modified 5 years ago

Hi Low Reverse with BJT

00:38:02

For MCU, sometime you need Hi Low Reverse, with pull up resister. This is how.

published 5 years ago

Robert_Kidd

5 years ago

It’s works but even with a transistor gain of only 100 you can increase base resistor to 47kOhm and reduce current consumption and, more importantly, load on source.

Robert_Kidd

5 years ago

It can be increased in value much more if input impedance is an issue.

peerajak

5 years ago

Thank you.Robert. 47KohmsThat's important notice. What value can be increased?

Robert_Kidd

5 years ago

The base resistor can go higher if you want or needed it to. Your collector current is approx. I=V/R=5/10000=0.5mA. Your transistor gain is set to 100 so the base current need only be about one hundredth of that, 5mA/100=0.05mA=50uA. The base resistor can be R=V/I=(5-0.7)/50uA=(4.3x1000000)/50=86000 Ohm. So using 82kOhm would suit.

peerajak

5 years ago

Agree. After testing with 82K base resistor I see whole circuit use much less energy.

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