So I have been researching on how a bipolar NPN transistor work. Here are my understandings:
- In order to turn on a transistor, you need to apply a voltage (from base to emitter) to overcome the depletion region, that voltage is usually 0.7Vdc
- Once the transistor is "on", as the base current increases, the current flowing from the collector to emitter will also increase proportionally by a hfe constant
Armed with this knowledge, what I should expect to see in a data sheet should be the following:
- The minimum current/voltage to turn the transistor on (voltage needed to overcome the barrier)
- The maximum current allowed at the base to avoid damaging the transistor
How do I navigate the data sheet to obtain this data?
Finally, there is a DC current gain chart in the data sheet, here are my questions
- Why they used the collector current instead of the base current? shouldn't this makes more sense to use the base current? because you would think "if I have x amount of current in the base, I will get x amount of current from collector to emitter?
- What if your Vce is larger than 1.0Vdc? say 5Vdc? what would the gain be then?
Datasheet:
transistor https://www.onsemi.com/pub/Collateral/2N3903-D.PDF
Relay https://www.circuitbasics.com/wp-content/uploads/2015/11/SRD-05VDC-SL-C-Datasheet.pdf
Circuit I am trying to solve
Thank you
As you can see from the diagram, the relay will only turn on is if there is 5Vdc and 71.4mA across it. Knowing this fact, how do I determine the current I need at the to achieve this?