Wednesday, October 26, 2011

Using MOSFETs as low voltage drop diodes 99MOSFETswitch

A MOSFET can provide a very low loss switch when diodes ( even Schottky diodes ) will not do.

Above we see two circuits that operate as follows:  If  A is more positive than B then MOSFET Q1 will turn on and M1 ( motor1 ) will run.   If  B is more positive than A then MOSFET Q2 will turn on and M2 ( motor2 ) will run.   The designer should select MOSFETs with a low turn-on resistance and a low gate turn on voltage.  Note that these MOSFETs are being connected in the reverse fashion from what is normally expected.  This reversal is to avoid having the instrinsic MOSFET body diode cause problems.  The MOSFETs must be the N channel variety.

For low voltage turn-on  ......  less than 1 volt .....

Here are some possibilities to be found at DigiKey


1 comment:

Anonymous said...

Due to my design needs I wonder if this technique would also work using channel P Mosfets. So, the switching of the Mosfet will activate the positive line rather than the negative one, as it is illustrated here. Anyone knows if this also work with channel P Mosfets? Why the author suggests using N channel Mosfets?