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Gate drive for source-to-source MOSFETs

Ken Anderson
Intellectual 325 points

Hi, looking for some advice here. My system has two independent batteries connected, each with their own power-disconnect switch. Since current cannot be allowed to flow either way through the switch when off, two MOSFETs are used in a source-to-source configuration to create a bi-directional switch. My question is, how to achieve the gate drive of these FETs. They need to be able to be fully on (100% duty cycle) or off for extended periods of time.  I don't expect that the attached schematic will work because the FET sources are floating when off. Note the 80ohm bypass which keeps the board MCU and voltage regulators powered even when the switches are off. Any suggestions?

Thanks.

 

 

  • 0
    TI__Genius 13700 points

    Hello Ken,

    Could you use a single low-side BJT? Single NPN with the Emitter toward system ground, Base controlled by trigger signal, Collector to battery minus. Then just drive the device deeply into saturation.


    I am still working out testing but if you have a chance to test it and are willing to give it a try your feedback would be great!

  • 0
    Prodigy 20 points

    I've used small little dc/dc isolated converters, such as NMA0512S or whatever the little 0.5W parts were. Because the 12V may vary quite a lot, a 5V linear reg can be used to generate the semi-regulated 5V input of the dc/dc.  If the FETs ar logic levels, then an 0505S would be appropriate.  There is always a need to tie the gates to source, say with 10k.