Elenco's PK-201 Experiment #17: Standard Transistor Biasing Circuit

This experiment uses a variable resistor to show that 0.7V is needed at the transistors base to allow current to flow in the circuit. As the voltage increase the transistor turns on until a larger collector current lights the LED.

 

 

 

Elenco's PK-201 Experiment #16: The Substitue

In this experiment, the NPN transistor base is connected to the collector making the transistor function as a diode. Once 0.7V is applied to the base current flows with only slight resistance and no current gain. Exactly as a diode functions. 

 



Elenco's PK-201 Experiment #15: The Current Amplifier

In this experiment, the right LED in the collector path is brighter than the left LED in the base path because the base current is amplified by the transistor. In other words, a smaller current is used to control a larger current. The term "amplified" is misleading and does not amplify an electrical current(Go to Figure 4 and read text below). Remember, in experiment #14 the transistor was used as a switch. Here, it is still functioning as a switch, and in this sense the transistor is used as an amplifier. This is called current gain. Current gain by a transistor can vary anywhere from 10 to 1000 depending on the type of transistor. But, battery voltage and circuit resistance will limit the current gain. The circuit resistances, not the transistor itself, are limiting the current and the transistor is said to be saturated. 





Current at base

Current at collector (about 10x base)








Wealth of Information

Transistor Formulas

Current Gain


Thank you University of Virginia for information that helped me come to an understanding of this experiment.





Elenco's PK-201 Experiment #14: The Electronic Switch

In this experiment, the transistor (2N3904 NPN Bipolar Junction Transistor) is acting as a switch. In the first picture there exists a closed circuit between the battery, 1k ohm resistor, LED, and transistor, but the LED is not lighted therefore current is not flowing. This is because the transistor is open and functioning as an electronic switch. When the on/off switch is turned on, current is applied to the base of the transistor closing the electronic switch (transistor) completes the circuit, which allows current to flow in the circuit. In the pictures below, I take voltage reading before and after turning the switch on. The first two pictures are at the collector. Notice the voltage before and after the switch is turned on or off. The next two at the positive side of the LED. The following two at the base. When the switch is turned on, 0.78 volts is needed to release the voltage between the collector and emitter. And the last two, the emitter. Note: all the readings are in volts except the last one. That is in millivolt because there is always a voltage drop across the NPN emitter. 

 

Very good visual for the NPN transistor



Switch is OFF Voltage is collected at the Collector 

Switch is ON Voltage is passing to the LED

Voltage at Diode with switch OFF.



Voltage at Diode when switch is ON.

 

 General information on transistors

The NPN Transistor

 



Super Stereo Ear MK136 by Velleman

The Super Stereo Ear is a stereo amplifier that will boost sound up to 50 times. The gadget has volume control via a potentiometer, on/off switch, two microphones, and one IC NE5532 for stereo tone control.

 

 

 

NE5532 Technical data

Elenco's PK-201 Experiment #13: One-way Light Bulbs

In this experiment, Diodes made of Gallium Arsenide are used or more commonly called LEDs. A turn-on voltage of about 1.5V is needed to pass current through these LEDs, but this voltage can vary depending on the type of LED. This current is so high that light is generated as it passes through the LED. In the video demonstration, the red LED lights up and slowly dims as the 100 microfarad capacitor is charged up. The second, blue LED does not light because it is wired in reverse-biased. Then the second wire (ground) is used to light the blue LED, which dims as the capacitor is discharged. The red LED does not light because it is wired in reverse-biased and not passing current. 

 

LEDs
Technical LED Color Chart
 

Elenco's Pk-201 Experiment #12: One-way Current

This experiment demonstrates that a Diode and a LED will only pass current in a one-way direction. A diode's turn-on voltage is 0.7V. In the first picture, the Diode and LED are wired correctly and the circuit works. In the following two pictures, the Diode or LED is wired incorrectly and the circuit does not work. 

 

Diode wired correct

Diode wired wrong

LED wired wrong

What is a diode.