OpenDrain with high voltage

[Alexandre T]

Hi everyone,

I did not find my answer on the forum or I did not understand exactly the others posts that are talking about this, so here I am.

I have a teensy 3.5 and need to control a 10V output with PWM. I tried using a PNP transistor but what I did does not work, I already have bought the PCB so I can just make a few corrections (yes maybe next time I will think a bit more about what I do).
Here is the schematics that I have:


Currently the output is always to 10V, I think the 3.3V of the teensy are not enough to make the transistor commutate.

My idea would be to add a pull-up resistor to the input of the transistor and to control the pin with the open drain mode. As I understood, the open drain mode allows to use a different voltage than 3.3V, as long as this voltage is supported. Do you think that the teensy will support 10V on one GPIO with the OUTPUT_OPENDRAIN mode? If not, do you have any idea that could save me? ^^'
Here is the schematics that I would have:


Thanks!
Alexandre

 

[PaulStoffregen]

As I understood, the open drain mode allows to use a different voltage than 3.3V, as long as this voltage is supported. Do you think that the teensy will support 10V on one GPIO with the OUTPUT_OPENDRAIN mode?

No, definitely not. The pin is 5V tolerant. It's not 10V tolerant!

 

[Alexandre T]

Okay, good thing I asked before trying then.

Thank you!

 

[jonr]

I'm curious - is there some amount of series resistance where a teensy 3.5 output does become 10V tolerant?

You could add a diode to limit the voltage seen by the teensy pin.

 

[MarkT]

I wouldn't have expected a PNP to be useful for level conversion to a higher voltage - NPN common-emitter inverter
circuit is what's used - in other words low-side switching. Since BJTs turn on at around 0.65V, 3.3V is plenty, just
set the base resistor so that the base current will be about 5 to 10% of the desired collector current.