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Class B Emitter Follower

IP.com Disclosure Number: IPCOM000093891D
Original Publication Date: 1966-Mar-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Oswald, RK: AUTHOR

Abstract

This class B amplifier is capable of supplying both positive and negative load currents. All the semiconductive devices are silicon. A positive signal applied to the base of transistor T1 causes conduction through resistor R2, T1 and load resistor R3. The resulting 1R drop across R2 tends to cut off transistor T4 which, in turn, cuts off transistor T5. Diodes D6 and D7 together with resistor R8 provide a fixed bias at the base of T4. Diode D9 conducts when the 1R drop across R2 threatens to become greater than the forward drop across D6 and D7, thus preserving the dynamic range capability of T1.

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Class B Emitter Follower

This class B amplifier is capable of supplying both positive and negative load currents. All the semiconductive devices are silicon. A positive signal applied to the base of transistor T1 causes conduction through resistor R2, T1 and load resistor R3. The resulting 1R drop across R2 tends to cut off transistor T4 which, in turn, cuts off transistor T5. Diodes D6 and D7 together with resistor R8 provide a fixed bias at the base of T4. Diode D9 conducts when the 1R drop across R2 threatens to become greater than the forward drop across D6 and D7, thus preserving the dynamic range capability of T1.

When a negative signal is applied, T1 is cut off. The resulting reduced IR drop across R2 causes T4 to conduct and supply base current to T5. The resulting conduction from the negative supply through T5 provides the negative current to R3.

With no signal to the base of T1, the bias current in T1 and T5 is equal to VF/R. VF equals the drop across one diode and R is the resistance of R2. This bias current prevents the occurrence of crossover distortion with low amplitude signals. The ratio of maximum negative load current to no signal bias current is approximate equal to the current gain of T5.

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