0
\$\begingroup\$

I am trying to make a circuit that will have 2 power sources. One will be be a main and one will be a battery backup. When backup or main is disconnected I want to make sure that the supplies are not being put into the other. (like a battery backup circuit) However most of those that i saw use 2 diodes. Ones on each of the positive rails.

I have wondered why not use mosfets to do this as they have a diode built in. But I can't seem to understand the datasheet. It seems that source to drain voltage is -1.5v so I won't be able to do it in this case. But I thought that power mosfets are used in some circuits this way. Here is my circuit. I have 2 irf9520 p channel mosfets I can use. I want them to also work as reverse voltage protection and in their current configuration I know they will work for that. But I'm not sure if this configuration will cause an issue with that also. I have kept away from the diodes as they cause to much of a voltage drop. The load takes 7v minimum and the battery backup does not last that long so I would prefer that method.

enter image description here

I believe I'm not reading the datasheet right. Can anyone tell me if this will work ? If it will not work can you help with an explanation and possible a circuit to be able to do this. Thanks.

Load current draw is between 25ma and 200ma. Being held mainly at 170ma.

\$\endgroup\$
4
  • 1
    \$\begingroup\$ The body diode of a MOSFET should not be used to conduct significant amounts of current. \$\endgroup\$
    – Hearth
    Feb 15, 2019 at 1:49
  • \$\begingroup\$ @Hearth how would it be conducting current in this manner ? \$\endgroup\$ Feb 15, 2019 at 2:10
  • \$\begingroup\$ I am not sure what you're asking. \$\endgroup\$
    – Hearth
    Feb 15, 2019 at 2:17
  • \$\begingroup\$ What would be significant amounts of current then ? I added my current draw of my load to the question. \$\endgroup\$ Feb 15, 2019 at 2:21

0

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Browse other questions tagged or ask your own question.