1.The explanation of the static current action of triode

The role of the bias circuit is to provide the base DC current for the transistor, which is also called the base static curse current. The quiescent working current is the direct current of the transistor when there is no signal input to the amplifying tube. This current is supplied by the DC power in the amplifier circuit.

The static working point of the triode is quite complicated. In general, the static current size is related to the magnification, noise and nonlinear distortion in the amplifier. In the various applications of the triode, the static current is related to the static working current.

When the triode operation is magnified, it is necessary to provide the static bias current to the triode. It is the necessary condition to ensure the operation of the triode in the amplification state. The static current is not normal, and the operation of the tri pole amplifying signal is not normal.

2.The relationship between static current and noise of triode

The size of the static current is related to the noise of the transistor. The quiescent current is large and the noise is large. Otherwise, it is small. In the small signal amplifier, the quiescent operation point is low, and it can be as small as possible when the maximum signal in the negative half cycle does not fall into the cut-off area, so that the triode noise can be suppressed.

In a multistage amplifier, there is a single stage amplifier that requires a small static current of the triode of the pre amplifier, to reduce the noise of the whole amplifier, because the small noise of the front stage circuit will be amplified by the post stage amplifier.

The smaller the quiescent current of the front amplifier, the larger the B of the transistor. At this time, in order to compensate for the amplifying power, the transistor with low noise and high B can be used. The static current of the triode is larger in the post stage amplifier.

The static current of the triode of the post stage amplifier is large, so that the magnification of the triode is larger and the magnifying power is stronger. At the same time, the input signal can be prevented from entering the tri electrode cut-off area, because the signal amplitude of the post stage amplifier is larger. For the NPN triode, the negative half Zhou Feng value part of its input signal will enter the triode tube. Cut-off area. The cutoff distortion is produced.

3.The relationship between the transistor's quiescent current and amplification factor.

The size of the static current is also related to the magnification of the triode. The relationship curve between the base current and the magnification B is shown. It is seen from the diagram that when the base current is a certain value, the magnification is the largest, and when the base current is greater than or less than this value, the magnification number B should be reduced. The characteristic curves of different types of transistors are different, but very similar.

4. push stage static current explanation

In a large signal class a amplifier, if the driving point of the amplifier is in the middle of the AC load line, the nonlinear distortion will be the smallest. This is because the nonlinear distortion of the signal is less than unsymmetrical, such as the distortion of the large head, and the nonlinear distortion of the positive half cutting of the top than the negative half cycle.

5. static current requirements in other triode circuits

(1) there is no static current in the transistor in the class B amplifier, so it can only enlarge the half week (half week or negative half) of the AC signal, and the magnified half of the signal is also distorted. This amplifier is used for power amplification where the signal distortion is not required.

(2) in a class a amplifier, the quiescent current is very small, so long as we overcome the crossover distortion. This kind of large device is widely used, such as OTL, OCL and BTL power amplifiers, which are used in class A and B amplifier to amplify the positive and negative half of the AC signal with two triode tubes.

(3) in the transistor switch circuit, the triode has no static current, and the working current of the triode has two states: one is zero, the switch is broken, the other is large, the switch is connected.

(4) the radio frequency conversion transistor has only a very small and small quiescent current. The tripole operates in the nonlinear region, so that the transistor has the function of frequency conversion.

(5) two transistor currents in differential amplifiers are equivalent to effectively overcome common mode signals and zero drift.

(6) the magnitude of the quiescent current in the oscillating tube affects the amplitude of the oscillation and the output of the oscillation signal in the sine wave oscillator.