Hi everyone,
I am looking at a schematic for an Arduino enabled board an am confused about one of the components used.
In the power regulation section, they use a DMP2035 P-Channel Enhanced Mode Mosfet (as seen in image).
What is this used for? Why is it useful?
Note: I have a very similar device which does not use this component. Thus, I know it is not required.
Thanks,
D
Looks similar to the power cct. found on the Arduino UNO R3.
Some kind of automatic switch for powering the regulator used with an external battery.
Several functions.
Diode, so the battery can't be charged from the 5volt source (battery safety).
Polarity protection, in case you connect the battery wrong.
Switch. If 5volt is absent, the mosfet is an almost ideal battery switch. No loss in the 'diode'.
Leo..
Watch this.
Hi larryd,
Does the MBR120 schotky diode already perform those functions?
Why do we need this additional mosfet then?
Thanks for any clarifications!
D
The MOS FET is very low resistance when turned on, i.e. 5v is missing on the left side of the drawing.
Battery voltage will be seen at the left side of the switch (pin 3).
When 5v is present, probably form USB, the FET is off, battery not connected to the switch.
D3 prevents battery voltage from connecting to 5 volts.
The 3.3 volt regulator will get input voltage from battery (through Q1) or 5v (through D3) or VCC_IN
larryd:
The MOS FET is very low resistance when turned on...
To clarify: a Schottky diode will always have a forward voltage drop [anywhere from around 0.3V to 0.5V], whereas, the MOSFET will have a low resistance [around 30 to 60mΩ in this case], thus nearly NO voltage drop.
