I want to have Vbat enter Vcc when Vdd goes Low. The schematic I'm following is using a P-channel mosfet with Vbat connected to drain. I feel like this is wrong and I should either use a n channel or flip the drain and source.
\$\begingroup\$
\$\endgroup\$
2
-
\$\begingroup\$ Are VDD and VCC related in any way or completely independent? \$\endgroup\$– Ste KulovCommented Aug 11 at 6:55
-
\$\begingroup\$ Please use correct English to the best of your abilities. Take hints from a spelling checker! (Note to self: find&use one for duckduckgo.) \$\endgroup\$– greybeardCommented Aug 11 at 9:00
Add a comment
|
3 Answers
\$\begingroup\$
\$\endgroup\$
P-channel is the right one for this. You just need to mirror it: Source (pin2) must be connected to Vbat.
\$\begingroup\$
\$\endgroup\$
You need to reverse the P-MOSFET source and drain as noted. Whether that circuit works depends upon the values of Vbat, VCC, and VDD. Is there another source for VDD? What are the voltage values?
\$\begingroup\$
\$\endgroup\$
2
Use another P-channel FET in series with the first one. Connected them at the sources. Put a resistor between source and gate. The way you turn it ON/OFF depends on the voltages levels of a vbat and Vdd.
