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A transistor is a semiconductor device that can amplify signals and switch power. The types that are used most are BJT (Bipolar Junction Transistor), UJT (Unijunction Transistor), and MOSFET (FET, for Field Effect Transistor).

4 votes
2 answers
13k views

NPN transistor to run 12V 0.5A from 3.3v 4mA

I assume this question is very common, because I read a lot of answers here, but I still missing somthing.. I have "Electric Imp" module, which have max I/O pin power output of 4mA, and its run on 3. …
4 votes
1 answer
5k views

Understanding hFE values in a datasheet to choose a proper BJT base resistor

I already read the post Which resistor for NPN transistor base? But I still cannot understand the base resistor calculation. I need the transistor to be a switch to 5V 200mA relay. The base will get …
3 votes
3 answers
1k views

MOSFET to run 12 V, 0.5 A door lock

After searching for a BJT solution, I decided to replace my Darlington pair with a single MOSFET transistor. I have a microcontroller with max I/O pin current of 4 mA at 3.3 V. I have a FQP30N06L MOSF …
1 vote
2 answers
2k views

AVR to drive 12V 1A motor

I never used FET transistors, so I had may some newbie questions (and this is after reading the datasheet for several times and spending hours online reading about FET) On one of the sites I saw this …
1 vote
1 answer
311 views

Choosing a transistor to Relay

I am building new project, which I will power up the water tank heater from my smartphone. I have few safety though I want to ask here to get your opinion. I am going to use AVR to run a relay, that …
0 votes
2 answers
2k views

Transistor to run relay

In addition to my last post I have more information and details. I want to run 240V Relay (5V Coil) from my AVR chip (ATmega328P). My EMR relay takes up to 200mA on it peak. I have 2N2222 transis …