Purpose of Q1 on Teensy 4.1?

T

tigger

Active member
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What is the purpose of Q1?
A high-side pass transistor would normally be wired from source to drain with a control signal on the gate, right?
This one seems to be wired from drain to source. Maybe it does the same forward and backwards?
 
It's a p-channel that will be hard switched on in normal operation - the body diode conducts, brings source more positive than gate, and then it turns hard on. If the incoming polarity is wrong it will not conduct at all.
 
MarkT said:
It's a p-channel that will be hard switched on in normal operation - the body diode conducts, brings source more positive than gate, and then it turns hard on. If the incoming polarity is wrong it will not conduct at all.
Click to expand...
MarkT, thanks. That's what I figured. I just wanted to make sure there wasn't some other reason.
I suppose it will essentially do the same thing with the source as the input as soon as the input gets above the gate-to-source turn on voltage. The turn on voltage will be different, though, since it doesn't have to overcome the body diode.
 
If the source were the input it won't protect the board as the body diode would conduct on reverse voltage.
 
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