So, the “+” input of comparator 1 will be positively charged against its “-” input. Here, if the above situation is paused, we would observe that the second transistor’s collector voltage is a tad lower than the first transistor because the whole collector resistance is larger.īecause R2 a has a lower resistance than R1, the potential at the junction of R2 a/R2 b will be marginally larger as opposed to the collector of transistor 1. The upward moving slope of the input voltage will turn both of them on simultaneously and consequently their collector voltages will fall. Let’s say the two transistors under test are exactly the same in terms of the U BE and H FE. This is the whole setup of the sampling circuit. R2 a and R2 b are somewhat larger in resistance compared to R1, but R2 a as a single unit has a smaller value than R1. However, we find that their collector resistance is fairly dissimilar. In practical terms, the two BJTs under test are powered by identical control voltages, as displayed in Figure 1. The discrepancies between their collector voltages are identified by a pair of comparators and indicated by the LEDs. The Transistors Under Test (TUTs) are subjected to a triangular wave-shape. The circuit does the heavy lifting as you just need to connect the transistor pairs and monitor for the lights. The LEDs will lit if there is a response from the transistor’s U BE and H FE. Still, it has to be occasionally done because the paired transistors are frequently utilized in differential amplifiers especially when they are operated as thermistors.Ĭommonly, a whole lot of transistors are checked using a multimeter and their values are recorded until there is nothing left to inspect. Searching for similar transistors is a detesting and taxing job. We know that how very useful it is to have matching transistors for applications like differential amplifiers or thermistors. The extent of precision may be from “vaguely same” to “exact” and can be tweaked as needed. The discussed concept is a remarkable tool that capably chooses transistor pair from all sort of possibilities in a nick of time.Ī pair of transistors will be “matched” if the voltage at the base/emitter and current amplification are identical. This simple circuit can be used for testing and matching transistors in mass production chains, without any hiccups or issues.Multi-Meters use battery power which at critical junctures tend to get exhausted, hampering the testing procedure.No cumbersome multi-meters and wires are involved, so there's minimum hassle.It provides a direct display whether the transistor or the BJT are accurately matched or not.The circuit idea presented here can be used for comparing two individual BJTs, and thus find out exactly which two are perfectly matched in terms of their gain specifications.Īlthough this is normally done using digital multi-meters, a simple circuit such as the proposed transistors match tester can be a lot handier, due to come the following specific reasons. To eliminate this, matching transistor pairs with their Vbe and hFE specs becomes an important aspect for typical applications.
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