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IRF740 N-Channel Power Mosfet Features, Application.C945 Transistor Pinout, feature, Equivalent.C828 transistor Pinout, Equivalent, uses, working.Darlington Pair transistor configuration and features.įor decades the quasi-complementary output stage made sense but because PNP and NPN power transistors are now equally available and have more closely matched performance characteristics, modern audio power amplifiers often use equivalent topologies for both pairs: either 2 Darlingtons or 2 Sziklai pairs.
In the quasi-complementary topology, the performance of the lower pull pair, which uses a single NPN transistor, more closely matches the performance of the upper push pair, which consists of two NPN transistors and an identical power device. Alternately, if a germanium PNP device was used, it would have significantly different characteristics than the silicon NPN transistor. This configuration, which uses 3 NPN transistors and 1 PNP transistor, was advantageous because for decades the most common small signal transistors were germanium PNPs (silicon PNP power transistors were slower to develop and were for years more expensive than their NPN counterparts). Historically, designers frequently used the "quasi-complementary" configuration, which uses a Darlington push pair (ie, 2 NPN transistors) and a complementary feedback pull pair (ie, 1 PNP and 1 NPN transistor). This is a very compelling reason to use the Sziklai pair in cases where output power is moderate (25 W to 100 W), fidelity is critical, and relatively low idle power consumption is desired. This means that idle power consumption is on the order of a few watts versus tens of watts for the same performance in many cases. Optimal quiescent current in an amplifier using complementary feedback pairs also tends to be much lower than in Darlington-based output stages, on the order of 10 mA vs 100 mA or more for some emitter follower output stages. This significantly reduces the number of components which must be in thermal contact with the heatsink and reduces the likelihood of thermal runaway.
This potentially simplifies the design and implementation of a stable class AB amplifier, reducing the need for emitter resistors.
#Npn darlington transistor switch configuration driver
This means that a Sziklai output stage in a class AB amplifier requires only that the bias servo transistor or diodes be thermally matched to the lower power driver transistors they need not (and should not) be placed on the main heatsink. In contrast to the traditional Darlington configuration, quiescent current is much more stable with respect to changes in the temperature of the higher power output transistors vs the lower power drivers. Ĭomplementary feedback pairs can also have the benefit of superior thermal stability under the right conditions. They are especially advantageous in amplifiers where the intended load does not require the use of parallel devices. Like the Darlington, it can saturate to only about 0.6 V, which is a drawback for high-power stages.Ĭomplementary feedback-based output stages Ĭomplementary feedback pairs are often used in the output stages of power amplifiers due to their advantages both in linearity and bandwidth when compared with more common Darlington emitter follower output stages. One advantage over the Darlington pair is that the base turn-on voltage is only about 0.6 V, or about half of the Darlington's 1.2 V nominal turn-on voltage. As with a Darlington pair, a resistor (e.g., 100 Ω to 1 kΩ) can be connected between Q2's emitter and base to improve its turn-off time (i.e., improve its performance for high frequency signals). Likewise, in a typical application the collector of Q2 (also connected to the emitter of Q1) functions as an emitter and is thus labeled "E". Hence the emitter of Q2 is labeled "C" in Figure 1. The emitter of Q2 functions as a collector. In a typical application the Sziklai pair acts somewhat like a single transistor with the same type (e.g., NPN) as Q1 but with a very high current gain (β). By replacing Q1 with a PNP transistor and Q2 with an NPN transistor the pair will act like a PNP transistor overall. Figure 1 shows an NPN-PNP pair that acts like a single NPN transistor overall. The current gain of the Sziklai pair is similar to that of a Darlington pair and is the product of the current gains of the two transistors. In contrast to the Darlington arrangement, the Sziklai pair has one NPN and one PNP transistor, and so it is sometimes also called the "complementary Darlington".
In electronics, the Sziklai pair, also known as a complementary feedback pair, is a configuration of two bipolar transistors, similar to a Darlington pair. Sziklai pair that acts like a single NPN transistor with collector C, emitter E, and base B.
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