Supercapacitor bank shunt current controller

Discussion in 'General Electronics Chat' started by smoothVTer, Feb 16, 2013.

  1. smoothVTer

    Thread Starter Member

    Jan 13, 2010
    I've designed a 27V supercapacitor bank, to be charged from a DC generator driven by human power. My design calls for 24V max on the cap bank, leaving some leeway for the series caps. In the case the human operator of the device keeps on cranking past the 24V max charge, I need a way to shunt the excess current.

    The concept is very similar to solar charge controllers, which charge up a battery rather than a cap bank. Some people call them "dump controllers". For a solar array, the solution has been proposed and talked about in this thread:

    The circuit in question is this:

    I've been able to use a TIP32CTU PNP along with a 24V zener diode to achieve my primary 24V sense circuitry, as in the PNP in the attached gif to this thead. My question has to do with the detailed circuit implementation above. Why use a voltage reference and a comparator at all? Why not take the output voltage from the QN3906 PNP and use that trigger ON the gate of the power nMOS device? The only thing I can think of is that using the comparator gives you a sharper turn-on characteristic and the voltage divider gives you control of the set point ... am I missing something else here?