Comment on How to improve my battery measurement circuit?

jjagaimo@lemmy.ca ⁨1⁩ ⁨year⁩ ago

• nilclass@discuss.tchncs.de ⁨1⁩ ⁨year⁩ ago

  Hm, I don’t understand how this is supposed to work - is that a n-channel or p-channel FET?

  When I sketch it using falstad’s circuitjs, it looks like the FET (n-channel) is a little bit on all the time

  Image

  and fully on, when a pulse is applied

  Image

  source

  • jjagaimo@lemmy.ca ⁨1⁩ ⁨year⁩ ago

    It is an N channel FET. The concept is called “bootstrapping” since Vgs needs to be greater than Vth for the MOSFET to be on. When the FET is on the high side and you want the full 9V on the output, you use the diode to charge the capacitor, and the other side of the cap is 0V. Then, when the other side of the cap is connected to 9V, the charge on the cap can’t go anywhere so the voltage on the other side jumps to 18V. This creates a Vgs of 9V. Ideally you would have something better to drive the gate to fully turn off the FET, but I just used a quick and dirty driver where the bootstrap capacitor directly feeds the gate instead of being the input to the driver. Because if this, the Vgs doesn’t drop completely to 0

    source

    • nilclass@discuss.tchncs.de ⁨1⁩ ⁨year⁩ ago

      Nice, than you for sharing!

      I won’t be using this for my measurement issue (the other options are much simpler, and i was aiming for less parts, not more), but I’ll do some experiments to familiarize myself with bootstrapping

      source