Good old reliable ON Semiconductor - enjoy As you can see an error of 7 μA out of 1000 is pretty close.Īs for the datasheet - Google is your friend. Again - close enough for government work. Just to double check that we did not drop a decimal point. If you look in a table of 1% resistor values you find the closest value is 4530 Ω - close enough for government work. You would diveide the voltage across the resistor (5.2 - 0.7) = 4.5 Volts by the current 0.001 to get 4500 Ω. For Example Lets suppose our power supply provides +5.2 Volts and we want a base current of 1 mA. (Vcc - 0.7)/Rb where Rb is the value of the base resistor in Ohms. Calculate the current in the base resistor as: The other side of the base resistor is connected to some voltage source, call it Vcc. When the transistor is on there will be between 0.6 to 0.7 volts across the Base-Emitter junction. Let us assume that the emitter is at GND (0 VDC). #2 is easier because you just need to decide how much base current will turn the transistor on.
#1 above is more complicated because there are at least three different amplifier configurations that you can use for a single device. As an amplifier, where a small base current is used to control a larger collector current.Transistors are used in two basic circumstances:
The parameter just has to be within a defined range with say a 99% probability. Because of this single fact, most designs avoid a dependence on a specific value of a device parameter. It is more like they can take random values, but confined to a range with a mean an a variance. Most transistor parameters are not precisely controlled or repeatable in the manufacturing process. Like everything else in life an electronics, it depends on what you are trying to do. Specifically for the 2N2222 transistor, what is the proper way to determine the resistor for the BASE? If not how do you identify the correct datasheet? This brings me back to the "random" examples on the internet with such a wide variance in resistors for the base of this transistorĪre datasheets specific to the manufacturer of a given generic component like a 2N2222? He says that you look at the peak current on the base and then test like thisĪssuming a 9V battery, a drop of 0.6V and a 100Ohm resistor the math would be I found this youtube video which seems to explain this. One additional question, what I am really trying to understand is why various sources on the internet use anything from 470 ohm resistor to 10K ohm resistor on the base. How do you know if you have found the correct datasheet for parts you may buy? To a n00b like myself this is not enough to go on to dig up a specific datasheet (if that is even required).