Would you be so kind to point out any errors in this schematic or anything else to improve (layout and clarity also greatly appreciated).

This is supposed to be the power/regulating/batterycutoff schematic of a device.

  • Device has a lipo battery and a switch (S1) to turn on and off.
  • Battery is connected to voltage detector (U3) which sends a high
    signal to U4 at 3.05V.
  • Battery also connected to analog switch (U4). Depending on signal from U3
    switches between battery low warning led and main circuit. (acts like relay)
  • U2 regulates power supply to 2.8V (VCC) which supplies main circuit .

Schematic: powercircuit

Bill of materials (only chips since rest isn't important, i think?) bom

  • 1
    \$\begingroup\$ Don't put ground up high. Do put VCC and VBATT up high. Add a fuse in series with battery. Value should be 1.5 or 2x the normal sustained current. I guess U4 is like a relay? The term NC is often used to mean "no connect" on schematic symbols, so I found that confusing. I guess it means "normally closed". I don't see any good reason for using so many resistors in series in the voltage divider for U2. Also, with such high values, you may need a feedforward capacitor from VCC to VSET. Make sure you read all the datasheets carefully. \$\endgroup\$ – mkeith Dec 13 '17 at 15:21
  • \$\begingroup\$ It seems that you are using U3 and U4 as a low-voltage cutoff. It would probably be easier and better to simply disable the regulator. So you could get rid of U4, feed reset to an inverter, and inverter output becomes your enable signal for the regulator. Another option is to use a battery with a protection circuit that cuts off at 3V during discharge. Then you don't need any low-voltage cutoff at all in your circuit. \$\endgroup\$ – mkeith Dec 13 '17 at 15:30
  • 1
    \$\begingroup\$ You have confused the functions of the IN and COM pins of the analog switch. In any case, we discourage broad, open-ended design review questions here on EE.SE: The answer(s) tend to become long strings of unrelated edits and/or comments. While this might help you with your immediate problems, it is of no value to the site overall. We DO allow design review questions in which you explain your choices and then focus on a few points about which you still have doubts. To get a better feel of what is or is not acceptable, search for "design review" on the meta site. \$\endgroup\$ – Dave Tweed Dec 13 '17 at 16:26
  • \$\begingroup\$ @mkeith Thank you for the layout remarks. NC is indeed not connected and U4 acts like a relay. Using the resistors to get the exact value I calculated for the programmable regulator (?). The datasheet did not mention a cap at the output but I will double check to make sure. I'd also like to thank you for last time you helped (other thread), I've tried to make something similar but it's just too difficult for now using so much lose components. A couple U are easier (for me). \$\endgroup\$ – cjsd Dec 13 '17 at 19:07
  • \$\begingroup\$ @mkeith The battery has a cutoff inbuilt but at 2.5V :(. I'll have a look at the options available with the inverter solution you mentioned. \$\endgroup\$ – cjsd Dec 13 '17 at 19:09

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