Unable to use T4.1 with external power

iznogoud320

New member
Hi everyone,

I'am probably missing something basic, but I'm new to teensy and have trouble using the board using external power supply.
I'm working with an (original) Teensy 4.1.
As stated in documentation I cut the pad close to Vin Pin and then attached a 5V power supply To VIn and GND Pin.
If I plug my USB cable to program the board, the LED close to the USB plug turns ON (RED continuous) and Serial port is not detected.

Edition with more details
I have noticed this: when USB powered, as soon as I plug something on 3.3V pin the Voltage measured drops to 2.9V. Might it indicate a problem with the onboard 3.3V regulator?


Any advice?

Thanks for your help,
Michael.
 
Last edited:
I usually cut the pad and use a pair of schottky diodes.

The VUSB-OUT needs to come off the Teensy, I have a 5V reg on board. They both hit the diode-OR, and feed back into VIN at around ~4.7V

Be careful not to over-draw on the 3.3V rail, as it's limited to 250mA, but stay under 100mA if you can. If you pull too much current, you might see the voltage drop as you described.

If that's not the case, I'd look at your USB cable, use a good one, and your USB port/hub/charger should be a good one too.


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If you are going to program your teensy 4.1 with the external power supply still connected, you will damage your precious teensy.

A phrase that has been said in the forum is more than eloquent: "the teensy do not know if the power is external or it comes from a USB port on the PC".

This means that it is not necessary to cut that bridge, you can connect your teensy with a powerbank or similar for portable use. Then you disconnect the external source and you can continue programming your teensy from any PC
 
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