2011
    Overrange indication.
  6. O.K.

    Thread Starter New Member

    Dec 10, 2014
    Here is the schematic. The behavior is strange. It shows 1 periodically, if I remove the capacitor from 7660 IC 4-5 pins, it stops showing 1, but value jumps without input, and with input nothing changes. I use a computer psu's 5V source, maybe it caused the damage. The first time I connected the rails to board after powering the unit, but last time I exchanged this to power up the unit after rails were connected.Could it be the problem? Also the second time I forgot to connect the common anode of the display to +5V and i did it after powering up, and the 10 K resistor were also missing between input wires and I added it after power up and touched it with hands.
  7. bertus


    Apr 5, 2008

    Removing the caps from the 7660 will stop the chargepump from working.
    There will be no -5 Volts generated.
    The 10K resistor is part of the input attenuator.
    Without it the sensitivity will be much higher aka 200 mV.

  8. O.K.

    Thread Starter New Member

    Dec 10, 2014

    I have replaced the ic with a new one, and it works. The next thing i dont understand is the folowing:
    I have one 10 k resistor between pin 35 and 36, and two 20 k resistors between pin 36 and +5 V. Why is it that when I measure voltage on pin 36 the display show 10 (this is ok) but when I measure voltage on the node between 20 k resistors it shows 20 and the +5 V equals 29 ?
    Thanks for reply