#Transistor base emitter collector how to
#Transistor base emitter collector trial

The base-emitter diode in the transistor offers a very low resistance to current flow when it is forward biased. When the base-emitter junction is forward biased, the carriers needed for current in the collector circuit find their way into the collector. The very small current in the collector circuit under these conditions is because the p-type material in the base is starved for the n-type majority carriers that the collector circuit requires if it is to conduct a significant current. The collector-base diode is reverse biased so that almost no current will flow unless the base-emitter diode is forward biased. The collector-base diode and the base-emitter diode appear to be in series, connected back-to-back. An n-p-n transistor configured as a common-emitter amplifier, where both the base and the collector circuits are referenced to the emitter, is normally connected with a positive voltage on the collector, as referenced to the emitter. These variations, called common base, common emitter, and common collector, produce different circuit actions each with unique characteristics. However a 2mA device is very different to a 10000mA device.There are three ways to connect a bipolar junction transistor into a working circuit, depending upon which of the three transistor elements is chosen as the common reference for the other two elements. My thumbs are a different size to LDEVRIES's thumb. You can do simple rule-of-thumb calculations. Power transistors tend to have hFE of 20.100 rather than the small transistors with high hFE of 200.600 This will supply 23 mA of base current to your power transistor. I think that you are referring to a 220R base resistor from the AVR pin. But I would feel safer with a nuclear designer that has done her schoolwork. So yes, a lower value pull-down might be safer with nuclear devices. Even a tiny 2uA leakage current could light your 2mA LED (2uA x hFE = 800uA is visible). at RESET)Īny CMOS pin is very sensitive to noise when it is an i/p. The reason for the 10k base-emitter resistor is to ensure that your transistor does not turn on when the PORT is configured as an i/p. Your simple general purpose 2.100mA type of transistor switch will be fine with a 10k base resistor. you need to calculate the base current, and check data sheets. You need a protective diode across the relay coil. (5) can be done the same for small currents. (2),(3) are easily done with a small NPN transistor with the load between 5V and collector. This is why you were asked what you want to switch on and off. In my experience I have always had to use a lower resistor, such as 220ohms on the base saturate the transistor sufficiently to drive things such as small 5V motors and relays etc. Rhoaste wrote: Someone also mentioned here that a 10K resistor between base and AVR for general applications. Good for buffering say audio signals generated from AVR. the emitter voltage follows the base voltage. The collector-emitter voltage is about 0.2V when transistor is fully on, so in a 5V system your load gets about 4.8V at high currents.Īnother nice feature of the transistor is that the base-emitter voltage is about 0.7V, so if you put the load on emitter and drive the base with AVR, the load can never have more than 4.3V over it in 5V system, i.e. Normally 4k7 would be good there but people may put some safety factor there and just put a 1k base resistor. So a 100mA motor on collector needs 1mA of base current. As a rule of thumb you can approximate a regular small-signal transistor to have a current gain of about 100. Transistors can be thought as current amplifiers. For digital control you almost always put the load on collector and ground the emitter if you have a NPN transistor. Well it depends are you trying to drive digital things on/off like leds, motors and relays or drive analog things like speakers etc. What, these things are not in electronics books these days? Someone also mentioned here that a 10K resistor between base and AVR for general applications.

#Transistor base emitter collector trial

I have been working with trial and error and dependent on google really.

#Transistor base emitter collector how to

My question is one for my own general understanding on how to connect the load to the transistor (via the emitter or collector) so I can take these reasons into account in my designs. I'm not referring to any specific application that I am currently building. I'm sorry, but I'm still a bit lost really.