Amplifier output drivers are increased using push-pull amplifier stages

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Amplifier output drivers are increased using push-pull amplifier stages

May 29 , 2023 0

Many portable circuits require precision measurement capabilities as well as low-power operation to minimize current and battery consumption. When looking for amplifiers with these requirements, it may be relatively easy to meet the low power and accuracy requirements, but the drive current may not be sufficient to meet the requirements of these low power devices.

For example, take a low-power precision amplifier released by Linear Technology. The LT6020 is a two-channel precision amplifier, Features 30μV imbalance (maximum at 25°C), 0.5uV/°C (maximum) low drift, low power (100μV/ amplifier), 400kHz bandwidth, and an impressive 5V/μs conversion rate. It provides 5.5mA current to the load when the output is short-circuited, which may not be sufficient to drive solenoids, valves, multipole filters, or other heavy load applications. Also keep in mind that as the load current increases, the open-loop gain decreases, which can adversely affect the accuracy of the device and the performance of the circuit.

To provide more current, a simple push-pull transistor output stage can be added to improve the drive capacity of the amplifier.

In this circuit, we add 2N3904 and 2N3906 NPN/PNP transistor pairs in push-pull configurations to increase the output current. 2N3904 40V, 200mA NPN transmitter, minimum beta (ß) gain is 80 (IC= 1mA, V administrator = 1V). 2N3906 is a complementary -40V, 200mA PNP converter with minimum beta (ß) gain of 80 (IC= -1mA, V administrator = -1V). A 1k resistor between the transistor base and emitter allows the LT6020 to deliver the first 600μA load current before the NPN and PNP begin to deliver additional current. The resistor improves linearity in the middle of the range when the transistor is off and on.