udn2981, limiting the voltage drop.

Discussion in 'The Projects Forum' started by rubicon99, Apr 25, 2012.

  1. rubicon99

    Thread Starter Member

    Apr 19, 2012
    So there will be a voltage drop associated with the udn2981, when used properly. Is there any simple way to buck that voltage back to the common voltage that is powering that IC, without having to use a relay. The Voltage drop can be 1-2 volts. I've seen about 1.3 volt drop. Pretty much looking fro an inductior/resistor/capacitor combination that can raise the voltage to common power, but would still keep the voltage at zero if the output from the udn2981 was zero.
    Last edited: Apr 25, 2012
  2. #12


    Nov 30, 2010
    The use of capacitors or inductors implies a frequency, as in "bootstrap circuit". Impossible to design without knowing a lot more about the application.

    I've seen many places where this circuit would fix the problem but people seem so reluctant to add 2 transistors and 4 resistors!

    With proper selection of the parts, this will fix your problem to within .2 volts at 500 ma.
  3. Ron H

    AAC Fanatic!

    Apr 14, 2005
    Replace the PNP with a MOSFET, and the voltage drop can be reduced to millivolts. Switching speed is not the greatest, but this may not be an issue.
    The beauty of the UDN2981 is the density - 8 in one package.