![]() ![]() This potentially simplifies the design and implementation of a stable class AB amplifier, reducing the need for emitter resistors. 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 (eg, 100 Ω to 1 kΩ) can be connected between Q2's emitter and base to improve its turn-off time (ie, 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 the figure above. 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 (eg, NPN) as Q1 and 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. The figure above illustrates 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. The symbols "C", "E", and "B" refer to the Sziklai pair, not the individual transistors. The required input current is below that of the SN75468.Sziklai pair transistor configuration. The SN75469 has a 10.5-kΩ series base resistor to allow its operation directly with CMOS or PMOS that use supply voltages of 6 to 15 V. The SN75468 has a 2700-Ω series base resistor for each Darlington pair for operation directly with TTL or 5-V CMOS. Applications include relay drivers, hammer drivers, lamp drivers, display drivers (LED and gas discharge), line drivers, and logic buffers. ![]() The Darlington pairs may be paralleled for higher current capability. The collector-current rating of each Darlington pair is 500 mA. Each consists of seven NPN Darlington pairs that feature high-voltage outputs with common-cathode clamp diodes for switching inductive loads. The SN75468 and SN75469 are high-voltage, high-current Darlington transistor arrays.
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