I know this question might sound obvious, but still I cannot find an answer.
What is the purpose and best-fit applications for field effect transistors?
I mean, we have bipolar junction NPN transistors. It can be used to control a high-current circuit with a low-current signal, for example enabling relay through a microcontroller pin output. The most important characteristics (please, no holywars on this statement) is working voltage, hfe and power dissipation. We may assume that a NPN transistor with hfe = 50 for fixed voltage and base-emitter current 10mA passes up to 500mA from collector to emitter. In general, we can say that collector-emitter current is determined by base-emitter current.
[Disclaimer: I am not sure about the following statements and making it clear is the purpose of posting this question]: Ok, now let's take a look at FET transistors. Source-drain current is determined by gate-drain voltage:
The second chart (above letter б) is the dependency of source-drain current of gate-drain voltage. So,
- While bipolar junction transistors' "useful" current amplification is determined by current between two pins, FET transistors' current amplification is determined by voltage between two pins;
- FET transistor consumes much fewer energy because gate-drain resistance is very high;
Assuming this two statements are correct, I do not quite understand how do I want to use this transistors, and when should I prefer them to bipolar.
Thanks in advance.