USB/BATTERY power switcher without altering the teensy board ?

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Hello,

I try to make a power switcher for a teensy board

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my problem is the thick wire in the schematic, is it alright to do so ? what if usb and batteries are plugged together ? should I add a diode ?

thanks
 
The question and the answer are trivial. You need to prevent battery current from flowing into USB and USB current from back feeding the 7805. Thus, you might drop all the resistor, opamp and mosfet stuff and just use a dual schottky diode like the BAT754C. Connect the 78(L)05 output to pin1, USB power to pin2 and pick the power to the Teensy from pin3.
 
That's relatively easy to explain: These Schottky diodes have a voltage drop of about 350-400mV. Thus, a 5V Arduino would have problems with the 5V ADC reference and 5V related analog PWM when "only" fed with 4.6 or 4.7V. A Teensy 3.x works with 3.3V and its voltage regulator doesn't really care if the input voltage is 5.0 or 4.6V, there is enough overhead for proper and clean voltage regulation.

I've been wondering for a long time why PJRC does not use a dual diode array on its T3 boards instead of that Vin-Vusb trace which needs to be cut or not.
 
yes, totaly, I thought the same, why not design teensy with a diode

but why is there no diode on the arduino schematic to protect the VREG ????
 
Albert Einstein has probably an answer...

Albert-Einstein-Quotes-1.jpg

If not, there is still the assumption that in the Arduino schematic, there is a different voltage regulator (an 1117-5) which can probably deal better with reverse voltage feeding than the old, asthmatic and outdated 78xx series.
 
maybe the NCP1117 allows such a setup

lol....well I'll do add a diode, so I get the nice mechanic and I protect the regulator too

I like to cut off the battery if the usb is plugged, quiet ellegant....and there is no need to discharge the battery if the usb is plugged in

tahsnk for the support dude ;-)
 
I'd go for the dual diode solution, though. That would have worked 40 years ago when I started tinkering with electronics, it works nowadays, thus we might extrapolate that it will still work in another 40 years.
 
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