Saturday, 9 September 2017

switching - Using transistor as switch with low voltage


Basically, I need to monitor a circuit's output so I can activate another system. The output voltage of active stage is 140mV.


If I am not wrong (from what I read about transistors) 140mV is not enough to put a BJT transistor into saturation (ON mode).



The end goal is turning on an LED and/or a relay, so I really need transistor in the saturation region.


I don't want to use a micro-controller's ADC to measure the voltage for such simple device (cost wise)


How can solve the problem in a simplest manner possible?



Answer



Use a comparator.


Just be sure to get one with an input common-mode range that extends down to the negative rail. TL331, for example, might work for you.


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