0

I'm building a modular DIY "smart battery pack" (I call it Kyoti - explanation another time,)starting with the on/off switch and basic under and over voltage protection built in. I know there are commercial solutions but the point of the exercise is to learn analog electronics and use up as many components from my jelly bean junk box as possible before they expire.

With plenty of inspiration from the internet, most notably these excellent examples, I've arrived at this circuit and simulation.

Soft latch switch circuit

Soft latch switch simulation

It works reasonably well but I'm looking for some advice on how to make the following improvements.

My electronic engineering knowledge is not quite up to the task and hours of playing with different values in LTSpice made me realize what's needed here is expertise, not experimentation.

  1. How can I delay the startup slightly to ignore a "bump" to the button or a "glitch" (see one at 6s)? The button should be held for 100ms to be a valid ON condition.
  2. A fault condition should shut things down faster. At the moment it takes a second to shut down, same as a button press. I tried pulling the gate of M202 low directly but that didn't work.
  3. Over and under voltage protection may not be adequate. The user can hold in the button and force it on for 1 second at a time - long enough for a really high OV or UV condition to damage the battery. Is there a way to prevent start-up at all if there is a fault condition, to switch off no more than 100ms after start-up instead of the 1s now?
JRE
  • 67,678
  • 8
  • 104
  • 179
RudShep
  • 1
  • 1
  • I answered [this question](https://electronics.stackexchange.com/questions/317851/cut-off-circuit-for-12v-battery) some long time ago. In my second diagram, I show a switch which won't be forced on if the input voltage is too low. I'm sure you could modify the idea for both uv/ov lockout. It also shuts off quickly. – Neil_UK Jun 01 '22 at 14:31
  • Thank you @Neil_UK. Your circuit does everything I need except requiring separate on and off buttons. I'd like to use a single button if possible. Very valuable nonetheless and I will study it again to learn how it works. – RudShep Jun 01 '22 at 15:01
  • The first circuit of that answer can use a single on/off button. However, it's done in a very kludgy way that can fail if the load has large capacitors holding the rail up, so it would be better to use an on/off to toggle a d-latch, and use those outputs to turn the switch on and off. Once you've got that complexity, and handling on/off delays, it almost sounds like a low powered uC should handle the switch logic (you could make it sleep all the time except when woken by button or uv/ov events) and the switch just do power. – Neil_UK Jun 01 '22 at 15:07
  • Which TL431 model are you using? – Bruce Abbott Jun 01 '22 at 19:30
  • @BruceAbbott TL431-A from HTC REF VOLT ADJ TO92 36V 0A1 1% ADJUSTABLE LINEAR SHUNT REGULATOR UP TO 36V 100mA THROUGH HOLE MOUNT – RudShep Jun 03 '22 at 05:56
  • I meant what spice model are you using for simulation, because a real TL431 will not work properly with cathode currents less than ~0.4 mA. – Bruce Abbott Jun 04 '22 at 00:33

0 Answers0