Testing of Bipolar Transistors and Diodes

Testing of Bipolar Transistors and DiodesCurrent gain is one of the main parameters of bipolar transistors. It shows how many times the base current is smaller than the collector current change it causes. Sometimes we have to solve real-world problems or choose modes of operation for DC transistors. In these cases we often need to coordinate transistor cascades between each other in a correct and reliable way. We usually start searching for a transistor in the reference data lists using the desired current gain H21. There is a wide variety of transistor parameters especially regarding their current gain. Sometimes acceptable values can vary significantly. This is why in real life we often need to make sure that a particular transistor has the right current gain. Another difficult case is when we need to select several transistors by their current gain. Here we simply have to test how they work in real life. It is worth mentioning that in the testing mode the base current is 10 microamperes. The measured current gain can differ from what is stated in the table.To illustrate this let's take the NY68 multimeter. We turn the function switch to the H21 position. BG139 is an n-p-n transistor with the following base configuration: emitter, collector, base. The current gain stated by the manufacturer is within the range of 40 to 250. Now we plug the leads into the corresponding sockets: the first one, the second one, and the third one. As we can see, the difference in current gain of the three transistors is below 10. This means we can use them. Current gain of high-power transistors is measured with the help of a specialised circuit. Using the multimeter we can also check integrity of p-n links in both directions. As we can see, the device shows infinity, when one direction is tested. When we test the other one, it shows several dozens of kiloohms.We often need to ring-out a diode. It's worth mentioning that not all multimeters have the mode for testing diodes. When we try ringing-out a diode in the circuit continuity mode, there is often no response. It is because the applied current is not sufficient. Let's test two diodes. One of them is a Shottky diode, the second one is a regular high-voltage diode. The direct potential drop of the Shottky diode is 0.15 V. The potential drop of the regular high-voltage diode is 0.51 V.We have told you about the most popular ways of measuring used by amateurs of radio electronics.

Category:

Science & Technology

Tags:

• diode
• gain
• p-n junction
• ring-out
• testing
• transistor

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