A transistor has three poles, three regions, and two PN junctions (observing the structure of it helps to understand how it works.ġ) The hollow in the figure is positively charged for holes, and the solid ones are negatively charged for electrons. The transistor is a current-type control device, similar in function to the field effect transistor ( FET), and can be used as signal amplification, oscillation and modulation. Unlike ordinary mechanical switches (such as relay, switch), transistors use electrical signals to control their own opening and closing, so the switching speed can be very fast.ĥ.1 Waveform Analysis of Basic Common Emitter Amplifier Circuitĥ.2 Feasibility and Necessity of Transistor Switch Circuit DesignĦ.1 Basic Switching Circuit of NPN TransistorsĦ.2 Basic Switching Circuit of PNP Transistors It is a variable current switch capable of controlling the output current based on the input voltage. This will help to see better the use of transistors.A semiconductor transistor is used to amplify, control, and generate electrical signals and power. In the next post, I will use a transistor to switch a DC Motor from a different power supply. Transistors can commute high currents and voltages.Yes, it is easier to use but your would miss the big advantages of transistors. Wasn't easier to just use the push button instead of the transistor. What can you do to increase the switching current in the base? When calculating the base resistor Rb, multiply the base current Ib by 5 in order to guarantee a more efficient switch.

For switching this is better news than the previous base transistor. The new voltage drop for the collector-emitter of the transistor is actually less! It was about 0.08V. Let's change the Rb resistor, from 68KΩ to 10KΩ, and let's see what happens. What happens if we choose a lower Resistor? Not necessarily bad if you are using amplifiers but no good for this case. For switching this means that the circuit that we want to command is going to receive less “electric force” so to speak. The new voltage drop for the collector-emitter of the transistor is actually more! It was about 1.32V. Let's change the Rb resistor, from 68KΩ to 100KΩ, and let's see what happens. What happens if we choose a higher Resistor? ( The mode selector will vary from multimeter to multimeter). If it's the 2n3906, then in the PNP socket and select the ‘PNP' mode. If it's the 2n3904, then insert in the NPN socket and select the ‘NPN' mode. Connect the transistor to the collector, emitter and base sockets of the HFE measurement. A few results under certain conditions can be found on the datasheet.īut let's use the HFE measurement tool from the multimeter to find out an approximately value. It varies on conditions such as temperature, collector current, etc. How much gain does the transistor has? It depends. The current Ic is proportionately dependent on the value of Ib it's translated to the following formula: Ic = Ib * HFE The more current that flows through Ib, the more current will flow through Ic, theoretically. The ratio between the collector current ‘ Ic‘ and the base current ‘ Ib‘ is called HFE gain (sometimes called β).

The Collector Current − Continuous is 200mA, which is more than enough current to switch the LED (9.84mA).

Since the maximum voltage is going to be 5V, the circuit doesn't reach any of the maximums of Collector−Emitter Voltage or Collector−Base Voltage. 2N3906, BJT PNP transistor with TO-92 package: 1 unit.2N3904, BJT NPN transistor with TO-92 package: 1 unit.In this tutorial, all the components are Through Hole. Requirements for Push Buttons Components and Devices What happens if we choose a lower Resistor?.What happens if we choose a higher Resistor?.

Transistor switch