0
\$\begingroup\$

I have a battery-powered circuit (2x 3.7 V LiPo batteries) and I want to use a push-button as on switch by using some sort of low power self-holding mechanism. I have two possible solutions in my mind:

Option 1

This option uses a switch to enable the battery voltage and the MCU will assert the SH signal, so the transistor Q206 is turned on permanently.

enter image description here

Option 2

This option applies the battery voltage directly to the LDO and enables the LDO when the push button is pressed. Again the MCU will assert SH and bridge the switch.

enter image description here

I´m unsure which of these methods is the better one with the aspect of the current consumption. And I´m unsure if Option 2 is working very well. Maybe booth circuits can be improved in terms of current consumption. The only thing that I would improve is the value of the resistors (replace 100k with 1M). Are there any other options to improve that circuit?

\$\endgroup\$
4
  • 1
    \$\begingroup\$ Why get a microcontroller involved? \$\endgroup\$
    – Hearth
    Commented Jul 8, 2021 at 5:01
  • \$\begingroup\$ In the 2nd circuit, the input voltage is continuously applied to the regulator and it will draw current even if the EN is kept below the threshold. You may want to check that current consumption from the datasheet to see if it's worth worrying about. Because there'll be a non-stop discharge. BTW, is button debounce important for you circuit? \$\endgroup\$ Commented Jul 8, 2021 at 5:05
  • \$\begingroup\$ @Hearth the microcontroller is doing some other stuff, so he is in the circuit anyway. I have only posted the self-holding part because I want to optimize it. \$\endgroup\$
    – Kampi
    Commented Jul 8, 2021 at 5:09
  • \$\begingroup\$ @RohatKılıç the current consumption of the LDO during the disable is around 0,001 µA according to the datasheet. \$\endgroup\$
    – Kampi
    Commented Jul 8, 2021 at 5:09

2 Answers 2

1
\$\begingroup\$

There is no symbol for the LDO with Enable so I used a logical equivalent AND gate. SW1 is turn ON latch only with positive feedback and R3 will current limit the over voltage from the LiPo with internal ESD protection using Sch Diode clamps on EN input. C1 filters our EMI.

schematic

simulate this circuit – Schematic created using CircuitLab

\$\endgroup\$
0
\$\begingroup\$

Shouldn´t the use be able to turn off the device using the same button? In that case you will also need to monitor the current button state.

schematic

simulate this circuit – Schematic created using CircuitLab

This is a pretty simple solution. Don´t forget to add a fuse right next to the LiPo.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.