Feedback vs Bootstraps

Discussion in 'General Electronics Chat' started by wlarsen, Jan 17, 2014.

  1. wlarsen

    Thread Starter New Member

    Jun 8, 2012
    I recently came in contact with an h bridge IC that was using bootstraps from its outputs feeding back into its inputs, and after looking up the general definition of bootstraps I didn't see much difference between it and feedback, am I on the right track or did I miss something?
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    What device type(s) were used in the particular H bridge?

    Have you looked at the Wikipedia page on Bootstrapping in electronic circuits?

    Certainly the use of bootstrap techniques in some cases is a form of feedback. For example when it is used to increase an amplifier's input impedance.
  3. wlarsen

    Thread Starter New Member

    Jun 8, 2012
    The bridge was controlling a 28 VDC motor with a voltage regulator regulating the motor's input voltage to 24 VDC
  4. crutschow


    Mar 14, 2008
    If it's a bootstrap circuit to generate the required gate voltage to turn-on a high-side N-MOSFET then it's not feedback in the usual sense of the term (positive feedback to provide hysteresis or negative feedback to reduce distortion, increase bandwidth, or stabilize gain or operating point). So I would keep the term bootstrap separate from the term feedback even if it does generate a voltage at the input from the output.
    wlarsen likes this.
  5. redplaya


    Jan 26, 2014
    Feedback is a generalized term for control theory. In all reality, everything has feedback from everything else, but from peer to peer we only point out feedback if it dominates in the system.

    Boostrap is a word to describe a way of charging a cap for a high side driver in series with a diode. When there is a low impedance to ground and the Diode is forward biased (Vboot < Vin - Vd), the cap will charge with a time constant relative to the load impedance.

    Feedback is a way of describing any two black boxes in series and seeing how the ladder effects the first one.

    Feedforward is the opposite, how the first black box effects the other.

    It's sort of like comparing apples to oranges. The bootstrap can certainly can have feedback but the feedback can't have a bootstrap (Monica has red hair, but red hair doesn't have Monica)
  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
    Common Redplaya, don't sell yourself short. Once you get her, red hair will have Monica!
    redplaya likes this.